Model Output Discussion - Spring Has Sprung

[LetItSnow!]

Looks like the divergence between the ECM and the GFS 12z starts on the Saturday the 11th. The GFS has a more robust area of high pressure up into the Norwegian Sea and also a more defined trough to our east.

By Monday the 13th the GFS 12z is exploring the idea of a rather flabby Scandinavian high with winds turning to the east, a common pattern at this time of year but one that makes eastern coastal residens shudder!  Meanwheile the ECM is sticking with the idea of a general breakdown from the west .

Dare I say both look like they lead to potentially not the best conditions. Of course they're very different options so it's not worth worrying about whether they verify but the trend for a shake up of the high around the 13th still looks to be there, but how it comes off is uncertain. Expect many different outcomes to be toyed with.

The ECM ensemble does show that the idea of the Atlantic coming in isn't without some support. Because it is a mean though, I could see how any one of the potential outcomes comes off. Perhaps high pressure to our north-east will nose in and turn the winds to the east, perhaps low pressure will come in off the Atlantic or berhaps it could stall and lead to some potentiall warmer conditions. Either way, nothing exceptional on the horizon and some lovely days to come shortly after some less bad than expected ones already. Enjoy the Bank Holiday everyone.

[WYorksWeather]

Bit of a shot in the dark at this range, but for those already interested in developments after next week, the ECM clusters are quite instructive for days 11, 13 and 15.

Model consensus is that all clusters turn unsettled around day 11. The key divergence is where we go after that. Cluster 1 says we stay unsettled for a few days and by day 15 no real signal. Clusters 3 and 5 are more consistently unsettled right out to day 15. Cluster 4 has more high than low pressure influence for the most part but generally west of the UK, so possibly cool and somewhat showery the bet with that. Cluster 2 is the best of the lot for warm and dry, with the unsettled period followed by a very warm to hot area of high pressure building over and to the east by day 15.

The safer option for making any prediction is probably to focus on days 11 to 13 just outside the reliable, which does look like an unsettled period. But whether it is a brief interlude of unsettled weather or a return to more prolonged and persistent unsettled weather is impossible to know at this stage, and it could still get delayed or pushed back.

I think predicting at this stage that the upcoming high is just an anomaly about to be replaced with another prolonged unsettled period is borne more of cynicism about the recent pattern than a fair-minded analysis of the models.

 

 

[WYorksWeather]

Separately but related to my comment above, worth also noting that the ECM weather regime charts also look relatively good for the longer range.

Very low probability of negative NAO and Atlantic ridging, both of which are poor patterns for May and June if you want warm and dry weather, increased probabilities of Scandi highs and positive NAO. Of course these charts can and probably will end up being wrong at times, but these actually look quite good for the rest of May.

[Uncertainty]

The ecm has joined previous gfs op runs in progging a scenario where the high builds northwards and connects with an Arctic high. This deflects the low next weekend and sends it to the south (where it could end up wet).

The gem has a go at this and does keep it dry till around day 9, but the high is less resilient and the Atlantic makes inroads nationwide

Forcing the low south could result in this sort of pattern, drier in the N and wetter in the S

But equally it could mean drier for all.

The key takeaway this morning then is that the high is forecast to be stronger and more resilient, bringing into question the switch to unsettled weather late next weekend. The NOAA charts weren’t so keen on this yesterday

I would like to see a bit of consistency on this; the last 10 months would seem to support a more low pressure dominated outcome but we are leaving this Nino behind (good riddance) and, as @WYorksWeather has pointed out, there is a tendency in the extended forecast for scandi or euro blocking rather than -nao so perhaps we’re finally seeing a change in the overall trend. Fingers crossed. 

[LetItSnow!]

 Uncertainty It’s a long way out so I don’t expect it to come off but the GFS and the ECM around the 13th-15th looking like a cold pattern once again for more Scandinavian areas, a winter that’s never left them it seems. Even here it would threaten a return to colder than average conditions… I don’t expect it to happen but those type of weather patterns are most likely in April and May. 

[WYorksWeather]

 LetItSnow! I think a return to truly colder than average conditions is probably going to be difficult without a prolonged northerly interlude, given the impact of the very high SSTs around the UK. That would probably limit the chilly nights which you would still need at this time of year to record anything much below average. There are only a handful of runs in the ensembles at the moment that take the 850hPa temperatures below 0C, which is probably what you'd need.

Even this chart for Newcastle shows at most a return closer to average, and that only by the 20th! In the reliable up to day 10 still solidly above average.

[Rain All Night]

On 04/05/2024 at 11:17, Rain All Night said:

0z ensemble means, out to Sun 19 May (day 15)

It's not good news this morning - the GEFS is similar to yesterday's runs with a shallow trough incoming, but the ECM is even more aggressive about shifting the jet stream way down south and introducing a vast Atlantic trough. Enjoy this coming week or so while it lasts.

0z deterministic runs, on Sat 11 May (day 7) - for all your Eurovision Song Contest parties

GFS op wants to carry on the party with continued anticyclonic activity well beyond the frame shown here.

0z ensemble means, out to Mon 20 May (day 15)

ECM has dropped its aggressive Atlantic troughing solutions of yesterday morning and has moved towards to the GEFS, which shows a shallow trough transferring from the Atlantic to the south of the UK for the week beginning Mon 13th May. This will presumably bring some unsettled conditions to my vicinity.

Beyond mid-May, though the means are heavily blurred, a couple of themes consistent between the models are the jet stream preferring a southerly track, and Atlantic high expansion remaining on the table.

0z deterministic runs, on Sun 12 May (day 7)

The settled regime looks as though it should survive through to the end of next weekend, with the chances of this appearing greater towards the southeast.

Edited May 5 by Rain All Night

[Addicks Fan 1981]

 Rain All Night it's times like this where we need @MattHonline as his knowledge on teleconnections is appreciated on here.   Always a good idea to have some balance on here to enlighten us on the goings on.   He is needed to iron out uncertainties and gives great detail in what he posts.   

[Cambrian]

A short but sweet one today. This is what so many of us have been looking forward to seeing, cross-model agreement coming into the close range for a good few days of dry, lovely warm afternoons and early evenings. Yeah…

Here at day 5, 0z ECM op or the 0z GEM op / 6z GFS op at various stages of day 6 - a frequent 19-21 degrees for very many, even for us in the hills, and a respectable mid to high teens at worst for many others, come the end of the working week and into next weekend. 

   

Nothing spectacular I know but at this stage, admittedly easily pleased and why not?

A very good opportunity to recharge. Plenty of time each day to take a hard-earned cup of tea outside and enjoy it without that draughty old wind licking at our delicate bits. Ooh err. 

[LetItSnow!]

 WYorksWeather I was just referring to the cold blob to our NE at days 8-10 that if that did happen would threaten at least relatively cooler conditions. If you have cool uppers and a NE flow it’s gonna be quite cool. But given it’s a long way out as stated I don’t expect it to happen. 

[Addicks Fan 1981]

After our unsettled bit of weather coming into the second full week of May there are signs of the weather becoming more ridge orientated but tentative at the moment according to the GEFS 6Z ensemble mean chart.  

Meteociel - Cartes Ensemble GFS (ENS/GEFS)

WWW.METEOCIEL.FR

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meteociel propose des rubriques météo temps réel, forums, modeles...

At this stage I would trust the GEFS ensembles over the ECM ensembles to be honest.    

[Daniel*]

3 hours ago, WYorksWeather said:

given the impact of the very high SSTs around the UK

Exaggerative.
 

[Alderc 2.0]

 Daniel*  people keep saying this, from what I see temps are generally within 1C of average. I don’t get it…

[Addicks Fan 1981]

 Daniel* they are the SSTS as things stand.   It's weird that the SSTS are above average for this time of the year considering the dull and wet weather we have had so far, mind you this year could set the tone for future years.   

Also it'll be interesting in the second full week of this month of what extent our undercutting low will do to our weather, I would imagine possibly a thundery pattern may kick in if the upper air can play ball.    

[Daniel*]

12 minutes ago, Addicks Fan 1981 said:

they are the SSTS as things stand.   It's weird that the SSTS are above average for this time of the year considering the dull and wet weather we have had so far, mind you this year could set the tone for future years.   

 

Sometimes there’s too much focus on anomalies look at actual raw temps the waters surrounding us are as cool as they were in December although I do take it they will be rising not falling. The North Sea is still pretty cold as yet there has been not been a dramatic warming, it’s still relatively early in year. Any winds from north, NE especially would be cool probably for sometime yet for east. 

Edited May 5 by Daniel*

[Addicks Fan 1981]

 Daniel* think the things to look out for with the weather going forward are if la niña develops which some of the new CFS members are either implying a delay or it not happening at all, what extent we exit the east QBO and the weather in the tropics.   

I also observed the stratosphere temperature on the JMA site and it to me seems like the final warming is sluggish, it is warming but not at the rate it was predicted to do by the GFS.   

So in turn the zonal winds haven't reversed as much as first thought.     

[WYorksWeather]

 LetItSnow! Yep that's definitely a good point. I suppose I was speaking more broadly about prospects for the rest of the month - any merely cool airflows will probably be near average, so it would take a cold airflow to get below average I think.

[WYorksWeather]

 Daniel* Please read the post in context - I'm talking about the context of the period after a potential breakdown of the high pressure, so around day 10 or beyond.

By that point, SST anomalies look like this:

A warm anomaly virtually everywhere around the UK. You're right that they're still 'cold' in absolute terms - I'm not suggesting a dip in the sea in early May will be particularly enjoyable! But that doesn't change the point about the impact on temperature anomalies - it still means temperatures will likely be higher than you'd normally expect based on the airmass source for the time of year, and in particular night-time minima will be elevated.

[Addicks Fan 1981]

 WYorksWeather also how comes the zonal winds haven't reversed as much as they could have? The final warming of the stratosphere isnt performing as well as it could do, mind you the PV could split at any time or break up.   

This could also transfer to the atmosphere, mind you we also need to keep our eyes on the other variables I have mentioned.   Also the MJO needs I think to be more coherent as its in the COD area which isn't that helpful with our weather going forward.   

Also I'd be very interested with what state our GWO is in currently as I think @Metwatchposted something in here about it, now I am wondering if its changed its stance on everything? All i know however is it seems to be interested in a neutral kind of pattern, well that was my interpretation of it anyway.   

[Metwatch]

20 minutes ago, Addicks Fan 1981 said:

Also I'd be very interested with what state our GWO is in currently as I think @Metwatchposted something in here about it, now I am wondering if its changed its stance on everything? All i know however is it seems to be interested in a neutral kind of pattern, well that was my interpretation of it anyway.   

The charts to some GWO / AAM stuff here: Click on the 30 day archive can give an idea of previous forecasts, but it does seem to change quite a bit from run to run.

AAM/GWO Mapwall

ATLAS.NIU.EDU

Some of the output of recent wants to have a drop in the AAM towards the end of the month with the GWO going into phases 1-2 but at the moment it's quite neutral so it's unlikely to be doing much to impact anything around the north Atlantic / Europe. MJO is also heading into the COD soon so probably won't affect the pattern around us much either. Perhaps that would help slow down this week's high pressure from moving away too far east of the UK / western Europe and the low meanders more around the Atlantic so keeping us dryish and warm for longer, or slowly transition into a more thundery pattern The GFS 00z earlier was a good example of that.

Edited May 5 by Metwatch

[TSNWK]

Really nice ECM up to day 9 even thinks about ridging in the Azores between day 7 and 8 fails on this run and day 10 is woeful with trough to our east…

however I’m sure this breakdown is being pushed back…;)

 

Edited May 5 by TSNWK

[Penrith Snow]

 TSNWK The ECM at day 9 might be OK in Kent but for most of the UK it would be pants with a cool westerly flow which intensifies further by day 10. GFS is very similar so any up coming warm spell is likely to be shortlived.

All could change but that's the output at the moment.

Andy

[WYorksWeather]

4 hours ago, Addicks Fan 1981 said:

also how comes the zonal winds haven't reversed as much as they could have? The final warming of the stratosphere isnt performing as well as it could do, mind you the PV could split at any time or break up.   

Not sure about the why aspect, but in terms of predictions, a paper I posted in here a few weeks ago suggested this might actually be a good sign for a warm and dry early summer pattern.

 

Edited May 5 by WYorksWeather
Put months instead of weeks - it's been a long day!

[Addicks Fan 1981]

Tonight's CPC NOAA 8-14 day output is looking very similar to the last ECM 0Z operational and the last ECM 0Z ensemble mean with an undercutting low feature.   I reckon in 10 days time it could be quite thundery with a slack airflow.   

 

[Scorcher]

 Penrith Snow Wednesday to Sunday (at least) is not 'shortlived'. Sometimes I think I must be looking at a different set of charts to certain others.

Day 9 is well into FI so not sure why you're emphasising that...

The ensembles continue to show a prolonged period of above average temperatures.