Model Output Discussion - Spring Has Sprung

[damianslaw]

And the ECM follows the GFS this eve.. reverting back to previous output in 12z runs a couple of days ago or so back.

The continued trend is the stretching of the polar vortex towards scandi opening up the window for heights to develop to the NW sending the jet south and kicking away the stubborn heights to our south. 

[Mark wheeler]

 ANYWEATHER well at least for once @Tim Blandhas an opportunity to post some.

[nick sussex]

And so the saga continues !

The ECM reverts to its output from two evenings ago . That evolution which it dropped then was then picked up by the GFS.

We do now have that old favourite the Arctic high entering the stage and we know that means . More drama !

It really has felt like pulling teeth the last week with the bloated high to the south refusing to leave the scene .

Overall this evening things have improved for coldies.

But a long way to go . We aren’t quite in last chance saloon time but if we’re to get some decent crunchy snow then the earlier into February the better .

 

Edited January 30 by nick sussex

[Daniel*]

No surprise to see det runs GFS & ECM playing with a wedge.. MJO has moved into phase 7 at decent amplitude this would manifest into second week of Feb with heights expected to fall to our south. February has been delivering more than January in recent years 2018, 2021 and 2024???

[WYorksWeather]

Before moving on to discuss the longer range, first a quick look at the possibility of date records from the 1st-3rd. The 1st has trended cooler over recent days, so a date record is highly unlikely.

Looking at the 2nd (target to beat : 16.1C) and 3rd (17.0C), the highest temperatures I can see on UKV are below.

The Foehn potential is greater on the 2nd than the 3rd. Strong south-westerlies into Scotland on the 2nd, warmth more focused over central/southern England on the 3rd.

Either day is a potential date record. Hard to pick which is more likely - a raw 12C maximum on the 2nd is ordinarily a little low to deliver 16C, but Foehn effect could get there as we saw on Sunday. The 3rd looks the warmer day on the raw charts, but has less Foehn potential and therefore might not punch much above the 14C raw maximum. I would put the likelihood below 50% on both days on that basis, as it is still fairly uncertain.

Looking at tonight's ensemble output from the GFS 12z, it's a bit of a mixed bag. I did get some pushback on the suggestion last night that the ensembles still aren't that great. Here's the charts for London and Newcastle.

My reason for still not finding them that inspiring is that the mean signal is still not an especially strong one. The mean is not dropping below -5C yet. Yes, getting us below the 0C line and into negative territory will make things generally feel a lot more seasonal, but the long-term mean is -1C or -2C. We shouldn't be overjoyed at seeing the mean reaching -3C or -4C. Is it a start, and something to work with, yes, but these sorts of charts are not going to deliver away from northern spots and/or at altitude.

You can clearly see this on the surface temperature ensembles. Very few ensembles are reaching 0C at the surface, and the mean from the 10th onwards is around a 5-6C daily mean in London, and a 4-5C daily mean in Newcastle. That is more seasonal, and cooler than what we've had for the most part of late. But it's only back in line with the seasonal average. Seasonal average temperatures are not going to cut it for widespread ice and snow, it's a simple as that.

The ensembles look better towards the very end than they do now, but we still need to see a further trend downwards.

The overall pattern on the mean still looks pretty flimsy as well.

At day 8, a Greenland high is building, but we still have the stubborn heights to our south.

At day 10, the Greenland high dissipates, but we're still free of heights to our south.

Day 12 and day 14 then looks promising.

But by day 16, the Euro high is making its presence felt yet again.

[Chesil View]

Ecm and gfs 12z ops converging on cold and possibly snowy outcomes in the medium range. 

One senses that we're back in the game or heading in that direction at the very least.

[Uncertainty]

The ecm and gfs ops are absolute best case scenario stuff. We’d need to see an awful lot more runs going for the wedge to have any confidence. Still the charts are stunning so here they are:

 

 

More likely (and better represented on the ensembles) though is the gem solution, perhaps not quite as intense.

However, what is starting to look more likely, is the long heralded blocking later in week 2. The target period is now just coming into the scope of the big 3 ensembles and the gem ensembles are really keen on this tonight.

This would reflect the sub seasonal picture that the 46 has been consistent on for weeks. And it’s not alone, the normally hesitant cfs weeklies are on the same page too.

 

We’re at the all or nothing time for this winter. February will define our perceptions: cold and snowy and the seasonals have the last laugh. Another bust and the told-you-so’s will be crowing forevermore (with good reason, to be fair).

[Daniel*]

Day 10 mean 00z and latest 12z, low heights are pushing further south. Notice again Scandinavia becoming very cold.

 

[ANYWEATHER]

Ecm 12z, No blocking in place anywhere where it matters for winter cold prospects.  There's only one way that day ten chart will go ,if it was correct!

[Cambrian]

It’s the extent and starkness of the change on the 12z GEFS between day 8 and day 11 that is the eye-catching signal of the switch to come, fringe anticyclonic with a southwesterly flow exchanged for a cyclonic northwesterly…

 

…with a drop in T850s that continues through to day 13, some properly cold air might well be in prospect if that’s the mean at this kind of range.

  

The models firming up on the stretching of the PV east being followed by the leaking back west of the Eurasian lobe of the PV to the Greenland side. 

A closer look at the heights contours, comparing yesterday’s day 12 with today’s day 11 shows the emphasis on a Scandinavian trough being subtly modified to more of an emphasis on a Greenland trough (deeper too) pointing sharply southeast through Iceland to the UK and Ireland, holding the trough back further west as a result. 

 

This could well serve in the event to prolong the cold spell as it takes its time to grind east, the trough a long way south through Europe into the Mediterranean all the way through to day 14, its western flank looking to provide the route for disturbances to head sharply southeast through Iceland down into Western Europe. 

The UK and Ireland as is often the case is close to the cold boundary, but plenty of scope for wintry opportunities developing here in what could be a notable cyclonic setup for being combined with generous feeds of Arctic-sourced air that are “just cold enough”. This is an increasingly interesting outlook. 

[Uncertainty]

As @sebastiaan1973 has pointed out, the signal on the ec 46 is incredibly consistent. And only getting stronger…

Enjoy the mild weather whilst it lasts!

[Mike Poole]

ECM clusters T192-T240:

The consistent part of this timeframe is the erosion of Euro heights by day 10.  Cluster 3 probably the best for some earlier cold, also cluster 4, but at this point, setting up the pattern change is the most important thing.

T264+:

Clusters 1 and 2 look excellent, with significant trough to our south, especially cluster 1 at T264, and a nicely placed high.  Cluster 3 has the pattern a little too far west.  Cluster 4 look like it might tee up an Easterly and cluster 5 builds heights into Scandi.

We are back in the game properly now.  Yes, this could go wrong, it could land with poorly positioned chess pieces!  But it could also go right, we will see…

[feb1991blizzard]

Even deeper trough over Europe end feb now.

[AO-]

Good evening, 

For what it's worth. Nice operational, but a downgrade of the EPS of EC, regardless of the value to be attached to it. If it is to be a trend, some consistency would be nice. There are not many members showing a similar temperature as the operational. But it might as well be a start. The synoptics are more favourable for Britain, that's for sure. 

I have seen the cold being postponed too often the past few days. Probably more members will follow showing positive synoptics for cold. Atm it's far FI, regardless of the background drivers that seem favourable. 

Edited January 30 by AO-

[sebastiaan1973]

EC46 cold. Massive upgrade from a couple of days ago. 

A dip to 15 m/s. The border of a weak stratospheric polar vortex is 20 m/s.

Edited January 30 by sebastiaan1973

[phil nw.]

Just coming over the horizon of nwp in week 2 is a pattern change now,from mild to something colder.

Still early days but enough of a change in the 500 anomalies to take notice.

The concern currently is the lack of amplification in the Atlantic pattern so any cold from the north will struggle to get far enough south to cover the whole of the UK..

This of course may well change as we go further on.The lowering of heights to the south and increasing heights to the north west shown in the ensemble means and clusters is a good sign and the essential first stage to a colder set up.

[sebastiaan1973]

Truly remarkable. The positive NAO regiem is falling back to a staggering low number at 20th of february in the ENS. 

[frederiksen90]

Big, big run again from EC46

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MJO phase 7 is very clear, and possibly next 8. It statistically gives this development :

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https://www.americanwx.com/.../FebENMJOphase8all500mb.gif

And it happens around the time the strato weakens strongly (mid-February). Then a response to the rise of strong Atlantic/Greenland blocking from below which weakens it all the way up and then the process may then intensify down into the troposphere again in the following weeks. As I see it, it looks like a coupling from below, where the MJO drives strong blocking and the cold propagation with an upward wave of high pressure that moves from the troposphere up into the stratosphere, weakens it above, and then prolongs this process in the troposphere . Then we don't have to wait for an impact after a SSW, as it occurs from below. So it also makes sense that the models have been so consistent about the development. In the case of warming, where high pressure starts in the stratosphere and moves down, you see the effect approx. 10-14 days after, but now you see the potential long before it weakens the stratosphere. This means that the MJO moving into the western Pacific will probably have the greatest influence on the flow change from around 10-15. February onwards. In addition, EC46 is strongly supported by CMC ENS and GFS35 with strong blocking and cold spread from mid-February onwards, and potentially colder over Northern and Western Europe before. It is certainly not certain that we have seen the best winter weather yet.

[Mike Poole]

7 minutes ago, sebastiaan1973 said:

A dip to 15 m/s. The border of a weak stratospheric polar vortex is 20 m/s.

I wonder if this might be another thing going right for us this time?  Weakening westerlies in the strat allowing a promising trop driven pattern to take hold, whilst not adding in the randomness of another SSW (probably).  

As I mentioned yesterday, MJO actual data continuing to progress calmly through phase 7 at decent amplitude (grey line) regardless of the bizarre projection the models have continued to predict in just the very near future:

[Eagle Eye]

 Mike Poole

I'm never entirely sure of the MJO, it's not my best subject but appears to be a new cycle sort of forming but not far behind the last one? 

Edited January 30 by Eagle Eye

[jules216]

Its just shocking again. High pressure to the west of Russia increasing in prominence just in time with other cyclonic Wave breaking event in the Atlantic. The Euro low has no real source of cold air to tap in to from resulting in average surface outcome or at best marginally below average resulting in very limited snowfall potential below 800m in Europe considering we are talking about Late February which needs -2/3 anomally at least for something interesting to occur. But on the other hand a lot of cold rain with very small amplitutes. 

[Rain All Night]

7 hours ago, RainAllNight said:

0z/6z deterministic runs, Tue 30th to Tue 6th

Still not a lot of variation between the models prior to Monday 5th. GFS and JMA are still trying to bring a taste of the northerly to northern Scotland. Otherwise, not a lot new to see for the next week.

0z/6z ensemble means, Tue 30th to Tue 13th

We see suggestion of the arrival of an appreciable sphere of low heights from the west around 8th Feb, which coincides with the return of the precipitation signal on the ECM meteogram (Reading shown), as well as roughly coinciding with a signal for a drop in temperatures. Since this has been shown consistently for a few days now, I'd say we can reasonably expect a spell of unpleasant weather for most of us during the second week of February, so maybe don't go planning any outdoor activities for that week.

Right at the end, on the 12th/13th, you can see hints of the low pressure perhaps progressing eastwards and pressure rising a little in the Atlantic behind it, but that's probably too far away to read much into.

12z ensemble means, Wed 31st to Tue 13th (day 14)

GFS is still determined to scrape us with the northerly on 5th/6th Feb.

At face value, the ensemble means are showing us a cyclonic period of weather from the 8th to 12th, as the high pressure to our south yields. But check out the northern flank of the mean low pressure area on the ECM ensemble... rather flat, isn't it? Now granted, the mean easterly is aimed at Iceland, but the deterministic run (further down this post) shows us that it's possible that it could end up further south.

At the end of week 2, pressure seems to be rising again from the south.

12z deterministic runs, Tue 6th (day 7)

The T+168h charts are messy around the UK, which I think is rather interesting to note in the circumstances.

12z deterministic runs, Fri 9th (day 10)

I wouldn't normally show individual runs at day 10, but let's give ourselves an excuse to view those ECM and GFS wedges once more, alongside some less savoury suggestions of what we might see instead should those wedges fail to form.

Edited January 30 by RainAllNight

[WYorksWeather]

ECM broadly similar to GFS. Absolutely nothing in the reliable to suggest anything other than temperatures dropping back towards seasonal norms, possibly very slightly below by the end.

Still a hint of more of a north-westerly at day 14 in the south (Reading), but nothing beyond that. Temperatures still favoured to be about average. Similar further north (Newcastle).

Temperatures nearer average is more seasonal, but it doesn't really equal widespread cold and snow. We need to see a stronger cold signal in the ensembles before I'm getting back on the hype train.

For an analogy, hyping this up at the moment feels like hyping it up if after a period of 16C and drizzle in July, we see some charts at day 10 that promise 22C and partly cloudy. I mean it's better, but it's really not all that inspiring. We're just going from absolutely horrendous winter charts to merely average, and that only as we approach day 10.

Still time for upgrades, and of course this says nothing about the second half of February. All I am saying is the period of interest does not begin until at least the 10th, and even at that point, the level of interest is very modest at this stage.

[Kasim Awan]

Steady on here because like in the past few weeks we've seen corrections North of the pattern as it comes into the reliable time frame. This is due to models underestimating the strength of the Iberian high in the extended range. As it comes into the reliable the models pick up correctly on the strength and the pattern is pushed North. So we're looking at low likelihood here at present.

[Jason M]

 Kasim Awan @RainAllNight

Yes, would not be surprising to see Iberian heights more stubborn. Maybe we will end up with a west based set up. Scotland would do okay I suppose.

Like all the other good charts though, they are way to far out to be bothered with yet. Story of the winter.