In depth (chilled out!) model discussion

[chrisbell-nottheweatherman]

1 hour ago, knocker said:

I did post a recent paper on this in the New Research thread

Simulated Atmospheric Response to Regional and Pan-Arctic Sea-Ice Loss

http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-16-0197.1

 

Malcolm - regarding the paper by Screen, I'm confused as to what he means by the following:

Quote

Sea-ice loss in the Barents-Kara Sea is unique in driving a weakening of the stratospheric polar vortex, followed in time by a tropospheric circulation response that resembles the North Atlantic Oscillation

Do you think he means that the tropospheric response to the weakened PV is to initiate a response similar to a strongly +ve or -ve phase of the NAO?  From my limited understanding of such matters, I'm aware that weakening of the stratospheric vortex which filters down to the troposhere tends to initiate a meridional jet which is characterised by some form of -ve NAO, whether east- or west-based, however, to my layman's mind, Screen's reference seems ambiguous.  Apologies for the slightly O/T nature of this post - might I ask the moderators for some leniency given the more laid-bak and considered nature of this wonderful thread?

[Singularity]

I know low Barents-Kara sea ice has been linked to cold N. Eurasian winter weather so I expect a negative NAO response?

The Arctic amplification link to increased meridional jet stream motion is something I became aware of about half a decade back and has seemed increasingly convincing ever since, from observing global tendencies.

Should a net poleward movement of climatological weather 'bands' join the foray then extremes will become even more frequent and severe. A few years back I ever thought I would soon be considering the possibility of such a climatic shift occurring within he next decade as opposed to between 2040 and 2100... oh how times have changed. Or seemingly,  bar a miracle in the Arctic which I for one am desperately hoping for.

I realise this discussion has dragged things off topic for this model discussion thread - sorry mods! Hopefully it can stay as something to reflect upon when considering what the models show us in the year of 2017? Thanks if so

[knocker]

11 minutes ago, chrisbell-nottheweatherman said:

Malcolm - regarding the paper by Screen, I'm confused as to what he means by the following:

Do you think he means that the tropospheric response to the weakened PV is to initiate a response similar to a strongly +ve or -ve phase of the NAO?  From my limited understanding of such matters, I'm aware that weakening of the stratospheric vortex which filters down to the troposhere tends to initiate a meridional jet which is characterised by some form of -ve NAO, whether east- or west-based, however, to my layman's mind, Screen's reference seems ambiguous.  Apologies for the slightly O/T nature of this post - might I ask the moderators for some leniency given the more laid-bak and considered nature of this wonderful thread?

There is always a problem when the paper is not open access Chris and one only has the abstract. Yes I'm assuming it indicates a negative NAO and an inclination to stationary waves but  one needs to read the full paper.

[Nouska]

11 hours ago, chrisbell-nottheweatherman said:

Malcolm - regarding the paper by Screen, I'm confused as to what he means by the following:

Do you think he means that the tropospheric response to the weakened PV is to initiate a response similar to a strongly +ve or -ve phase of the NAO?  From my limited understanding of such matters, I'm aware that weakening of the stratospheric vortex which filters down to the troposhere tends to initiate a meridional jet which is characterised by some form of -ve NAO, whether east- or west-based, however, to my layman's mind, Screen's reference seems ambiguous.  Apologies for the slightly O/T nature of this post - might I ask the moderators for some leniency given the more laid-bak and considered nature of this wonderful thread?

An earlier paper talks about autumn/early winter response being a negative NAO one - this new work is more region specific but maybe assume the NAO comment is as before?

http://www.cgd.ucar.edu/staff/cdeser/docs/screen.seaice_atm_impacts.jclim13.pdf

I do think it has a place in an in-depth model thread as long as we stick to the subject with reference to models and not the debate on causes. I'm sure we were seeing modelling difficulties last autumn due to the incredible temperature contrasts at high latitudes.

Edit to include another recent paper on the same subject.

http://centaur.reading.ac.uk/51159/1/jcli-d-15-0316%2E1.pdf

The model simulation in two monthly segments - showing the parameters we all look at in the NWP.

Edited February 12, 2017 by Nouska

[Catacol]

9 hours ago, blizzard81 said:

Good post. However, there is the opposite side of the coin isn't there? What I mean is what about the long mild run of winters the UK experienced back in the 1920's and 30's as well as the early to mid 70's? Low Arctic sea ice cannot be blamed for these. 

Agreed. There is obviously a lot more to it than just arctic sea ice, but this is the factor at the moment that in the NH is changing most radically and swiftly. Thanks for the paper @knocker

[Guest]

@Singularity @Catacol and several other fascinating posts. I am nowhere near as technical as you guys and would be out of my depth commenting on many of the teleconnections other than in a fairly basic way - so I need to keep this simple!. I have, however, taken a very keen interest in following the decline in the Arctic Sea ice since the 1960s. I am really going to be "thinking out aloud here" just to express some of my ideas to provoke further discussion.

Some of the general climate drivers one might expect to seriously impact on the extent and rate of recovery of the ice sheet each Autumn and Winter are far from logical. For instance, last Winter, we had the near record breaking El Nino; a near record strength PV; extremely strong and persistent circumpolar winds (more reminiscent of those driven by the circumpolar currents around Antarctica) keeping the cold retained at very high latitudes for prolonged periods for all of the first half of Winter but less so later on. The Jet Stream in the Atlantic powered through towards the pole on a south-west to north-east axis for at least 8 weeks from late November to mid-January. This drove warm sea currents and warm air right up to the ice sheet and greatly reduced recovery in the Barents and Kara Seas. Obviously the far side of the Arctic is almost land locked, so the Pacific Jet would always have much less of an impact. This winter, we had a weak La Nina trending towards neutral conditions, a record weak PV up until early December which then strengthened rapidly for a while sending a strong cold plunge into North America followed by it losing some strength again with the USA seeing some unusually persistent very mild conditions; the Jet has been generally weaker and more meandering and only blew directly into the Arctic for very short periods.

Now "logically" one would conclude that 2015-16 would have seen much lower Arctic ice build up than this Winter. Obviously logic or normal understanding does not apply here. Other forces and factors must be at play and the tropospheric patterns can only be part of the equation. I have read that following the impacts of the 2015-16 Winter, there were some residual much higher than average SSTs left in the Arctic which continued into this Winter (see the charts below in "edit 2"). So, a multi-Winter impact from the initial warming. As you know, I used to include part of Judah Cohen's weekly Arctic Oscillation Reports in my own weekly reports. I only dropped this feature recently as Judah's forecasts had become very inconsistent (perhaps partly in line with the extreme variability of the model output for much of this Winter). Like many others, I do have huge respect for his theories and studies into the impact of October Asian snow cover extent and the likelihood of SSW events later on. We had above average Asian snow cover building up in Autumn 2015 and then near record early build up in Autumn 2016. I'm wondering if this has various other (probably even more complex) impacts than just a relationship between stratospheric-tropospheric couplings and encouraging or interfering with downward propagations following warming events. The snow cover extent over Asia continues at near record levels (in recent decades) having spread further south than usual and much further south-west. In northern hemispheric terms, this snow cover might restore a balance (while it lasts) in the loss of the albedo effect from less Arctic sea ice extent. Obviously in mid-Winter there is no Arctic sun to be reflected but in the shoulder Autumn and Spring months it may have some kind of impact. For example, helping to retain the Asian snow cover for even longer (with a delayed melt). We talk about HLB allowing entrapped Arctic cold at the surface to be displaced towards the middle latitudes. What happens when we have a reservoir of deep cold in the centre of the large continents in contrast to the Arctic? Yes, the former is entirely normal for almost every winter and even more so back in the 1960s and before then. The difference is, like in some recent Winters, when we have that land mass cold but far less cold in the Arctic. There is also a big difference in the two continents. While Asia can manufacture most of its own Winter cold, North America (below the Canadian Arctic) usually needs the assistance of the PV and a cold plunge from the Arctic to kick start its coldest weather. The last few Winters have seen this pattern. Obviously Asia is a larger continent and even a strong west to east Jet Stream rarely makes more than temporary and partial inroads into its entrenched cold. What I'm getting at is might this changing relationship have further impacts on preventing sea ice growth? 

In the 1960s Arctic Sea ice typically reached the shores of northern Iceland by February in most Winters and sometimes further. Some ice bergs were seen quite close to northern Scotland at the end of the 1962-63 epic Winter (edit: it was actually at the end of the 1969 Winter - see "edit 1" below). Although we had more colder and sometimes severe Winters back then, we still had some much milder Winters too. .As @blizzard81 points out, we have had warmer period before, like in the 1920s and 1930s but the Arctic ice extent was not particularly low in those two decades. Again other factors are at play. 

I read some of the studies into past periods of low solar activity and severe Winters. The 300 to 350 year Maunder minimum cycle coincided with frequent severe Winters in the mid 17th to early 18th centuries and the "Little Ice Age". That lasted for 5 x 11 year cycles. The one now is expected to last for more like 3 x 11 year cycles from around 2020 to 2050 with impacts possibly slightly outside this period. I was surprised when I learnt quite recently that records of sun spot activity extend back for over 400 years - about 90 years before we started to measure rainfall accurately!  What we do not know is how much is global warming and any other man made factors changing these natural cycles. It is believed that previous ice ages might have been triggered during solar minimum periods but there are various other theories on the causes like earth being further from the sun and having a more elliptical orbit with the northern hemisphere being further from the sun during its summer;  or major volcanic eruptions; it could even be an asteriod impact or even a natural very long term cycle. There are so many plausible theories. 

That's enough for now. I hope that this sparks some responses.

EDIT (1):  @ArHu3 An interesting period that you referred to but it does need to be put into context. Here's a link to an historic record going back to the 1850s: 

https://www.carbonbrief.org/guest-post-piecing-together-arctic-sea-ice-history-1850

and here is the yearly chart: 

        Arctic Ice Extent 1850 to 2012

  

Going by the end of season March plot, there were a couple of much lower individual years in most decades from the 1910s onwards but nothing compares to the last 20 years. Interestingly, 1969 was the year with highest ice extent - it was dominated by Arctic air streams in the UK and western Europe. That was the year with ice bergs seen off Scotland in Spring, not 1963 (although there may have been some then too) - my memory played tricks on me there. The September trend is even more worrying as long term ice is melting and thin new Winter ice melts much quickly in the summer. More later on this. The paper is a great read.

EDIT (2):  Here are three Arctic Sea Surface Temperature charts that I found:

   NOAA: Actual SSTs For Feb 11th              NOAA:  SST Anomalies For Feb 11th           SST Anomalies From 1982 to 2012

                                    

There is a huge area of considerably warmer than average SSTs from Iceland, beyond Svalbard and right up to the ice sheet edge in the Barents and Kara Seas. With SSTs of 4c to 6c in this part of the Arctic it is difficult to see much new ice growth during the rest of this Winter. The anomaly is over 8c in places and over 4c over a much wider area. This is quite extraordinary and extremely worrying.

EDIT (3):  Here's something else that is absolutely extraordinary and demonstrates the extent of the Arctic sea ice loss in recent years. The first chart below is from August 1926 and was compiled by the Danish Meteorological Institute with information taken from shipping logs. Now compare this to the current chart. There was more "permanent" ice on our side of the Arctic in late Summer back then compared to even "temporary" ice in late Winter now! The permanent ice sheet engulfed eastern Svalbard and stretched further south into the Barents Sea all of the Kara Sea. Obviously, the overall extent was less in the summer, with the temporary winter ice on the peripheries melted - eg: Hudson Bay, around the southern tip of Greenland, the Davis Strait, the Bering Sea and the Okhotsk Sea. Note that the actual position is considerably worse. The 1926 chart shows "tight pack ice" with a 70% to 90% concentration. The "February 2017" and the "Current Ice Extent " charts show areas of the ocean with at least 15% sea ice extent. It is the permanent ice sheet extent which is most important. The "January 2017" chart shows the sea ice concentration. The dark blue is the 15% extent. The palest blue (almost white) shades are nearer the 70% to 90% concentration and the brilliant white is over 90%. Using the 1850 to 2012 graph (first chart above) I estimate that the September 1926 ice extent was about 8.25 million square kilometres. The current 15% ice extent is about 13.25 million square kilometres. The minimum 15% ice extent last summer was around 4.5 million square kilometres. From the graph I estimate that the March 1926 extent was about 16 million square kilometres. 

          August 1926 Ice Extent                              February 2017 Ice Extent                              Current Ice Extent Compared to 30 Year Mean                         January 2017 Sea Ice Concentration 

                                                                                    

I will add more comments later.

EDIT (4):  @ArHu3  Unfortunately, with the greatest of respect, I 100% disagree with your your comments concerning the merits and accuracy of the 1926 chart. Of course they didn't have satellite imagery available and there were very few flights in that region back in those days. What was used were the highly accurate ship's log books. They kept meticulous records in those days. Many ships (and there were a lot more of them 90 years ago than there are today), particularly fishing trawlers, sailed right up to the edge of the main ice sheet as defined by the 70% to 90% "tight pack ice". The caption below the chart reads:

....."A Danish Meteorological Institute ice chart for August, 1926. The red symbols mark the location of observations recorded in ship logbooks. Source: Walsh et al. (2016)"..... 

Then, in the main text above the chart they say: ....

"You can see another source of data below, this time one of the maps from the Danish Meteorological Institute. These are remarkable for their information value and because they represent a cooperative international effort to report ice conditions in a systematic way that was sustained over decades. The red symbols and terms in the legend (see close-up below the map) indicate the sea ice extent. “Tight pack-ice”, for example, indicates ice of 70% to 90% concentration of ice over the sea"... 

There are a great many red symbols, especially on our side of the Arctic - the most important in terms of ice loss in recent years. By analysing the readings and plots of the ice sheet edges, the Institute was able to put together a highly accurate map of the ice extent for the whole of the Arctic. There were also many coastal observations around the periphery. Perhaps the only slightly weaker area was towards the Bering Straits on the far side. If anything, the old method was even more reliable in terms of measuring the extent of the thicker (longer term) ice. Satellite images are restricted in terms of an overall picture but struggle to show the detail of depth of ice and areas of slightly broken ice. The sensory equipment only gives a very approximate reading. There are, of course, specialist expeditions and surveys carried out and several ice breakers take ice depth readings every year. Overall, the old method provided a highly accurate measure of ice extent.

So rather than concluding that my remarks were speculative, I would say that they are based on very reliable data. We should be very grateful that scientists devoted so much time in the past to research and put together these records. They form such an important part of today's analysis. Judging by both of your comments in your posts below mine, you cannot have read the whole report that I quote from, as otherwise, you would form a very different opinion. It is never my intention to criticise anyone on this forum but I had to put the record straight for the sake of those who might otherwise be confused by your comments.

Finally, on a more positive note, you asked to see the September 2016 sea ice extent - here are the charts:

            September 2016 Ice Extent                                           September 2016 Ice Extent Compared to 30 Year Mean                            October 2016 Ice Extent Compared to 30 Year Mean  

                                                                                                       

As can be seen, extremely low but not the lowest back in September. The recovery in October and November 2016 hardly got going with periods of further decline. That was when 2016 started setting record lows. I have also added the October chart as that shows the cross over from the previous record low and fills the gap that is covered by the current chart (shown further up).

EDIT (5): @knocker I have read some of your impressive posts on this subject and your specialist paper. Several members have suggested that we should really be posting on the "Arctic Ice" thread and I tend to agree with them. My post was a response to yours and several other earlier ones. Although we agree that the low ice extent does have an impact on the models, I do think that this "in-depth" thread was not really intended for, shall we say "slightly" off topic posts. I have just asked Paul, to feel free to move all these particular posts across to the specialist thread. I shall be happy to make further contributions on that thread. I shall also put out the occasional reminder in one of my main MOD thread posts or in status reports. This is a really fascinating subject which is fast becoming an essential part of meteorological studies. 

EDIT (6):  @Interitus I am somewhat puzzled and surprised by your comment/query as you of all people (with your experience and knowledge) will know what I was referring to.  I felt that the "general" reference that I made to the strength of the PV (amongst other influences) in my brief comparison of the two Winters 2015/16 and 2016/17 would not require any empirical and/or written support as it has been so widely accepted and known by most of the meteorological community.  We are all aware of what has happened this Winter and there is plenty of data and reports around for last Winter  including here on NetWeather and covered on Judah Cohen's weekly AERs but here is one from an external source:

Quote from "Researchgate" - Geophysical Research Letter no.43, November 2016 (full pdf available from the site quoted at the end):

"Abstract.........The Arctic polar vortex in the early winter 2015/16 was the strongest and coldest of the last 68 years. Using global reanalysis data, satellite observations, and mesospheric radar wind measurements over northern Scandinavia we investigate the characteristics of the early stage polar vortex and relate them to previous winters. We found a correlation between the planetary wave (PW) activity and the strength and temperature of the northern polar vortex in the stratosphere and mesosphere. In Nov/Dec 2015, a reduced PW generation in the troposphere and a stronger PW filtering in the troposphere and stratosphere, caused by stronger zonal winds in mid-latitudes, resulted in a stronger polar vortex. This effect was strengthened by the equatorward shift of PWs due to the strong zonal wind in polar latitudes resulting in a southward shift of the Eliassen-Palm flux divergence and hence inducing a decreased deceleration of the polar vortex by PWs....."   here's one of several links to this paper:   http://elib.dlr.de/108690/

Now come on guys, I am trying to generate some interesting discussion here. I really do not expect people to pick holes in some of the general facts that I quoted especially as they fully stack up. What I do expect is your constructive comments on the suggestion that I put forward regarding the relationship between the imbalances of a warming Arctic but continuing deep cold in northern Asia and Siberia and also your reactions to the current extreme positive anomalies in Arctic sea surface temperatures - which are unprecedented and almost in a new dimension. 

 

Edited February 16, 2017 by Guest
Additional comments and charts

[ArHu3]

2 hours ago, Bring Back1962-63 said:

 

In the 1960s Arctic Sea ice typically reached the shores of northern Iceland by February in most Winters and sometimes further. Some ice bergs were seen quite close to northern Scotland at the end of the 1962-63 epic Winter! Although we had more colder and sometimes severe Winters back then, we still had some much milder Winters too. .As @blizzard81 points out, we have had warmer period before, like in the 1920s and 1930s but the Arctic ice extent was not particularly low in those two decades. Again other factors are at play. 

 

 

In 1922 this was written, though it is hard to compare today with then:

The Arctic seems to be warming up. Reports from fisherman, seal hunters, and explorers who sail the seas about Spitzbergen and the eastern Arctic, all point to a radical change in climatic conditions, and hitherto underheard-of high temperatures in that part of the earth’s surface.

In August, 1922, the Norwegian Department of Commerce sent an expedition to Spitzbergen and Bear Island under the leadership of Dr. Adolf Hoel, lecturer on geology at the University of Christiania. Its purpose was to survey and chart the lands adjacent to the Norwegian mines on those islands, take soundings of the adjacent waters, and make other oceanographic investigations.

Ice conditions were exceptional. In fact, so little ice has never before been noted. The expedition all but established a record, sailing as

far north as 81° 29′ in ice-free water. This is the farthest north ever reached with modern oceanographic apparatus.

The character of the waters of the great polar basic has heretofore been practically unknown. Dr. Hoel reports that he made a section of the Gulf Stream at 81° north latitude and took soundings to a depth of 3,100 meters. These show the Gulf Stream very warm, and it could be traced as a surface current till beyond the 81st parallel. The warmth of the waters makes it probable that the favorable ice conditions will continue for some time.

In connection with Dr. Hoel’s report, it is of interest to note the unusually warm summer in Arctic Norway and the observations of Capt. Martin Ingebrigsten, who has sailed the eastern Arctic for 54 years past. He says that he first noted warmer conditions in 1918, that since that time it has steadily gotten warmer, and that to-day the Arctic of that region is not recognizable as the same region of 1868 to 1917.

Many old landmarks are so changed as to be unrecognizable. Where formerly great masses of ice were found, there are now often moraines, accumulations of earth and stones. At many points where glaciers formerly extended far into the sea they have entirely disappeared.

[stodge]

Morning all

Back to the output after a busy weekend which saw falling snow but no settling snow in lowland East London.

I said last week my view was we would move into a 21-day milder spell of weather from Tuesday (after six days of below average temperatures in London) as we had, as is often the case, a pre-spring warm up in mid to late February before early March sees a pattern change to something colder again.

Where are we this morning ? Starting with the situation next weekend and UKMO opens with a benign offering as the Azores HP ridges from the south of SW albeit with an interesting orientation toward the British Isles.

ECM at the same time:

Note the absence of the Iberian LP on the ECM output.

GFS 00Z OP at the same time:

A bit of a halfway house - conditions settling from the SW though quite breezy over the far north of Scotland.

GEM 00Z OP at the same time:

So the models all pretty much in the same place with UKMO if anything on a slight limb this morning with the small Iberian LP.

Moving on..

GEM at T+240:

ECM:

GFS offers something different:

This may just be a question of timing but note how the LP systems are further south over Scandinavia indicative of a stronger dig of the PV in that area and that leaves the British Isles in a cooler W or WNW'ly flow with some quite cold air not far away from Shetland.

Switching to the Northern Hemisphere view, here's the same time:

The PV has cleared Canada but is sitting to the north of Russia/Scandinavia closer to the Pole with enough residual energy back over Greenland to prevent heights.

Further into FI and a lobe of energy sheers off and heads south sending the trough down right over the British Isles so colder unsettled conditions would return:

Not entirely unsupported by the GEFS but a strong cluster wants to keep the PV over Canada/Greenland by the end of the month.

We've talked about the next warming due in 10 days or so - the 10HPA profile enters March looking like this:

If the next warming is the one that really shreds the PV - fine - I'm not surprised to see no immediate tropospheric response and as Ian F suggested the other day, maybe it won't have an impact but it's too early to make that call. However, as that's outside the range of most publicly-available modelling (bar CFS), we won't know for a week or so but I've seen little to change my overall view though GFS OP's traditional FI tease this morning might not be wholly improbable.

We're done with cold for now but we're not done with cold - I think it unlikely we'll see anything before the very end of the month and I maintain three weeks in the new pre-spring pattern before the impact of the next warming (and the traditional lag) offers the next opportunity for something more amplified. I also think a prolonged N'ly outbreak is the form horse rather than anything from the East and while lowland snow options will be limited, for those with altitude and those further north, there's plenty of time for significant snow through March and nothing I've seen so far suggests the possibility and even the probability of a renewed wintry outbreak early next month isn't on the table. 

 

[ArHu3]

On 2/12/2017 at 00:05, Bring Back1962-63 said:

 

          August 1926 Ice Extent                              February 2017 Ice Extent                              Current Ice Extent Compared to 30 Year Mean                         January 2017 Sea Ice Concentration 

                                                                                    

 

All the white on the 1926 map isn't snow or ice but no data available, that is a lot of unavailable data to make accurate comparisons. I would like to see September 1st 2016 vs normal extend 

Edited February 13, 2017 by ArHu3

[knocker]

I suspect there is a danger of this becoming a climate discussion and there is already a climate area where much of this has already been discussed and where discussions are ongoing. This is not to say sea ice is not relevant here, it most certainly is IMO, and I would suggest that this graph, which covers the satellite era, highlights this quite well. We will will have to wait on some post winter analysis to perhaps gain some insight into what the effects have been

 

[BornFromTheVoid]

On 2/12/2017 at 01:20, ArHu3 said:

 

In 1922 this was written, though it is hard to compare today with then:

The Arctic seems to be warming up. Reports from fisherman, seal hunters, and explorers who sail the seas about Spitzbergen and the eastern Arctic, all point to a radical change in climatic conditions, and hitherto underheard-of high temperatures in that part of the earth’s surface.

In August, 1922, the Norwegian Department of Commerce sent an expedition to Spitzbergen and Bear Island under the leadership of Dr. Adolf Hoel, lecturer on geology at the University of Christiania. Its purpose was to survey and chart the lands adjacent to the Norwegian mines on those islands, take soundings of the adjacent waters, and make other oceanographic investigations.

Ice conditions were exceptional. In fact, so little ice has never before been noted. The expedition all but established a record, sailing as

far north as 81° 29′ in ice-free water. This is the farthest north ever reached with modern oceanographic apparatus.

To put the 81° 29′ ice free extent in summer into context, over the last 3 months we've regularly been ice free north of 82°, and even north of 83°N just before Christmas. That's in the middle of winter too.
The warmth and ice loss back in the early 20th century just isn't at all comparable to now

[stodge]

Morning all

As the current cold spell finally ends and we move into the warmer pre-spring period, what are the models telling us for the future this morning ?

I won't bother with the T+144 output as that's telling a consistent story of a benign weekend with the Azores HP moving NE toward but not quite over the British Isles. While the core of the HP moves towards us, the ridge isn't orientated in the same way so the airflow is a bit more W'ly than SW'ly with quite strong winds to the NE as a small LP passes to the North of Scotland.

Moving on to the T+240 point and starting with GEM this morning:

Strongly mobile  but note the trough digging down almost to the Azores so not flat by any stretch and it wouldn't be far fetched to see that ridge building into Scandinavia becoming a more pronounced feature but the jet is too strong to the north.

Something a bit different from ECM and this was hinted at yesterday. As we often see in late winter, the boundary between very cold residual winter air and the emerging warm air can be quite stark and encourage cyclogenesis. This feature would bring strong winds and heavy rain for most but the Scottish hills and some other higher ground would see snow. The Azores HP is suppressed with a different (more N-S rather than W-E orientation).

GFS:

Close to ECM I would argue and perhaps a shade quicker. The following LP (currently developing off the east coast of Greenland) takes an even more SE'ly direction crashing through the British Isles into Europe but the attempt to build heights to the NE behind it is quickly eroded and FI ends with the PV still established over the Pole and N Greenland leaving the British Isles in a SW'ly flow. It would be a 24-36 hour cold snap and again snow for elevations would be likely (and perhaps even a transient covering to lower ground depending on a number of other factors).

The forecast 10 HPA profile after the next round of warming (which is about a week away) is interesting:

Comparing with early March 2013 which the profile was as follows:

2016:

All very different and it may mean something or nothing.

To bring in some other charts to help:

Another view of the 10 HPA showing the huge variation in temperature this winter. The temperature has fallen back with the ending of the first warming last month.

And here's the 70 HPA chart. I'm left with the view for all our observations, the stratosphere has behaved in a fairly average way in terms of temperature so far. The huge difference between the 10 HPA forecast profile for early March and what happened in that exceptional month is making me question the likelihood of a cold month but the pieces of the puzzle aren't in place yet 

[stodge]

Morning all

Day 2 of what I think will be a 21-day milder spell of Atlantic-dominated weather and certainly too early to see more than the faintest hints of the next change in the pattern.

Looking out at the medium term from this morning's 00Z outputs and starting with ECM:

The storm hinted at in yesterday morning's output has continued but as a more consolidated LP moving east into Scandinavia and drawing down a chilly NW'ly which although offering only a glancing blow would, you would imagine, bring snow to the Scottish mountains and possibly some higher elevations further south. Pressure is rising behind but only weakly while the next LP is in a very different place so an interesting evolution going forward.

GEM at the same time and as we often see with the Canadian model, the only thing better than a deep LP is a deeper LP. A strong storm well to the north of the British Isles and a brisk WSW'ly of returning PM air so not terribly warm and perhaps snow to higher elevation in any showers. Interesting to see if the trough would swing east in later evolution.

GFS OP at the same time and as I noted yesterday this model seems keen to have everything happen that bit quicker. The storm has already passed to the east (more ESE'ly track than ECM) and pressure has risen nicely behind it leaving the British Isles finer after a possibly chilly start. The LP  to the west seem to be gathering - here's the NH perspective of the same chart:

The PV in its usual place but not perhaps as strong as some modelling in recent days has suggested and indeed by the very end of FI:

Well, are we looking at the beginning of something here ? The PV is now over Hudson Bay and the Azores HP displaced back into the Atlantic encouraging a lowering of heights over Europe and the hint of a height rise over Greenland. All very speculative at the moment but it's the possible direction a tropospheric response to next week's big warming might produce.

Finally for today, my favourite chart at the moment - the 10HPA view of the stratosphere:

Fragmented and warming up nicely as has been shown in lots of recent GFS output.

To recap, an initially benign start to the three weeks before a slow but gradual transition to colder, more unsettled conditions by the end of next week and the hint early into March of a possible change to something more wintry. To be emphasised though, very early days and huge numbers of hoops to jump through. The chances of those in Scotland seeing snow before month end look good (especially to elevation) while rain and strong winds become more of a feature in the forecasts from this time next week.

[Interitus]

On 2/11/2017 at 23:05, Bring Back1962-63 said:

For instance, last Winter, we had a record strength PV

This winter, we had a record weak PV up until early December which then strengthened rapidly for a while

Just on these two points, how have they been determined?

[ArHu3]

18 minutes ago, Interitus said:

Just on these two points, how have they been determined?

They are compared to historical zonal wind strength for that day

 

Edited February 15, 2017 by ArHu3

[stodge]

Morning all

With the mild/very mild regime now firmly established, it's easy to forget how cold it was just a few days ago. The current synoptic set up of HP to the south and LP to the north is the default for most times in the UK and with he HP in charge at present, it's a largely benign scene.

This morning's GEM 00Z OP output at T+240 continues in a similar vein:

A stiff WSW'ly breeze in evidence but nothing terribly threatening about that chart.

ECM at the same time:

 

A flicker of interest perhaps ? The hint of height rises to the NE was mentioned yesterday and with a solid Italian low to prop up the MLB and a hint of a ridge from the north, who knows ? The last block came from the east but in the past cold Scandinavian blocks have set up from HP areas tracking NE from Iberia. In this instance, the jet is just too strong and were there a T+264 chart I suspect it would show a flat picture. For the British Isles, a brisk but fairly benign SW'ly and fair for most of the south and east with a likelihood of drizzle for the north and west,

GFS OP:

Very different although it's a benign outlook for the British Isles under a ridge of HP. Scandinavia is awash with low heights as the last of the series of troughs which will affect us earlier in the week exists and the jet re-adjusts back to the north.

The Northern Hemisphere view at the same time with the PV centred to the north of Greenland.

However, more interest at the far edge of FI:

We get to this interesting point as the PV shifts to interior Canada and the jet weakens. An HP over the British Isles joins with the mid-Atlantic ridge and is able to begin ridging north into Greenland as the PV splits between lobes over Canada and Siberia. This is Day 18 of the current milder interlude so perhaps a N'ly by day 21 ? We'll see - it's an evolution we've seen before. but the GEFS are, as you'd expect, all over the place at this far range so it's one possibility among very many.

Finally, my favourite chart of the moment:

The big warming next week isn't the final warming I would conjecture. Indeed, the PV starts to get colder again into early March. It's akin to a boxer against the ropes having been pounded for the best part of the round but still able to throw a punch. I still think some form of tropospheric response in terms of an amplification is likely in early March but it may again only be brief before the PV tries to reset. Again, a long way off but a very different profile to both 2016 and 2013 so not quite sure where this will take us for March. I've seen suggestions it will be drier and warmer - could be - I wouldn't call it at this stage though it's entirely possible if we get an amplified regime, the block will be favourable for S or SW winds - this morning's OP evolution isn't but that's one OP run in FI.

[Interitus]

On 2/11/2017 at 23:05, Bring Back1962-63 said:

I felt that the "general" reference that I made to the strength of the PV (amongst other influences) in my brief comparison of the two Winters 2015/16 and 2016/17 would not require any empirical and/or written support as it has been so widely accepted and known by most of the meteorological community.  We are all aware of what has happened this Winter and there is plenty of data and reports around for last Winter  including here on NetWeather and covered on Judah Cohen's weekly AERs but here is one from an external source:

Quote from "Researchgate" - Geophysical Research Letter no.43, November 2016 (full pdf available from the site quoted at the end):

"Abstract.........The Arctic polar vortex in the early winter 2015/16 was the strongest and coldest of the last 68 years. Using global reanalysis data, satellite observations, and mesospheric radar wind measurements over northern Scandinavia we investigate the characteristics of the early stage polar vortex and relate them to previous winters. We found a correlation between the planetary wave (PW) activity and the strength and temperature of the northern polar vortex in the stratosphere and mesosphere. In Nov/Dec 2015, a reduced PW generation in the troposphere and a stronger PW filtering in the troposphere and stratosphere, caused by stronger zonal winds in mid-latitudes, resulted in a stronger polar vortex. This effect was strengthened by the equatorward shift of PWs due to the strong zonal wind in polar latitudes resulting in a southward shift of the Eliassen-Palm flux divergence and hence inducing a decreased deceleration of the polar vortex by PWs....."   here's one of several links to this paper:   http://elib.dlr.de/108690/

Now come on guys, I am trying to generate some interesting discussion here. I really do not expect people to pick holes in some of the general facts that I quoted especially as they fully stack up. What I do expect is your constructive comments on the suggestion that I put forward regarding the relationship between the imbalances of a warming Arctic but continuing deep cold in northern Asia and Siberia and also your reactions to the current extreme positive anomalies in Arctic sea surface temperatures - which are unprecedented and almost in a new dimension. 

 

Thanks for your reply, it wasn't picking holes but rather genuine curiosity. I was always under the impression that meteorology was essentially a scientific endeavour, though on these forums it does at times tend towards a more creative pursuit! Thus what is widely accepted or taken for granted here may not be the actual truth.

The interchangeable use of the term 'pv' for either strat/trop polar vortex can be ambiguous (not to mention normally meaning potential vorticity in 'serious' meteorological circles) but blurring the distinction also causes problems when defining the notable characteristics of winter 2015/6 which will be examined in a moment. But firstly now it is clear by pv you were referring to the stratosphere, how one defines a record weak or strong vortex is not trivial. Thank you for the link, it is an interesting read and there is no need to question the veracity of their findings and it provides convincing empirical evidence, though it does raise a few points.

What time period? The study covers November and December. An anomalously weak, and maybe more so a strong vortex is unlikely to last for a full two months, or even one month, and also how well the anomaly coincides with the time period will skew the results. What height range to examine? The use of the microwave limb sounder and ERA interim extends to the mesosphere well above the 10mb of the NCEP/NCAR (which they include) and MERRA (not included) reanalyses. The data are essentially similar though there are differences. Also is the 'meat' of the vortex eg. 50 or 30 mb more important than higher up? What area to examine? They looked at 60-80°N which may or may not capture the whole vortex. Also zonal means by their very nature blur the details and some sort of 2d moment analysis could be used, though a stronger unperturbed vortex is likely to be fairly zonally symmetric, concentric about the pole. What metrics to include? They looked at a combination of temperature and wind speed, but maybe could've looked a some measures of potential vorticity or geopotential perhaps (though of course these are all linked by quasi-geostrophic theory).

The strongest average MERRA November wind at 60°N was in 1990 with 25.04 m/s (ranked 1st at 10, 30, 50, 70, 100mb, 2nd at 150mb). 2015 was 2nd at 22.84 m/s. Interestingly, the 10mb speeds were 1990 39.31 m/s vs 2015 38.61 m/s, however very different in NCEP/NCAR - 1990 34.85 m/s vs 2015  37.86 m/s - tricky to be definitive with such large discrepancies.

There's a selection of temperature metrics that could be used, but averaged over 6 levels mentioned above, 2012 was coldest at 80°, between 60-90°N and 55-75°N. 1982 at 90°N and 2015 had lowest absolute minimum 50-90°N. Combined rankings - not very scientific and unweighted - gives 2015, 2011, 1982 & 2012 (joint 3rd).

December seems more clear cut, 2015 was coldest at 90°N, 80°N and absolute, but 2nd to 1980 for 60-90°N polar cap. Wind speed average was 1st with 30.56 m/s average for all levels ahead of 1986 with 29.86 m/s. However, while 1986 was strongest at 70, 100 and 150mb,  2015 was strongest at 10, 30 and 50mb - obviously the higher wind speed with altitude skews the averages so is not totally conclusive. Combined rankings - 2015, 1980, 1994.

Regarding weak November vortices (ie 2016), from MERRA data, overall 2009 was weakest by temperature, 2000 by wind speed (weakest for bottom 4 levels, 2016 weakest at 10 and 30mb). Combining rankings gives 2009, 2016, but then 1996 ahead of 2000.

Incidentally, the preponderance of more recent years may possibly have a link to sea ice.... or it may not!

Turning to December 2015 in particular, it undeniably featured a very strong stratosphere vortex, but then is there a link to the weather conditions experienced?

On the face of it an AO ranking 9th of 67 years (since 1950) would suggest a strong troposphere vortex, perhaps tying in to the Antarctic circumpolar wind analogy locking cold into the Arctic. However, this is a contradiction with the notion of the jet powering towards the Arctic which requires some sort of compensatory flow southwards. This can be seen in this plot of 500mb meridional wind anomaly -

Southerly flow into western Europe and the US are clear but so is northerlies for Eastern Siberia, the northwest Atlantic, and from Russia into the Middle East and North Africa. The effects such as record European warmth can be seen below, but also some substantially colder though largely 'empty' regions so not receiving mention -

Full details from https://www.ncdc.noaa.gov/sotc/global/201512

Working down through the pressure levels, the NCEP/NCAR data shows that the December 60°N zonal wind was 3rd strongest (of 69 years from 1948) at 100mb, 18th at 250mb, 35th at 500mb, 33rd at 850mb and 36th at 1000mb - so the strength of the stratosphere doesn't seem to have been experienced lower down. Also, the NAO was a relatively modest 0.48 for such a mild December in western Europe (and wet for UK) ranking 23 of 67. The reason appears to be due to anomalous meridional circulation, which is one of the hallmark effects of ice loss theory.

edit: with a bit more time a better ranking of monthly values based upon combined standard deviation of wind and temperature anomalies (T80° or T60-90°) gives -

Strongest November, T80 - 1990, 2015, 1982 - T6090 - 1990, 2015, 2011

Weakest November, T80 - 2000, 2016, 2009 - T6090 - 2009, 2016, 2000

Strongest December, T80 - 2015, 1980, 2011 - T6090 - 2015, 1980, 2011

Weakest December (for interest's sake), T80 - 1987, 1998, 2000 - T6090 - 1987, 2000, 1998

Edited February 17, 2017 by Interitus

[stodge]

Afternoon all

A delayed report on the morning model output and it's a beautiful day here in London and whether you want to call it spring-like, Caribbean or just pleasant depends on your perspective but it's a world away from this time last week when we were watching snow flurries. It shows how the transition from winter to spring can be rapid but to be fair, that transition often comes with a sting in the tail.

Looking at the mid term outlook for the end of the month - Feb 27th to be precise - and starting with the GEM 00Z output:

Perhaps not as benign as it may first appear - a WSW'ly flow of modified PM air from a large LP just off SE Greenland. The attempt to ridge into Scandinavia will come to nothing even though heights are rising as the trough exits east. Note also the wintry flow over the Balkans with plenty of late snow.

ECM 00Z at the same time:

A milder airflow for the British Isles but a stiff breeze especially to windward coasts. The HP is centered over Germany but the slightly unusual orientation over Finland/NW Russia is already showing signs of being swept away by the strong SW'ly. Note how far that Atlantic trough is digging - almost to the Azores.

GFS 00Z at the same time:

The secondary LP in advance of the main feature quickly flattens the flow and the HP has no northern ridging. A lot of similarities with ECM in terms of the trough digging down.

The 06Z OP at the same time does something rather different with that secondary feature:

This allows the opportunity for a transient raise of heights over Scandinavia.

The 00Z output hinted strongly at a pattern change at the very end of FI:

The PV eases west into Canada, the jet slows and amplifies and pressure rises in the vicinity of the British Isles with a possible ridge to Scandinavia.

The 06Z however maintains the mobile theme:

The NH overview of the 00Z and 06Z tell the story:

It may simply be a question of timing - the movement of the PV on the 06Z is gradually NW into Canada so the possibility of a Greenland height rise three or four days later can't be discarded and that would fit with my timing of March 7th onward.

Finally, my favourite chart and indications of another assault from the Siberian side into early March:

[stodge]

Morning all

I deliberately haven't looked at any model output since Friday morning - two reasons, one I have a life and second, I refer you to the previous reason. 12c already here in my part of London and it could well be the warmest day of the year so far but perhaps already the warmest day of the 21-day Atlantic spell which is now at Day 6.

Looking ahead and after some unanimity last week, the medium term looks much more variable after what may be a brief 24-36 hour N'ly blast at the end of the week:

Starting with the 00Z GEM this morning at T+240:

From an unpromising position, GEM conjures a weak MLB to the NE of the British Isles. It's not really a Scandinavian HP as the one from earlier in the month and there looks too much energy to the north to stop it sinking. A small cut off feature off Biscay helps prop it up in the short term and I note the Atlantic trough digging well to the south.

ECM at the same time:

Very slack flow and an archetypal "haven't got a scooby doo" chart. The possibility of a height rise over Scandinavia and the British Isles can't be ruled out and with the Atlantic moribund you'd think there was plenty of opportunity for that. One of charts that makes you wonder where the evolution would go next.

GFS 00Z OP at the same time:

Perhaps a half way house of sorts between GEM and ECM. Again, as the lobe of PV energy exits Scandinavia, we see pressure rise and more than a hint of it on this chart and perhaps something more sustainable than GEM with a lack of energy to the north. The Atlantic seems moribund here as well.

From here of course the GFS "goes off on one" as some might say and by March 7th, Day 21 we are at:

Something very different and potentially much colder than we have currently with the hint of some colder air feeding in from the east and the Atlantic well displaced to the south and west.

The NH view at the same time shows the weakened PV displaced well over Canada:

On a more cautionary note the 10 HPA st the same time:

I say "cautionary" because the PV won't be finished off by the second warming about to start and the third warming from the Siberian side for early next month is now looking weaker. Comparing the forecast 10 HPA with the equivalent actual from 2013

I'm interested in the positioning and the intensity - it was a colder, more organised PV back then and the resulting tropospheric picture was:

Some similarities in the synoptic evolution but it was a few days later we got that really cold feed of air from the east. MY view at the moment is that this March will be a watered down version of 2013 - less cold and possibly drier but it will still be cold and the possibility of snow has far from disappeared.

To conclude, very early days but I do think we have a possibility of a significant pattern change soon after the beginning of March. The options of an MLB over the British Isles or perhaps some HLB ridging SE from Greenland are both on the table - it may even be the HP will set up to the south and continue our early spring weather but I think that's the least likely option at this time.

The ongoing stratospheric developments remain of interest - oddly enough, we don't want a third strong warming if we want cold.

Enjoy today's warmth - it may be as good as it gets for a while. 

[stodge]

Morning all

After yesterday's exceptional warmth in the south east (18c recorded at a number of locations), it's back to more traditional mild temperatures at 13-14c for the next couple of days - still well above the 9-10c which is the normal London maximum for late February.

The weekend may or not see a N'ly blast of dubious severity (quite likely northern hills will see some snow and perhaps some lower ground in the far north but for the rest of us a short chillier burst) before a reset to more normal Atlantic conditions next week. Today is Day 7 of the 21- day milder Atlantic dominated spell forecasted last week as a direct result of the second major warming of the stratosphere which is shortly under way.

Let's have a look at the medium term taking us to the end of next week - Friday March 3rd.

GEM 00Z at T+240:

On first look, a strongly Atlantic dominated chart but not quite as clear cut with a strong Gulf of Genoa LP providing the opportunity for the Azores HP to ridge into Scandinavia - there's a little spoiler in the way but that may or may not be relevant so we could see a new pressure rise. The northern arm of the jet appears strong however and absolutely no sign at this stage of any height rises in Greenland.

ECM at the same time:

A more defined Atlantic profile and the Azores HP more suppressed. A mild SW'ly flow and generally pleasant conditions for much of the British Isles. A more confused pressure set up over Scandinavia - hints of a ridge but no more. The jet may be weaker to the north but you can't really say there's much evidence of blocking.

GFS 00Z at the same time:

And the 06Z OP at the same time:

A very different evolution from GEM and ECM in all honesty. We get the HP building over the UK and then sinking SE in the face of the strong northern arm of the jet. It's a repetition of the pattern from earlier in the month up to a point. A fairly non descript E'ly on both charts for the south.

Switching to the Northern Hemisphere view for the end of the OP run, here's the 06Z:

And the 00Z OP;

As similar as two completely dissimilar things in a pod (as someone once said). The 00Z OP evolution is actually similar to yesterday's though with the core of HP more to the NE of the UK than Greenland but the vortex is pushed over Canada allowing for height rises to the north of the British Isles. The 06Z is entirely different and maintains a very strong PV.

Finally, the chart everyone else loves to ignore - the 10 HPA temperature. Here it is for the 00Z OP at the end of the run:

Not dissimilar to yesterday with the tropospheric outcome we've already seen.

Here's the 06Z OP:

It's different - not very different but different and perhaps this is the key to the tropospheric evolution. The question for me remains whether the weaker third warming scheduled for 6-8 March will either displace the PV further to the Canadian side or re-consolidate it in the Canada/Greenland area. The 2013 evolution I showed yesterday is closer to the 00Z than the 06Z and that explains the tropospheric scenario. I just wonder if the 06Z OP is playing a more traditional response to the Siberian warming.

Just glancing at the 00Z GEFS and plenty of support for raiding heights in the Greenland area so we'll see where that goes in the coming days.

[stodge]

Morning all

Apologies for the lack of report yesterday - a busy day.

Plenty of weather happening at the moment as Doris moves in - good luck to those in Scotland seeing some snow and I hope the strong winds further south don't cause too many problems but it's the first notable storm for a while. This was well forecast in concept if not detail a week or so ago.

We're midway, as I reckon it, between the end of the early February cold spell and what I hope will be an intriguing pattern change going into March. Earlier in the week, there were clear signs the models were sniffing something (aren't we all ?) into next month so let's see where we are looking ahead to March 5th or thereabouts:

I'm going to take the Northern Hemisphere view for a change this morning so starting with GEM:

No sign of a pattern change there it has to be said. The PV continues very strong between NE Canada and Greenland and a broad SW'ly flow over the British Isles is maintained. There is a strong Eurasian HP but poorly orientated (North-South rather than West-East) so of no use to western Europe. The Azores HP remains suppressed so an unsettled mobile regime looks to dominate.

ECM at the same time:

Similar but different would be my view. The British Isles remains in a SW'ly flow with the PV still well in place but the Eurasian HP is much better positioned and aligned but still too far away to have any influence at this time.

GFS 00Z OP at the same time:

Something very different here and not wholly out of tune with some of its evolutions over the past week or so. The PV is that bit further west into Canada and this has allowed heights to rise to the north of the British Isles with the jet displaced further south. The LP systems are further south yet it's still a broadly WSW'ly flow albeit very unsettled with rain or showers.

Unfortunately, the PV simply dumb-belles round in situ and the Greenland heights are killed off albeit with the jet still in a more southerly position into furthest FI.

The Control at the same time is very different and goes on to deliver the pattern change in a very good run for fans of cold:

Looking at the GEFS at T+240 there are plenty of cold solutions in the mix. The spread is not on the Greenland heights but on the strength of the Atlantic LP systems. If the trough is aligned more to the SE than the E the chance exists for the Greenland ridging to become more influential so there's plenty of scope for change at this stage.

The differences in the two Trop evolutions are evident in the way they are forecasting the 10HPA stratospheric temperatures.

Here's the GFS 00Z 10 HPA T+384:

And the equivalent PRMSL chart:

And the same for the Control at the same time:

Very different. The OP maintains the PV, albeit weakened and the next warming sends it back over to NE Canada/Greenland starting the next 10-14 day tropospheric lag. With no warming on the Control, the PV meanders around allowing the tropospheric response in the form of height rises over Greenland and the resulting trough into Scandinavia.

All in all, perhaps a step back as it would have been ice to have seen the GFS OP go strongly on a pattern change but it's still there very strongly in the GEFS. The other models aren't sniffing it so strongly as yet but it's only just coming into range. The warming occurring now is going to have the usual 10-14 day lag so it could be March 9th before we see the full manifestation of the pattern change or it may be nothing will happen at all.

 

Edited February 23, 2017 by stodge

[stodge]

Morning all

After the perturbation of Doris yesterday, something a deal calmer today. Even in lowland East London, we lost a fence slat in the big squall around 8.30am and we had quite a few hours of strong gusts until well into the afternoon.

Enough of the past and present and time to muse on the future looking ahead into March as we try to establish if this winter has any "bang" left or whether it will whimper quietly into an early spring. It's been 10 days since the end of the last cold spell and I predicted at that time a 21-day period of milder Atlantic-dominated weather before the major warming (on going as we speak) provided a window of tropospheric opportunity for a pattern change.

Theoretically, the medium range of the model outputs should be showing that change so let's see if I'm on the money or heading for the café for a double helping of humble pie with a side order of egg on face:

Let's start with GEM and the 00Z OP:

 Not sure what to make of this in all honesty. Some signs of pressure rises over Greenland but nothing very significant and a deep but small LP going nowhere slowly in mid-Atlantic. Ridging from the Azores offering the chance of height rises in Scandinavia via a shallow ridge. All a bit messy.

ECM 00Z OP at the same time:

Not a million miles away from the GEM. The first obvious point is the southerly tracking jet which would keep the weather unsettled at best. Heights are more to the north of the British Isles than over Greenland and aren't strong at this time and there remains a notable PV presence to the far north. The Azores HP is much more suppressed to the south and you'd think the LP would more likely more SE into Europe than NE into Scandinavia. Interesting.

GFS 00Z OP at the same time:

Once again, we have the deep mid-Atlantic LP but there are definite heights over Greenland and the jet looks to be keeping to the south. We have a more organised trough over Scandinavia with a lobe of very cold air which could track SE and graze the far NE of Scotland.

Switching to the NH view of things, the chart for the same time as follows:

Moving on into further FI and we end with this:

Am I looking at a west-based negative NAO ? Perhaps. I am seeing a southerly-tracking jet and plenty of heights over the Pole and to the NE. An interesting evolution and one to keep an eye on.

As far as the GEFS is concerned at T+240, there are a lot of cold options on the table and very little spread suggesting the OP outcome may not be wholly implausible. At T+384, it's interesting to note the spread in mid-Atlantic is affected by a couple of members building a mid-Atlantic ridge so again the spread suggests the OP is there with the majority at this stage.

Looking at the 10 HPA temperature profile, it's interesting to note the "third warming" has been downgraded considerably this morning and this is, I think, excellent news for cold fans. The likely warming would have had the effect of re-consolidating the PV back over Canada/Greenland. Without that, the weakened PV begins to wander and while I've been putting this together, the 06Z has rolled out and the T+384 chart from the NH perspective demonstrates this:

A very good chart for pattern change fans. The PV is lifting out to Scandinavia and the angle of the LP is shifting more NW-SE so the heights can build as pressure drops over Scandinavia and the possibility of a cold NE'ly flow remains very much on the table.

All in all, using the dreaded "P" word, there is much potential for a pattern change into March. The weakened PV is eased further west allowing for heights to build to the NW or N of the British Isles and with the jet heading south, the chance of an early spring cold outbreak before mid March is clearly there. As always, the British Isles needs a touch or more of good fortune but at this early stage, the signs are encouraging and there'll be plenty of chart interest, I think, once we get past the end of this month.

 

[Interitus]

 

On 2/7/2017 at 11:05, Bring Back1962-63 said:

Another useful indicator for assessing the likely future strength of the Jet Stream in the Atlantic is the thermal contrast between the eastern USA and the adjacent ocean. Right now and for at least the next week much of the USA will continue to have an unusually mild period. Canada is pretty cold but it rapidly turns milder further south. So, nothing here at all in helping to power up the Jet Stream.

Just a minor quibble, while the temperature observations were generally correct, the comment relating to the jet stream was slightly awry. The temperature contrasts helped create a powerful nor'easter, the formation of which was widely described as "bombogenesis" (the weather bomb is popular at the moment). This gave blizzards for the northeastern States, described in typically fine fashion at wunderground - https://www.wunderground.com/blog/JeffMasters/comment.html?entrynum=3556

In association with this depression, the contrasts went on to generate a powerful jet streak over the northwest Atlantic -

It just wasn't aimed in our direction, instead with the extreme amplification it headed into the Arctic, with the subtropical originated air giving Iceland a provisional new record February maximum temperature of 19.1°C.

I had meant to mention this a while ago, but much has been made of the jet stream in relation to 'Doris' this week which gives the opportunity to post this excellent cross section by Hannah Attard of the jet streak shown above -

The right hand side shows the mild Atlantic air with a dynamic tropopause height defined by 1.5 potential vorticity units at or above 200 mb, and roughly between 300 and 500 mb in the cold Arctic air on the left. In the centre is a deep tropopause fold bringing stratospheric air down to a ridiculously low 700-850 mb, beneath a jet core in excess of 90 m/s or over 200 mph. The blue shading highlights the strong horizontal potential temperature gradients involved. edit: Just to add it shows a classic example of an upper-tropospheric / lower-stratospheric front system with the jet sandwiched in between, which has been a focus of Attard at the Lang research group, compare with chart below, more details and explanation - http://www.atmos.albany.edu/facstaff/andrea/research.html#jet

Edited March 5, 2017 by Interitus

[Singularity]

Great chart there Interitus, thanks for sharing 

Just taking a moment now to think about whether the MJO is going to produce interesting events for early March 2017 or not.

Looking at this MJO-filtered product, we see that the wind signal left phase 8 on 20th at 850 hPa but back on 16th or 17th at 200 hPa. Since then the 200 has become weak but 850 is holding on better and looks to retain some degree of signal through phase 2.

It's the phase 8 timing that's of most interest for the mid-range though, as a 10 day lag for encouraging height rises to the NW of the UK is not uncommon, and we have been seeing hints from recent model runs of such events around the turn of the month. In fact more than that; a clear 'bubble' of higher heights across Greenland by 1st which may have some support from the stratosphere as a ridge is also evident up at 30 hPa for example. Or perhaps the ridge works up from the troposphere? Either way it has scope for being very persistent in early March.

Trouble for us, though, has been a lack of much indication that the Atlantic jet will take a breather in the mid-Atlantic and allow the subtropical high to link up with the Greenland High and at the very least pull us out of the unsettled regime. Without that happening, lows just keep on rolling in further south than usual and producing excessive amounts of rain and perhaps some strong wind events. The 00z (day 10 shown below) was in line with this and most recent operational runs from it and ECM.

There have, however, been some attempts among the ensembles to hold up the Atlantic troughs long enough to allow the connecting ridge scenario to unfold, and the GFS 06z is the first operational in a while to at least give it a go, as shown below using the day 10 and 12 charts.

 

Interestingly, this run then moves the ridge into Scandinavia for a time before retrogressing it to become a stronger feature to our N/NW (see day 16 chart below-left). This may be tied in with the stratospheric vortex being kept more displaced toward Siberia (see below-middle) than was the case in the 00z run for example. Either that or the model has started taking the MJO to phase 3 in the mid-range as per the notably enthusiastic UKMO (see yesterday's update, below-right), which corresponds to height rises to our NW and would probably shake things up a bit.

   

Coming back to that displacement again though and believe it or not, pre-winter one of the strongest matching years for 2016-17 in terms of a wide array of teleconnections/drivers, including the state of the stratospheric vortex in late autumn, was 1952, and that winter saw the vortex displaced to Siberia more persistently than any other that I've seen. In light of which, frequent displacements that way have not been surprising to see this winter - but I had hoped they would be further toward East Asia with a stronger warming and positive GPH situation around Canada and Greenland. as opposed to the current situation which just seems to encourage a (somehow?) still dominant tropospheric Canada/Greenland vortex to keep handing off lows to a weaker one across Siberia, on a path that brings the UK either predominantly mild and quite benign or - based on next week's output - very changeable conditions in terms of temps, with a fair bit of rain around.

[stodge]

1 hour ago, Singularity said:

Coming back to that displacement again though and believe it or not, pre-winter one of the strongest matching years for 2016-17 in terms of a wide array of teleconnections/drivers, including the state of the stratospheric vortex in late autumn, was 1952, and that winter saw the vortex displaced to Siberia more persistently than any other that I've seen. In light of which, frequent displacements that way have not been surprising to see this winter - but I had hoped they would be further toward East Asia with a stronger warming and positive GPH situation around Canada and Greenland. as opposed to the current situation which just seems to encourage a (somehow?) still dominant tropospheric Canada/Greenland vortex to keep handing off lows to a weaker one across Siberia, on a path that brings the UK either predominantly mild and quite benign or - based on next week's output - very changeable conditions in terms of temps, with a fair bit of rain around.

Interesting contribution and I've snipped only for ease of reading for others.

I see two issues and I wonder if these happened during other spells of predominantly snow free winters in the UK: - first, the warmings seem to come disproportionately from the Siberian side and that has the initial response of throwing the PV back to NE Canada/Greenland. We would need a significant Canadian warming to displace the PV to Siberia.

Second, even when vortex displacement occurs, it isn't a "clean" lift leaving enough residual energy over Canada/Greenland to help the LP factory going and prevent the formation of HLB.

So the process is warming leading to vortex consolidation over NE Canada/Greenland leading to a messy secondary displacement to Siberia leading to a new warming sending the energy back to Canada/Greenland and the cycle repeats and the best the British Isles can hope for is either a brief N'ly regime or a Scandinavian HP which inevitably sinks as the PV displaces back to Siberia and the northern arm fires up.

Later in the winter/spring the PV is weaker and there is more opportunity for it to be further displaced west into Canada giving Greenland HLB a chance so a cold March is always more likely than a cold December on that basis. Exceptional winters (which this hasn't been) need a break in the cycle either via a Canadian warming or a clean displacement to Siberia.