Model output discussion - proper cold spell inbound?

[ICE COLD]

Can't stop looking at this peach of a chart . I just LOVE it ?. 

[winterof79]

This is worth the entry fee alone the lump of PV across the ARCTIC may feed and support our HLB as the weather starts flowing in reverse in the NH

Edited February 8, 2018 by winterof79

[Banbury]

13 minutes ago, winterof79 said:

Well the way I read it is it will be fairly HLB and it aint going to be over Canada so that leaves Greenland or Scandi or both ,heavens that would be rather nice.There is the chance that we may get a blend of Svaldanavianland....sends a shiver down the spine.

I wouldn’t disagree with that , just a bit of luck and we are laughing 

[andymusic]

ecm and gfs models firming up on 18th - 20th Feb to start the ball rolling on the easterly cold track - a little tweety bird has spoken too - Major blocking develop, First place to get it, western Europe. Already started around Paris, but plenty of snow on the way for UK and western Europe next  2-3 weeks.

[Chevron12345]

1 minute ago, ICE COLD said:

Can't stop looking at this peach of a chart . I just LOVE it ?. 

Where can I get a closer look at the uppers on such a chart. Thanks.

[winterof79]

1 minute ago, Chevron12345 said:

Where can I get a closer look at the uppers on such a chart. Thanks.

[Guest]

LOOKING FOR SIGNS IN THE OUTPUT OF THE UPCOMING "POSSIBLE" MID MONTH COLD SPELL

My posts written directly for the model thread are becoming increasingly rare as I focus much of my spare time developing the teleconnections learning thread. Although I still enjoy cold and snowy weather like the majority on the MOD, I have become a good deal more balanced in my posts this winter. Today we saw an outstanding post from @Tamara explaining in pretty simple terms what the rather conflicting background signals are telling us. As usual she pointed out what can go wrong as well as what can now go right in terms of delivering a more significant cold spell after mid February. I have been learning a lot more about the importance and relevance of these drivers but I will not dwell on these in this post - just a very brief summary of what the background signals are telling us. I shall write a more comprehensive post for the learning thread on this in a week or so. There has been quite a bit of excitement and hype on the MOD recently regarding the longer term potential for a broad pattern change to a much colder regime. I will assess some of the longer term output and look for possible signs of the changes.

Very Brief Summary of the Key Background Signals and Drivers:

The east pacific based La Nina weakened its grip very slightly in the second half of January. It is still making a fairly significant impact. Atmospheric Angular Momentum (AAM) tendency had been negative for much of this winter but spiked upwards towards the end of January. Frictional Torque (FT) spiked and went positive from around January 22nd. With the usual 10 to 14 day time lag this eventually led to strongly rising Mountain Torque (MT). This process began just a few days ago and there is a further overall 10 to 14 day time lag for this to impact (probably around or just after mid February). Despite the persistent Nina signal, the bounce back in AAM and rising torques overcame this. The MJO which had been suppressed in its key phases of 7, 8 and 1 when it last reached that stage of it's cycle in late December (mostly due to falling AAM and the quite strong east Pacific La Nina at that time) has now reached phase 7 at very high amplitude. So, the AAM, FT, MT and the MJO have at least temporarily overcome the underlying Nina signal. The +ve MT is setting a wave train in motion through the troposphere which "can" control the jet stream, set up ridges and troughs and also favour HLB patterns. Concurrent to this we are seeing signs of a significant warming in the stratosphere and potentially a sudden stratospheric warming (SSW) event. The tropical energy forcing that eventually leads to the rising MT also reaches high up into the lower stratosphere. It can be at least a partial contributory factor to assisting with warming events and SSWs but there are other processes at play as well (and all this is the subject of considerable debate amongst the experts and some of it is discussed on the strat thread).

From a coldies' perspective, it might appear that on this occasion, we have at last got almost all our ducks in row and a prolonged cold spell would seem to be inevitable. Unfortunately, it is not quite as simple as that as Tamara was very careful to point out this afternoon. Yes, things are generally in place to see at least "some" blocking patterns develop just after mid month (give or take a couple of days) even without any SSW assistance. The actual timing is not quite perfect. The MJO will already be progressing through its cycle and there has been some disagreement between the GFS and ECM output for several days as can be seen in today's charts below:

          NCEP/GEFS  Feb 8th to Feb 22nd                    ECM  Feb 8th to Feb 22nd

                            

GFS holds the MJO in phase 7 throughout and maintains it a good amplitude whereas ECM takes it quite quickly through phase 8 and towards phase 1 at steadily decreasing amplitude and showing signs of entering the circle of death. I believe that even with the less attractive ECM outcome, the MJO should remain pretty active in the favourable phases for long enough to at least assist initially. Then we are starting to see AAM and FT dropping back and with conflicting forecasts of whether it will go negative again or stay at least slightly positive for longer. If it goes quite strongly negative this may abbreviate the length of the cold spell. I will not show any charts here (Tamara and others have shown a few) but the last couple of days show a reining in of the degree -AAM and it might assist for a few days longer. Remember that these changes all have a 10 to 14 day time lag which would take us into the final week of February - so probably not too much initial damage. Then will the stratosphere play ball? Will MT remain positive for long enough to assist.? Will the combination of earlier attacks on the stratospheric polar vortex and the anticipated renewed attacks be sufficient to impact on the troposphere/ Will this impact quickly or more slowly? If this is all favourable then it should assist in developing some extended HLB patterns with cold being released from the Arctic towards the middle latitudes. Will all this be in sufficient enough time to take place before other drivers start to hinder rather than help the process? Will the blocking set up favourably to deliver the cold to western Europe and the UK? An awful lot of uncertainties. Some of the strat guys who post on here have been pretty bullish, perhaps with good justification. I believe that we'll see at least of few days of a much colder pattern. Once this develops it may become entrenched. Certainly, the Met Office with their sophisticated tools are "currently" suggesting a period of quite prolonged colder weather but this might change. All the above drivers need to be kept under review. We have probably entered a period offering the greatest "potential" for a decent cold spell since the March 2013 spell.

Current Model Output for Mid February and Beyond:

Let's now have a closer look at the current model output. This is one occasion when we need to focus on the extended period. I am not looking for any detail at this stage but for general signs of whether the models are starting to sniff out these changes. Just judging by the the MJO forecast discrepancies and the MetO longer term outlook, I am expecting quite a lot of uncertainty. I'll start with a cross model analysis for day 10 but will include UKMO which only goes up to day 6 and NAVGEM (up to day 7/8). This will be from today's 12z output accept the JMA from yesterday's 12z (T+264 to match timings).

                UKMO T+144                                        GFS T+240                                       ECM T+240                                      GEM T+240                                   NAVGEM T+180 

              

        JMA T+264 (Feb 7th 12z)                   GEFS Control T+240                         GEFS Mean T+240                               GEFS Panel T+240   

               

As expected UKMO is really 3 days too early. Nevertheless it shows a strong build of pressure through eastern Scandinavia and north-west Russia right into the Arctic. It looks primed for a further build of pressure to our north-east which would be consistent with its 30 day forecast - one to watch.  GFS has been showing a strong build of pressure to our north-east in FI for quite a few runs now and this is moving forward progressively with each run. ECM has joined the party and is showing a strong build of pressure from the Azores right into the Arctic. The LP to our south-east is sinking and there is strong HP over Russia. There is a strong indication that this will build through Scandinavia. GEM is in the process of building the the classic Siberian/Russian/Scandinavian/Greenland belt of HP with LP over us sinking southeastwards into Europe. Navgem only goes up to day 7/8 but has strong HP over Siberia and Russia building into the Arctic and Greenland. The LP to our west is stalling and filling so there are again signs that there will be a strong rise of pressure to our north-east with 2 to 3 days from there. JMA also has LP over us sinking south or south-eastwards with the Azores HP ridging strongly north-eastwards and looking set to link up with strong HP over Russia.  The GEFS control is very similar to the GFS operation chart. The mean is rather misleading (as often is the case) as it averages out all 20 ensemble members + the control and op runs. Nevertheless, it shows strong HP over Russia and into the Arctic and LP over the central Med. Moving on to the panel. What a fascinating mix of almost entirely cold charts. Some are rather more progressive than others in developing the HP to our north-east. Several have slack LP near or over us. Several others have stronger LP to our west but stalling against the developing cold block to our east. Several show a Scandinavian, Arctic or Greenland HP. Now I can see why the mean charts was so misleading. Almost all of the members are at various stages of ushering in a cold or very cold pattern. Overall, I was surprised to see such strong cross-model agreement of the upcoming cold spell. There is room for further enhancements and we should be seeing some very attractive cold weather charts moving into the reliable period during the next few days. 

As I indicated above, it is far too early to know how long the cold spell will last. Early signs are pretty positive. Just how cold will it get? I did a comprehensive temperature, snow, ice and sea surface temperature analysis of the Arctic and Eurasia in my long reports last week. All three parts of this appear on page 5 of the Teleconnections Learning thread. Here's the link:

 https://www.netweather.tv/forum/topic/89161-learning-about-teleconnection-science-and-background-signals/?page=5             

Finally, I will take a look at some of the ensemble charts for certain locations. These are all GEFS 12z 15 day charts from Feb 8th to Feb 23rd:

                   London 2m temps                                     London 850 temps                                         Berlin 2m temps                                     Berlin 850 temps    

                   

                  Moscow 2m temps                                     Moscow 850 temps                                       Helsinki 2m temps                                     Helsinki 850 temps     

                     

There is still quite a spread for London but the mean temps towards the end drop into the 0c to 4c range with 850s close to -5c. With hieght rises most likely to our north-east we should be looking in that direction. The Berlin temps are generally close 0c and falling closer to -5c towards the end with 850s below -5c with some much lower members. Moscow is now seeing it's coldest weather of the winter with the mean mostly in the -10c to 15c range but with some much lower values that go off the chart. The 850s fall away steadily from -5c to 10c  to -15c and lower. Helsinki is mostly 0c to -5c but falling slightly later on with the 850s averaging around -8c.

Overall there is plenty of evidence of at least a decent cold spell lasting for at least a week. There is potential for it to become very cold and last a lot longer but we need to watch a number of indicators. It is far too early to say whether this will be a dry spell or a snowy one. We should get far more detail on that by the middle of next week. My next post will be on the learning thread and I expect that this thread will go into overdrive very soon. This is the most exciting period for model watching for at least 5 years. Are we on the cusp of something quite memorable? 

 

 

Edited February 8, 2018 by Guest
Correct typos and check charts & links

[Chevron12345]

Just now, winterof79 said:

Thanks, but is there a link. Thanks kindly.

[winterof79]

2 minutes ago, Chevron12345 said:

Thanks, but is there a link. Thanks kindly.

http://www.meteociel.fr/modeles/ecmwf.php?ech=72&mode=0&map=1&type=0&archive=0

Have a play Chevron.

Edited February 8, 2018 by winterof79

[Summer Sun]

6 minutes ago, Chevron12345 said:

Where can I get a closer look at the uppers on such a chart. Thanks.

Here http://www.meteociel.fr/modeles/ecmwf.php?ech=72&mode=0&map=3&type=0&archive=0

If it doesn't directly link click UK

Edited February 8, 2018 by Summer Sun

[Shunter]

7 minutes ago, winterof79 said:

This is worth the entry fee alone

Synoptically appetising yes.....but in reality its 16 days away and shows temperatures of between 4 & 6C nationwide. Nothing out of the ordinary. 

[winterof79]

10 minutes ago, Shunter said:

Synoptically appetising yes.....but in reality its 16 days away and shows temperatures of between 4 & 6C nationwide. Nothing out of the ordinary. 

 

I meant the evolution really if you click it bud. I know its miles away

Edited February 8, 2018 by winterof79

[markw2680]

Let’s be positive...when not if these kind of charts come within a couple of days I think most on here including myself will become very excited ? 

[Met4Cast]

I think people need to realise that this isn't the usual "the GFS is showing something decent in FI, but it's FI so it's not going to happen".

We have solid background signals for a strong reversal of the Westerly zonal winds, we have the SSW taking place, we have the MJO also working in our favour for HLB. Of course, looking at detail 10-16 days out is never going to work out well for you, but looking at the overall trends and broad patterns, we can be more confident when the models are showing HLB because the background signals are fully supportive of it. 

We know HLB is likely, this was being said by the strat experts on here before the models were showing it. We're starting from a point of knowledge, an expectation based on the background signals of what the models are likely to be showing, and thus far they're matching those expectations.

All winter we've been "chasing" cold patterns out in FI, hoping they materialise. This time, we're expecting the cold patterns to appear, and they are.

[markw2680]

8 minutes ago, Daniel Smith said:

I think people need to realise that this isn't the usual "the GFS is showing something decent in FI, but it's FI so it's not going to happen".

We have solid background signals for a strong reversal of the Westerly zonal winds, we have the SSW taking place, we have the MJO also working in our favour for HLB. Of course, looking at detail 10-16 days out is never going to work out well for you, but looking at the overall trends and broad patterns, we can be more confident when the models are showing HLB because the background signals are fully supportive of it. 

We know HLB is likely, this was being said by the strat experts on here before the models were showing it. We're starting from a point of knowledge, an expectation based on the background signals of what the models are likely to be showing, and thus far they're matching those expectations.

All winter we've been "chasing" cold patterns out in FI, hoping they materialise. This time, we're expecting the cold patterns to appear, and they are.

Very well explained. Just got to hope it all lands well for uk cold in the end

[Singularity]

 

How's that for a stratosphere-troposphere influence? It even has the shallow remnant vortex lobe over Scandinavia quite well connected.

Let's see if we can build on this in the morning i.e. see no delays to the 'rise of the high latitude blocking' while following them up with further mouth-watering charts. 

[Stuie]

2 minutes ago, Singularity said:

 

How's that for a stratosphere-troposphere influence? It even has the shallow remnant vortex lobe over Scandinavia quite well connected.

Let's see if we can build on this in the morning i.e. see no delays to the 'rise of the high latitude blocking' while following them up with further mouth-watering charts. 

2nd chart, not a single figure below 1000mb, not sure I have seen that before.

[damianslaw]

Alot of cross model agreement tonight - not often you can say that, and right up to the 240 hr mark. What are they showing? A slowly sinking trough through the UK next week, with cold air embedded within, thanks to the cold canadian source, indeed the next few days will bring some very cold uppers into the north atlantic, with threat of snow down to low levels in the north at times.

At the same time we have continued signal for heights to build out of Siberia into NW Russia. An attack on the PV looks imminent, and combined with the slowly sinking trough on a SE trajectory, we then have a classic signature pattern for a much colder northern blocking set up, azores high ridging north through the atlantic, shooting north in no time, linking with the heights ridging SW out of NW Russia. Both ECM and GFS showing such a scenario which would tie in with some of the expectations being made with regard to impact of SSW.

The models are showing an almost text book evolution to a marked colder pattern. 

I haven't seen the AO and NAO forecasts, but I suspect these will be showing very negative values for the latter part of the month. We have had not one day this winter so far with a negative NAO value, look how it turned positive bang on 1 December.

Colder blocked patterns tend to be far more likely once we hit mid February, and as yesteryear has show can become very entrenched for lengthy periods, with the atlantic in far less gusto mode compared to Oct-Jan period.

I'm reminded back to late Feb 2005 and how the easterly appeared out of nowhere, and lasted a good 2-3 weeks on the back of a very mild atlantic driven winter. 

As others have stated a colder sustained outlook is certainly not a dead cert, but we are seeing signals aligning together that suggest the highest odds of such a outcome occuring since Feb-Mar 2013. We've had five years with barely a dose of northern blocking at all in the colder months of the year..

Edited February 8, 2018 by damianslaw

[Mucka]

I feel sure we will find ECM 12z was actually quite progressive.

My take on it is that both ECM and GFS are half right and half wrong but in different ways 

What I mean to say is that I think GFS is probably modelling the deep Atlantic trough better but ECM is modelling the upstream from there better,

I said this morning I thought ECM was too organised and progressive with the trough, pushing it right over the UK with virtually no disruption or weakening

It has improved that somewhat this evening holding the trough back and disrupting energy SE.

However it is still progressive compared to GFS which is somewhat the reverse of how these models usually perform.

GFS wants to split the trough and send energy SE which results in much better blocking to our E/NE for the same period

However these differences are areversed upstream where ECM is slow and amplified and GFS fast and flat.

So I think it is fair to say neither model can be relied upon to have the right outcome at this stage but what if GFS is correct with the better trough disruption earlier and  ECM with the upstream amplification?

Sure, the downstream interacts with the upstream and vice versa, the data is shared so to speak, so change one downstream variable and you change the value of an upstream variable - eg more blocking downstream, less progression upstream - but I think it very possible we will see a blend of the two models.

That is to say I expect ECM to have a little more disruption still of the trough and blocking to the East further West than currently modelled but GFS to be a little less so enthusiastic with that but then be more amplified in the Atlantic later.

Either way it is good to see that the outcome is well placed MLB leading to HLB with GFS pushing a ridge to our East NW and ECM pushing a ridge to our West NE but again the perfect scenario (and plausible one) is that they are both only solving half the puzzle, so we may well see both a strong Atantic ridge and high pressure to our NE with Atlantic blocking being more prominent and so potentially a cut off Greenland high later reinforced by Scandi ridge. 

We shall see.

 

 

 

 

Edited February 8, 2018 by Mucka

[Ice Day]

Well this is what's causing the kerfuffle in here, the strat warming is underway at midnight tonight (or near enough anyway)

This has been incredibly modelled by the GFS all the way down from 300 hours plus.

So now we need a few days to see how this bleeds into the weather on the ground, but I suspect it will be early next week until we start to get a true handle on where the ridging (assuming there is some) happens.  What is clear to me is that is quite a long window of opportunity, especially given the second warming event that's being modelled.  We're going to have some incredible ups and downs over the next few days, enjoy the ride and remember....it's only the weather!

[Catacol]

5 hours ago, prolongedSnowLover said:

Need to get rid of the cyclogenesis showing south of Greenland at t186.

Dont agree - that's what brings the snow. Fronts disrupting and sliding against the block until we end on SW England's version of Narnia

Not much from me at the moment.... I'm underwhelmed by the coming weekend and just drumming my fingers impatiently to get to the middle of next week when the models will begin to firm up on what is coming.

 

[fromey]

15 minutes ago, damianslaw said:

Alot of cross model agreement tonight - not often you can say that, and right up to the 240 hr mark. What are they showing? A slowly sinking trough through the UK next week, with cold air embedded within, thanks to the cold canadian source, indeed the next few days will bring some very cold uppers into the north atlantic, with threat of snow down to low levels in the north at times.

At the same time we have continued signal for heights to build out of Siberia into NW Russia. An attack on the PV looks imminent, and combined with the slowly sinking trough on a SE trajectory, we then have a classic signature pattern for a much colder northern blocking set up, azores high ridging north through the atlantic, shooting north in no time, linking with the heights ridging SW out of NW Russia. Both ECM and GFS showing such a scenario which would tie in with some of the expectations being made with regard to impact of SSW.

The models are showing an almost text book evolution to a marked colder pattern. 

I haven't seen the AO and NAO forecasts, but I suspect these will be showing very negative values for the latter part of the month. We have had not one day this winter so far with a negative NAO value, look how it turned positive bang on 1 December.

Colder blocked patterns tend to be far more likely once we hit mid February, and as yesteryear has show can become very entrenched for lengthy periods, with the atlantic in far less gusto mode compared to Oct-Jan period.

I'm reminded back to late Feb 2005 and how the easterly appeared out of nowhere, and lasted a good 2-3 weeks on the back of a very mild atlantic driven winter. 

As others have stated a colder sustained outlook is certainly not a dead cert, but we are seeing signals aligning together that suggest the highest odds of such a outcome occuring since Feb-Mar 2013. We've had five years with barely a dose of northern blocking at all in the colder months of the year..

Here you go

[Catacol]

Deleted...

Edited February 8, 2018 by Catacol

[lorenzo]

Right Pub run - you are due us a been on the vodka since noon special  - if not tonight - Friday is fine to lead us into the weekend... 

One of the 'weather lore' bits of model watching was that a) the 18zGFS followed the ECM and, b) the pub run has the habit of sniffing out easterlies. Perfect time to test this vs, the #standard W>E bias...

[Banbury]

Interesting how we view the models and are most of us anyway optimistic that HP will develop.....Beeb rating it as a small chance ......also watching Tuesday as the front could bring a covering of snow for many