Model Output Discussion - Spring Has Sprung

[February1978]

 *Stormforce~beka* Completely agree. I'm north of Basingstoke, we've had 950mm in 9 months, way more than in a normal year (750mm). Lacking in sunshine too.

Easter doesn't look like helping that....but there is time for that to improve - current GFS looks slightly better.

[Rain All Night]

ICON 0z vs 12z, lol...

[andymusic]

gfs 12z sticking with cold and dry for the moment for the weekend onwards

and approaching Easter

Edited March 19 by andymusic

[danm]

 

[feb1991blizzard]

GFS looking very decent - snow showers.

 

Edited March 19 by feb1991blizzard

[andymusic]

GFS 12z Snow Easter Saturday as the cold gets pushed back

Edited March 19 by andymusic

[Jordan S]

 Cambrian
 

Really good post Cambrian 

 

I was also about to comment on the comments mentioning models only reliable to 5 days or 3 days etc, it’s actually more often than not a rather inaccurate statement otherwise for example I wouldn’t bother with my outlooks past day 3  but I see why they may think that with operational runs (excluding the ensembles) 

There is genuinely high predictability (if you are knowledgeable in reading and interpreting the model output) at days 6-10. 

Less reliability between days 11-15 ofcourse but the broad pattern has more often than not been accurately estimated/forecasted that far ahead and enough that you could on average get correct at least 25% of the time, I think the furthest ahead in time “ceiling” of being able to forecast (computer models/ human input)  area of local parts of country precise details being around day 8-9. With relatively accurate broadscale hemispheric patterns and what they could entail for our part of the world excluding teleconnections being around 3 weeks time. For anyone interested I highly recommend those Noaa 500mb height anomaly flow charts that are posted every now and then, really useful forecast method I’ve found, even though I’ve only started looking at them as part of my outlooks in the last few weeks, they aren’t 100% accurate but they are accurate way more often than they aren’t but more for a general overview than any specifics in a location of course and that’s for the human to take apart and forecast from it.

 

Easter still looks most likely unsettled in central/ southern UK and a bit colder and less wet further north with snow risk (probably mainly on high ground).

[feb1991blizzard]

That would surely be a huge anomaly in SW EIRE in Jan, never mind April!

[Summer8906]

 johnholmes Coastal strip of southern Hampshire, south of the Downs.

[Summer8906]

 Jordan S Really want that huge area of low pressure at our latitude to dissipate somehow. Not sure what the most likely route to that is... high pressure pushing down from the north or in from the northeast?

[Jordan S]

 Summer8906

I would say any lengthier drier spell from a high coming from north/northwest would be most likely given the overall pattern likely to take place but wouldn’t rule out a ridge from the southwest on occasion but this probaby further into second week of April because even into early April low pressure probably dominating our part of the world. But the hint I mentioned of perhaps more widespread drier weather in the second week of April from yesterdays post being from the exact evolution I’ve just said above let’s hope those slight more lengthy drier conditions do turn out correct for the second week.

[Mike Poole]

4 hours ago, Cambrian said:

Noticeable too that winter T850s appear to be handled better than summer ones, probably due to the winter PV, with typically fewer meridional episodes and less dramatic fluctuations in the winter as a result. 

Good post.  The fact that the models perform better in winter than summer in the northern hemisphere is well known and goes back ages, here for heights:

There are a couple of things of interest here.  First, the same thing cannot be said for the southern hemisphere, where it is much more erratic.  Guessing here, but I wonder if this is due to inherent differences in the strat vortex for each hemisphere in winter, and may be related to the reason that SSWs are very rare in the southern hemisphere, and this leads to lower predictability.

The second point of interest relates to the way the models are perceived in summer and winter on here, because I think most would probably expect them to be worse in winter not summer.  And I think this is down to the weather most people want and look out for.

In winter, people are looking for setups that are the exception to the zonal rule, i.e. the models find the high latitude blocking patterns very difficult, but that isn’t reflected in the stats becuase they are comparatively rare (now becoming exceptionally rare it seems!).

In summer, people are looking for the build of high pressure over the UK, and this is usually modelled well in advance because it involves a slow moving high local to the UK, these are sometimes even seen coming as a 1030 hPa high on the ensemble mean at 10 days away and usually count down.  But here, the good prediction locally is the exception to the rest of the northern hemisphere, so again the stats don’t show this.  

 

[ANYWEATHER]

Omega block of sorts by Good Friday from gfs , models are Flippin totally everywhere , totally unreliable. ....

[Methuselah]

 ANYWEATHER Why are you posting charts for nine days' time?

[ANYWEATHER]

 Methuselah because a few on here like posting charts 3 weeks ahead

[stodge]

Evening all

An early look at tonight's 12Z output.

The path through to the end of the week seems set - after an almost early summer like day tomorrow, it's downhill all the way as an LP weakens and moves SE into the North Sea introducing a not terribly potent N'ly but it will take temperatures back below average and be quite a shock to the system.

The early part of next week, as you might expect, is still far from resolved but there seem to be two scenarios in town. The GFS OP offers a build of heights to the north and the trough moving SE to the west of the British Isles leaving us in an E'ly flow with the north and west fairly dry but rain never far away from the south and south east and a switch to the NE offers the "promise" of something colder with plenty of ground and air frost in northern areas..

The other option keeps a lot of energy close to the British Isles and basically LP takes up residence over England.  That doesn't bode well for those wanting a respite from the high rainfall totals of recent times. Indeed, GEM keeps the LP right up to Easter with periods of rain or showers for all and little in the way of spring sunshine or warmth.

GFS has stuck to its guns the past two or three days but looks on its own currently. 

[KTtom]

 stodge ecm going for the same scenario gfs was showing yesterday, and indeed what ukmo 168 shows tonight with a deep low dominating in the run up to the holiday weekend. Gfs 12z as you say on its own tonight. The Mets video posted above alse pretty identical, maybe with the trough a bit further out west but with all that high lattitude blocking to the west and east around its not shifting away quickly.

[stodge]

 KTtom The exact position of the LP is going to be important but the net effect will probably still be the same. If it ends up to the west, it'll be milder for us all but with rain or showers moving in a cyclonic pattern from south west to north east.

If we end up with the LP over us, we'll probably generate our own showers especially in the south and west with thunder and hail but in the north with E'ly winds more cloud and longer spells of rain with snow on northern mountains.

The least likely scenario is the LP to the south but not to be disregarded at this time.

[Cloud 10]

ECM 12z decides to throw a chunk of the PV directly over the UK,and only 8 days away.

 

[damianslaw]

Mmm not liking the direction of travel being thrown up by ECM and GFS as we move closer to Easter, the choice of a deep trough locked in situ a la ECM (UKMO heading this way), or a chilly easterly and no doubt dull airflow, with possible cold rain plaguing many placed, probably drier further north a la GFS.

Naturally people's attention is turning to Easter right now, but its 10 day plus away (Good Friday) and there is much time to go through before we can begin to have more confidence in likely developments.

In the immediate, a couple more very mild albeit dull and in places wet days, followed by a colder polar flow Friday and through the weekend, with the return of frost, wintry showers northern high ground and temps back to average, slightly below further north. Importantly polar air means clean clear air which means sunshine hooray! but by this time of year can also bring increased convective activity, sudden showers of hail and squally winds, something different on the way after 2 weeks of mild gunk. 

Edited March 19 by damianslaw

[Kirkcaldy Weather]

Excellent

Taking all the following points and composites in the above post we are seeing the manner in which the upcoming pattern shifts will transpire.

On 15/03/2024 at 21:54, Kirkcaldy Weather said:

With further feedback including that of phases 4 and 5 we'll see a number of noteworthy developments.

 

On 15/03/2024 at 21:54, Kirkcaldy Weather said:

The next cyclone to approach Ireland and the UK will transition into a cut off low which heads through Spain and into Northwest and Northern Africa, likely rossby wave breaking involved.

On 15/03/2024 at 21:54, Kirkcaldy Weather said:

Per the above there will be opportunity for the Atlantic - Azores High to ridge across more southern parts of the UK and Ireland.

Another main aspect of phases 4 through 5 is the building of a strong Pacific > Alaska > Arctic Ridge and Blocking regime which extends into Greenland likely more of a -AO during this sequence.

 

 

On 12/03/2024 at 03:07, Kirkcaldy Weather said:

Pairing with feedback of the Super El Ninò we can see this is supportive of a warmer pattern including the development of high pressure from Africa which extends into Europe again bringing increased temperatures at surface and 850hpa levels.

On 12/03/2024 at 03:07, Kirkcaldy Weather said:

Linking this to the feedback of phases 2 through 3 during February and March again nice representation here for an above average temperature setup.

Starting at these focal points here we see as expected an above average temperature setup extending from Africa through parts of Europe with significantly above average temperatures at surface and upper levels perhaps some temperature records.

Here's the Rossby Wave Break Event with the high pressure and dual cut off lows 

As the High ridges into the UK and Ireland this brings a period of significantly above average temperatures at surface and upper levels, perhaps enough for some temperature records at these levels 

Into the 22nd we start to see quite a significant pattern shift.

As a system which began as the troughing across Canada across the Great Lakes and currently into the Canadian Maritimes per MJO feedback as discussed, begins to move over the Atlantic high this will bring stormy winds particularly toward the Faroe Islands with an accompanying strong Jet Streak and as this system continues Eastward these stronger winds will begin to extend into the UK

During the 22nd we'll see a cold front moving through and this begins the pattern shift to that of a colder pattern during week 4 of March.

As thickness levels lower and with the 528 dam and below air being present across the UK and Ireland this will cause precip to turn wintry with a risk of snow for all regions of the UK and Ireland ie Ireland, Scotland, Wales and England with most across higher elevations though mixing even to low levels cannot be discounted, probably a setup where West and Northwest Scotland does well for snowfall. Similar to the snowfall risk areas the frost risk will be most prominent further Northwest and North though all areas of the UK and Ireland seeing below average temperatures at surface and upper levels. 

This initial storm system will produce significant snow events across Iceland and Norway.

As this system descends it will bring a new significant snow event for the Alps.. Swiss Alps especially and a heightened risk of a heavy precip event into Slovenia which could be rain and or snow so a risk of flash flooding needs considering, these events are from the 23rd through 26th.

In roughly a weeks time we will start to see the feedback of ongoing MJO progression across the Pacific, phases 6 and 7 with new trough developments from Greenland tilted negatively toward the west of Ireland and the Atlantic 

We'll begin to see an increasing influence from blocking further East which could push the Atlantic trough further west and perhaps an opportunity for a plume type setup given past experience and the time of year becoming more supportive.

So we're seeing a below average temperature setup for week 4 of March

This is also ongoing feedback from the IOBW warm phase which supports a colder setup during March.

Also factoring in the overall season of stratospheric developments including multiple stratospheric warming events which I'd like to revisit my comments here 

On 27/02/2024 at 21:05, Kirkcaldy Weather said:

Also worth noting once more with the precursor patterns continuing we've got good signals for a new reversal of zonal winds at 10hpa (possibly 50hpa though no agreement on that just yet) with this looking like a stronger reversal than the previous 2 of winter 2023-2024.

This was a significant SSW event with a significant reversal of zonal winds 

10hpa values exceeding -20 m/s

Plus a reversal at 50hpa 

Given recent and current MJO progression paired onto weak vortex events again further excellent and expected correlation 

Impressive cold setup this with multiple minus double digit temperatures in Iceland and Scandinavia which are of particular note.

Cheers KW

[Bats32]

Well, the GFS 18z is aligning with the rest for a miserable week next week.

[Uncertainty]

A predictably pathetic climb down from the gfs. Run after run it has produced a phantom block giving chilly easterlies but we all know what we’re going to get is U.K. low number 353 since last July.

Even the icon gave up the nonsense earlier.

Last run

What we’re actually going to get is something like this monstrosity

I mean come on. What is that? 
 

Save us, La Niña.

[Rain All Night]

10 hours ago, Rain All Night said:

0z deterministic runs, out to Tue 26th (day 7)

GFS and ICON are still finding height rises to mix things up a little at the beginning of next week.

0z ensemble means, out to Wed 3rd (day 15)

The one bit of hope to cling to is that the trough signal seems to peak just before the start of the actual Easter weekend. The GEFS is as keen as the GFS on the idea of "wedgyness" after the northerly this weekend, perhaps slowing the trough down a bit.

12z deterministic runs, out to Tue 26th (day 7)

Let's enjoy the brief but welcome influence from the Azores high for the next couple of days, before the  hits the fan next week.

To further illustrate @Uncertainty's post above, here is the GFS 18z run...

12z ensemble means, out to Wed 3rd (day 15)

[Uncertainty]

 Rain All Night it’s basically a U.K. low taking the best part of a week to fill. Horrific for crops and yields nationwide.

Probably to be replaced or superseded by another one. God what I’d give for a 2018 or 2022 summer now. On that note my initial analysis hints at a reasonable summer - in the se especially - so maybe not bad for you mate. Long way off mind. We’ve had 2 one week U.K. highs in 9 months (sept and Jan). We need one asap. AI model has this in goo goo land.

Bank?