Model Output Discussion - Summer 2024

[WYorksWeather]

 Greyhound81 Not sure which one you mean so I'll do both:

This Saturday and Sunday will be somewhat less cold than the last few days, but temperatures still generally below average.

In terms of conditions, Saturday looks dry away from western parts of Scotland. Sunday has more of a shower risk further south but dry and bright further north.

Looking further ahead to next Saturday and Sunday, I think the real message is just that uncertainty is quite high. Some output is going for the high beginning to retrogress by that point, which would turn things cooler and possibly more unsettled. Other options bring wet weather into the south but keep the north dry. Still other options just see high pressure continue. Hence I don't think it's worth looking that far ahead just yet.

[WYorksWeather]

EC clusters below.

Days 3-4

High pressure taking over on Sunday into Monday - increasingly warm easterlies.

Days 5-7

Cluster 1 (55%) has strong high pressure centred over and to the east of the UK. Warm easterlies, perhaps one or two days bordering on very warm.

Cluster 2 (45%) is very similar, but high pressure just fractionally further north, which may possibly allow some showers into the far south by day 7.

The OP was in Cluster 2.

Days 8-10

Increasing uncertainty by this point due to tropical features.

Cluster 1 (43%) has the general warm easterly pattern continuing, but high pressure centred slightly further north. A reverse N/S split by day 9 and 10, with the warmest and driest conditions further north, and relatively cooler and wetter further south. Quite unusual.

Cluster 2 (31%) starts with a UK high at day 8 - very strong high pressure so likely warm initially. By day 10, signs of a retrogression, but the UK is still under the high. Turning somewhat cool, but remaining dry up to day 10.

Cluster 3 (25%) has high pressure remaining centred just to the north at day 8 and 9, so again a warm easterly pattern overall with a reverse N/S split at day 8 and 9. By day 10, there is a complicated setup. A retrogression signal possibly brings the wind direction around to a cool north-easterly, but low pressure to the west, or high pressure to the south, may intervene instead. Hard to know where that would end up beyond day 10.

The OP was in Cluster 1.

Days 11-15

Clearly even more uncertainty by this point!

Cluster 1 (25%) has warm south-easterlies at day 11, then the Atlantic breaks through at day 13, then another build of heights from the south turns things warmer again for the south by day 15, with a NW/SE split overall.

Cluster 2 (24%) has a much more typical autumnal pattern, with a series of lows moving in from the Atlantic. By day 15, again an attempt to raise pressure from the south which could lead to at least a transient warmer and drier spell for the southern half of the UK.

Cluster 3 (18%) has mixed conditions at day 11, a brief cool and unsettled north-easterly at day 13, then back to warm easterlies or south-easterlies by day 15.

Cluster 4 (18%) has the UK on the eastern side of high pressure to the west at day 11 and day 13, leading to a cool or very northerly. Generally still dry. By day 15, high pressure becomes centred over or just south of the UK, bringing warmer air back from the SW.

Cluster 5 (16%) has a cool and unsettled north-easterly at day 11, but then flattens this off into a more typical flat Atlantic westerly at day 13 and day 15. Remaining unsettled, though.

Summary

The next seven days has very strong agreement in the output. Still a cold day tomorrow, then a gradual warm-up over the next few days. The strength of high pressure coupled with the fact that we're still early in the season means easterlies will still deliver warm weather, with the possibility of one or two very warm days in favoured spots.

Beyond day 7 gets very tricky. There does appear to be a retrogression signal between day 8 and day 10, but it's far from universal, and clearly the detail matters in this case as to whether the high moves west but we remain under it, or whether it moves far enough NW to allow a cool or very cool NW, N or NE air source. Definitely a few more runs needed on that.

Beyond day 10 is pretty much complete guesswork. Still some retrogression options, still some generally warm easterly options. Probably if anything a signal though for a slightly more typical autumnal pattern by this point, with low pressure trying to move in from the west, with transient attempts to build high pressure over the UK.

All in all, beyond day 7 still uncertain, day 10 and beyond a complete guessing game really. Need a few more days to see whether the retrogression is likely to happen before speculating on what might happen beyond that.

[WYorksWeather]

Demonstrating the uncertainty, instead of much of a retrogression, the GFS 18z wants to bring the Atlantic back. Deep low pressure by T+300, though associated with relatively mild tropical air.

Not a forecast at all - models will continue to play around with possibilities over the next few days. But illustrates the sort of changes we're seeing run-to-run in the latter stages of September. No real consistency yet.

[LRD]

Felt very cool coming home from the boozer this evening

ECM seems to have shifted to the GFS E'ly. Fascinating to see which model 'wins' out on that

Recent history tells us it won't look like this but we will see

Edited September 12, 2024 by LRD

[damianslaw]

GFS continues to suggest heights advecting to the NW eventually, the warm easterly becoming a possible chilly north or north easterly, timeframes for such change outside of the reliable, a case of a watching brief.

ECM this morning holding heights to the east for longer, a good week of very fine dry pleasantly warm weather if it materialises. It then suggests quite a plausible evolution with heights sliced by a trough to the NW ushering in cool showery conditions. A repeat performance of what happened last weekend to some degree.

September may end up being an interesting month overall, locally northern and western parts could end up seeing a rather dry sunny month, contrasting with a wetter south - largely due to the very wet first week or so.

Temp wise it could finish very near average masking a rather topsy turvy month with spells of warm and cool weather. Also a very easterly/northerly month - not very common for September. 

Edited September 13, 2024 by damianslaw

[Scorcher]

 damianslaw I'd be very surprised if this month ends up average- after next week there will have been a lot more above average weather than below average. This current spell has been unusually chilly but not that long in duration.

The ECM looks warm well into next weekend. No guarantees at all that a cool spell will follow that.

[Don]

 Scorcher We don't know what will happen after next week?  Like you say, no guarantees a cool spell will follow the warmer weather next week, however, a fair chance it could.

[Scorcher]

 Don The odds are very much favouring an above average month however, and the warmer spell looks nailed on now. Anything cooler after that is well in FI.

[damianslaw]

 Scorcher Too early to call, give it a week and we will have a better idea. 

[Met4Cast]

This is the 500mb anomaly pattern for La Niña years & years where we saw a transitioning eQBO > wQBO. 

Only two drivers but they seem to correlate to a -NAO pattern during Dec-Feb. 

A -NAO increases the likelihood of colder weather across the UK & NW Europe. 

 There are signs that this developing La Niña will be east based, i.e coldest anomalies in the east Pacific which may allow for stronger MJO cycles through the Maritimes & into the west/central Pacific, something cold weather fans want but something that needs further observation.

This MJO progression will lead to more positive AAM tendency which in turn supports slower, more blocked patterns across the Arctic/Atlantic.

Early days & we need to watch the MJO to see how this current cycle & indeed the next cycle behaves through October. 

We also need to monitor the developing stratospheric vortex in the coming months, a major driver of our weather patterns during the winter.

[jmp223]

Interesting re -eQBO > wQBO. .  No doubt something anomalous will throw a spanner in the works for these Isles, while the rest of Western Europe enjoys a snowfest  

[northwestsnow]

I'm sure there are many cold weather fans watching how this la nina develops.

Hopefully the current set up continues with the colder anomalies in the Eastern regions.

Models seem split if this continues or a more CP nina takes hold.( dont want the latter).

[Mike Poole]

 Met4Cast That’s interesting.  I would agree.  However, at the moment, the seasonal models seem to be going for a +NAO winter (maybe a hint of something more interesting in December) which looks add odds with these drivers to me.

It will be very interesting to see how the La Niña does develop (as @northwestsnow says), but at the moment the seasonal model output is quite disappointing, but plenty of time to change yet…

[Don]

 Cheshire Freeze Yeah, if the ECM seasonal is correct, we may have already had our winter - this week?!   

 Scorcher My hunch has always been for a warmer than average September and remains that way, but possibly not by much?  However, it all hinges on the final third of the month now.

Edited September 13, 2024 by Don

[Met4Cast]

27 minutes ago, Mike Poole said:

That’s interesting.  I would agree.  However, at the moment, the seasonal models seem to be going for a +NAO winter (maybe a hint of something more interesting in December) which looks add odds with these drivers to me.

Last years September ECM update was very inaccurate compared to what actually happened, this chart shows the predicted NAO values compared to the observed; 

I’m not too concerned with what seasonal models are showing at the moment but it does make me wonder how they calculate outcomes. 

On paper, La Niña + wQBO = bad for colder weather patterns but it’s far more nuanced than that, so i’m curious if they just take A + B = C, given those two drivers would usually favour +NAO as the model (and other models) suggest. 

[northwestsnow]

 Met4Cast

one of my go to posters from the other side is gunning for a - NAO

as long as EP Nina holds im hopeful of a flip in the october updates ...

doing a  bit of reading online and the Wqbo / Nina combo might be a little more nuanced than A +B = C ( c being strong PV ).

All eyes on octobers update ,as ever something could scupper us  but right now I'm kinda hopeful).

Edited September 13, 2024 by northwestsnow

[Met4Cast]

23 minutes ago, northwestsnow said:

doing a  bit of reading online and the Wqbo / Nina combo might be a little more nuanced than A +B = C ( c being strong PV ).

Indeed. And even beyond those two variables there remains a lot of unknowns, state of the SPV in terms of coupling, how will very high SST’s impact things? 

Even if we do end up with a -NAO that doesn’t automatically = the cold & snow patterns we all want either. Still very early days of course, La Niña and QBO are just two variables that we can have *some* idea about at this range!

[MoonlightShadow]

The one anomaly I really want under or near average is ppn, not seen any strong signal either way yet 

[sundog]

 northwestsnow

3 Signs that Winter 2024/2025 could be Colder than you might expect » Severe Weather Europe

WWW.SEVERE-WEATHER.EU

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A colder than expected Winter 2024/2025 could develop over the United States, Canada and Europe, based on the 3 Oceanic and Atmospheric signs

[Mike Poole]

58 minutes ago, northwestsnow said:

doing a  bit of reading online and the Wqbo / Nina combo might be a little more nuanced than A +B = C ( c being strong PV ).

Another piece of the jigsaw is, although we’d prefer an E QBO,  W QBO and high solar seems to be the next best thing in terms of promoting a weak vortex, so although it is a W QBO this year, there is still a good chance of a weak vortex and therefore blocking potential.  

I’m just hoping the seasonal models haven’t picked on something else that overrides these factors - October update will be very interesting.

[Don]

32 minutes ago, Mike Poole said:

I’m just hoping the seasonal models haven’t picked on something else that overrides these factors - October update will be very interesting.

Always seems to be something that overrides positive factors for a colder winter these days, so wouldn't be surprised!  However, we shall see.

Edited September 13, 2024 by Don

[Mike Poole]

 Don Yes, I still have nightmares about 2019!

But, sleep easy, the Indian Ocean Dipole is forecast to stay securely in its box all winter:

Edited September 13, 2024 by Mike Poole

[Don]

 Mike Poole Yup and last year!  Could the positive IOD also contributed to the failure of last winter?!

[Mike Poole]

 Don It was certainly one real indicator of concern as we approached last winter, so it could have had a role I think.  It wasn’t as extreme as the 2019 one though.

[Don]

 Mike Poole Of course the other long term factor to consider (just been reminded in the autumn moans thread) is the expansion of the Hadley Cell which will likely make cold synoptics ever harder to achieve?!

Edited September 13, 2024 by Don