Model output discussion - 20th Feb onwards

[phil nw.]

The GFS 12z run compared with the earlier 06z is vastly different in the later frames and shows how differently the pv is modeled.

There is certainly a case to be made for mid-latitude blocking and doubtless the UK high modeled in all the ops and ens runs for about 5 days onwards will  appear.

It looks set to hang around for some days and should produce some warm sunshine in many places. Of course the exact details will need fine tuning in near time forecasts though under any calm and clear conditions we may well see night frosts and patchy fog.

Looking beyond day 10 the trend in the ens does support a Scandi trough and a cool down but as yet i cannot see any strong support for a cold easterly in the next 2 weeks

Beyond that who knows a lot depends on how the vortex splits during it's demise but currently, in the modeling period i can see, any remaining deep cold from the Arctic looks like heading further east.

Edited March 7, 2016 by phil nw.

[Singularity]

So what, we kick the theoretical impacts of a SSW and vortex split centered NE of the UK out of the window and stick with mid-latitude blocking for the foreseeable?

I understand that a response as fast as the GFS 06z and ECM 00z runs showed is at the speedy end of possibilities, but to consider following a path like the GFS 12z days 10-16 just seems ridiculous to me unless - and this is a big unless - the split doesn't propagate down as effectively as the majority of splitting events in times past have managed.

Puzzling times, and a complete nightmare for those who have long called for a mostly cold March this year with mean temperatures more than 1*C below the LTA. You think you can see the trend in the models aligning with expectations, and then bam! - it all goes haywire again.

You see I have conflicted interests here; I don't like cold weather in March (unless, I suppose, it's a brief snowy spell), but I have spent so long expecting it based on scientific reasoning that for the month to be near average (let alone above) would be a heavy blow to the field of forecasting via the use of teleconnections (relationships between phenomena that exist over large distances).

Best solution, I feel, is to take it easy for a few days and watch for any consistency in the output.

Edit: and pay attention to the ensembles/anomaly charts as they are somewhat less volatile 

Edited March 7, 2016 by Singularity

[Man With Beard]

Well the GFS 12Z takes us down another unusual route - a stable UK high! When did we last see one of these! 

It's a slightly dodgy time for such a scenario - potential for days of sun and good temperatures - but is it too early in the season to avoid the plague of the fog?

Still, it's just one of many options presented ATM. It does, though, have full anomaly support for now

[nick sussex]

9 minutes ago, Singularity said:

So what, we kick the theoretical impacts of a SSW and vortex split centered NE of the UK out of the window and stick with mid-latitude blocking for the foreseeable?

I understand that a response as fast as the GFS 06z and ECM 00z runs showed is at the speedy end of possibilities, but to consider following a path like the GFS 12z days 10-16 just seems ridiculous to me unless - and this is a big unless - the split doesn't propagate down as effectively as the majority of splitting events in times past have managed.

Puzzling times, and a complete nightmare for those who have long called for a mostly cold March this year with mean temperatures more than 1*C below the LTA. You think you can see the trend in the models aligning with expectations, and then bam! - it all goes haywire again.

You see I have conflicted interests here; I don't like cold weather in March (unless, I suppose, it's a brief snowy spell), but I have spent so long expecting it based on scientific reasoning that for the month to be near average (let alone above) would be a heavy blow to the field of forecasting via the use of teleconnections (relationships between phenomena that exist over large distances).

Best solution, I feel, is to take it easy for a few days and watch for any consistency in the output.

Yes I think it would be bizarre to have an average or above average March after one of the biggest zonal wind reversals of the strat we've had since being on the internet. As for the GFS past day ten blowing up the PV to the nw seems the least likeliest solution.

The UKMO at T144hrs differs from the GFS and I'm still unconvinced that any output really has a good handle on things as to where exactly any block will set up. I wouldn't be surprised to see the ECM come out with another solution.

[knocker]

Very consistent

 

[phil nw.]

We can only summarize the outlook for the next 2 weeks and as i see it any deep cold is heading south from a developing Scandi trough with signs of our high retreating to the south west at the end of the 2 weeks.Any cooling off  for us is more likely coming from the north west. 

What may happen further on is indeed open to speculation and just to be clear i am not ruling out anything beyond the period of current modeling.

The way i see it we can expect anything in early Spring as the vortex starts to break up-this year is no different to any other in that respect and i have seen more than i care to remember.

Edited March 7, 2016 by phil nw.

[feb1991blizzard]

10 minutes ago, knocker said:

Very consistent

 

Yes very consistent, the third chart shows mean Greenland heights and a whacking great elongated sceuro trough, having more experience than me, what would be the predominant weather type from this setup?

[Guest]

Well another day passes and we see some of the models starting to toy with the idea of significant pattern changes around mid-March. Let’s look at the latest AO and MJO ensemble charts.

AO Ensemble Charts: 

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/ao_index_ensm.shtml

We start off with the AO slightly negative, then generally go through neutral to a briefly positive period. Then, apart from two ensemble members (which stay positive), all the other members are continuing to trend down around mid-month, if anything rather more sharply than yesterday. Several members do not have the positive “blip” (which they all showed yesterday) and stay negative throughout. One stray member goes even more quickly and more deeply into negative territory. We do need to see how the trend beyond mid-month develops over the next 2-3 days but it certainly looks like the AO index is likely to be remaining negative for at least a few days and may be rather longer.

So, this is one indication that shows us what NOAA are expecting in terms of HLB. I see that there have been quite differing views and interpretations today regarding the NOAA (500mb) anomaly charts. I suggest that there should be reasonable correlation between these and the NOAA AO index (1000mb) charts (please correct me if this is not the case and explain why). The AO is negative right now before returning to neutral and then going broadly positive later this week. The NOAA 6-10 days “mean” anomaly chart seems in line with this with the decay of the current northerly regime and some flattening with lower pressure in charge to our north west. Most of the AO ensembles only start going negative around March 16th and this takes us out to 9 days or just into the NOAA 8-14 days “mean” anomaly charts. This is starting to pick up on some HLB (not a full on Azores high ridging north and an Arctic high ridging south but going in that general direction). The AO ensemble charts now take us as far as March 18th/19th. This is up to 12 days out and towards the end of the 8-14 NOAA anomaly chart period. With most (but not all) AO ensemble members trending negative and increasingly indicative of the greater HLB, I would expect to see the "mean" charts on next few 8-14 day runs pick up on this with stronger ridging in the Arctic (either north-west, north or north-east of Iceland and extending southwards towards the more northerly positioned Azores high. If we continue to see the AO index ensembes trending further negative, then the 8-14 day anomaly charts should also trend to showing greater HLB. Anyway, that is my take on it and I would be happy to be corrected if this is too generalised or not right. 

MJO Ensemble charts:

Here are todays MJO ensemble charts for the big 3 and Kyle MacRitchie’s for March 7th. 

UKMO: http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/CLIVAR/ukme.shtml

ECM: http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/CLIVAR/ecmm.shtm

NCEP/GEFS:  http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/CLIVAR/ncpe.shtml

Kyle MacRitchie: http://www.kylemacritchie.com/real-time-maps/realtime-mjo/

UKMO has changed very little but has slowed down the progression with most ensemble members keeping the MJO out of the circle of death and moving it into phase 1 tomorrow for only a day or two and at very low amplitude. They then take it more quickly into phase 2 and on into phase 3 at extremely low amplitude, nudging the circle of death..

ECM is again very much in line with UKMO. 

NCEP/GEFS like yesterday, take quite a different view. They keep the MJO in phase 1 for longer but then most of its ensemble members enter the circle of death with almost a complete stall. Then some ensembles (more than yesterday) show signs on the very confused looking chart that it will re-enter phase 1 in about 7 to 8 days time.

Overall, the big 3 show  very little change from yesterday.

Kyle MacRitchie continues to take a more positive view. He actually held the MJO back in phase 7 for longer and into phase 8 today (March 7th) and then pushing through phase 8 and on into phase 1 on March 11th/12th and eventually through to phase 2 on March 16th/17th. All 4 of his ensemble members retain good amplitude throughout this period and are shown at even higher amplitude than yesterday..

No time for further comments now as I am preparing another post on Judah Cohen’s AO report, which has just been updated and looks very encouraging for coldies. Should be ready around 7pm tonight.

Feedback Noted: I see that several fellow posters have remarked about my comments regarding the negative AO I made on yesterday’s post (on page 60 of this thread). I can see how my wording in my paragraph beginning..."My view"...caused the confusion. I realise that the AO indices that I have been publishing and commenting on in several recent posts are a predicted measure of HLB and are not another teleconnection. If you check my words in other paragraphs in that post or in my other recent posts you will see that there is no confusion. I am sorry that I muddled up the wording in the offending paragraph and I hope that other readers of that post have not been misled.

Edited March 7, 2016 by Guest
EDIT: improved links now - hopefully

[Milhouse]

I'm well aware there is still the possibility of something colder returning for the run up to easter but in the meantime the GFS12z is painting a lovely picture of settled and even warm conditions developing through this weekend and persisting into next week. Temps pushing into the mid teens and remaining warmest for longest in sheltered western areas. As mild as this winter has been, we have lacked some pleasant settled weather so something like the gfs would be most welcome.

 

 

 

 

[shotski]

10 minutes ago, Milhouse said:

VI'm well aware there is still the possibility of something colder returning for the run up to easter but in the meantime the GFS12z is painting a lovely picture of settled and even warm conditions developing through this weekend and persisting into next week. Temps pushing into the mid teens and remaining warmest for longest in sheltered western areas. As mild as this winter has been, we have lacked some pleasant settled weather so something like the gfs would be most welcome.

 

 

 

 

Bbc and met office are less convinced, 10-12 degrees max and 4-5 mins for your area under cloudy sky's. A sunny high would be nice but it's  not looking that way at the moment. 

Edited March 7, 2016 by shotski

[John Badrick]

10 minutes ago, Milhouse said:

I'm well aware there is still the possibility of something colder returning for the run up to easter but in the meantime the GFS12z is painting a lovely picture of settled and even warm conditions developing through this weekend and persisting into next week. Temps pushing into the mid teens and remaining warmest for longest in sheltered western areas. As mild as this winter has been, we have lacked some pleasant settled weather so something like the gfs would be most welcome.

 

 

 

 

Max temp of 11 degrees with thick cloud  forecast for here in cornwall really dosent float my boat!!

[CongletonHeat]

16 minutes ago, Milhouse said:

I'm well aware there is still the possibility of something colder returning for the run up to easter but in the meantime the GFS12z is painting a lovely picture of settled and even warm conditions developing through this weekend and persisting into next week. Temps pushing into the mid teens and remaining warmest for longest in sheltered western areas. As mild as this winter has been, we have lacked some pleasant settled weather so something like the gfs would be most welcome.

 

Quote

Yep dry and above 12c will do for me at this time of year, bit of sun and could easily get 15c if lucky.

 

 

 

 

Edited March 7, 2016 by CongletonHeat

[I remember Atlantic 252]

10 minutes ago, shotski said:

Bbc and met office are less convinced, 10-12 degrees max and 4-5 mins for your area under cloudy sky's. A sunny high would be nice but it's  not looking that way at the moment. 

yes, as much as we all want Spring, 14C a bit optimistic, no real TM air here just high over us, could struggle with low cloud even early freezing fog, need high further SE for warmth i feel anyway

[Captain Shortwave]

Well the ECM like the other big hitters seems to be going down the more prolonged UK high route.

So... betting on zero at the roulette wheel again. JMA delivering the cold goods.

   

Edited March 7, 2016 by Captain Shortwave

[feb1991blizzard]

1 minute ago, Captain Shortwave said:

Well the ECM like the other big hitters seems to be going down the more prolonged UK high route.

So... betting on zero at the roulette wheel again. JMA delivering the cold goods.

   

The ECM could also deliver an absolute rip snorter by 240.

[Cheshire Freeze]

6 minutes ago, Captain Shortwave said:

Well the ECM like the other big hitters seems to be going down the more prolonged UK high route.

So... betting on zero at the roulette wheel again. JMA delivering the cold goods.

   

ECM 216......UP SHE GOES

[bobbydog]

13 minutes ago, Bring Back1962-63 said:

 

Feedback Noted: I see that several fellow posters have remarked about my comments regarding the negative AO I made on yesterday’s post (on page 60 of this thread). I can see how my wording in my paragraph beginning..."My view"...caused the confusion. I realise that the AO indices that I have been publishing and commenting on in several recent posts are a predicted measure of HLB and are not another teleconnection. If you check my words in other paragraphs in that post or in my otherv recent posts you will see that there is no confusion. I am sorry that I muddled up the wording in the offending paragraph and I hope that other readers of that post have not been misled.

hi mate, can i just say, someone such as yourself, who takes the time to write detailed, informative posts, is most welcome on this forum. it is not a forum full of qualified professionals, it is a broad spectrum of weather enthusiasts- from a few current and retired professionals right down to those just learning what a cloud is made of - and everything in between. you will discover that there are people who will argue that black is white and those who will pick out parts of a post and completely mis-interpret its actual content. there are strong opinions (whether right or wrong) there are 'coldies' and 'mildies' who will fight their corner to the bitter end. thats just how it is. you will always find someone who disagrees with your opinion, no matter what you say. 

this goes for anyone really- if you have used your own time to make a genuine, informative contribution to this community, listen to others and take on board differing opinions but NEVER feel the need to apologise to those who disagree. 

keep the posts coming, you seem to know your stuff and therefore are a welcome asset to the forum.

Rob.

[knocker]

39 minutes ago, feb1991blizzard said:

Yes very consistent, the third chart shows mean Greenland heights and a whacking great elongated sceuro trough, having more experience than me, what would be the predominant weather type from this setup?

Well to me we have positive heights build up south of Greenland with a weak trough through the North Sea into SW Europe (the main cold trough is still over NE Europe).  Thus we have the upper flow veering to NW over the UK which would likely bring some unsettled conditions with average temps or maybe tad below. And then it rather depends on how it develops.

[feb1991blizzard]

Just now, knocker said:

Well to me we have positive heights build up south of Greenland with a weak trough through the North Sea into SW Europe (the main cold trough is still over NE Europe).  Thus we have the upper flow veering to NW over the UK which would likely bring some unsettled conditions with average temps or maybe tad below. And then it rather depends on how it develops.

Thanks for the reply, I agree about the NW flow although a N'ly  (stress only temporary) wouldn't be impossible though.

[knocker]

Just now, feb1991blizzard said:

Thanks for the reply, I agree about the NW flow although a N'ly  (stress only temporary) wouldn't be impossible though.

 Yes it's possible as systems traverse the UK you will get a transitory northerly.

[Guest]

Dr Judah Cohen's weekly AO report has just been updated: http://www.aer.com/science-research/climate-weather/arctic-oscillation  

Here is his summary in full.

“….Summary

The Arctic Oscillation (AO) is currently neutral and will remain near neutral most of the week before trending negative next week following the peak in the sudden stratospheric warming (SSW), which already qualifies as a major warming but will challenge the greatest stratospheric warming ever observed. 

The current neutral AO trend is reflective of mixed pressure/geopotential height anomalies both across the Arctic and the mid-latitudes of the Northern Hemisphere.

The neutral AO atmospheric state is likely a combination of offsetting or compensating influences.  The SSW in February favors a negative tropospheric AO (and since the SSW in February the tropospheric polar cap heights have been predominately warm) while the still active vertical energy transfer favors a positive tropospheric AO.

As has been the story all winter the still active vertical energy transfer predicted for this week will lead to yet another round of mild weather for Europe but especially eastern North America.  So while this latest pulse is leading to extreme negative AO values in the stratosphere it is delaying similar negative AO values in the troposphere.

The polar vortex (PV) is located over northern Europe and is predicted to split once again over the Eurasian continent.  With the PV displaced and split so far south over the Eurasian continent that is where the largest negative temperature departures are expected post the peak in the SSW.  With one lobe of the PV predicted to be over Siberia that is where the most extreme cold temperatures are expected.  However a second lobe is predicted over Europe that should bring relatively cold weather to Europe as well.

With the lack of any direct influence from the PV and with the vertical energy transfer still active, temperatures should average relatively mild for North America for the next two weeks.  However the PV lobe over Europe is predicted to drift westwards and eventually over the Eastern United States (US), this should allow temperatures to eventually cool over the Eastern US as well…..”

Judah goes on to outline the likely impacts in his view. As this is so relevant to many of the ongoing and current discussions on this thread, I feel that I should copy this part of his report in full. For those wishing to view the charts and figures that he refers to, you’ll need to use the main link (shown at the top) and view the report in full

“….Impacts

For me the story of this winter has been the incredibly active atmospheric vertical energy transfer or vertical wave activity flux (WAFz) since late December.  The active WAFz this winter is unprecedented as far as I can tell and therefore it is not surprising that it is culminating in what is likely to be the greatest disruption of the PV and negative stratospheric AO that we have observed (Figures 1, 8 and 9).  However in the troposphere it has the opposite effect of forcing a positive tropospheric AO.  The active vertical energy transfer is also related to poleward heat transport and each of the pulses of WAFz this winter has coincided with mild to very mild weather patterns across the eastern US and Europe.  And what is possibly the most incredible pulsing of the WAFz is the one predicted for this week (Figure 8).  The winds have already reversed direction in the polar stratosphere (the winds have changed direction from coming out of the west to coming out of the east).  According to our understanding of meteorology, the atmospheric vertical energy transfer should be impossible once the wind direction reverses and yet both the Global Forecast System (GFS) and European Centre for Medium Range Weather Forecasting (ECMWF) models predict more vertical energy transfer for this week.

Regardless of the theory more active WAFz for this week will result in the same temperature pattern for the Eastern US and Europe as it has has all winter – mild temperatures (Figures 3 and 5).  Across North America the mild temperatures will further be enhanced because the PV will be completely confined to the Eurasian continent and with the PV goes the cold air (Figure 9).  The PV is predicted to split into two pieces or lobes yet once again next week, with one lobe over southwestern Siberia and the other over Western Europe (Figure 9).  To the north of these two lobes and south of a strong high pressure over the North Pole, easterly flow will become established across northern Eurasia in the stratosphere.  However with time this same circulation pattern should descend into the troposphere as well (Figure 4).  With easterly flow from the East Siberian coast to the United Kingdom cold continental air will dominate northern Eurasia.  This should allow relatively cold temperatures to pool across Siberia.  And with easterly flow established that cold air will be carried westward to northwestern Eurasia, Eastern Europe and Western Europe (Figure 6).

As mentioned above the combination of another week of active vertical energy transfer and the complete evacuation of the PV from North America will result in a very mild period for the North American continent.  One exception will be the Western US where a mid-tropospheric trough or region of negative geopotential height anomalies will result in a wet and cool period.  The PV lobe predicted over Europe for next week is also predicted to be carried in the strong easterly flow westward across the North Atlantic and eventually the Eastern US.  This should eventually lead to an end to the very mild pattern in eastern North America (Figure 9).

As I have discussed previously we are in unchartered territories for many reasons including the lateness in the winter of a major warming which preferentially occurs in January followed by February.  The impact of the PV disruption in the stratosphere is clear resulting in a highly anomalous weakening of the PV and extreme negative stratospheric AO.  The polar cap geopotential height anomaly (PCH) plot shows the classic “dripping paint” signature of the warm geopotential height anomalies/negative AO descending with time from the stratosphere to the troposphere (Figure 7).  Therefore the negative phase of the AO should become increasingly favored as we progress through the month of March.  Also the negative AO should be favored well into April as well.  However given the lateness of the PV disruption I am uncertain how well the current PV disruption will follow the paradigm established for mid-winter.  Also a negative AO in April dos not have the same impact across the mid-latitudes as it does in January and a snowstorm in January becomes a cold rain in April.  But regardless the current PV disruption should reverse the trend of the past two late winters/early springs where most of the cold air was confined to eastern North America while temperatures across Eurasia where well above normal.  The opposite is more likely this year with a widespread cool start to spring across Eurasia, while much of North America gets a head start on spring like temperatures…..”

My Comments:

Dr Judah Cohen explains a number of issues that have troubled many of us on this thread. He tells us why we are seeing this temporary warm-up. The polar vortex displacement and the disruptive energy pulses generating an extremely negative stratospheric AO but delaying the AO values going negative in the troposphere. Judah is puzzled and critical of the GFS and ECM modelling of the continuing energy pulses into the high Arctic (something I think that Singularity commented on yesterday) and says that this should be “impossible” with the winds having already reversed from westerlies to easterlies in the polar stratosphere. He then expects the polar vortex, over Europe to split again and to be positioned over Eurasia and further south with another lobe over Europe with the largest negative temperatures in Siberia and “relatively” low temperatures in Europe initially. Then long fetch easterlies from the east Siberian coast pushing right through to Western Europe and the UK with the cold polar continental air already in place.

Judah states that “we are in chartered territory” and he continues to add his recent caveats regarding the lateness in the season for these events to occur. He expects that April may deliver cold rain to much of lowland Europe rather than any strong snowstorms. So, perhaps we should focus on the second half of March to deliver and for some more wintry conditions. It is possible that we will get the worst of both worlds. A prolonged cold spell but not quite cold enough for the coldies but no sign of anything significantly warmer until the second half of April.

With all the uncertainty, we can expect some quite unusual weather (even for the changeable Spring season). So, coldies or warmies, let us accept that we cannot do anything about it and at least enjoy some interesting charts. There is still a chance of something quite exceptional after mid-March.

 

[Singularity]

Thanks for communicating Cohen's blog update to us, BB62-63 

No wonder the models are proving intermittent with the signal to initiate a period of high latitude blocking; the Arctic profile is in a peculiar sort of mixed state which makes it hard to call things one way or the other; a ridge could gain a foothold over Svalbard later next week, which ECM again has a go at this evening, but equally it could be held at bay by areas of low pressure still managing to find their way into the high Arctic and circulate in the usual, zonally orientated manner.

Generally the models are not yet producing height rises in the Arctic on a scale that I would expect to see from major SSW impacts. Perhaps this is why they aren't indicating a shutdown of vertical energy transfer at this point in time (though perhaps the GFS 06z went down that line, given the huge omega block that was shown to develop).

That 06z GFS was the closest to what Cohen described that we have seen from the deterministic output so far this month, but the ensembles have been suggesting that sort of thing for a while now. If the polar vortex segment does eventually retrogress all the way across the Atlantic having started off in Europe, that will be a remarkable event. Such an event would allow for height rises across Europe and perhaps a very warm scenario for NW Europe and the UK to follow whatever extent of colder weather is experienced. The 06z illustrated that late on, having retrogressed the vortex segment at breakneck speed. In reality I expect it would be a slower, but more extreme evolution (colder than it showed and for longer, then even warmer than it suggested for the follow-on period!).

 

I agree that we could see a predominance of unusual weather patterns Mar-Apr and perhaps a contender for the least westerly such combination on record. For the UK that usually means an unusual lack of rainfall which will probably have some on here worrying about the similarities to 2007/2012 

[fergieweather]

3 hours ago, CreweCold said:

High pressure already couple of hundred miles further N than the 6z at day 6

SSW effects creeping into modelling now?

 

Yes, the signs are evident between D7-9 as the easterlies propogate down to the troposphere. Initially this manifests as a SSW'ly anticyclonic flow in most ensembles, albeit the potential for this to turn into a colder set-up has been signposted by (as yet) a smaller number of members, but the risk is clearly there. The downward trend in GPH from around 21st signalled in recent runs continues to look potentially suspect (ie spells of blocking could show greater longevity, with any supposed unsettled return perhaps a red herring, as models lean back towards climatology). GloSea5 continues downward propagation of E'lies for a fair part of March, so the potential for colder weather remains latent throughout, albeit not any certainty. As noted a day or so back, MJO (below, latest) remains of little influence within the inner circle for a protracted period and thus offers no forecasting steer.

[TomDav]

12z GEFS clusters suggests generally above avg temps D10 with a number of members showing a deep cold pool to the east:

By D16 around half of the suite showing well below avg temps and the other half upper air temps closer to avg

All subject to change of course, especially with perhaps a record-breaking SSW in the background. Also, as a disclaimer I am still not totally sure whether the clustering is accurate (!)

[fergieweather]

Well, at least it's now just down to a 50-50 to contend with further into medium range in 12z EC at T+240....!! 

EDIT but more expansive set of cluster solutions thereafter out to T+360, with (yet again) many opting back to a cyclonic, unsettled/changeable regime by 21-22nd (refer to my post above re that)

Edited March 7, 2016 by fergieweather