Model Output Discussion - Spring Has Sprung

[damianslaw]

The remainder of February set to stay mostly unsettled ending what will go down as a very unsettled, dull and very mild month. However, a change from very mild to closer to average is on the way Thursday onwards, quite probably continuing into March as we see the atlantic trough amplify and push azores high out west.

Becoming very wet, windy at times, snow on northern high ground and light frosts in any sheltered areas in northern and central parts thanks to polar maritime air. Its the type of set up that can bring bright brilliant blue sky one minute then a sharp blustery hail shower the next and generally a cold feel. 

Longer term, just hints we might see more concerted northern blocking calming things down somewhat but not clear whether will be cold or nearer average with the jet riding across the UK bring cyclonic conditions.. 

Edited February 20 by damianslaw

[LRD]

21 minutes ago, AO- said:

but it is to soon to draw a conclusion. 

Well, yeah, but I haven't drawn any conclusions. Thought that's what the exact gist of my post was

[LRD]

Well the 12z op wasn't quite an outlier but...

First it was amongst the coldest members of the suite, then it was amongst the warmest, then it ended as the coldest

[ANYWEATHER]

50 minutes ago, AO- said:

True, but what may be more important is the disappearing of the Iberian high and the rain that finally hits Spain. Over 100 mm in the next two weeks according to GFS. It is not the first run with this amount of precipitation. 

I mentioned last week ,as the pattern change takes place ,Iberia will see Biblical rainfall during March and April, nothing to do with teleconections, but I have been told in confidence!  Watch this space...?

[RJBingham]

Pick the bones out of that 

[LRD]

Looking at the ensembles and 12z ops, we could be looking at dramatic changes of weather type and airmass from day to day. Typical for late winter/early spring, I guess

ECM 144 and 168

[CoventryWeather]

The GFS built the ridge over Iberia again towards day 10. Different outcome this time as it is less warm and more unsettled. But I can't see why I can't place my opinions on the op run, if others do exactly the same thing. 

The GFS is consistently showing this. I'm not cherry picking or anything. Not unlike many people here who posted a chart from one ensemble 16 days ahead - at least I'm placing the charts from the reliable range. Considering the way the weather has been recently and the models underestimating the Iberian ridge I can't see why this is an outlier solution (it may be consistently wrong but atleast it's not rapidly changing). 

There's support over on the GEM ensembles now, I'd say that enough evidence to start saying it's a cluster that you can't rule out. 

Edited February 20 by CoventryWeather

[jellybaby1969]

 damianslaw similar to my thoughts ...some gusty north westerlies throwing everyone at us Barr the kitchen sink . Heavy winter showers at 3c then brief sunshine at 7c ...rinse n repeat. Not a winter wonderland unless your in the Highlands but interesting weather..which we have lacked since the various named storms

[AO-]

 LRD

Still quite a strong tp vortex over Canada/Greenland given the forecast that it was a backloaded winter. GFS is more reliable atm than EC, I suppose. 

[Frigid]

Looks like quite the reversal if these charts are anything to go by

 

[damianslaw]

Whilst quite normal for late Feb, ECM is showing 4-5 days of sub 528 dam air north half of UK Thursday onwards and uppers touching -5 degrees. Likewise GFS12z which pushes 528 dam air further south and -5 uppers and for longer. Something we've not seen since 16-19 Jan. 

[Rain All Night]

9 hours ago, Rain All Night said:

0z deterministic runs, Tue 20th to Tue 27th (day 7)

GFS op runs, like its ensemble means, continue to make more of the trough going down into Europe, with the Atlantic high more reluctant to topple over it.

0z ensemble means, Tue 20th to Wed 6th (day 15)

ECM and GEM still seem to send in a second big low behind the toppling Atlantic ridge by around 29th Feb (day 9), which may be followed by a second toppling ridge behind it.

GFS continues to want to sink, rather than topple, the Atlantic ridge (and make more of the trough going into Europe), which appears to delay the arrival of the next big low by perhaps a day or two, and possibly hinder its progress through the UK.

12z deterministic runs, Wed 21st to Tue 27th (day 7)

Divergence after 96 hours (Sat 24th), though the difference between the outcomes on offer is not likely to be of great interest to many here since there are no deep cold air masses in the mix.

12z ensemble means, Wed 21st to Wed 6th (day 15)

Looking back at my posts over the past week or so, I think our three 15-day ensembles have, as a team, given us good guidance on the progression through our upcoming battering:

21st Feb - round 1

25th Feb - round 1.5 (with GEFS making much more of the trough going into Europe after this point)

29th Feb - round 2

What happens beyond that (day 10+, the first days of March) remains unclear for now - as illustrated by the rather different directions each of the three ensemble means take after this point - but personally I'm not going to count on it being anything settled.

Edited February 20 by Rain All Night

[Daniel*]

The man has spoken…

 

[WYorksWeather]

ECM and GFS ensembles are still struggling with the divergence towards the end of the month. Will we see a warm sector to guarantee a record-breaking CET February, or is it going to be knife-edge stuff? First uncertainty around 25th-26th, then again around 28th-29th.

Still need a day or two more to see what is going to happen here.

[Mike Poole]

 Frigid The last two SSWs showed up as big reversals on some model runs before getting watered down to the absolute marginal, and the 3rd Jan event disappeared completely.

I can see this one being different, partly because it is too late to bring a proper cold spell, but we’ll have to wait and see.

[Methuselah]

But, haven't all this year's SSWs amounted to nothing; just like 2019's SSW amounted to nothing? IMO, something (AGW?) is outcompeting the usual teleconnective drivers. . . 

Edited February 20 by Methuselah

[Rain All Night]

GFS continues to want to be different, its 18z run tries to link the Azores high to Scandinavia

Edited February 20 by Rain All Night

[Jason M]

The METO Deep Dive suggested they think this will likely be a final warming but by the time impacts are truly felt in 2nd half of March its probably too late. A coldish March coming?? 

Edited February 20 by Jason M

[raz.org.rain]

 Jason M depends if the SSW impacts our part of the world or not. It could just as easily be displaced by a growing Azores high, which the models seem keen on as a factor going ahead.

[Daniel*]

Of course EPS experienced a massive bust but similarly to latest GFS run interest in -NAO in early March.

[Frigid]

 Jason M Possibly, or it could all be an illusion and we see the warmest March on record. Jokes aside it can still get quite cold at the end of March into April.. think March 2013/Apr 2021. Even late April 2016 had a pretty potent cold spell with snow showers. Definitely nothing like what we could get in January but cold, yes. 

[feb1991blizzard]

 Frigid

Yes, looks like a real polar vortex breakdown coming now - too late!

[baddie]

 Methuselah What will our SSW lead to?? Nothing, whether its mild and wet, or dry and sunny

[Rain All Night]

1 hour ago, Mike Poole said:

I can see this one being different, partly because it is too late to bring a proper cold spell

Sod's law, the second strongest background driver after global warming!

[Met4Cast]

2 hours ago, Methuselah said:

But, haven't all this year's SSWs amounted to nothing; just like 2019's SSW amounted to nothing? IMO, something (AGW?) is outcompeting the usual teleconnective drivers. . . 

Yes, I think too much emphasis is being placed on this likely SSW in early March. Firstly because the timings involved here are worth mentioning, we've seen how poor modelling has been with SSW's this winter, why should we assume this one will be any differently? Secondly, an SSW in early March, assuming the usual 2 week lag we're looking at the 2nd half of March for tropospheric impact. Too little, too late imo. 

That said - As stated a day or two ago, I do think a -NAO regime is more likely than not going into March regardless of a potential SSW or not. AAM tendency has fallen through the floor as the MJO now sits inside the COD, this removal of tropical forcing has caused the previously sustained +MT to collapse into strongly negative territory, as a result westerly inertia is now being scrubbed from the atmosphere.

Another way of visualising this is with the 850hPa anomaly hovmoller, a rather sharp increase in easterlies just west of the dateline following the collapse of the MJO.

There are signs the MJO will return into phase 5/6 but the forecast on this is rather uncertain. The important part though is the sharp fall in momentum which is driving the pattern change currently advertised within NWP outputs. Atlantic ridging/Scandi trough scenario currently the favoured option but huge uncertainty over Scandinavia with regards to possible height rises around the Urals, the precursor to the early May SSW.  I suspect any high pressure that does build to the NE will likely end up too far NE to provide much hope to those still chasing colder outcomes.

In terms of the UK - Chillier than of late but little currently to suggest widespread cold/snowfall, as we go through March we require more spectacular synoptics to produce the goods. 

So to summarise, -NAO regimes are likely, UK will be colder than of late as a result but in terms of UK specific cold/snow likelihoods I'd still rate these as being rather low.