Storms and Convective discussion - 25th July 2021 onwards

[Supacell]

Following some big storms for parts of the south early yesterday an active period of weather likely to continue for at least the first half of this coming week. Today the storm risk is in the southeast, with the risk then becoming more widespread over the following days as our resident area of low pressure ambles slowly northwards.

Please continue discussions here. 

Old thread here

Please remember to keep on topic and use the relevant No Storms thread for complaints about the lack of storms.

[tesaro]

Drizzle here in West Suffolk. Temp 17.8. Humidity 87%. Feels very Muggy. Good luck all

[Alderc]

A tricky day ahead with a range of possibilities from bust to some pretty strong and slow moving surface based storms. First we need to shift some of the clag - which can take longer than modelled but if we can there’s tonnes of moisture to tuck into. Could see dew points of 20C later in the south. 

[karyo]

The Euro 4 shows a line of torrential downpours over London for this afternoon!

[Norfolk Sheep]

Weather seems to have morphed into November...

[AnvilCrawlers]

5 minutes ago, Norfolk Sheep said:

Weather seems to have morphed into November...

Church Lawford (106m)

2021-07-25 08:00-15.9 °C here,doesnt seem to look or feel like a convective day.

[Harry]

27 minutes ago, karyo said:

The Euro 4 shows a line of torrential downpours over London for this afternoon!

AROME, WRF-NMM and Euro4 all painting a similar picture a pronounced line stretching from somewhere in EA southwestwards across the London region and through the other side.

That line could as ever be a 10-20 miles further east or west and if the line does not move far very quickly, could mean some very high rainfall totals. 

Edited July 25, 2021 by Harry

[Harry]

@staplehurst forecast just published Thanks, Dan.

Day 1 Convective Outlook

VALID 06:00 UTC Sun 25 Jul 2021 - 05:59 UTC Mon 26 Jul 2021 

ISSUED 08:01 UTC Sun 25 Jul 2021

ISSUED BY: Dan

An upper low will linger close to SE Britain on Sunday, the associated cool mid-levels aiding to increase instability, especially in conjunction with surface heating. Fairly extensive low cloud across much of England this morning, with some showery outbreaks of rain in the east and southeast. With time, this should gradually thin and break to allow some brightness to develop. Depending on how much insolation and surface heating can occur, there is scope for 500-900 J/kg CAPE to develop across East Anglia, S / SE England and perhaps the S Midlands. The 00z Nottingham ascent suggests a couple of warm noses that may inhibit deep convection initially, but these should be overcome in East Anglia and SE England given fairly high dewpoints (16-18C) and potential for low 20s Celsius air temperatures in the best of any brightness. Onshore breezes are expected to develop over East Anglia, which combined with the synoptic north/northeasterly flow will create an area of enhanced convergence generally along a NE-SW line between Norwich and London, and perhaps beyond towards Brighton. The exact location of this CZ varies depending on the degree of surface heating. Either way, this will provide the main focus for a line of heavy showers and thunderstorms to develop from around 12-13z onwards.

Given very moist profiles with PWAT in the low 30s mm, slow storm motion due to weak mid-level flow (a tendency to drift slowly to the west) and the potential for back-building/training over similar areas, there is a significant risk of localised flash flooding - especially where showers/storms affect urban areas. As such, a SVR has been introduced given the potential for 50-100mm to occur very locally. If any cells can punch closer to 30,000ft then they may be able to utilise some stronger flow aloft to aid with venting and cell longevity, and could potentially become quite electrically active for a time. Some hail is possible, although given the overall weak shear and moist profile this is unlikely to be severe.

 

Across Cen S / SE England, the evolution is less clear given showery outbreaks of rain here this morning and this may inhibit sufficient surface heating. Assuming sea breeze convergence can develop, then these areas will also be at risk of heavy showers and a few thunderstorms during the afternoon and evening. Again the slow storm motion could result in some localised flooding. In all areas, given fairly low cloud bases, vorticity stretching along convergence zones could allow a couple of funnel clouds or a weak tornado to occur.

 

A few isolated heavy showers / weak thunderstorms will also be possible across parts of Ireland and western Scotland, but most areas here will remain dry. Showers/storms will only slowly fade through the evening hours - indeed new cells could keep developing in southern England until quite late in the evening - and as was the case on Saturday night some elevated thunderstorms could develop over the southern North Sea, although this perhaps less likely to push into East Anglia given an unfavourable/weaker steering flow. 

 

 

[karyo]

9 minutes ago, Harry said:

AROME, WRF-NMM and Euro4 all painting a similar picture a pronounced line stretching from somewhere in EA southwestwards across the London region and through the other side.

That line could as ever be a 10-20 miles further east or west and if the line does not move far very quickly, could mean some very high rainfall totals. 

Yes, the convergence zone has the potential to re-create what happened nearly two weeks ago when parts of London were affected by flooding.

[Alderc]

Hmmm I think places east of Southampton will be ok, further west touch and go, a lot of precipitation coming from barely negligible radar returns and it looks like several hours of this to come. Was really optimistic at 7am for here, much less so now. 

[Dbarb]

Brightening up in Maldon, could be ground zero for the worst today haven't had a thunderstorm in a while

[VillagePlank]

Hmmm: for SE:

SkewT suggests moderately convective atmosphere with possible sparse and scattered thunderstorms. However, no DLS, no DpD, and CIN darting in and out all afternoon. CZ looks like it depends on isolation, and at the moment, cool but humid, and completely covered skies with time ticking by.

Showers, some heavy, seem likely. Whether they upgrade to t/storms remains to be seen.

Edited July 25, 2021 by VillagePlank

[VillagePlank]

If I had to place a bet on heaviest of showers (read: possible thunderstorms) I'd go for E Anglia and Essex if (and only if) the sun comes out for a few hours from now. I think it's broke for Kent, and E Sussex - at least for now.

[Alderc]

 

[Andy Bown]

A little note to anyone thinking negatively. Here yesterday was extensively dull and sometimes damp until 16.00 then an hour of sunshine as well as convergence set up a very thundery evening!

[Electricmumma]

I’ve got 57% chance of storms at 4pm with torrential rain - anyone want to guess how accurate that’s looking? Currently 18, humidity 89%, DP 16

[Paul]

Severe storms are possible today. @Nick F has issued a storm forecast:

Severe Convective Weather & Storms Forecast - Netweather.tv

WWW.NETWEATHER.TV

[tomp456]

22 minutes ago, Electricmumma said:

I’ve got 57% chance of storms at 4pm with torrential rain - anyone want to guess how accurate that’s looking? Currently 18, humidity 89%, DP 16

such predictions are better off in the bin. 
I’ve had storms on 0% before.

[tomp456]

Not too much to report so far, some steady rain earlier, then a bit of brightness, now the rain has returned. 

[VillagePlank]

Skies just showing signs of clearing, here in Rochester ....

[Azuremoon2]

Thought to myself this morning it would be so nice if anywhere other than the South have a storm chance....i look at the forecast and to my shock and horror yes its the same as always, the South hogging all the good stuff. I just want a raindrop up here, none at all for nearly 7 weeks now, all the grass is brown. 

[Alderc]

Raining but the sun is trying to break through, need a couple of hours of sun to get a sea breeze going. 

[karyo]

Brightening up in central London. 

The radar shows a nice line of heavy showers to the east. They have intensified in the last half an hour.

[TN9]

9 minutes ago, VillagePlank said:

Skies just showing signs of clearing, here in Rochester ....

Got storm to my north west ,couple of rumbles of thunder ...

[TN9]

Just now, TN9 said:

Got storm to my north west ,couple of rumbles of thunder ...

Seven oaks way I'm guessing  ..