Model Output Discussion - Spring Has Sprung

[That ECM]

Just catching up, looking at longer term, looks like a high over us forever.

[Rain All Night]

9 hours ago, Rain All Night said:

0z deterministic runs, Wed 7th to Wed 14th (day 7)

Most of these runs are showing long-fetch southwesterly winds either reaching, or very close to the UK by the end of week 1, and given the trend over the last couple of days, I wouldn't be too surprised to see that verify, although you can see on the UKMO and GEM that there is a possibly of either weak high pressure or weak low pressure sitting in the way of that southwesterly flow.

0z ensemble means, Wed 7th to Thu 22nd (day 15)

The models still think that we are likely to see rising heights over the UK and to our east that will prevent the Atlantic trough from advancing into us in week 2, but nonetheless that trough continues to look more influential with each new set of runs. Significant height rises to our northeast and later our northwest seem to be less well represented amongst the members of all three ensembles this morning than in recent runs, and you can see that from 21st Feb (admittedly very late in the run), a return to Atlantic low pressure systems seems to be well represented, though I wouldn't yet say "expected".

12z deterministic runs, Thu 8th to Wed 14th (day 7)

We were due a reprieve, and at least in terms of "dry" and "potential", these runs are that. There is still room for doubt, since it is only in the last two frames that pressure really starts to build properly, and there's no guarantee that it will build in the way that the ensemble means below suggest that it will, but it's at least showing fairly uniformly across all five models shown here, though the UKMO leaving some of that low lingering to our east is an interesting variation.

12z ensemble means, Thu 8th to Sat 17th (day 10)

Since the full ECM ensemble is still loading more slowly than usual and I need an early night, I'll just take us up to day 10 this evening. It's a little odd seeing ECM as the least supportive model for a strong Scandi high tonight, given it has generally been the most enthusiastic about high pressure (be that to the northeast, northwest, or over the UK) for the past few days. At day 10, the mean surface pressure contours are just about coming from the Atlantic side. Still, it's just one run, and the GEM ensemble is looking very shiny indeed (albeit not stonkingly cold, for those that way inclined).

[Ice Day]

 Rain All Night Great post RAN.  Well, here's the ECM ensemble mean at 300, another step forward I'd say

The ECM Control for the same time

There are so many options on the table now, it's somewhat mind-boggling!  We'll need A LOT of patience over this next chase, if that's what it turns out to be!?

[WYorksWeather]

I'll get on with my usual post, but first.

2018 vs 2024 comparison

Seeing a lot of 2018 comparisons being thrown around with the BFTE, so first a bit of a chat about that. I very much doubt this post is going to make me very popular, but I really don't see something similar happening this time. First of all, you have the timing. The 2018 SSW resulted in a zonal wind reversal which began on the 5th February.

Here's the current forecast from ECMWF.

At best, the reversal will happen about two weeks later, if it happens around the 18th. After the usual lag, that would put any resulting cold spell, if the SSW were favourable, into early March. At that point, you need something absolutely extraordinary to deliver. -5C 850hPa won't cut it - you probably need the -8s or even -10s and lower. Which brings me on to the second issue.

The BFTE chart for the 28th February 2018 looked like this. You have the entire UK under -12C 850hPa, and eastern coastal areas under -14C. It's absolutely incredible cold for this country to deliver the result that it did.

So, how did the cold get to that point? Well, in order to reach charts like those, you first need a source of cold air. Here's what the NH cold pool looked like at the same time in 2018 as we are at now (7th February), on the left. And on the right, where we are today, 7th February 2024.

The two charts aren't even in the same league for cold at our latitude. If you imagine drawing a circle over the chart, you can see that today, almost everywhere at our latitude or further south is near normal or above average. in 2018 there's a huge blob of -12C over not just Scandinavia but over Central and Eastern Europe as well. There's also an even more impressive area of cold over North America, down to the -20C isotherm widely.

With the cold pool like it is this year, I don't even see how a BFTE event is possible. If we got the identical synoptic pattern to 2018, the air source would only be -12C 850hPa or so, it would moderate as it headed our way, it'd be happening a week or two later than in 2018 due to the SSW lag, and we'd end up with marginal snowfall at best, probably a similar event to this week, frankly.

I think this explains why we've had a lot of good looking charts this winter, and very little in the way of outcomes. Milder cold sources means that even good looking charts are underwhelming in terms of the resulting temperatures.

Tomorrow's snow

Here's UKV again. To add to the frustration, this looks like a further downgrade, to be honest. More of the initial precipitation band tomorrow looks to fall as rain, except over high ground, where there will of course be the potential for some disruption, hence the Met Office warnings. 

By Friday afternoon, even the -5C 850hPa line is pushed back to central Scotland, and further rain will probably wash away any remaining snow, and temperatures well into mid to high single figures away from high ground will aid in melting.

Medium range outlook

The medium range just looks relatively boring. We may get some sort of easterly flow, and it's not looking overly mild, but there's a distinct lack of any cold to work with, as shown in the above charts.

You can see this in the ECM meteograms.

I mean it literally is like the models are trolling us at this stage. We finally get the much promised easterly in the extended at day 10 and beyond, and it brings average to above average temperatures! It's an absolute joke.

Long-range

As for the longer range output to whether we might expect a change beyond the current NWP horizon (so into late February or early March), it's a mixed picture.

CFSv2 is going average to slightly cooler than average for the most part for the next four weeks, but it's not a notable enough anomaly to really amount to anything.

The GFS 35 day mean is notably above average after the coming week until early March, before then dropping back below average.

The ECM extended for week 2 (19th-26th), week 3 (26th-4th), week 4 (4th-11th), beyond which possibilities for cold and snow are pretty much done, also show nothing of any note. If anything, slightly on the mild side. Also worth accounting for the fact that ECM is using the 20-year average in these charts, so near average conditions on these charts are still mild.

Summary

It's not a good outlook. Possibly the best we can hope for is some overnight frost and fog under areas of high pressure, and maybe some sunshine by day in gaps between the rain.

I think the most probable outcome is just average late winter conditions - a few colder spells with overnight frosts, interspersed with milder, wetter periods, but with no cold or snow of any note away from the usual prone spots on high ground and in Scotland.

I may turn out to be wrong, but we're rapidly running out of time here, and we need a strong signal to appear in order to change things around before its too late. That means a strong cold signal beginning to appear in the ensembles within the next two weeks. Extended range model output is currently not supportive of such a change either.

 

[Don]

2 hours ago, blizzard81 said:

Indeed mate. It started with the much improved ecm 06z control run this morning and that trend has continued across the main models this evening. We really needed this after the dire morning runs, especially gfs. We have something to build upon now

Even if things do look better moving forward, the chances are it will just end up another let down.  As others have mentioned, the EC46 look relatively poor tonight with HLB too far north with a more low pressure influence.

[bluearmy]

If anything, the strat split slightly greater on the pub run 

[Singularity]

For what it’s worth, a 2018 style result is feasible but only with a quick tropospheric response to a split type SSW with a high retrograding from NW Asia to Greenland such that very cold air is drawn swiftly around from the high Arctic.

Not asking for much is it?

We are technically in the game for such a thing, but just barely. More likely we’ll end up looking for surface cold development which is something the forecast models tend to underestimate at more than a few days lead time (insufficient resolving of the boundary layer to free air energy exchange).

[Met4Cast]

On 06/02/2024 at 09:54, Met4Cast said:

What did previous look like a good chance of sustained high latitude blocking during February is rapidly fading. 

Despite an increasingly favourable MJO signal into the western Pacific, we’re missing a vital ingredient & that’ poleward propagating +AAM (westerly momentum). 

The arrow shows the previous “starting pistol” of +AAM anomalies propagating poleward through December & indeed into early January, this along with the MJO helped to support & sustain the recent blocking we’ve seen around the UK/over Greenland. 

Unfortunately, this time +AAM is increasingly glued to the equator & we’re not seeing this fluxing towards the pole, this helps (despite the MJO) to inflate the European ridge & indeed, a very strong signal for this within NWP through the remainder of January. A flat, mostly mild end to the month with low pressure systems deflected northwards, potentially stormy at times for Scotland. 

The reflective wave from the SSW hasn’t helped things either. So.. my hopes for something sustained in terms of cold/snow are rapidly fading. 

I want to go back to this post from the 22nd January (the quote shows a different date, had to bodge the quote due to that thread being locked, original post here:)

Unfortunately much of this has rung true. There remains a lack of poleward propagating +AAM anomalies hence, despite the huge surge in momentum in the tropics/sub tropics & despite a relatively favourable MJO signal there remains little HLB on offer. Now, we have lost the Iberian heights and we are seeing some brief cold weather thanks to cyclonic wave-breaking but this is temporary.

Going forward, there is some evidence within NWP modelling for height rises to the NE but these will be coming up against a broader Atlantic trough. It's possible we could see energy undercutting this but given the current situation regarding background forcing I'm not overly optimistic, it seems plausible that the height rises to the NE will be too far east to really advect cold air into the UK & allow for significant trough disruption SEwards into southern Europe. 

A SSW seems likely later in the month so the polar field is likely to become increasingly unstable but in the short-mid term, if you're lucky enough to get snow in the coming couple of days I'd enjoy it whilst it lasts..

[frosty ground]

 

This is the jet you want to see if you want to drag cold air from the east.

This is a rather large high building.

[offerman]

 That ECM until summer then northery or easterly blasts take place 

[WYorksWeather]

 frosty ground 

Still the problem of a lack of any real cold air to our east though. The nearest serious cold at -12C 850hPa is in the most northern reaches of Scandinavia or way out in eastern Russia. And at this time of year, that's increasingly the kind of air we'd need to be advecting in our direction to get anything notable.

Edited February 7 by WYorksWeather

[WeatherArc]

18z gives me some hope of easterlies but a real lack of cold air here. 

[frosty ground]

 WYorksWeather this run is heading one way thou so that will soon sort it out.

With anything to advocate the air west it doesn’t matter what air mass is there 

[topo]

The lack of cold is a result of the synoptics of the previous days/weeks.

Believe me there is cold. It can be unleashed really fast with the proper synoptics.

 

[Daniel*]

1 hour ago, WYorksWeather said:

At best, the reversal will happen about two weeks later, if it happens around the 18th. After the usual lag, that would put any resulting cold spell, if the SSW were favourable, into early March. At that point, you need something absolutely extraordinary to deliver. -5C 850hPa won't cut it - you probably need the -8s or even -10s and lower. Which brings me on to the second issue.

What you say is not strictly true actually with 2018 major SSW given the nature of split it was actually quite a long wait. It’s been known for the big SSWs to have impacts within a week, I think this occurred in Jan 2013 there are other examples too like Jan 2009 both splits a week later London saw its biggest snowfall since 1991. The fact the AO indexes are already on side is another indicator of a potential quick downwell before the end of February I’d say.

[ICE COLD]

 topo just like at the end of the 18z . Strat looks good also

[feb1991blizzard]

Look what's here again, 

[Daniel*]

7 minutes ago, feb1991blizzard said:

Look what's here again, 

A great example of QTR.

[WYorksWeather]

 Daniel* Even if that turns out to be correct, that would still leave any impacts slightly later than in 2018, and the Northern Hemisphere this year is far warmer overall than it was in 2018, so we have less to work with.

Not trying to be unduly negative here, but I don't see how we get a 2018 repeat out of this even if you assume all the dice fall in our favour to get a similar synoptic.

[bluearmy]

 feb1991blizzard some consistency from gfs op with the split solution.  And three of the past  four runs have created a strong reversal coupled top to bottom 

and still we would worry that southern parts may be that bit too far south …..

[Purga]

Can we bear to be led up the garden path again?

[Daniel*]

5 minutes ago, WYorksWeather said:

Even if that turns out to be correct, that would still leave any impacts slightly later than in 2018, and the Northern Hemisphere this year is far warmer overall than it was in 2018, so we have less to work

It was warm in 2018 too when extreme cold was seen. February 2018 actually featured record anomalous warmth in Arctic.

 

 

[WYorksWeather]

 Daniel* Not across the entire Northern Hemisphere. The second warmest year was 2016 as your quoted tweet shows. Here's 2024 vs. 2016 on the entire NH view.

EDIT: For those who can't see the chart well - 2024 as of 1st February was just under 1C warmer than 1st February 2018.

Edited February 7 by WYorksWeather

[Johnp]

P16 shows the kind of setup we need, with a deep cold pool advecting towards us

 

[Don]

8 minutes ago, Purga said:

Can we bear to be led up the garden path again?

Not me, the towel is well and truly in!