Man With Beard

Time for an uncomfortable discussion: Is the UKMO still fit to be considered one of the "big three"? This used to be the "reliable" model. The one that didn't go with every whim, the one that was maybe over-conservative at times. We used to say "don't believe it until the UKMO is on board". Not anymore I feel. Today was one example. The difference between the 00Z and 12Z was pretty huge, considering it is a D7 maximum model. Way beyond the normal swings you'd expect at such a short timespan. And this, I feel, is becoming regular for the model. I imagine the global verification stats suggest it is still "ok", but my gut is telling me ... it simply isn't worth the time that following the ECM or GFS is anymore. Thoughts?

ECM ensembles for London largely given up the ghost regarding the full effects of plume for next week, although the small number left that bring it in are potent: Yet just 200 miles south in Paris ...

I'd agree completely. Such a steep gradient in temperatures appearing around the channel, small differences are going to have big implications. Until some consensus appears, best not to get to attached to anything after T120 right now.

GEM 12Z ... I've never seen anything so mickey mouse on these charts in 20 years - 20C uppers from a NW flow?

Quick look at the ECM Ensembles for 06Z run, which only goes to T144. Looking at 850s for London, it shows the warmth for this week does get flushed out around Sunday - a not insignificant number of members bringing more substantial heat in around the T138 mark, but perhaps an equal number do not.

As it's hard to make head nor tail through the various plume attempts for next week, I'll stick to the nearer timeframe. It has slightly slipped through the radar on here that this weekend is now potentially the best since late June, except perhaps for the areas close to western coasts. True, Friday afternoon and evening look increasingly wet, but this has passed by Saturday. Saturday and Sunday, then, are warm and mostly dry for central and eastern areas with temps low to mid 20s which will feel much more pleasant than previous weekends! However, potential for showers affecting northern and western areas at times.

A hot looking D7 mean chart on the ECM ensembles:

No one can promise you anything when there are ensembles ranging from this (hot and sunny for west Wales): to this (chilly and a bit wet on the west Wales coast) Look again in 48 hours I'd say!

I can understand the fear that yet another potential settled/warm period with magically vanish somehow, but the chances of missing out on 2-3 days of warm, sunny weather at the start of next week look actually quite small for the southern half of the UK - more in the balance further north but even here it could turn warm for a time. Operational and ensemble support look pretty strong for a fine three days between Sunday and Tuesday for many (perhaps even Saturday too), and that's at a fairly short timescale now. Friday looks the only day with serious dread due to rain, and even that may possibly be reserved for the evening/overnight in the main. IMO the questions to be resolved are: 1) the extent of heat involved, as there is still considerable scatter between warm and very hot conditions, along with a very tight gradient between the two. Still many ensembles and the GEM op going for very hot conditions across the south, but an equal number of ensembles flush out the heat completely by keeping things more westerly. 2) whether northern areas join in with a longer settled spell rather than merely a day or two here and there 3) whether any fine weather continues via a new extension of the Azores High, although this would be warm rather than hot at least at first - this is also in the balance as it depends on the positioning of the Atlantic and whether a trough splits down towards Iberia, which would promote a high over the top.

ECM ensembles (London): too much scatter beyond Saturday for any firm prediction, but interesting that several members keep it hot from Thursday deep into next week without a break:

It looks like Friday has swapped places with Saturday in terms of being the wet day. Saturday now looks more reasonable:

Another hot ECM for the southern half of the country early next week: 32C raw max on Monday, 31C raw max on Tuesday.

The evolution has sped up so much that a renewed plume attempt takes place in the ECM op this morning, successfully enough for temperatures to reach the low 30s next Tuesday. Although the general idea of another ridge for Sunday - Tuesday looks to have ensemble support, not to the extremes of the op run. No doubt we'll be getting warmer weather from midweek onwards due to the main trough staying out west, but one couldn't call the picture "settled" what with so many moving parts - so it will be hard to pin down the specifics at mid-range.

I think looking through all the charts over the past 48 hours, the forecast for the coming weekend is probably "warm and wet". The mother low stays west throughout, causing a push of air from a source much to our south, but frequent disturbances look likely to hit us on the edge of its flow. With a bit of luck, the majority of the rain (thunder?) will swing through overnight Friday into Saturday morning, leaving the daytimes mostly dry and feeling fairly hot with mid to high 20s possible for many away from the north and west. Wednesday and Thursday beforehand potentially quite good though dryness not guaranteed even on these days according to some runs. A bit of uncertainty Sunday into Monday/Tuesday - the faster the front clears on Saturday, the more chance perhaps of a weak high building in behind for a time and just the chance of hotter uppers approaching from the south once again - although by this stage I think northern and western parts are likely to return to a less settled regime, and this drier slot (still warm) doesn't look guaranteed for the south at all. Overall I'm a little disappointed that the models (again) did not pick the strength of the Atlantic flow between D8 and D15, and that slight extra oomph in the Atlantic has removed the chance of a slightly longer hot and settled spell that looked a possibility just 48 hours ago, just as happened this time last week. And, given the time of year, that might be it for chances of hitting the 33s/34s/35s in 2023, and if so, the hottest day of the year will, rarely, belong to June - and by some distance!

Although the clean cut plume looks to be on the ropes, I'd draw people's attention to one constant that hasn't changed - the main trough remains forecast to be stuck off the Irish coast. That means any unsettled weather, particularly for eastern parts, will be dependent upon secondary lows travelling round from the south and west. Such secondary lows are not as certain as the primary low, and so will be a menace to pin down. How intense will they be? Will the split against the heights to the east? Will they form at all, and when? If these factors fall a certain way, hotter air may still be able to reach us. Also, being mini-features, they'll be temporary, meaning warm weather should follow quickly behind once again. There's a still a route to a better plume in there, I'm not writing it off just yet.

Wow, the weather hates us on Saturdays this summer:

Yes, it looks like the latest GFS 06Z panicked a bit at the thought of a weekend without a low pressure system so decided to throw one in for next Saturday! Certainly, the evolution of the ECM ensembles this morning reduces the confidence level in a nationwide heatwave, and the GFS 06Z throws in further doubt too, but the overall picture still strongly backs settled (and warm) rather than unsettled weather between 17th August and 20th August in spite of the minor wobble just now, imo.

Probably a three day affair, but still a chance it might be longer:

A slightly different profile on the ECM ensemble mean this morning - the high to the NE is slightly less established at D8-D10, resulting in shorter plumes on most runs, and this also allows the low to slip NW rather than hitting a wall and stalling.

27 out of 51 runs get 18C uppers to London between 18th and 20th. I'll see you all at the beach next weekend, then? (I can just about walk it if I'm feeling really fit )

Strike that. The ECM control run is a degree hotter than the op at midday.

ECM D9 mean T850s D10 pressure + Z500 - no way through for the Atlantic low

ECM op showing a raw 33C around London on 19th August, which on past experience would verify more like 35/36C. I guess this will be close to the top of the envelope, if not the very top. Nevertheless, all routes leading to something hotter at the end of next week as the trough (finally) gets stuck out to the west?

I can't imagine we'll miss out on at least some settled weather at the next week now - A small spanner in the works for those seeking the highest temperatures may be if a high becomes anchored to the north bringing a cooler NE surface flow underneath baking uppers (was it June 2020 when this happened before?) - there is an ensemble member on ECM with 25C uppers yet surface temps below 30C I'm not sure why this would be a problem considering the past 5 weeks (!!) as it would still be hot and dry enough, but just a thought to bear in mind if the super-plume runs continue to grow in number.

That's 9 days forward. 10 days forward is better! You can see the mean chart sucking the warmth up from the continent within this 24 hour period. The ECM mean 850s then stay pretty much in the same ballpark between D11 and D15, if anything the warmth edging slightly further up the country.