Winter Approaching: Forecast and Model Discussion Commentary

[Frosty.]

I must say, I’m looking forward to this! ️ …who needs the models?   

[WYorksWeather]

EC clusters below.

Days 3-4

A westerly pattern at this range, as expected.

Days 5-7

Cluster 1 (27%) builds a mid-Atlantic ridge, with an unsettled north-westerly by day 7.

Cluster 2 (27%) has a stronger mid-Atlantic ridge somewhere higher in latitude towards Greenland, more of a true northerly by day 7.

Cluster 3 (20%) is somewhere in between Cluster 1 and Cluster 2.

Cluster 4 (16%) has a trough through the UK and more of a north-easterly by day 7, a ring of heights to the west, north and east of the UK.

Cluster 5 (10%) keeps stronger heights to the south, which is probably the mildest option of the five, with the north-westerly or northerly likely restricted to areas further north.

The OP was in Cluster 2.

Days 8-10

Cluster 1 (33%) has a block to the NW at day 8 with a cold north-easterly, then the block sinks slightly over the UK. Cold and dry the likely outcome, with a cold easterly underneath our high for central and parts of southern Europe.

Cluster 2 (29%) is also very blocked, with an initial north-easterly at day 8 which looks cold. Beyond that, a tendency for the block to link back to the Azores likely means a milder high than Cluster 1.

Cluster 3 (27%) keeps the block to the west throughout, with a further extension of the high towards Scandinavia. Winds from the north, then the north-east, and finally the east. Cold, perhaps notably so.

Cluster 4 (10%) has high pressure further south. Still a dry pattern, but this is much milder, with a persistent link back to the Azores. Could still be cold at the surface at times.

The OP was in Cluster 3.

Days 11-15

A lot of uncertainty, and six options, so I'll run through them relatively quickly.

Cluster 1 (25%) is cold and unsettled, winds from the NE.

Cluster 2 (24%) has an easterly at first, then a north-westerly.

Cluster 3 (20%) is generally dry, with an easterly, followed by a north-westerly, flattening off to a more typical westerly by day 15.

Cluster 4 (12%) has an initial north-westerly, becoming a cold-looking northerly later on.

Cluster 5 (12%) has an easterly for southern areas, becoming more of a south-easterly by day 15.

Cluster 6 (8%) has winds mainly from the NW or N, with a persistent block over Greenland.

Summary

As @Mike Poole suggested, a big upgrade from a cold point of view tonight, after the bit of a wobble we saw yesterday.

After a mild next few days, the initial mid-Atlantic ridge develops around day 7. This alone is not enough for anything especially cold, with an initial northerly or north-westerly not likely to last too long.

However, the days 8-10 timeframe has moved strongly in the direction of extending the high to the east, which opens a window for a north-easterly or easterly.

Beyond that, the extended range is a long way off, but all signs again point to cold, with all six clusters being cold to varying degrees, and some of them could bring notable cold.

Very positive output if you're looking for a cold spell as we move into the second week of December and beyond. I would as always temper this with the fact that we are still at least a week away from the start of the period of interest, and so a lot can change before then. Nevertheless, on the face of it, you're not going to get a much better set of clusters for cold than this from day 7 onwards. Let's hope we get to see these charts count down.

[Mike Poole]

ECM extended clusters, T264+:

Oodles of uncertainty here!  Cluster 1 (13) and cluster 5 (6) look like a continuation of the best from the previous timeframe, cluster 1 the high drifts towards Russia, cluster 5 holds and then declines.  Meanwhile, cluster 4 (6) and cluster 6 (4) build a strong MAR pushing towards Greenland, these are probably the coldest in this set.  Cluster 2 (12) flattens out, and cluster 3 (10) the high moves west and loses influence.  

I think, now we have something to work with in the 8-10 day timeframe, it makes sense to wait until we understand that evolution a bit better, before worrying too much about what happens after.  

[Blessed Weather]

21 minutes ago, Mike Poole said:

Just to note re the strat - all the GEFS show the warming at the end of the run, so there’s clearly something going on there.

Is it the upcoming Atlantic block generating vertically propagating planetary waves (Wave 1) into the stratosphere? It's quite some block that GFS is forecasting to commence on 7th Dec and last for 4 or 5 days.

And the Wave 1 forecast from the 8th Dec is certainly on the up, reaching reasonable amplitude by the 13th Dec:

Source: http://weatheriscool.com/page8.html

And we know from research that Atlantic blocks are normally the cause of a sPV displacement:

Source: Blocking precursors to stratospheric sudden warming events

Blocking patterns don't always go on to cause trouble to the sPV, but the forecasts are of interest. Any impact, if any, won't be showing up in model output just yet. Certainly something to keep an eye on.

[WYorksWeather]

 Mike Poole Most of the clusters showing the high declining towards the end though are showing that at day 15. If you look at day 11 and day 13 separately, they all look cold at that point to be honest. I really don't think you can ask for much more!

[Mike Poole]

 WYorksWeather True.  Just that my interest has moved forward to the previous timeframe now, which is all good!

ECM 46 zonal winds:

I think that’s 9 SSW members now, so that signal slowly grows - however, this is 0z data, and won’t reflect what we’ve seen from the 12z GEFS for example.  

ECM 46 MJO:

Remaining amplified through phase 5 now, but the scatter looks large after that, so again, we wait for this to firm up as we move towards phase 6…

[I remember Atlantic 252]

 Frosty. for 300m+ in Scotland, may not be that unrealistic, for Tues 3rd, then from 7th

[Dennis]

have more hope on the 12z today to see a block late next week (weekend)

[knocker]

 Blessed Weather I am not sure I fully understand all this talk of an Atlantic block . From where I am sitting the amplification of the Azores HP slowly subsides as the flow trends towards zonal, although keeping its influence over the UK despite coming under pressure. Temps likely a soupcon below average.

[Frosty.]

I think we (coldies) just need to be patient and trust in the cfs?and all will be well?! ️ …joking aside, I don’t trust the models beyond T+ 1350 hours..but, you never know?!  

 

[Legend.Ice]

I think we started the winter well and in high spirits ( tomorrow 1 Dec )  , on the one hand there are cold temperatures that are gradually getting stronger and on the other hand SSW signals are starting to become a little more apparent in the models, of course it could be better but there are reasons to be hopeful

[Blessed Weather]

 knocker Sorry, I'm not sure I understand your point. The 500hPa anomaly chart from this evening's GFS 12z clearly shows an anomalous high pressure in the Atlantic in the position that the research paper I quote describes as being an "Atlantic block". Just to clarify, the period I'm referring to is from the 7th Dec through to the 13th Dec. Btw, I see no zonal flow in that period. Maybe it is the Azores high shifted north but it's still a block in the Atlantic in terms of potential stratosphere impact? The paper describes the process:

"In the troposphere, blocking events severely disrupt the extra-tropical circumpolar tropopause-level jet, which is either displaced poleward of or splits around the block's core of anomalously low PV (positive height) at tropopause levels. Their comparatively long duration and quasi-stationary equivalent barotropic structure is manifest at the ground as a high surface pressure system that impacts directly upon the pattern of surface weather."

The GFS animation for the period I discuss shows the disruption to the Jet Stream as it encounters the Atlantic high:

As the Wave 1 activity commenced at the onset of the high pressure block I have speculated in my post that the block was the cause. Your thoughts on the cause most welcomed.

[nick sussex]

Always best to be a bit dubious of the Azores high ridging north until it’s in the more reliable timeframe . 

As the high will topple it’s then crucial to get it as far north and as amplified as possible before that happens so as to tap into some decent cold 850s . 

It’s likely there might be repeated attempts to ridge the Azores high north . In terms of the ECM it did have a bias of over-amplifying the upstream pattern over recent winters so best bear that in mind . 

The GFS had a flat bias at longer range ,

[phil nw.]

I tend to agree Nick.Based on experience we need to be cautious on how much traction the Azores high is being modeled at longer range.

It looks odds on for a developing high around 50n and just to our west in the day 9/10 range which according to the majority of ens guidance will ridge/topple towards Scandinavia.

There's every chance of the surface temperatures getting cold under this regime but maybe it's too far out to be certain that this is leading to a very cold pattern just yet.

We still see the jet riding over the top so until that changes we may need to settle for an Atlantic mid latitude block and hope the mjo and an increase in momentum does it's thing .

 

[Mcconnor8]

Pub run looking nicely amplified at Day 6 compared to the 12z

[WYorksWeather]

Before we get to the interesting bit from a cold perspective, GFS 18z brings the potential storm system closer at days 4 and 5. Could be a wild period mid-week.

Strongest winds look to be for Scotland and far northern England.

 

[LRD]

Looks like a very lively cold front moving through late next Friday

[Mcconnor8]

 LRD

GFS still showing an above 1050mb high in the Atlantic at Day 7, practically record breaking for December in this region.

[blizzard81]

There will certainly be a nice biting feel to the air next weekend.

[Dennis]

gfs18z 1050Hpa on the Atlantic

[LRD]

Raw in that wind. Unfortunately not snowy away from northern hills

[Mcconnor8]

 LRD Setting itself up for that retrogression attempt at days 9-10 again which is when we have a shot at deeper cold. This could be a good run in that regard with the high holding out further West than on the 12z.

Edited November 30, 2024 by Mcconnor8

[Big Kev]

A few American meteorologist on X starting to say it will turn milder for them by mid month. Hopefully things fall into place for us for a change.

Edited November 30, 2024 by Big Kev

[swfc-ocs]

 nick sussex HI nick in regard to the azores high/Atlantic ridge what  is the main player in getting it pushed further north.is it waa up the west side of Greenland,the jet digging south or us it more in regard to the qbo mjo etc.

Edited November 30, 2024 by swfc

[Dennis]

 Big Kev

you can see that thought on the midmonth EC already  (a bit)