It'll be returning tropical maritime airmass, something rarely talked about. The air mass originating in the far subtropics (S of Azores to Caribbean) travelled somewhere to the N then returning SE over UK. It's (obviously) very warm & humid, but cooled to variable extent in lowest layers. The cool layer allows extensive Sc & St clouds to form & cover the W coasts, but over warm E UK can sometimes promote subtle instability in lowest layers. The rTm airmass's true nature is revealed when it is blown over the mountains as Fohn winds, giving unusually high temperatures on the lee side.

Yes that's what it looked like. I think today's UM 00z is actually quite similar.

https://www.theweatheroutlook.com/twodata/ukmet.aspx?run=00&charthour=144&chartname=850_temperature&chartregion=na-region&charttag=850hPa%20temp%20C

https://www.theweatheroutlook.com/twodata/ukmet.aspx?run=00&charthour=156&chartname=850_temperature&chartregion=na-region&charttag=850hPa%20temp%20C

https://www.theweatheroutlook.com/twodata/ukmet.aspx?run=00&charthour=168&chartname=850_temperature&chartregion=na-region&charttag=850hPa%20temp%20C

Yes, they are holding firm. And last night's EC run (I haven't looked at this morning's offer) showed potential heatwave conditions becoming established post day 10 once again. 

Glad to see the Op well below the majority in the GEFS spread. Mean ensemble surface max temps low & occasionally mid twenties through to the end. Some hot outliers.

The models are flip-flopping around; ignore yesterday's wx summaries, it's now warm and dry for the SE esp week 2, and even some improvement in temps in the far NW. the jetstream forecast is also for much weaker than yesterday, with little activity near Uk after the next day or two until Wed 25th when streaks begin to affect NW Scotland (not, as yesterday, England)

GFS op - LP currently over Scotland augmented by small disturbance running up from the SW sun 15th after which a general rise of pressure to the W and a period of NW winds (but origin of air is tropical Atlantic and had travelled round the top of the HP; FAX shows occasional fronts embedded in this). The HP in the W finally pushes the LP over Scandi properly out of the way Thu 19th and sets up as N-S ridge drifting E-wards and hanging on in the E despite LP developing in the Atlantic through to Sun 29th when it collapses to allow the return of the W-lies.

GEFS - in S & E England temps dropping off a little around Mon 16th, rising to norm around Mon 23rd, after which a wide spread but most runs warm or very warm. Very dry throughout. Scotland Wales & SW England stay closer to norm to start with but also suggest warmer in week 2, significant amounts of rain after Mon 23rd.

ECM - similar synoptics to GFS 

WX summaries show prospects for much more warmth and drier esp in week 2 in SE but not bad elsewhere

GFS op - small LP SW Ireland tomorrow, moving NE and being swallowed up by general rise in pressure, the Hp settling as a  N-S ridge over UK by Wed 18th. It gets pushed E-wards somewhat Sun22nd by LP near NW Scotland but re-forms strongly 1030 mb N Sea Tue 24th and persists. On Mon 30th it is weaker as new HP forms in Atlantic and shallow LP is near Rockall

GEFS - near of a little below norm to Sun 22nd then nearly all runs warm (mean 2-3C above norm) and some spectacularly hot output from op & control (10C above norm) around Wed 25th. Very dry in S, and only small amounts of rain in the N in some runs later on

ECM - is less good than GFS with ridge Wed 18th positioned further W (so N-ly winds) and LP Sun 22nd close to S ireland with lower pressure generally over UK. The HP on Tue 24th is there but as a narrower ridge and threatened by LP to W & E of UK

Thank you DEW!  I always read your morning reports and I’m sure many others do, even if no one posts!  

[quote=Caz;1369362]

Thank you DEW!  I always read your morning reports and I’m sure many others do, even if no one posts!  

Total agreement here, thanks so much

Surprised there isn't more interest at the moment.  There is a chance of exceptional heat reaching the UK later this month. Obviously it isn't the most likely outcome at the moment, but it would cap a very odd summer.

Agree with the DEW comments keep it up.

Still positive signs for a heatwave starting about 22nd. I'd give it a 40/50% chance this morning. 

Yes. Thank you. Always look forward to reading your summaries esp if short of time to view the models myself.

GEFS cumulative rainfall chart for the SE is the flattest I've seen for a long while...

WX summary not showing as much warmth a yesterday, closer to average for all, and a lot more rain arriving in the NW week 2

Jet - running down the N Sea for a couple of days, then no action near the UK until Tue 24th when a streak develops across England and after a pause becomes very strong Mon 30th. Not closely aligned with models below

GFS op - pressure rising from the W, aligning itself as a N-S ridge, weakening around Thu 19th but back again 1025 mb N Sea Sun 22nd before being twisted into a zonal flow by LP deepening on Atlantic and moving E-wards (which gets to W Norway 980mb Mon 30th)

GEFS -  temps rising to norm by Sat 21st and then the mean staying 2-3C above norm to Tue 31st - though yesterday's extreme hot runs have gone and the op & control are on the pessimistic side, there is still a wide spread of outcomes. Also not as dramatically dry though still only small amounts of rain in some runs.

ECM - similar to GFS at first but Thu 19th weakens to the point where shallow LP runs across the UK to Sun 22nd. There is then a strong rise in pressure with  a N-S ridge but positioned to the W of UK 1030mb W Scotland Tue 24th

I would say it's still uncertain! And probably trending more towards unsettled and less hot with recent runs.

Tell me about it.

The low over Scandinavia was initially modelled to have filled/buggered off by the next day or so with a huge high ridging first over the UK then becoming a cut-off feature in itself.

Nope

More unsettled rubbish.

That what I been pointing out the models had been very wrong and poor this summer.   I prefer if models can be more accurate and honest by showing day 10 unsettled until when it really going to be settled to see it going down from day 10 to 0 successions. 

I don't think we should expect the models to be super accurate at day 10. I always think unless there is cross model agreement and high confidence in the ensembles also then anything beyond about day 5-7 should not be taken too seriously.

One step forward, two steps back - the summary charts now look cool and damp for most of NW Europe. SE England might get a few good days. The situation not helped by the amount of cloud associated with returning tropical maritime air after its journey vis Greenland.

GFS Op - HP west of Ireland more or less static with a prolonged flow of NW winds bringing in the aforesaid  tropical maritime round its N edge. No real change until Wed when it collapses into a col between LP on Atlantic and another in Scandi. There is then a general rise in pressure, HP centred Scotland 1030mb Wed 25th, splitting nd the two parts moving away S and E as trough approaches from SW

GEFS - temps back to and slightly above norm Sun 22nd  and continuing there but with exceptional variation between runs (from 8c above to 8C below norm to be found on most days) A little rain in the S from Sat 21st, Similar for Scotland but slightly more rain esp around 21st.

ECM - similar to GFS but runs a small LP across S England while pressure is rising in Scotland ca Mon 23rd