Model output discussion - first hot, thundery plume of the summer

[mb018538]

If only it were January....

Anyway, on the whole things don't look too disastrous this morning, with most model runs keeping low pressure just about at arms length so it doesn't ruin things for the UK. No early June washout for the moment, UKMO still the pick of the bunch today.

[Frosty.]

My money's on the ukmo..well it would be if I had any money!!..it's sticking to its guns, not backing down!! 

[danm]

The difference between the UKMO and ECM output for Saturday is clear if you look at the Met Office and BBC apps - for London, the former has 26c and the latter has 22c. 

Edited July 2, 2019 by danm

[Singularity]

An encouraging shift in the mid-long range modelling has occurred; first the FV3 18z and now the ECM 00z have greatly reduced the longevity of the broad Scandinavian trough. In fact, it falls apart very quickly now. This seems to be what UKMO's been suggesting since Sunday, judging by its D6 output, so kudos to that model.

With the Scandi trough fallen apart, we just need the Atlantic trough to amplify south of Greenland as per the FV3 18z. That's a Nino-like behaviour sorely missing from the 00z ECM, which seems to get over-excited by the cool air moving west across the N. Atlantic, resulting in an unusually flat trough formation for the time of year, which then throws secondary lows toward the UK.

Generally, the model output is about as unconvincing as it gets; there's a lot of variation going on between runs and models. Conflicting sources of tropical forcing combined with an unusual amount of Arctic high pressure (i.e. negative AO pattern) will tend to do that.

[Derecho]

A pretty good 06z as Singularity mentioned the Scandi trough at the weekend looks like being less coherent now. The energy splits and we have an area of low pressure cutting through the mid Atlantic high. This cuts off our cool air supply and a cheeky little ridge of high pressure comes in.

 GFS 06z T120

As a result the run is pretty settled up to T240, some low rainfall totals but only average temperatures until then. The ECM now has a low cutting through the North Atlantic block but instead of the low weakening it strengthens and a cheeky little ridge of high pressure is prevented from moving over the UK. This has implications for later in the run (unsettled) so FI at the moment is roughly T120.

 ECM 00z T144

It appears to me the models have overestimated the strength of the high in the North Atlantic sector. Blocking is still strong further north though... can't imagine that is good news for the arctic though as it provides more warmth for that region... as the global temperature anomalies show. Intriguingly the North Atlantic is looking warm in terms of its air temperatures. Hopefully that will weaken the cold blob SSTs which helps cause more westerly winds.

[Man With Beard]

The EC clusters this morning show how a small ridge may magically save next week from the mercy of the Scandi trough / Arctic ridge:

However, the general idea of the clusters remains to crash the pattern longer term. Sort of encouraging that a major breakdown keeps getting pushed back, and still enough wriggle room in the pattern for yet another ridge to emerge and extend the more settled scenario.

  

[MATTWOLVES 3]

Interesting evolution from the 6z by mid next week... Low pressure to the West of us helping to pump up some very warm conditions, how long before a breakdown though!! Temps surely high 20s perhaps 30c if this scenario plays out. 

[knocker]

The progression of the ext EPS mean over the last five days is pretty reasonable all things considered. And if anything it's gone downhill a tad. And we are still looking at a fair westerly upper flow under the block.

And today in the ext period it develops the trough in the eastern Atlantic which is certainly not good news

Edited July 2, 2019 by knocker

[StormChaseUK]

Interesting 6z as noted above.   I think the colder pools we had in May/early June are struggling to impact at this time of year they just can't make inroads.

Looking like it will sink down into Eastern Europe/Black Sea instead

[h2005__uk__]

50 minutes ago, Mattwolves said:

Interesting evolution from the 6z by mid next week... Low pressure to the West of us helping to pump up some very warm conditions, how long before a breakdown though!! Temps surely high 20s perhaps 30c if this scenario plays out. 

.......

Am I right in saying that setup could result in warmer conditions for the east than those experienced on Saturday? Much of Norfolk, Suffolk and Essex failed to hit 30C at the weekend.

Edited July 2, 2019 by h2005__uk__

[mb018538]

2 minutes ago, h2005__uk__ said:

Am I right in saying that setup could result in warmer conditions for the east than those experienced on Saturday? Much of Norfolk, Suffolk and Essex failed to hit 30C at the weekend.

Unlikely from that set up - probably 25-28c maximum temperatures from there. Still very decent though.

[h2005__uk__]

Just now, mb018538 said:

Unlikely from that set up - probably 25-28c maximum temperatures from there. Still very decent though.

What sort of setup is required to get 30C+ in such areas? I remember it happened on several occasions last summer where East Anglia was hottest.

[MATTWOLVES 3]

4 minutes ago, h2005__uk__ said:

Am I right in saying that setup could result in warmer conditions for the east than those experienced on Saturday? Much of Norfolk, Suffolk and Essex failed to hit 30C at the weekend.

With a direct feed from the South that would be a more likely scenario. Obviously an onshore North Sea breeze will reduce temps towards the coast... Any plumes moving forward would result in higher temperatures anyway, with surrounding sea temps warming... The situation I illustrated with the 6z shows potentially high 20s... Obviously subject to change at this range, and as you will be aware, both man and machine had a right game at nailing the previous predicted maximums.

[mb018538]

4 minutes ago, h2005__uk__ said:

What sort of setup is required to get 30C+ in such areas? I remember it happened on several occasions last summer where East Anglia was hottest.

There are a few things to note re last summer...

It was very dry, which helped boost temperatures. There was also a lot of anticyclonic weather, with some intense upper/surface highs such as this one:



These helped give very warm/hot temperatures. Heights were also persistently low over Iceland/Greenland, which is what you want to see for UK warm and settled weather. 

The really hot stuff at the end of July came from a southerly from an Atlantic low/Scandi high setup (35.3c Faversham):



What's notable there is that 850 temps are about 6-7c lower than what we had last weekend, yet gave higher temperatures. Proof that 850s aren't everything!

[summer blizzard]

As ever I get suspicious when there is little mention of a run. The day 10-16 6z GFS highlights why.

[Jonathan Rhodri Roberts]

22 minutes ago, mb018538 said:

There are a few things to note re last summer...

It was very dry, which helped boost temperatures. There was also a lot of anticyclonic weather, with some intense upper/surface highs such as this one:



These helped give very warm/hot temperatures. Heights were also persistently low over Iceland/Greenland, which is what you want to see for UK warm and settled weather. 

The really hot stuff at the end of July came from a southerly from an Atlantic low/Scandi high setup (35.3c Faversham):



What's notable there is that 850 temps are about 6-7c lower than what we had last weekend, yet gave higher temperatures. Proof that 850s aren't everything!

Indeed, surface temperatures were very high last year all thanks to prolonged dry weather with light winds, coastal west Wales for example was frequently hitting the high 20's especially in June but all that daytime heat didn't go very far overnight either, Mumbles weather station nr Swansea recorded quite a few nights with a minimum overnight temperature of 20C, something which thankfully hasn't occurred so far this year 

[danm]

19 minutes ago, summer blizzard said:

As ever I get suspicious when there is little mention of a run. The day 10-16 6z GFS highlights why.

6z GFS out to day 9 looks good to me. Plenty of high pressure dominated weather with warm sunshine. Post day 10 looks dreadful but is so far out not to get too concerned at. 

Edited July 2, 2019 by danm

[MATTWOLVES 3]

Post 10 day doesn't look good, I agree. It's certainly a million miles away from the Exeter update... The control run looks good.. Yes it's not really backed up by the mean, but it certainly doesn't put us slap bang in the middle of low pressure which I think the op is overplaying a tad... Anybody would think it was winter with its bully dartboard lows The mean is less severe with its low pressure than the op. 

[danm]

1 minute ago, Mattwolves said:

Post 10 day doesn't look good, I agree. It's certainly a million miles away from the Exeter update... The control run looks good.. Yes it's not really backed up by the mean, but it certainly doesn't put us slap bang in the middle of low pressure which I think the op is overplaying a tad... Anybody would think it was winter with its bully dartboard lows The mean is less severe with its low pressure than the op. 

And more importantly, the reliable timeframe looks good for the majority, and is actually improving from previous GFS runs. 

[Tamara]

Just wanted to send a 'thank you' to several kind members who have sent lovely supporting messages over the last 10 days.

It has been very much appreciated

So to keep on topic, I had better add some relevant substance to the post.

Its another of those regular occurrences when addressing NWP requires caution - both in terms of shorter term detail around the weekend period and also in the extended period.

The areas of relatively greater uncertainty just to the NE in terms of how much the eastward migrating trough digs southwards and the extent to which cool air advection comes south is suggested from the recent spread maps for the start of the weekend

The overnight UKMO being representative of an opposite end of the spectrum comparison to the ECM in terms of retaining warmest uppers within the parameters of such a spread

In terms of the picture beyond this time, ensemble suites are, as always, simply snapshots in time within an evolving situation and the clusters themselves (e.g that can seen within the ECM) usually identify the solution(s) that the diagnostic points to. Though these too can be prone to change direction like shoals of fish in midstream when contradictory factors are providing different diagnostic solutions.

I think to break such an overview down into straightforward terms, then @Singularity has done this very well already today in terms of the diagnostic - and @Man With Beard identifies the post weekend likely route of the pattern equally well as per the NWP solutions that the diagnostic identifies.

As long as a convergence zone c/o of westerly winds close to and to the east of the dateline in the Pacific is present, then it is unlikely that any fast breakdown from upstream is likely to occur. Those +ve zonal westerly winds clearly visible on the Hovmollers plot

 

The Southern Oscillation (SOI) remains indicative of a very weak El Nino standing wave, despite the more neutral SST pattern overall across the ENSO zones. This too, an indicator therefore of that convergence zone within the Pacific

Furthermore, tropical activity has finally emerged in the EPAC since the trade wind burst during June ended (and which helped wreck UK prospects with all the Atlantic blocking in tandem with late season final warming downwelling from the stratosphere).  The greatest  -ve VP200 anomalies (velocity potential) dovetail very well with the location of this tropical activity and where ocean>atmosphere feedback is taking place, concurrent with greatest SST anomalies. These plots, borrowed from Mr Ventrice site, are very good illustrations of the activity that is helping direct the upstream pattern. Note also the corresponding convective suppression c/o downstream wind shear across the Equatorial Atlantic.

The Atlantic blocking pattern (and which in turn encourages heights to amplify in the Greenland region) is exacerbated by any upstream amplification occurring in the Pacific (setting the downstream configuration of ridges and troughs) - but a weak trade wind pattern within the Pacific as described already (ie lack of -ve zonal easterly winds which therefore allows persisting Pacific tropical activity) will make this hard to achieve sustainably over the coming period. This is correctly acknowledged as such by @Quicksilver

Taking into account the upstream forcing as described, then it makes sense that in the medium term at least, there is more likely to be the presence of a trough rather than any sustainable ridge in the Atlantic. 

That leaves the conundrum of the arctic high pressure pattern. As described this is exacerbated during peak summer wavelengths as a product of the tropical cycle when it enters the Western Hemisphere where an African standing wave co-exists with the Pacific wave - and creates a more 'destructive' element to the Pacific standing wave when the low frequency MJO signal is passing through this part of the tropics.  Precisely what happened in the first half of June.  

I think, for what it is worth, that the trend of the remainder of the summer is for this to become less 'spasmodic' (to coin a phrase from a well respected member not on this site) - but that does rely on how the tropics behave heading towards August to prevent the type of breakdown we have seen in quite a few recent years for the last third of summer. Even the glories of last summer succumbed to this trend  - albeit with a more +ve AO/NAO signature retained. There is however no strong signal of this happening just yet - and just one other good reason not to extrapolate anything at all just yet from any 2 week extended ensemble suites that might want to hint at programming extensive Greenland heights and a southerly tracking Jetstream

Taking into account the persisting inclination of the long term trend of the NAO to retain a -ve signature...

 

 

...whilst uncertain and low confidence, it is still not impossible that rather than any inevitable eastward extension of an eastern Atlantic trough across the UK, an interim ridge next week amongst a mixed overall UK wide pattern might prove more resilient instead with a slower advancing or even stalling trough to the west emerging in that extended term period and create considerable warm air advection ahead of it. Especially if the models continue to correct the strength of heights across the US as they have been doing over the last day or two ( they have been adjusting to the greater suggested +ve zonal wind-flow across the Pacific than they anticipated)

This is turn implies relatively lower Atlantic/Greenland pressure and more tendency for downstream ridge manifesting. 

Anyway, I just wanted to acknowledge good folk. Whatever the weather, enjoy the rest of the summer

. 

Edited July 2, 2019 by Tamara

[fujita5]

Great to see you back @Tamara, have missed you!

[MATTWOLVES 3]

Thanks Tamara for  a wonderful post and delivered under difficult times for you.. Much appreciated. 

Icon 12z bringing a decent end to the week, and it looks potentially very warm in the S/SW to boot, mid to high 20s perhaps given sunnier sky's. 

Moving into Friday we bring down cooler conditions from the North, but all in all its looks to be a rather decent weekend at this stage. 

[northwestsnow]

UKMO looks a lovely run this evening...

Starts off warm -

And ends warm..

Although i have yet to see the 850s , which might prove my post utter poppycock !!

edit, OK 850s show it warm right through across the south- cooling down midlands north

Edited July 2, 2019 by northwestsnow

[Man With Beard]

2 minutes ago, northwestsnow said:

UKMO looks a lovely run this evening...

Starts off warm -

And ends warm..

Although i have yet to see the 850s , which might prove my post utter poppycock !!

Nice UKMO up to D5, but D6 is a bit of a "what happened next" - lots of conflicting influences very near the UK! 

[northwestsnow]

GFS taking a slightly different route to UKMO and its 6z run with the azores high springing into life by 138

Who knows !!