Model Output Discussion - Summer 2024

[Don]

48 minutes ago, Mike Poole said:

Have to say, I had hoped for a better update, but we’ve still got 3 months to go…

Need to see these improving from October, otherwise we will be staring down the barrel at another stinker, which lets face it is the norm now!! 

[MP-R]

 raz.org.rain Pretty sure 16/17 fitted that bill… or maybe January was too cold.

[Don]

2 hours ago, damianslaw said:

Yes, correct, not an overly warm source, with heights projected further north then west, with the airflow from NE Europe. ECM trending same way.

Is this looking like a similar setup to September 2009 would you say?

[WYorksWeather]

Days 3-4

High pressure becoming established from the west by Saturday (day 4). A link from the Azores to Scandinavia.

Days 5-7

Cluster 1 (24%) has an unsettled blip for the far north at day 5, before an increasingly strong high builds over the UK and centred to the north and east. Warm easterlies. Cluster 2 (22%) is broadly similar, as is Cluster 3 (16%).

Cluster 4 (14%) has the high further east, and hence winds more from the SW. Still warm. Cluster 5 (14%) is similar to Cluster 4, but as low pressure edges closer from the west, potential for a plume event.

Cluster 6 (12%) provides a different option, with low pressure failing to build as far north. A NW/SE split. Still fairly warm further SE close to the Azores High.

The OP was in Cluster 2.

Days 8-10

Some increase in uncertainty at this point due to potential tropical developments.

Cluster 1 (29%) keeps high pressure in control centred to the north and east. The high is oriented to bring south-easterlies. Warm or very warm. Cluster 2 (24%) has a high centred to the north bringing easterlies, but under a very strong high still warm or perhaps even very warm.

Cluster 3 (22%) has more of a UK-centred high. Warm by day, perhaps somewhat cool by night by this time of year.

Cluster 4 (16%) again has warm or very warm easterlies under a very strong high centred to the north.

Cluster 5 (10%) has high pressure further south - this brings more of a south-westerly flow. Still fairly warm.

The OP was in Cluster 2.

Days 11-15

Even more uncertainty by this point, of course.

Cluster 1 (24%) has a UK high. Warm at day 11 and day 13, perhaps somewhat less warm towards day 15 as the high slowly edges west.

Cluster 2 (22%) keeps warm easterlies going from day 11 to day 15 - a strong area of high pressure centred just to the north.

Cluster 3 (20%) keeps the easterlies going at day 11 and day 13 but westerlies break through from the Atlantic by day 15 - reverting to much more typical autumn conditions.

Cluster 4 (18%) has a strong UK high but with winds from the SW at day 11. The pattern then switches to N/S split, albeit with most of the UK except northern Scotland on the warmer and drier side of the split, at day 13. By day 15, the high retrogresses introducing a cooler north-westerly.

Cluster 5 (12%) edges high pressure further north. Wind direction swings around more to the north-east. Still dry as the high still influences the UK, but potentially quite cool.

Cluster 6 (6%) starts with high pressure largely in control at day 11, albeit not a particularly warm high. Beyond that, the Atlantic breaks through - turning more unsettled from day 13 onwards.

Summary

After the immediate next few days of very cool conditions, increasing support for warmer conditions in the day 5-7 and day 8-10 ranges. Only very small minorities within the ensembles are interested in any unsettled weather - no more than 10-15% of the ensemble.

In terms of resulting temperatures, one point that I don't think has been discussed enough is also the strength of the highs. Some of the modelling, at least at the moment, is showing extremely robust highs over the UK, around 1030mb or more. These are associated with strong 500mb heights as well - for example the ECM OP tonight has a ridge of heights exceeding 588dam over the UK by day 9 and 10. Even in mid to late September, that is still going to promote daytime heating. Hence why warm or very warm conditions would still be quite likely.

Beyond the day 10 range into the extended, things do become a lot messier. Some options keep fairly warm and dry conditions going. Others introduce more of a flat westerly and Atlantic-driven conditions - a more typical autumn pattern. Others retrogress the high and turn cooler again. In short, we don't know, and there's little point in speculating beyond day 10 at the moment anyway due to any tropical developments.

 

[WYorksWeather]

2 hours ago, damianslaw said:

ECM trending same way.

The high is centred to the north, but very different to the GFS at day 10. The ECM has a 588dam ridge over the UK at day 10 and 850hPa near 10C.

The GFS has the 500mb height quite a lot lower over the UK (ignore the colour scale - the key shows it around 10dam lower for most of the UK except for Scotland). It also has the 850s a degree or two lower.

I suppose relatively small differences in the grand scheme of things but overall they will make a big difference to the resulting surface temperatures.

It should also be noted that even the GFS solution with a slightly weaker high still leads to fairly high surface temperatures for the time of year. At day 8-10 we still have a few spots at mid 20s in the south, widespread low 20s for a large portion of England, then still high teens almost everywhere. For the ECM solution you could easily add 2-3C or more to these values given the differences between them.

 

[WYorksWeather]

To not leave any early cold fans out of the picture, here are the latest UKV forecasts for the next few nights:

Friday morning especially still looking cold. Ground frost certainly possible for many further north even away from especially prone spots. Air frosts look unlikely for most though.

Towards the weekend, morning temperatures returning back closer to average.

[Don]

 WYorksWeather I sound like a broken record and won't mention it again (try not to anyway!!) but the next few days will probably need to do a lot of damage to the CET before it recovers next week, it's to be sub a 15C month?!  However, like you say, lots of uncertainty for the later part of the month and with the NAO/AO forecast to be negative, another cold outbreak could potentially occur before months end?

[WYorksWeather]

 Don I'd say another cold outbreak before month's end is certainly possible, for no other reason than that going beyond day 10 is very tricky. The EC46 isn't interested in the idea, neither is the CFSv2, but again both those models could be wrong if something crops up at short notice. I don't consider it especially likely given that information but clearly it's far from impossible.

However, based on what we can see, there does appear for the moment to be this signal for quite a strong high centred somewhere just north of the UK in the interim. The 500mb heights are probably sufficient for low to mid 20s by day, which means that even if nights aren't especially warm the CET is probably still going to rise steadily under that sort of pattern.

To get a sub-15C you probably need this week's pattern to then repeat again at some point in the last 10 days of the month, beyond how far we can reliably look at the moment.

On the subject, GFS 18z not interested in any further cold, quite the opposite at day 8-10.

A strong ridge to the north, tilting to bring the wind slightly from the SE.

Warm 850hPa temperatures - consistently around 10C.

 

And the result is well above average surface temperatures.

Again, difficult to know exactly how much to trust the detail of these scenarios at that range - probably a case of waiting to see for a little longer. But if much of the CET region records low to mid 20s by day, and overnight lows are staying in double figures, then you're going to see the CET rise rather than fall.

Of course, much does depend on the period beyond the 20th - we can't see to that point yet with any accuracy.

 

 

[SunChaserWales]

 raz.org.rain Would 2022/23 count? Mostly mild from the last third of Dec onwards and bone dry other than 3 weeks from late Dec to mid Jan.

[Cambrian]

On the 0z GEFS, a distinctly better setup on the mean, now at day 7, than a couple of weeks ago when we were ultimately let down a tad!

Here, the heights contours form their own closed off 585 dam cell slap bang over the UK and Ireland. The MSLP chart indicates a 1026-1029 mb mean pressure at the surface, slightly higher in the north, so that’s a strong and continuous column of high pressure, warm air descending all the way from above the 500mb level to the surface. We saw nothing like this last time we were presented with the possibility of a decent settled spell.

  

The 500 mb level polar trough is oriented southwest through Greenland all the way to the west of the Azores way down south in the mid Atlantic, while the surface trough runs parallel though a bit out of line with this, from the Kara Sea through Svalbard to the west of Iceland. The surface trough is thin and has little real cold mixed in with it, unlike last time when the upper trough ran from the pole through Greenland but then arced southeast through Iceland down towards our neck of the woods, with a broader surface setup and tapping into a greater and more direct supply of cold off the pole that punched through our heights.

But perhaps the key difference more locally is that this setup doesn’t depend on a continual bridging effort between a mid Atlantic ridge - tempting the northwesterly infiltration - and the Scandinavian / Ural high, resulting in the weaker area of heights in the bridge that last time provided a sustained weak spot for the trough to push at, that ultimately resulted in these charts from a week ago. 

  

Indeed this time, it appears that we might be in just the right place for the extended Atlantic trough to be a great help in building an anticyclone, feeding the UK and Ireland high a very solid flow of warm air at all levels being pumped up from the southwest, which in turn is stabilised by high pressure, heights and notable warmth over western Siberia (top T850 anomalies chart) all of this working to undermine the surface trough development to the west, establishing a strong anticyclone of 1030mb centred over the Northern Isles at day 10, at that stage associating with heights further north and west over Greenland (charts below). 1030mb on the mean at day 10 - not seen that in a very long while!

  

In general, the whole setup is much more favourable, with the UK and Ireland positioned in a more generous sweet spot and with much residual seasonal warmth still in place and being moved about most conveniently, this could be a very pleasant spell all round! 

[bomdabass]

@Cambrianvery informative.....shame it's a few months too late (the weather not the post...)

[danm]

Firming up on a spell of high pressure. The differences in the morning runs are where exactly the high is centred. The GFS has it drifting north and being centred over Scotland quite quickly next week. The UKMO and ECM keep it centred further south, albeit the latter does see it drift towards the north later next week. 
 

Overall, a much better outlook for those who like it dry, with sunshine and some warmth.

[Mcconnor8]

 danm

Yes still variations between the models at day 6 as you would expect, but cross model agreement on a nice area of high pressure on top of or close to the UK.

[Scorcher]

I hope I can be forgiven for remaining cynical about this potential spell of high pressure next week after the last few months.

It seems to me that the high is gradually being modelled further and further north. The GFS 06Z continues that trend it seems.

Looks like potentially a keen north-easterly wind for most of the UK to me and if the high ends up that far north, it will prevent the warmer air reaching us.

Probably remaining fairly cool if this latest run is anything to go by. This is why we should be cautious about thinking a warm, settled spell is nailed on just because the mean is high in terms of pressure.

 

[MP-R]

 Scorcher Same thing happened last time. The high lasted a day at best, then scooted NEwards and low pressure arrived underneath. Hopefully not the same this time but I also remain cautious.

[poleup]

36 minutes ago, Scorcher said:

I hope I can be forgiven for remaining cynical about this potential spell of high pressure next week after the last few months.

It seems to me that the high is gradually being modelled further and further north. The GFS 06Z continues that trend it seems.

Looks like potentially a keen north-easterly wind for most of the UK to me and if the high ends up that far north, it will prevent the warmer air reaching us.

Probably remaining fairly cool if this latest run is anything to go by. This is why we should be cautious about thinking a warm, settled spell is nailed on just because the mean is high in terms of pressure. read more here about free time

 

 

 

The weather has really been full of surprises this year. We are used to it.

[Don]

2 hours ago, Scorcher said:

hope I can be forgiven for remaining cynical about this potential spell of high pressure next week after the last few months.

It seems to me that the high is gradually being modelled further and further north. The GFS 06Z continues that trend it seems.

At least would still be dry and pleasant by day?

[northwestsnow]

 Don West of the Pennines and Western parts in general would be better placed.

exeter ref cold nights so i suspect the centre of any anticyclone may end up just the north of the UK.

Ps , as a winter fan we need an east based Nina and its a close call as to whether we get one right now..

Fine margins potentially big repercussions..

[Don]

 northwestsnow Warmish sunny days and cold nights are fine by me.

Ref to winter, I agree an east based Nina (not too strong?) would be best for us.  I think some forecasts are going for an initial east based Nina before becoming more central based?  I'm guessing that would give us better chances of cold shots early on and then a milder/wetter second half to winter?

[GokouD]

 Mcconnor8 Looks like flood-mageddon in South/Central Europe if that happens...

[northwestsnow]

 Don

There is some excellent material on twitter on this.

It appears there are two camps looking at sst forecast in the Pacific.We really really want to see the east based camp win out.

I suspect the Strong PV /+NAO seasonal models  see a central based nina..

[Don]

1 minute ago, northwestsnow said:

I suspect the Strong PV /+NAO seasonal models  see a central based nina..

Most likely.  If a more central based Nina is forecast during the coming weeks, expect the seasonal models to look more favorable come the October update?

[Scorcher]

 northwestsnow Surprised they're saying cold nights as that sort of setup probably wouldn't lead to cold nights.

The high being further north would probably lead to less cold nights I'd have thought with more of a breeze. The high directly over the UK would lead to chillier nights with lighter winds etc. 

[northwestsnow]

 Scorcher

yeah I was a little surprised.

A sustained settled spell looks nailed on now and im just going to enjoy mother nature - September seems to have become an extension of summer in the christmas pudding so to have an anticyclone centred to our North will mean a totally different outcome than HP centered to our south as is usually the case.

As an aside the PV is sleeping which might allow for a more tradional Autumn.

 

Edited September 11, 2024 by northwestsnow

[Mcconnor8]

 Scorcher

The UKMO has been set on establishing the high pressure quite a lot further South than the GFS for the last few runs including today's 12z so still plenty of uncertainty over it.

Edited September 11, 2024 by Mcconnor8