Model Output Discussion Autumn 2024

[Sweatyman]

 Jacob well would ya believe it !

[WYorksWeather]

In terms of prospects for the next few months, the C3S series of charts have updated in the last few days.

For October, the charts are showing no signal for pressure, increased chance of above average temperatures, and no signal for precipitation.

For November, we have above average pressure to our south extending into southern England (the Euro / Iberian high), a stronger signal for above average temperatures, and again no signal for precipitation.

Moving on to winter, for December we have a strong anticyclonic signal for the UK, temperatures above average, and no signal for precipitation.

For January, the anticyclonic signal weakens, temperatures above average, and no real signal for precipitation again.

Finally we come to February. A fairly strong Euro / UK high signal yet again, and once more no signal for precipitation.

Summary

I think the C3S long range output is not very good for cold this winter, like most of the other output so far. I suppose periods with the UK high might generate more in the way of frost / fog type setups, which is likely why the temperature anomalies are above average but not in the deep red colours (chance of top tercile temperatures not excessively high).

Of course, seasonal model outputs performed very poorly both this summer and last winter, so I wouldn't spend too much time worrying about these in any case.

[damianslaw]

 WYorksWeather I can't recall seeing a seasonal model forecast going for anything but above average, season on season for well over 10 years. Its the default forecast nowadays. I pay little if any attention to them. 

Edited September 17 by damianslaw

[WYorksWeather]

 damianslaw I think generally you look for the variation within that - the month that is a little closer to average, for instance. And also sometimes the monthly summary hides the detail. For example we could have a Euro high and raging mild south-westerlies for three weeks of a month, but the other 10 days or so provides a memorable cold spell, but overall it's slightly above average.

I think the worse bit really is the pressure signal. If it were showing higher pressure to the north but average or above average temperatures, then maybe you doubt the temperature signal. But on the face of it, a high centred to the south would mean a lot of mild weather.

I do agree that seasonal models have low skill, though. They are an educated guess, and only a slightly educated one at that. I simply view it as indicating a slightly elevated chance of a milder than average winter, and nothing more than that. Just as last winter the blocking signals amounted to nothing away from some parts of Scotland and the odd very brief cold shot elsewhere.

 

[damianslaw]

 WYorksWeather Agree with what you are saying, in these warming times, the probability of an elevated chance of milder than average temps season on season is about 95%.

[WYorksWeather]

Going back to the shorter range, a decent signal for above average temperatures through the rest of this week, and thereafter perhaps a slightly cooler than average trend towards the final days of the month, though not yet certain given the large amount of spread beyond the 25th.

Latest temperature projections from UKV show fairly mild nights further south and east but still closer to average further north and west through to around Friday, then becoming mild across almost all areas relative to average. Bordering on very mild / warm nights in the south. Generally useful to take a degree or two off these 6am temperatures though if you're looking for daily minima.

For daily maxima, UKV usually performs better, and the projections have converged towards the GFS, with temperatures approaching mid 20s in the SE tomorrow and Thursday. Areas close to NE coasts becoming cooler though as the breeze picks up as the week goes on.

 

EDIT: Forgot to add - not got time for my usual look at the EC clusters tonight, I'll try to pick that up again tomorrow.

Edited September 17 by WYorksWeather
Added note.

[cheese]

 WYorksWeather I notice that GFS actually has higher maximum temperatures here for the next few days than UKV, which doesn't happen very often. GFS has the warmth on Thursday being far more extensive in general than UKV. 

I assume that means UKV thinks any low cloud will be more stubborn/extensive than GFS.

3pm Thursday according to GFS vs UKV:

For some places there's a good 4-5C difference between the two models!

For once I'm hoping GFS is closer to the mark here!

 

Edited September 17 by cheese

[Ladyofthestorm]

Interesting signals coming towards the ends of these runs, building the high to the north and over Greenland letting brief excursions of much colder air in over the UK .  Very reminiscent of autumn 1998 . That was also an awful unsettled summer . Let's see if the trend continues like the wintry blast we had last week! 

Edited September 18 by Ladyofthestorm

[damianslaw]

Interesting to see the ECM holding firm with a possible repeat of last week, though not quite the same depth of direct northerly airflow... GFS 0z trending the same way, indeed quite a cold outlook to end the month and start October with repeated digs of chilly NW airflow with low pressure on a southerly course at the base of the trough and heights to the NW.

 These forecasted synoptics are outside the reliable though, so all conjecture, but if verify Sept 2024 will go down as a highly variable month, and very easterly to north westerly.. 

[northwestsnow]

EC 46 has a strong PV by October ..

I picked up on a post on X last night with a suggestion a CP Nina now looks more  likely during winter too.

Not overly fussed about the strong PV but really don't want to see a CP nina!

 

 

Edited September 18 by northwestsnow

[StretfordEnd1996]

 damianslaw

Yes certainly some chilly looking charts around again for the time of year, the GFS op on the chilly side for the majority of beyond D8 or so (one of the more colder runs of the ensemble)

As you say these aren't necessarily direct N'ly flows but still there

ECM NW'ly flow for a time 

 

Yes it's quite interesting that the bulk of our systems/flow recently have been from that side of the compass, NW'ly to E'ly. Be interesting to see if these repeated bouts continue for the next couple of weeks/months. 

Certainly a lack of it from the other direction, i.e. W/SW'ly, S'ly, SE'ly flows. The latter of which in contrast from this September to last year for example delivered some very hot air from the South as below.

It's felt like we haven't been close to flirting with this type of hot air in the last few weeks/months. 

 

 

[minus10]

Gosh....gfs0z fi going for the unsettled ...

...four separate lows crossing the south on this latter part of the run..

...while at the bottom of the pack and fi, i think it does look like after this week Autumn will come in with avengence..

...ecm 0z showing quite a nasty low for day 7..

...better make the most of this pleasant week i think...get the grasses cut..

[LRD]

 minus10 Yep, definitely looking disturbed from about the middle of next week (and breaking down in the south earlier than that).

However, just as high pressure cells being modelled straight over us tend to be over done (especially the last 18 months), I find low pressure influence is also overplayed, away from the north-west.

It won't surprise me to see these low pressure systems modelled further north nearer the time but the Met Office do see lows on a more S'ly track in their long range forecasts

Edited September 18 by LRD

[Bricriu]

 northwestsnow

So i take it a CP nina is bad news for those of us wanting snow  this winter. So this current  pattern  maybe  flipped sometime in October to our more default pattern. 

[northwestsnow]

 Bricriu

It's all very complex - perhaps one of our more knowledgable members will expand but my understanding in a WQbo and Nina the ideal combo is EB Nina ,not CB.

[Crackerjack]

 northwestsnow I honestly am going to ignore any background drivers this winter NWS as 1 - I don’t have vast knowledge on the subject and 2 - last winter tested my faith in them anyhow and in April I built a bonfire and tore all the rule books up and had one big early bbq. It just seems now we are in uncharted territory where either there is a mystery connection we haven’t sorted yet or things have just changed

[damianslaw]

 northwestsnow There is always one factor it seems that points away from a cold winter, indeed even if all factors seemingly point to increased risk of a cold winter, no doubt a new factor will appear scuppering it, or one of the factors didn't play ball.. this seems to have been a regular occurance as long as Ive been on this forum. Would be interested to know the drivers at the time of our last true cold winter 09-10 pointed to a cold one or not.. 

[summer blizzard]

Models appear to be in unison in pushing lows from an abnormally low latitude.

 

[Downburst]

Yep. next week mean anomaly says it all

 

New to me at least is this possibly useful chart combining a few metrics for anomalies on ECM weekly

[danm]

Next week looks like taking us back down to earth with a bang. Looks grim. 

[I remember Atlantic 252]

 danm depends where you are, this Sunday looks grimmer here

[Metwatch]

If only it was December, exhibit #93

[WYorksWeather]

Due to limited time once again I'm not going to do my usual clusters update today.

For a quick post, there's an increasing trend on the evening GFS ensemble for another cooldown from around the 26th. An early look at October just suggests massive scatter at the moment - we could be in for an exceptional early October warm spell, an early cold spell, or anything in between. Not worth worrying about!

[Kentspur]

 Jacob luckily I'll be in the far South/SE of Australia just before this period looks warmer than average according to BOM but possibly wetter as La Nina usually is down under. What's ECM showing for November and December? As Gavsweather reckons we could be in a 14 year cycle I know I'd love a 2010 repeat the week i get back from Australia in late November!

[Beanz]

 damianslaw background drivers are mostly taken for what they are not, a guarantee of certain seasonal weather.  I’m not sure why there is so much focus (hope) given to them.