Model Output Discussion - Summer 2024

[Bats32]

 Mcconnor8 Which is interesting because the MetOs own 10 day outlook(ECM) has it almost over Scandi 

[Cheshire Freeze]

Looking at the GFS, I’m not sure whether the outlook would equate to warmth given the strength of that E’ly. Sheltered northern & western areas probably fairing best I’d have thought-

 

[HarvSlugger]

 Cheshire Freeze perfect then

[WYorksWeather]

 Cheshire Freeze To be fair, the strength of the high in terms of the 500mb height counts for a fair bit as well. Heights over 580dam.

850hPa temperatures generally around 8-10C from day 7 to day 9. It's not ridiculously warm, but relative to average for September still somewhat above average.

Surface temperatures also pretty warm during this period, particularly in the south.

Beyond day 10, things do turn a lot cooler - the high then retrogresses.

It should be noted that the GFS was an outlier in going this cool though - not much backing for it.

Overall I think reasonable support for a warmer period. Nothing spectacular, but a few days of widespread low to mid 20s from around the middle of next week. Last third of the month could offer another cold shot, it's not impossible, but no strong support for the idea at the moment (though I will check EC clusters later).

[damianslaw]

 WYorksWeather At what point typically might we expect a similiar positioned high to deliver below average means? Possibly by mid October, largely thanks to cool nights I imagine.

Alas its a reminder that a easterly flow off the continent in September is most likely to deliver decent warmth. 

Interesting to see the GFS going for a retrogressive alignment of the high, suggesting a very weak atlantic. Ex tropical storm developments may throw more energy into the atlantic, does seem rather quiet this year. 

[Mcconnor8]

 WYorksWeather

The ECM looks like it is warmer than the GFS run with the high centered further South, sort of a mid point between that and the UKMO run.

It keeps it looking very pleasant all the way out to day 10.

Edited September 11, 2024 by Mcconnor8

[I remember Atlantic 252]

 Cheshire Freeze sea mist/low cloud written all over it, will feel cold too I guess! yuk!

[WYorksWeather]

 damianslaw I think it's more complex than just time of year - it's also to do with the prevailing temperatures over central / eastern Europe (and let's not forget it has been a very warm summer for most of central / eastern Europe). The strength of the high also counts for a lot - some of the high pressure being modelled is closer to 590dam which induces a lot more surface heating.

Overall though I think you're probably broadly right - heading towards October you might get to the point where the clear skies would allow temperatures to drop more by night - sufficient to counteract any warm days in low to mid 20s.

I think on an overall monthly basis, dry weather is associated with warmth from around May to September. It is then associated with cold weather from November to March. April and October a bit in between. Of course always a few exceptions - this May was warm and wet, but that's against the usual rule.

[WYorksWeather]

 Mcconnor8 A very warm run actually from day 5 right through to day 10.

A very strong ridge throughout - centred close to the UK with heights around 590dam. That's quite exceptional for the time of year really.

  

850hPa temperatures typically around 10C at 850hPa across the country, even warmer than that at times.

Should easily be enough for a number of days in the low to mid 20s. Not too late for home growth warmth if you can get those kind of heights and 850hPa temperatures. Clearly not going to be spectacularly hot like it might have been six weeks ago with the same charts, but it looks generally warm or very warm.

Of course day 10 is still a long way away, but been a while since we've had a 1025mb high over the UK at day 5.

[WYorksWeather]

Worth remembering of course that before all that, still some cooler days to come.

For daytime maxima, UKV still has temperatures struggling around mid teens for the next couple of days. Things do then start to warm up from the south as the high builds, but it will take some time for temperatures to recover further north. Southern areas back to average by Sunday or Monday, but still cool in northern England and Scotland.

For overnight lows, tomorrow morning will be somewhat colder than this morning was, and then Friday particularly cold, perhaps the most notably cold September morning for some time, with a widespread ground frost across many northern areas.

Beyond that though, overnight lows quickly warm up again, becoming somewhat above average from Saturday onwards.

  

[Dennis]

hi all 

greetings from Norway where some snow is coming in the first time to the new winterseason

[damianslaw]

 WYorksWeather The 10 day ECM synoptic is quite an abnormal.one. All the low heights far to the SW, and a low to the NW ready to pounce and swing the high out NW, with cold sinking south towards the UK. This could go down as a very interesting September synoptic wise, with far more northerly and easterly influences than usual. 

[WYorksWeather]

EC clusters below.

Days 3-4

High pressure building in by day 4 (Sunday).

Days 5-7

Cluster 1 (24%) has a strong high over and to the north and east of the UK. Orientation switches the wind direction to more of a south-easterly by day 7, so perhaps becoming very warm.

Cluster 2 (22%) is similar, but more of a straight easterly, so warm rather than very warm. Cluster 3 (20%) is broadly similar. 

Cluster 4 (18%) is closer to Cluster 1 - perhaps more of a south-easterly by day 7. 

Cluster 5 (18%) has a similar high orientation to Cluster 2 and 3, more of a straight easterly. However, the 500mb heights are very strong, so in practice it might well be very warm regardless.

The OP was in Cluster 1.

Days 8-10

Some increased uncertainty from tropical developments by this stage.

Cluster 1 (57%) keeps high pressure in control from day 8-10. Easterly winds, but a very strong ridge at the 500mb level. Warm or very warm.

Cluster 2 (43%) also keeps high pressure in control, but with the addition of a low over SE Europe, which further aids in bringing warm air north. Again, very warm weather likely.

The OP was in Cluster 2.

Days 11-15

Clearly very uncertain by this point, but still worth a look.

Cluster 1 (33%) has warm weather initially but the high retrogresses by day 13, allowing another northerly blast. Becoming cool or very cool and unsettled.

Cluster 2 (20%) keeps high pressure centred just to the north at day 11. Warm easterlies. Generally remaining on the warm side with high pressure to the north and/or east bringing winds from between east and south up to day 15.

Cluster 3 (18%) has warm easterlies at day 11 and day 13. Wind direction possibly turning a little more north-easterly by day 15 so somewhat cooler, but again the strength of the ridge at 500mb should counteract that to some extent. Temperatures probably above average at day 11, dropping to average by day 15 (warm by day, cool by night).

Cluster 4 (18%) has a very strong high centred close to the UK at day 11 and day 13. Warm. Becoming somewhat cooler by day 15 as the centre of the high moves west, possibly allowing northerly winds into more northern areas of the UK.

Cluster 5 (12%) starts with a warm UK high at day 11. The high breaks down beyond that, and we revert to a default autumn pattern with flat westerlies and a N/S split. Dry and fairly warm in the south, cool and unsettled further north.

Summary

Overall, after the current cool spell (very cool by Friday), an increasing signal for a significant warmup in the day 5-10 range. A remarkable degree of ensemble consensus. All options going for high pressure. The only detail is whether it will be more of a warm easterly or a very warm south-easterly, and also the exact strength of the ridge, and other such details. Nothing is certain, especially towards the end of that range from day 8-10, but the strongest signal for high pressure we've seen in a very long time anyway.

Beyond day 10, things do get more uncertain. Perhaps the interesting point is that there's little enthusiasm for a return to a default autumn pattern of flat westerlies driving in from the Atlantic - barely more than 10% support for that option. The rest of the ensemble is fairly evenly split between a continuation of generally fairly warm weather under high pressure, and options that in a repeat of this week end up retrogressing the high, allowing another northerly outbreak.

Overall I would say not to take any option beyond day 10 very seriously - it is still too far away to tell. This is especially true now that tropical activity is picking up in the Atlantic. Before that, a cool or very cool next few days, then a significant warm up looks likely.

Edited September 11, 2024 by WYorksWeather

[WYorksWeather]

 damianslaw Not to mention the ex-tropical storm remnant as well! As you say, potentially a very interesting month. Not much enthusiasm for the more typical flat westerly N/S split autumnal pattern in any of the output at the moment.

[MP-R]

 Cheshire Freeze Meh. Let’s revisit that synoptic in 3 months time

[Don]

8 minutes ago, WYorksWeather said:

The rest of the ensemble is fairly evenly split between a continuation of generally fairly warm weather under high pressure, and options that in a repeat of this week end up retrogressing the high, allowing another northerly outbreak.

Interestingly, Mark Vogan has been talking about the possibility of another cold shot in the next few weeks.  Definitely plenty to keep the interest going ATM!

[I remember Atlantic 252]

hope he is wrong Donald! next few weeks I assume means late Sept/early Oct, no use then at this elevation for snow

[WYorksWeather]

 I remember Atlantic 252 Don is looking at this from the perspective of the old needing a sub-15C September to avoid guaranteeing a mild winter perspective. In which case a cold shot in late September would likely be needed.

Personally, I don't buy into it - I just think it's one of those strange coincidences, though it is still interesting to track the September averages. But I think that is what Don means by interest, rather than any snow at this stage.

I agree that unless you live on top of a very tall mountain, the odds of any snow in the next few weeks are extremely low!

[I remember Atlantic 252]

I certainly think what September is like makes absolutely no difference to winter, even in 80's

Edited September 11, 2024 by I remember Atlantic 252

[HarvSlugger]

Unusually cold for this time of the year here

[Mr Marky Marky]

One last plume would be nice 

[Don]

 I remember Atlantic 252 You know my views on this, so shan't repeat them.  I'm certainly not looking at it from a snow perspective in September!

 WYorksWeather You've summed up my views perfectly!  

[Mike Poole]

 Don I’m not rising to it this year.

[Don]

 Mike Poole Good!   I'm trying to keep quiet about it, honest! 

Edited September 11, 2024 by Don

[Mr Marky Marky]

Could the Mighty Navgem be right just for once .