Model Output Discussion Autumn 2024

[KTtom]

This is quite some chart from UKMO for just a weeks time, probably the largest euro high ive seen. Even Finland will be snow free, temps high teens likely here. Whilst ridiculed in winters gone by, I feel fi charts will be posted more often this year!

 

Edited November 1, 2024 by KTtom

[AO-]

 KTtom good morning, 

You might be right albeit that it's just the 1st of November. What interests me at this moment is the cold being projected in FI over the Barentsz sea over a few runs now. Also room for ridging (a long way to go, I know) over the Atlantic can be seen over the past few runs. It's a hard bargain, but let's see if it gets momentum in the medium range. 

 

Edit: 

Here is a large Euro high as well. We all know how that winter turned out (very mild with a massive -1956 like- cold spell here in the first two weeks of February)

 

Edited November 1, 2024 by AO-

[E17boy]

Hi peeps,

Hope you are all well. Looks like we are stuck in a benign weather pattern for quite a while. Looks like next week we could see some very mild values for the time of year especially down south. How long is this pattern going to last? Who knows, but I am glad we have got this now rather than when real winter starts. 

I am hoping something to come along after next week to break this block as now is the time we want to start to see Europe cooling down quick. I think it’s more likely that the first half of November has writing on the wall. Once these sluggish high pressures get established they can sometimes take weeks to shift hence I am glad we have got this now.

After mid November we have to start seeing some shifts if we are to get anything set up for December. I know it’s frustrating but we have to crunch our teeth for the next few weeks or so . Sometimes I wish the Atlantic would break through then at least the weather is flowing and the chances of something cold setting up after weather fronts is more there.

So not to get too downbeat at the moment we still got a month before actual winter starts and hopefully by then this slug high will have moved on .

Have a great Friday all

regards

[northwestsnow]

GFS still promoting some kind of warming over NW Russia

 

[Catbrainz]

We are going to have this Euro high for the forseeable future. Some GFS runs going for the Atlantic breaking the high down mid month which could lead to a pattern reset but no real ensemble support and in far FI. 

[Bats32]

Cansips update showing a high pressure dominated winter over us, similar to just now. Very interesting. https://x.com/WorldClimateSvc/status/1852341550874788102?t=V78Ji2lrqxVSVFw_y1-_4g&s=19

[Cambrian]

The models are in a curious limbo, here on the 6z GEFS mean at day 7. Though the Canada / Greenland lobe appears in the ascendence, the balance and separation between the Siberian and Canada / Greenland lobes is echoed by a balance and separation between the latter and the Aleutian trough over far western North America. 

 

So we get clefts to the south of the gaps, into which the heights and ridges build. 

We’d normally expect the hemispheric ridge / trough pattern to click counter-clockwise around the pole about a time zone every couple of days, but this isn’t happening at the moment. 

To go back to the balance. The main driver to the current global pattern is the strong Pacific jet stream. On that side, the north to south, cold to warm temperature contrast is fuelling the jet stream.

Until, that is, it reaches Alaska, where it encounters a block of warm air. This sucks the power out of the jet stream and diverts it south, forming the Aleutian trough. By the time it turns back north over the Canadian Pacific coast, it is much weaker. The warmth of the ridge has built in to gap to the east of the trough, consolidating the split in the jet stream, and it’s there that the pattern is getting flattened. Also, with the local exception of the Greenland plateau, the Arctic itself is warm for the time of year, so the polar troughs are relatively weak, and so not playing ball with any amplification efforts either.

 

As a result, the west Canada ridge doesn’t build far enough north to do what it would otherwise do to the lee of an Aleutian trough, so there is no downstream trough running south through the eastern seaboard nor formation of an Atlantic ridge downstream of that - instead, as the jet stream re-merges on entry to the Atlantic, it doesn’t have enough energy to power across the ocean, but has enough to dig southeast and form a modest, though broad, Atlantic trough. Like sticking a chubby old leg out to the ground while riding a bike, this ocean-wide upper trough is acting as a brake on the hemispheric wheel.

The trough also serves to pump up the heights into Western Europe, while the again weakened jet stream is forced north around the top of the UK, Ireland and Scandinavia, indeed split again on the approach to Iberia, and the whole pattern is further locked in place by the firm continental block…

  

…so that even a whole week later, here at day 14, the setup is broadly the same, as the temporarily elevated NAO+ signal again returns to neutrality. 

Just enough amplification to bring us high pressure, not enough to push it far enough north to bring some colder air around it. Just enough in the jet stream to set up shallow, oceanic troughs, but not enough to prevent these being easily held at bay by the continental blocks, modest NAO signals gently oscillating around neutral. 

6z GEFS mean T850s, days 8 and 16. 

 

So we enjoy the quiet, write occasionally to our mates on here, and wait - either for some energy to shift the pattern, or for the core Arctic cold to start to build and some of it to start seeping down around the high pressure, which if it sticks around long enough, will happen, potentially cooling Europe down very nicely as the month goes on.

[IDO]

 johncam, I am not convinced post-D10, but I would guess that HP will be more likely than not. GFS op, post D8:

I am not convinced due to the mean:

All models support HP dominance up to and including D10. The ECM at D10:

 

[Cambrian]

The 12z GEFS EOF1 - EOF2 phase diagram says it all really, going slightly positive for the Northern Europe block over the next few days, maintaining that signal but also then going a bit more positive for the NAO in around a weeks time, as the Atlantic trough develops, before reigning back on both signals, the rock and the hard place just about cancelling each other out in the ensembles…

 

…while the plot of the mean appropriately sketches an image of “old man GFS” himself bending over to scratch his backside, and reflecting on how it’s still there - in the same place where it was two weeks ago.

[Jacob]

Couldn’t it be possible for the high to move west and since it’s so strong and wide, it would cause some extremely sustained cold? Judging by what people are saying this seems unlikely though 

[WYorksWeather]

Yet again, another look at the 12z ECM clusters to try to figure out the way forward.

Days 3-4

High pressure, winds from the south-east or south. Mild and dry.

Days 5-7

Cluster 1 (51%) has strong high pressure over and to the east of the UK. The UK is on the western edge, so mild with south-westerlies. Cluster 2 (31%) is broadly similar, as is Cluster 3 (18%).

The OP was in Cluster 2.

Days 8-10

Cluster 1 (65%) has high pressure over and to the east of the UK. Yet again, the UK is on the western edge, mild and dry.

Cluster 2 (22%) has high pressure initially centred more to the east of the UK at day 8, but has a slight retrogression by day 10. Mild and dry at first, perhaps nearer average by day 10.

Cluster 3 (14%) has high pressure to the south and low pressure to the north, initially fairly flat and westerly at day 8 with unsettled conditions in the north and drier further south. By days 9 and 10, high pressure rebuilds again, setting up a long-fetch south-westerly. Very mild.

The OP was in Cluster 1.

Days 11-15

Cluster 1 (57%) has high pressure over the UK at day 11, then moving to the east of the UK by day 13, and then pressure building in the mid-Atlantic by day 15 and low pressure over the UK. Potentially fairly mild and dry initially, then milder by day 13 with more of a southerly or south-easterly, then turning cooler and more unsettled with winds from the NW.

Cluster 2 (43%) has a partial retrogression of high pressure at day 11, with cool or cold but dry conditions, winds from the NW around the top of the high so especially cool in the far north, but unlikely enough for any wintry interest so early in the year. By day 13, high pressure is more to the south of the UK, so turning milder again by day 13. At day 15, very weak pressure signals that conflict somewhat - some potential for an Atlantic breakthrough from the west, but the low pressure to the east could bring down a cold northerly or north-easterly, especially for areas further east.

Summary

Still not a clear signal for any change within the reliable or semi-reliable - up to day 10 it is a mild and dry pattern, at times very mild. Beyond day 10, the two clusters both show a little bit of potential for some change, but only by day 15 really.

I think the wait goes on for now. We really need to see a stronger signal emerge in the extended and start to move closer in time. At a minimum, I think the first half of November is a write off for fans of cold weather.

The ECM charts here for the next two weeks (4th-11th and 11th-18th) tell the story. For the 4th-11th, western and central areas showing 3-6C above average, and areas further east still 1-3C above average. By the 11th-18th, a slight drop in the anomaly, but still the whole of the UK projected 1-3C above average.

A very mild first half to November now highly likely. However, a lot can change in a short of time, so too early to say for certain where things will go beyond that.

 

[WYorksWeather]

 Jacob If you're talking about a 'true' retrogression right up to Greenland, allowing a direct northerly to reach the UK, I really haven't seen any runs showing that. However, a few model runs have shown what I have often termed a partial retrogression. This is where the high moves a little further north and west, perhaps to around Iceland, but this generally brings cool and unsettled weather from further north in the Atlantic from a north-westerly direction, rather than cold enough weather for anything wintry.

None of this is showing up with the reliable timeframe anyway - up until day 10 at least it is mild and dry all the way.

 

[blizzard81]

 WYorksWeather

[WYorksWeather]

 blizzard81 Sorry, meant on a main operational run, control runs and individual ensembles excluded - I have seen one or two people posting interesting looking control runs over the last few days!

Definitely a possibility that can't be excluded entirely, but I would rate the probability as pretty low given the lack of much of a signal in the extended.

[blizzard81]

 WYorksWeather We'll see.

[WYorksWeather]

 blizzard81 Yep, definitely some interesting model watching to see when this pattern breaks. I'm not a pessimist on cold chances beyond day 10 or so - it is just a case of watching and waiting for some sort of more robust signal to pop up. Typically this is when the cluster charts start to indicate changes at day 15, and then these move nearer in time. Today we have some signs of cold chances at day 15 on the clusters, the test is whether in a few days those are still there, having moved up to day 11, or whether they've disappeared or are still at day 15, in which case we are back at square one.

 

 

 

[blizzard81]

 WYorksWeather Indeed. We've been here before so many times. We know which way it 'normally' goes. Not always the case though

[WYorksWeather]

Always interesting just to see what possibilities the models are exploring. We know the pattern is mild up to around day 10, so much of the interest lies beyond that. Tonight's 18z offers up the following.

At day 10, we still have the exceptionally mild setup.

Leading up to this point, as an illustration, the afternoon maxima for days 5-10 are as follows. Generally mild or very mild. Absolute max of around 18C on any day would be exceptional for the time of year, though far from unprecedented.

 

Of course, the key is then what happens afterwards. By day 12, the ridge flattens off.

We then go into a much more typical westerly pattern by day 14.

A slight build of heights into the mid-Atlantic then turns it into more of a 'cold zonal' setup, with winds from the west or NW. Not especially cold, certainly not for any wintry interest, but more seasonal.

 

Of course, this outcome is just one of many possibilities at two weeks out. Need to keep watching to see if a succession of runs show any trends - so far nothing particularly clear.

[clark3r]

First time been on here for a while, typical high pressure exceptionally mild as we enter November! Why didn’t we get this in summer! Why now heading in to late autumn we get exceptional mild. Our weather is all over the place! I will come back in a month probably to more of the same.

[Sky Full]

As everyone has been discussing for a few days now, our weather is set in a mild and cloudy pattern for at least another week or more.  However, I find it extraordinary that three models can be so much in agreement regarding the weather in mid-November with ten days or more still to go….

ECM    +240

GFS    +240

GEM    +240

Normally at this time of year there would be all kinds of variation in the models after only three or four days keeping us all guessing wildly, but there seems no doubt that November 2024 will be generally mild, settled and unseasonably dry.  One good outcome from the lack of any stormy weather to date has been the degree to which the trees have kept their leaves which in turn have had the chance to develop more colour this autumn than for many years.  

[carinthian]

Morning all. At last the models out at day 10 now showing some signs of the weakening and migration of the Euro-high as pressure falls being indicated over over mainland Europe. I hope this trend continues to get more seasonal colder conditions in the outlook for most. Of course that is if you hate mild at this time of the year.

C

Edited November 2, 2024 by carinthian

[Penrith Snow]

Big changes on GFS this morning but these are all deep in FI with a cool shallow through becoming established across the UK.

However in the meantime it's the same intense UK high with lots of dull, cloudy weather and near average surface temperatures.

Tedious in the extreme.

Andy

[stodge]

Morning all

It's all been said as it often is in an anticyclonic pattern but unusual it isn't.

We often get a prolonged dry spell in the autumn if the jet isn't strong enough to break through the block and gets deflected. Two or three years back we had weeks of HP parked just to the south west of us and a seemingly eternal wash of mild WNW'ly winds in its circulation. At least this year the HP is moving round a bit though it seems to finish up close to or over the British Isles.

The GFS 00Z OP "breakdown" is well into far FI but it's entirely plausible as a scenario when you finally get the HP to split between a Sceuro cell and another over the Azores and the trough drops down between through the British Isles. That again suggests a weak jet for the time of year and those forecasting an anticyclonic dominated winter may have a point - too early to tell of course.

The good thing about a more mobile HP cell is the airmass gets moved round and there's a chance for some sunshine - the converse at this time of year especially is the possibility of morning fog but that's detail and nowcasting. 

IF we get a Siberian warming (big "if" at this stage) you'd expect the PV to move back over to Greenland/NE Canada and that would fire up the jet offering a more unsettled spell especially for northern and western Britain but a long way off and by no means certain.

[AO-]

Morning all,

Having seen the charts this morning, it seems like the pattern is about to stick around for quite some time. My bet would be that the hp will be the key factor and wintry weather can be written off for this month. Taking the plume for here the colder options definitely gain momentum,but they are the ones with hp over our heads. Precipitation rates are low fortunately. I can't see the cold air building up in the north getting transported to the south. 

 

 

[Mike Poole]

 Sky Full Yes, one can get cross model agreement out to 10 days if the main ingredient in our vicinity is a slow moving anticyclone.  (This is why despite summer patterns generally being very fluid, a really decent spell of settled weather in summer can often be surprisingly well predicted by the models.)  

How will the pattern change?  This morning’s ECM clusters in the T264+ timeframe seem to me to capture the options:

Cluster 1, 24 members, so about half - and the high really hasn’t budged up to day 13.

Cluster 2, 16 members, retrogression scenario, which might result in a colder spell of some sort.

Cluster 3, 7 members, high gets fed up and just seems to dissolve back to a more mobile pattern.  I think this is rather unlikely, but I guess that’s reflected in the number of members.

Edited November 2, 2024 by Mike Poole