Model Output Discussion - Spring Has Sprung

[Uncertainty]

Are we finally heading towards the promised land? As in, a U.K. high? The ensembles certainly think so.

GEFS

GEPS

I’m not going to fret about random GFS Ops progging the big Greenland high. As long as the means stay solid on the U.K. high, we’re all good.

[Scorcher]

The coldies are suddenly getting excited again but I think they need to settle down. The GFS is going off on one in deep FI as it always does.

Cooler next week but probably not far below average by day for most of us. The Met Office aren't predicting frosts for my area either. Any sunshine will be most welcome, even if it's cool in the shade.

The ECM is showing a very different evolution with the high eventually being pushed over the UK, leading to a gradual warmup towards the end of next week.

[WYorksWeather]

With thanks to plenty of other contributors on the main model output, I thought I'd take a look at the 12z GFS ensemble spread chart at the hemispheric level. In terms of next weekend, it's around day 8 we're looking at for next Saturday.

The key uncertainties seem to be the heights over the high latitudes, most obviously over the far side of Greenland and towards northern Canada, but these do impact the UK as well.

You can see this clearly with some ensemble comparisons. Perturbation 1 has higher heights over the Canadian side and more of a UK high.

By comparison, Perturbation 30 has the core of the high latitude block closer to our side of Greenland, and this stalls the core of the high a bit further west, allowing a colder flow from the NW/N/NE. Both look dry though as the high still influences the UK.

Anyway, hope that illustrates some of the options to consider. As we've discovered throughout winter a Greenland block doesn't guarantee cold - it all depends on the positioning.

[Mike Poole]

After a pretty torrid couple of months, the pieces are starting to move towards something much more palatable.  It is no surprise that this is happening now, as the effects of the significant zonal wind reversal in the strat at the end of February start to wane.  

The NAM index over the last couple of months looks telling:

This is effectively the Arctic Oscillation (AO) but at all layers of the atmosphere, and you can see from the plot how the negative values from the SSW have continued to just sit above the troposphere and impinge our weather ever since.  That doesn’t mean we’ve had constant easterlies here - not all SSWs result in this anyway for the UK locally (and I think the ones that do are becoming rarer, I’ll come back to this), but the effect on the northern hemisphere more generally has been marked.  

The plot also shows that into the forecast period, that reign of terror from the strat is now over it has fully downwelled - it is benign from now on, so normal spring patterns have a belated chance to take hold.

A final comment re the strat, and how things may be changing with global warming.  With only 6 SSWs historically per decade, it is perhaps too early to tell, but my intuition is, well, two things, a) that SSWs are becoming more frequent, and b) that, when they occur, they are becoming less likely (than the 66% rule of thumb) to deliver cold scenarios for the UK in winter.  

A much more settled outlook is starting to become apparent in the 8-15 day modelling, here’s the ECM clusters T192-T240:

Clusters 1 and 2 (combined with 44/51 of the runs) showing high pressure in charge over the UK, how welcome is that!

T264+:

Clusters 2,3,4 show a continuation of the high pressure local to the UK, but the main theme from all the clusters is the lack of anything from the Atlantic, finally, with the other clusters generally having a ridge to the west of the UK, which would be a cooler scenario.  

 

[Cheshire Freeze]

 Scorcher not really seen anyone get excited about cold at this point?

Think most people, me included, want a bit of warmth and sunshine?

[stodge]

Evening all

Well, yes - our brief "heatwave" doesn't last long though it's been welcome and as the HP recedes west, a new area of LP dives SE across NE Scotland and into the North Sea bringing back more seasonal conditions - close to or only a notch below average - next week,

From there, general agreement the HP will inch back towards us but declining as it does after which all manner of scenarios on offer including an almost wintry nirvana from GFS OP (supported to an extent by Control). Other models more circumspect at this time but the HP remains susceptible to easing back west as the trough sinks from the north and heights start to rise around Greenland. A colder spell in mid to late April is hardly unusual but with the HP core in mid Atlantic we're a way from serious warmth and if the LP sinks south to our east, we risk pulling in a cool or very cool N'ly.

[Scorcher]

 Cheshire Freeze There were a few posts on the previous page about the GFS FI charts and a lot of unsurprising likes on them.

[Derecho]

 Scorcher Yup I certainly wouldn't call it a spectacular change by any means.

[Don]

2 hours ago, Cheshire Freeze said:

not really seen anyone get excited about cold at this point?

Think most people, me included, want a bit of warmth and sunshine?

Too late in the season to get excited about cold now, although any period of below average temperatures is something these days!  However, warmth and sunshine (like today) would be pleasant!

[Daniel*]

2 hours ago, Derecho said:

Scorcher Yup I certainly wouldn't call it a spectacular change by any means.

If you could read correctly I was not making comment for UK… in Central Europe highs will collapse from 30C to 10C in a matter of a few days. The change is considerable but of course it begins from a very elevated position. 

[Pauski]

I live in southern Finland and it looks like that something colder is coming in next week, altough nothing special. 

The thing i want to see next summer in My country is year 2010 or similar repeat, So the warmest air should be somewhere in Russia and spread from there and not from central Europe. 

[Derecho]

 Daniel* Fair enough, just goes to show how warm it has been there though with these cooler temperatures being only just below the 81-10 average.

GFS looks depressingly familiar at D10 but the EC remains rather chilly at this time with a high to the NE

[minus10]

From a gardeners perspective yesterday was a lovely day for cutting grass....warm but not too warm...DRY......breezy and yes...that gold disc in the sky was out...allbeit a bit hazy at times...good day for working...actually felt like late spring/early summer...well after today which should also be good here in the south east i am desperately looking for any signs of more of this..not that promising from the gefs0z..

..Looking towards the end of April and cooler and maybe cloudy with brighter breaks with some rain seems to be on the cards..

..geop anoms showing that block to the north west..

..good example of the 5 wave pattern there with the trough to our south east and north or north easterly air flow possible..as indicated by the mslp anoms..

..both at 850 hpa and 2m temps wrong colour of average..

..this translates to a very uninspiring temp on the ground..

...however in any sun i would think it would be a bit warmer than what is shown..particularly dependent on topography  location and wind direction with south western areas favoured..

at least we wont have much rain ??

...well...not quite as much rain..again south western areas favoured...

..crucially from gardeners point of view will there be any frosts?

..with the exeption of couple of outliers i would say we would hopefully avoid a frost here in wgc  although if the wind falls light it could be a close run thing..

..this signal for below average 850s pretty consistent to varying degrees over the models now and the gesf mspl showing why for the 26th..

...however looking on the more positive side the Atlantic looks stonewalled as @Mike Poole stated earlier and it wouldnt take a lot to tweak that high to have more influence over the uk and thus reduce the nne wind flow ...longer days..growing strength of the sun...enjoy the spring and make the most of any brighter/ drier slots if you can...have a good day...

 

 

[Cambrian]

The end of the coming week looking settled sooner and for longer now on the models. We’ve been watching this change develop for several days now, but it’s always good to see a signal:

a) firm up

b) come forward in time

And this one’s really beginning to look very good.

0z EPS for next Thursday (18th) from last Monday for day 10, and today at day 5, showing the two sides of the coin becoming more clearly imprinted - the bubble to the west of the UK and Ireland gaining in modelled heights and steadily being modelled further north, and the low heights earlier focused over Scandinavia, now modelled as a deeper trough extending down into southeast Europe. 

 

Typical of how these models often work as they firm up, we can see the uncommitted, white gaps and softer shades getting gradually taken up by stronger signals, Atlantic heights growing stronger and more expansive, while a fully-fledged polar trough becomes marked out running down into Europe, the most notable synoptic difference being the development of the small low pressure to the east of Greenland that aids the link-up of low heights.

Though some colder, less settled conditions are slowly departing to the east, for the UK and Ireland, the more relevant feature is the decisive edging east of the modelled ridge, and more noticeably into southern Greenland and Iceland too, which sets up the prospect of an earlier arrival of a much quieter end to next week, and combined with the better build, dare we say it (!), hints at this being followed up by several back-to-back usable days…

….this positively illustrated by the EPS MSLP charts for day 7, with the high pressure edging in from the west at day 7, gradually establishing itself slap bang over the UK and Ireland by day 10. 

 

Rightly being picked up on is the Atlantic becoming sealed off, but this looks a more substantial block than just that, with high pressure extending from the Azores through our stretch of Western Europe to Siberia, so by that stage it’s not only a block to weather off the Atlantic but also a block to further troughs running down through Scandinavia - with the added benefit that with the removal of the threat of the colder air to the east, in the gentle and variable circulation of the high pressure, daytime temperatures should be building to much more encouraging levels into the last week of the month - drier and warmer - good news for those yearning to give their spring freckles an airing. Have a great weekend. 

[Rain All Night]

On 12/04/2024 at 11:37, Rain All Night said:

0z deterministic runs, out to Fri 19th Apr (day 7)

Our current short spell of warmth from the south will be followed by a few westerly and then northwesterly days before the Atlantic anticyclone takes over during next week.

I wonder if there's any chance of colder air from the east making it underneath the high?

0z ensemble means, out to Sat 27th Apr (day 15)

ECM wants to keep the good times (if maybe not the warmest times) rolling right through to the last weekend of April and perhaps longer still. GEFS seems a teensy bit less sure towards the end.

0z deterministic runs, out to Sat 20th Apr (day 7)

GFS showing some interest in retrogression of the high later, in line with its ensemble mean below.

0z ensemble means, out to Sun 28th Apr (day 15)

GEFS seems more keen on the high eventually moving northwest than the other two models.

All three agree that the Atlantic will be steadfastly blocked right through to the end of the month. Been a long time since we've been able to say that!

Edited April 13 by Rain All Night

[Rain All Night]

 Mike Poole  Cambrian Great posts from you both, thank you. @Cambrian It's noteworthy that the outlook is finally good enough that you don't need to resort to any of your wonderful humour!

Edited April 13 by Rain All Night

[KTtom]

Just like to the 10 days before Easter the models were in full agreement of a deep Atlantic low just to the west of the UK, now we have solid agreement of an Atlantic high setting up to the west, and maybe shifting east to sit over the UK. Nothing particularly warm in sight at the moment  but definately an end to the constant deluge is now pretty much guarenteed...Thank God!

[WYorksWeather]

Quite remarkable given what we've seen recently - the GFS 12z keeps the Atlantic firmly blocked for the rest of the month, largely with high pressure in control.

Generally near average to slightly on the chilly side temperature-wise though, especially further north. At the surface though it looks closer to average apart from the middle part of next week, probably due to warmer than average SSTs around the UK keeping things a bit milder than you'd otherwise expect. In extreme FI right at the two week mark, possibly a sign for a warm up, but very weak signal at this stage.

The ECM ensemble meteograms also show the pattern quite clearly - a very strong signal for the winds to be coming from some sort of northerly direction for the foreseeable.

So, the upshot is we've got what I think most of us were wishing for - a period of much drier weather on the way overall once we get the rain early next week out of the way. But generally staying quite chilly. Good weather for walking, but pack the T-shirts and shorts away for a bit longer. A sustained period of both warm and dry weather looks like it will have to wait until the very end of the month at the absolute earliest, or more likely early May.

 

[ANYWEATHER]

BREAKING NEWS:-  The first Nationwide dry spell , for 9 months ,predicted by the end of this week.....!☺

Edited April 14 by ANYWEATHER

[Rain All Night]

22 hours ago, Rain All Night said:

0z deterministic runs, out to Sat 20 Apr (day 7)

GFS showing some interest in retrogression of the high later, in line with its ensemble mean below.

0z ensemble means, out to Sun 28 Apr (day 15)

GEFS seems more keen on the high eventually moving northwest than the other two models.

All three agree that the Atlantic will be steadfastly blocked right through to the end of the month. Been a long time since we've been able to say that!

0z deterministic runs, out to Sun 21 Apr (day 7)

The ECM AI model shows the UK high coming under threat from an Icelandic system next Sunday, but it stands alone. All of the other models display splendid frames for next weekend, especially further west.

0z ensemble means, out to Mon 29 Apr (day 15)

You can see that perhaps towards the last days of April, beyond day 10, some member runs in these ensemble suites may be showing outcomes where the blocking breaks down.

[SunSean]

 Rain All Night Rubbish in the East once again? 

[danm]

GFS for next weekend? Yes please….

[Scorcher]

Looks like it might finally be happening- after a good 6 months at least! It has been a long slog but let's hope we get a prolonged dry period now.

This GFS run is one of the best it's produced for some time with high pressure drifting over the UK as opposed to staying out west.

 

[Mike Poole]

 Scorcher Yes, high hangs around in some shape or form until the end of the run on the GFS, although drifts slightly northwest later.

GEM 12z run is a cracker through to T240, things starting to properly firm up now:

Edited April 14 by Mike Poole

[WYorksWeather]

Once we get the next couple of days out of the way, pressure looks to stay above 1015-1020mb pretty much through the rest of the run if the GFS mean can be trusted.