Model Output Discussion - Spring Has Sprung

[damianslaw]

A changing outlook shown by ECM, UKMO, and GFS from Thursday onwards, as we lose the very mild tropical maritime airstream for a polar maritime one. A classic cold front being the trigger with the azores high kicked to the west. A week of two halves ahead, more of the recent same Mon- Wed, Thursday the transitional day, Fri- Sun, feeling much colder thanks to a cold NW wind. Interest lies in how the trough behaves, we may see a secondary low develop on the southern base.. certainly snow looks probable to relative modest levels in the north in the form of showers by the end of the week..The high tops could see a fair amount. 

Edited February 18 by damianslaw

[Mike Poole]

ECM clusters T192-T240:

Good support for the UK=>southern Europe trough at day 8 - cluster 4 pulls in a northeasterly (contains the op run) which make the absolute most of what’s on offer, it brings the trough west into Spain, cluster 1 has it furthest east.  Moving on the strength of the ridge variable across the clusters

T264+:

Cluster 1 swings the trough into the Atlantic, bringing milder air, cluster 2 maintains it to our southeast, so remaining colder, cluster 3 pushes the Atlantic ridge through and replaces it with westerlies.  

[Dennis]

here comes a scandi ......

[WYorksWeather]

 Daniel* It's still about average overall - you're only looking at the daytime maxima there. I just looked at Kew Gardens and the average minima would still be between 2C and 3C, whereas the forecast is for around 4-5C.

If you average the two, daytime temperatures a little below average and night-time a little above, it's close to or maybe ever so slightly below average.

I'd still be comfortable saying 'about average' though.

[WYorksWeather]

In any case, moving on to the ECM. The 12z actually looks slightly more keen than the GFS in getting the temperature a little more below average, presumably with some clearer spells getting temperatures a little closer to freezing. Possibly quite a widespread frost for a few days if we do end up towards the bottom of the ensemble, with a few more runs getting the temperatures down below freezing overnight, especially further north.

The depth and duration of any cold spell is still quite uncertain. Both GFS and ECM have a milder trend showing into early March but that's a long way off, so I think we can say turning colder from the 22nd onwards for at least a few days, but how much colder and for how long beyond the end of this week is very much up for grabs still.

As mentioned previously, a lot of uncertainty in the models around day 8 or so. I think we still need a clearer idea of what the tropospheric response will be to the brief zonal wind reversal on the 20th, as that will undoubtedly be affecting the models at longer timescales at the moment.

@Daniel* - think you might like this ensemble slightly better!

[Rain All Night]

7 hours ago, Rain All Night said:

0z/6z deterministic runs, Sun 18th to Sun 25th (day 7)

I am generally looking for the trough to either do something interesting or to naff off as soon as possible. Looks like there's some prospect of it chucking us a storm at some point during its tenure.

0z/6z ensemble means, Sun 18th to Mon 4th (day 15)

Not a lot has changed with the ensemble means in the last few days (so we can credit them with giving us some good and consistent guidance), with the UK under control of the imminent trough from 22nd to 26th Feb, and the ECM and GFS means then remaining more or less aligned showing a sinking upstream Atlantic ridge until around 1st March (day 12), after which point we diverge with ECM then bringing us under the influence of a further mean trough, whereas the GFS mean instead goes pretty flat.

Perhaps most notably, no supply of subtropical air to the UK shown by any model after 21st Feb. I personally would have preferred to have had the chillier air in mid-Feb and then the milder air for the start of March, but you know how it goes...

12z deterministic runs, Mon 19th to Sun 25th (day 7)

These are the first runs I've seen in a little while where I could almost dare to dream - if that high pressure in the Atlantic by day 7 could only take it up a gear, something interesting could follow next.

12z ensemble means, Mon 19th to Mon 4th (day 15)

The ensembles suggest that nothing especially interesting will follow, that the low pressure will end up in Europe to our southeast, and the Atlantic high pressure will collapse on top of it.

The ECM ensemble then looks like it wants to chuck another trough at us from around 29th Feb (day 11) - thanks, dude. The GEFS perhaps does something similar a day or two later.

However, you can tell from the last few frames that there are rather more runs showing high pressure in the opening days of March than there were in this morning's ensemble suites, so there's a little straw to clutch if you want it.

Just for fun, here is an ECM ensemble member run that I feel extrapolates nicely from the ensemble mean, and also today's ECM zonal winds forecast, since no one else has posted it.

Edited February 18 by Rain All Night

[Dennis]

Winter , can we have a real one soon ....(March)?

I know it sounds a bit crazy but why not .... the days has come i think

Lets make some good fun here together

lets go in first for late febr24

 

[Ali1977]

 Dennis certainly looking interesting again Dennis heights building into Greenland again 

[Mike Poole]

 Rain All Night Interesting zonal winds chart:

It looks like the second technical SSW is guaranteed, and just as marginal as the first!

And then the ECM 46 has the garden path laid out once more for the first week in March!  We may run into some complications as to whether that might constitute a 3rd SSW, it isn’t if it is also the final warming (which it might be) and it isn’t if there are less than 20 consecutive days westerly winds since the previous one (which also might be the case).

[Ali1977]

Looks like it should be a show storm - shame on the 850s

 

oh, actually ️️

Edited February 18 by Ali1977

[bluearmy]

 Mike Poole forgot about the 20 days Mike 

Seems almost certain that it won’t make 20 days so the early March reversal (if it occurs) will register along with the current brief dip as tech ssw  no 2 of this winter 

[Rain All Night]

 Mike Poole Would be funny if there is a much more significant reversal later that ends up not being registered because of the tiny one this week.

[Tim Bland]

GFS & ECM both have some wintry precip next Sun or Monday. looks like. Mainly high ground & perhaps temporary coverings to lower ground , but better than anything we’ve seen so far this year for most (if it happens of course ) 

Edited February 18 by Tim Bland

[Daniel*]

Well seasonal models did say backloaded winter?

[Rain All Night]

 Daniel* I think they meant more like this:

(for the benefit of our younger readers, it snowed in England on this date)

Edited February 18 by Rain All Night

[*Stormforce~beka*]

 andymusic Lyme Regis 

[Cloud 10]

 Daniel*

Lets hope the extra day of winter this year turns out like this.

 

[MJB]

An unsettled week on the cards 

[Penrith Snow]

Some big snowfalls for Scotland then the Alps coming up with lots of cold rain for the rest of us.

Thank God this awful grey warmth is coming to an end, who wants a black spring in February

Andy

[Dennis]

good monday

when the puzzle fits.....

Edited February 19 by Dennis

[RJBingham]

Cooling off slightly, no frost, should feel nice when the sun comes out, if it ever does 

[Flub136]

Second SSW peaked. Interesting to note this time, as opposed to January, that the rise in temps were lower at 10hpa but greater at 30hpa. Look forward to one of the many more meteorologically educated members of the forum to provide some enlightenment if possible.

[bluearmy]

 Rain All Night it was limited to elevation as I recall. Eg -  Cricket called off in Buxton 

those were the days 

winter was winter and summer was summer …..

[Rain All Night]

12 hours ago, Rain All Night said:

12z deterministic runs, Mon 19th to Sun 25th (day 7)

These are the first runs I've seen in a little while where I could almost dare to dream - if that high pressure in the Atlantic by day 7 could only take it up a gear, something interesting could follow next.

12z ensemble means, Mon 19th to Mon 4th (day 15)

The ensembles suggest that nothing especially interesting will follow, that the low pressure will end up in Europe to our southeast, and the Atlantic high pressure will collapse on top of it.

The ECM ensemble then looks like it wants to chuck another trough at us from around 29th Feb (day 11) - thanks, dude. The GEFS perhaps does something similar a day or two later.

However, you can tell from the last few frames that there are rather more runs showing high pressure in the opening days of March than there were in this morning's ensemble suites, so there's a little straw to clutch if you want it.

Just for fun, here is an ECM ensemble member run that I feel extrapolates nicely from the ensemble mean, and also today's ECM zonal winds forecast, since no one else has posted it.

0z deterministic runs, Mon 19th to Mon 26th (day 7)

UKMO's Atlantic high looks a little more robust than the other two, I guess, but it's not gaining much latitude.

0z ensemble means, Mon 19th to Tue 5th (day 15)

ECM remains keen on a second trough coming in from the west around 29th Feb, and GEM lends support for this. GEFS looks different earlier with the Atlantic high sinking rather than toppling, and an unclear signal afterwards.

The proportion of runs showing (mid-latitude) high pressure in deep FI (4th/5th Mar) looks to have increased again slightly, for what that may be worth.

Edited February 19 by Rain All Night

[knocker]

 Flub136 I do not think this a true representation of the warming

An important character of sudden warming is its downward propagation from 45 km into the lower stratosphere. This feature is not zonal in character, but has nonzonal structure, with a planetary wave tilting westward with height. In the middle latitudes, warming in the stratosphere (40 km) is followed by cooling in the mesosphere (65 km). Simultaneously, the opposite occurs in low latitudes, with stratospheric cooling and mesospheric warming, but the magnitude of the changes in the lower latitudes is one order less compared to that noted in higher latitudes