Model Output Discussion - Spring Has Sprung

[Stuie]

 Theresnoway I threw the towel in on 10 day charts years ago.

[Theresnoway]

 Stuie Very wise, but occasionally a trend does get picked up on , and come to fruition. Having not been following the models all winter, I probably have more patience and hope than others.

[RJBingham]

 minus10

7 minutes ago, minus10 said:

gefs 12z still showing colder from soon after 22nd...

That's the GFS 

[nick sussex]

Any interest isn’t till FI .

We have seen this script before and have the sledges gathering dust in the garage to show for it ! 

As you head towards the end of February you need better synoptics to deliver and we need some northern blocking if we’re to tap into a decent cold source.

A two hour slush fest just isn’t going to cut it .

Personally I’m not a fan of cold springs where the perfect synoptics turn up to remind you of what might have been !

I love snow and cold but have a low opinion of slush ! 

[seabreeze86]

Definitely a cooling trend from the GEFS 

Cold enough for anything interesting will be the question 

[Mike Poole]

ECM just hinting at a change by T240, similar to what we’ve seen on recent GFS runs that go past that point:

[RJBingham]

 seabreeze86

1 minute ago, seabreeze86 said:

Definitely a cooling trend from the GEFS 

Cold enough for anything interesting will be the question 

So is that 

[minus10]

 RJBingham was showing the gefs mean and comparing with the gfs op..

[Tim Bland]

Day 10 hrs potential it’s been an awesome winter…at day 10

[damianslaw]

 Mike Poole Yes ECM aligning strongly with GFS, indeed there is strong correlation between both models right out to 10 days, rare we've been able to say that most of the winter so far. 

[daz_4]

GEFS this evening illustrate why I'm not impressed. It would be a struggle to get night frost in that set up in my backyard.

[WYorksWeather]

Firstly, on a personal note - should have a bit more time for the rest of this week as after a particularly busy period I've booked myself some time off work. In addition of course to many other things it should mean I'll have a bit more time to devote to trying to figure out where things are going as we begin to close the book on winter 2023-24 (at least meteorologically speaking).

Thursday - the first day of Aprilbruary?

So, we all know the story for the next week or so, exceptionally mild. However, it is worth highlighting I think just how mild the pattern is, especially for Thursday. We have the 10C 850hPa isotherm into the UK, which given the average even in the south is around -1C at this time of year, is really quite notable. It would be equivalent, in anomaly terms, to the 20C isotherm in mid-summer.

The result is that overnight temperatures remain in double figures in many areas on Wednesday night, and high single figures on Thursday night, though dropping away a little as the mildest air clears away into Friday.

Daytime temperatures are also impressive on Thursday for the time of year despite the cloud and rain. It's the first time I've seen the UKV chart breaking out the lime green colour this year - very much a sign of spring. Temperatures reaching 14-15C over a wide area, probably the first day this year where a substantial part of the country will reach 15C. I have a feeling that it may feel quite April-like, with the stereotypical 'April showers' and spells of sunshine in some areas that aren't stuck under the rain and cloud all day.

GFS ensemble

My initial thoughts on the GFS ensemble are to echo what was said above - it looks like a partial victory for the ECM ensemble. The GFS ensemble has downgraded the cold spell. Previously, the mean was reaching to -5C or below across a wide area. It will be interesting to see whether this is just a blip, the GFS converging to the ECM, or whether the two will meet in the middle somewhere.

All I know is that it's very unlikely that we'll get anything substantial out of a -3C to -5C 850hPa temperature in late February, even if the GFS doesn't downgrade any further. Of course an unsettled north-westerly type pattern could still deliver substantial snow accumulations for parts of Scotland or over high ground across much of England, but for most of us it just isn't cold enough going by the mean.

Summary

A very mild next week or so overall, and a general downgrade in the signal for cold towards the end from the GFS ensemble. We await the ECM ensemble for comparison later.

I do think some people are too quick to give victories to the GFS - whilst it often picks up on signals earlier in the OP runs, I have generally found that the ECM this winter in its ensemble runs has been less keen to be taken in by many of the false starts than the GFS. Whilst the GFS did call the January cold spell better with its mean, it overcooked the phantom mid-December cold spell, and if it does end up converging to the ECM it would be yet another victory for the ECM ensemble. Always wise to check the ensembles means as well as the operational runs.

[seabreeze86]

 RJBingham The GEFS is the GFS’s ensemble suite 

[Mike Poole]

ECM clusters T192-T240:

Cluster 1 which contains the op, and follows the line of thought that the GFS has had recently, has 29 members, so the northerly by day 10 is definitely on the table.  Cluster 2 remains flat.

T264+:

Cluster 1 with 19 members continues the blocked theme, although it diffuses by day 15.  Cluster 3 also has some interest, but looks like the ridge is a toppler.  Cluster 2 is westerly, and so is cluster 4 with heights to the south.

Edited February 13 by Mike Poole

[jellybaby1969]

Next 10 to 12 days look relatively mild n fairly wet for many parts...I do still feel this winter can going out on a cold note. Be interesting to see if this gathers momentum over the coming days.   

[johncam]

 Mike Poole do you think the models are dropping the colder sign for end of month?

[Mike Poole]

 johncam Difficult to say, I would say the signal has actually increased for something cold in the day 10-13 timeframe, GFS and ECM both pointing that way.  After that, I’m not sure, just going by the extended EPS, the signal looks to falter a bit compared to this morning’s.  But there’s obviously more uncertainty at that range anyway.

I noticed that the ECM 46 had backed away from the second dip in zonal winds again today.  In fact, post-SSW the winds now look more likely to recover, which might suggest a reduced chance of cold.  On the other hand, some recent GFS runs have shown a more favourable split SSW. 

[WYorksWeather]

The ECM is sticking to its guns, but more detail below.

Ensemble

Not much sign of a cold spell here. Even those runs that do go colder show a distinct lack of any deep cold, whereas the same can't be said for the mild runs, some of which are truly extraordinary with the warmth of the airmasses. Still not a clear signal either way.

Meteogram

The meteogram below, showing the potential surface temperatures for Reading, would very much mean that a potential record-breaking February CET is possible, especially if the current uncertainties were to resolve slightly on the mild side. If we do get a cooler zonal period even if not overly cold, that would scupper it. The fact that it remains a possibility though just shows how badly wrong long-range forecasting has been for February. Even a very cold final week would not be enough to bring overall temperatures down to average, let alone below average.

Also worth noting there's a fair bit of rain in this forecast, particularly for Sunday, and also that the model has pretty much dropped any opportunity to get an easterly. The GFS-type solution with more of a north-westerly flow is represented in the ECM ensemble, but the ECM is overall much more keen on the flatter option which would keep things generally mild and westerly, and at times very mild where the wind is south of west.

SSTs

SSTs from ECM for days 0, 5, 10, and 15 are shown below. I can't get the usual North Atlantic view from the ECM site, so it's UK only today. Overall, we still have a cooling trend through day 15. Just hints that SSTs may be beginning to bottom out with a fairly small change between days 10 and 15. Once we see this begin to turn in the other direction, that is a clear sign that winter is finished. Not quite there yet.

SSW / zonal wind

ECM looks to be downgrading the impact of this SSW - it now looks like only a very brief reversal. An increasing cluster also drop the continued weak vortex idea, and return the vortex close to its climatological strength for the time of year. The mean still has a weak PV after the reversal, but not to the same extent as was showing a few days ago.

I think this may be responsible for a lot of the uncertainty in the models. If we do see a quick recovery of the vortex (which to be clear, is still a minority option), then that would be a reflective type SSW, which are actually associated with mild conditions for the UK. It is not as simple as SSW = cold.

To be clear, the majority option is still for the vortex to remain weak, but worth watching how this evolves as we approach the date of the zonal wind reversal, which is currently projected for around 19th or 20th February. Unless we get a quick tropospheric response, impacts of this SSW are unlikely until March.

ECM extended

Given the fact that I've just rubbished the long-range forecasts for February based on how it's gone so far, I should add a major health warning to any extended range output from here on in. I think these charts should really be treated as just for fun. Nevertheless, here is what they're showing.

19th-26th is mild at 1 to 3 C above average - no surprises there.

A colder signal for the north especially from 26th-4th March, but at this time of year slightly cooler than average is unlikely to be enough for anything interesting.

Near average 4th-11th, slightly milder than average in the far south.

Similar 11th-18th.

18th-25th strengthens the milder signal.

CFSv2 weeklies

Useful to add the CFSv2 weeklies just to contrast with the EC46 to see if we have any agreement in the extended.

Week 1 has no analogue on the EC46. However, week 2 (20th-26th) already shows disagreement with the EC46 - CFSv2 is more confident in a colder signal for week 2 (roughly corresponding to ECM week 1).

For week 3 (27th February - 4th March) and week 4 (5th - 11th March) corresponding to weeks 2 and 3 and the ECM, there is a bit more agreement, and we head back to the idea of a relatively average start to March.

Overall though, I wouldn't put too much stock in either extended range model.

Summary

ECM is sticking to its guns. No clear cold signal on the horizon, a continued unsettled pattern for the most part. Will be interesting to see over the next few days whether the GFS ensemble continues to converge towards the ECM ensemble regarding temperatures for the end of the month.

[Kirkcaldy Weather]

Impressive wave break event this, whilst it may not look much on pressure charts its gonna be fueled by an impressive plume by February standards which will bring temperatures of between 15C > 17C into Southeast England on the 15th.

Another Wave Break event by the 17th - 18th which sends the low into Italy.

[Rain All Night]

9 hours ago, Rain All Night said:

0z/6z deterministic runs, Tue 13th to Tue 20th (day 7)

Following a naff couple of days, the little low out to the west will pass over us on Thursday and Friday and pop out on our eastern side. Thereafter we'll be caught in a struggle between high pressure from the south and low pressure from the west until at least day 7.

0z/6z ensemble means, Tue 13th to Wed 28th (day 15)

From about 21st Feb (day 8 ) onwards, GEFS is strongly and persistently suggesting that an Atlantic low will push from northwest to southeast into Europe, forming the "Scandi trough" that we have been seeing in the week 2 ensemble means for the last few days. ECM clearly sees this possibility as well, but is less willing to commit to it. GEM is more of a mess, as is often the case. How deep into Europe the low gets will determine whether there is any prospect of cold air being pulled over the UK.

12z deterministic runs, Wed 14th to Tue 20th (day 7)

I don't think I've learned anything new at all from this afternoon's deterministic runs. We see the big purple blob forming to the south of Greenland by day 7, which the ensembles have been suggesting may end up traversing over to our eastern side later on.

12z ensemble means, Wed 14th to Wed 28th (day 15)

And here we see that blob heading east from 21st Feb (day 8), though it is now not until around 26th Feb (day 13) that we see much of a trough to our east on the ECM and GFS ensemble means. Pressure seems to recover from the southwest after the blob has passed through.

Here is ECM ensemble member 46, which offers an explanation for what's happening between days 8 and 13 that I think is rather elegant:

Edited February 13 by Rain All Night

[stodge]

Evening all

Still outside the reliable so only eye candy at this point but a much more unsettled theme especially later next week with a vigorous LP close to or over the British isles in ten days which in turn, as it clears, offers the possibility of a 3-4 day N'ly to close off February.

The 10 HPA stratospheric charts continue to show a very much weakened vortex by month end and while I'm still very much of the view March will provide fascinating synoptics (as it often does) how this will play out for the UK in terms of cold vs mild (and it's that which defines March and the transition to spring most years) is far from clear.

[BLAST FROM THE PAST]

I think we are now seeing an escalation again…..I thought the hemispheric cold pattern would be setting up now for a cold/to very cold last 1/3rd of month, doesn’t seem so.  I think last 1/3rd is still on…..maybe a very quick switch?  Still holding out for something notable and lengthy…..

 

 BFTP

[Cloud 10]

The models are keen on a deep trough dropping down from the NW later next week,so the next named storm could be on the cards.

 

[KTtom]

 Cloud 10 Not such an intense low modelled overnight but still the theme of dropping a lobe of vortex down over the UK. It looks quite impressive when viewing the H500 charts in terms of cold potential, however when viewing 850 chart the lows are just pumping warm air up into europe and Scandinavia with the deep cold retreating back to the arctic.

 

[IDO]

The GEFS mean supports the initial west-based dropping of the trough, from around D7-8:

So for the South a wishy-washy affair with 850s bringing mostly cold rain (London 2m temps):

The temperatures are below average at points, but there is nothing like a cold spell.

GEM also supports the initial drop, and it looks like post-D10, it will support the GFS op second drop. GFS op D8-16:

The EC run this morning has a spoiler low off the ESB that kills the oscillating Azores high. D10 0z -v- 12z (yesterday):

So, is EC having a blip or the op in another cluster? No northern blocking, maybe just a slowdown of the NH pattern and the Azores high oscillating to send the trough over the UK. For most of us, this setup in the last third of February is a waste. But looking like it will take us into Spring.