Storms and Convective discussion- 7th August onwards

[Summer Sun]

Day 1 Convective Outlook

VALID 06:00 UTC Mon 10 Aug 2020 - 05:59 UTC Tue 11 Aug 2020

ISSUED 14:49 UTC Mon 10 Aug 2020

ISSUED BY: Dan

UPDATE 14:49 UTC MDT introduced across N Wales and NW England for this evening/tonight, SLGT extended into W Scotland for tonight and expanded across southern England for the risk of a few scattered elevated showers/storms tonight

Atlantic upper longwave trough will gradually sharpen on Monday, placing the British Isles under a broad southerly flow aloft. This will continue to advect a plume of high Theta-W slowly northwestwards through the forecast period, with a marked elevated mixed layer (EML) covering much of England and Wales and creating an environment with notably steep mid-level lapse rates.

... SUMMARY ...

• Scattered thunderstorms are likely over parts of Wales / SW England / Irish Sea / SW Scotland during Monday daytime
• Severe thunderstorms with large hail, flash flooding, strong gusts of wind and an isolated tornado will be possible over the Midlands and E Wales during Monday afternoon and evening
• Scattered thunderstorms may affect parts of N / NW England, Irish Sea and southern Scotland on Monday evening and night
• Isolated thunderstorms may be possible elsewhere, but with lower confidence

... WALES / NW ENGLAND / IRISH SEA / SW SCOTLAND - MONDAY DAYTIME ...

Elevated convection (bases around 8-10,000ft) is likely to be ongoing on Monday morning across parts of Wales, SW England and perhaps NW England, lifting gradually north through the day while expanding in coverage as a shortwave engages with a Theta-E ridge. Given the steep mid-level lapse rates and 500-700 J/kg CAPE, lightning is likely to be quite frequent in the most intense cells - especially over west Wales and parts of the Irish Sea where a greater coverage of lightning is expected. Lightning activity may weaken as storms approach the Isle of Man / eastern Northern Ireland / SW Scotland as profiles become increasingly saturated and instability weakens. Some hail may be possible, although the high cloud base and depth of hot air below suggests a lot of this will melt or shrink in size by the time it reaches the surface.

Elsewhere, isolated elevated showers/thunderstorms will be possible in a zone from Wales across the Midlands and SE England as a weak PV filament lifts north and engages the plume.

... MIDLANDS / E WALES - MONDAY AFTERNOON / EVENING ...

Strong surface heating is expected across southern and eastern England, with a slack low evolving in the vicinity of the M4 corridor. The EML will serve as a cap to surface-based development, and with T850s gradually warming through the day across SE England and East Anglia, these areas are likely to remain capped. However, some slight cooling at 850mb is possible over the West Country / SW Midlands, and IF surface temperatures can nudge close to the required trigger temperature of 30-32C (assuming dewpoints around 18-19C) this could breach the capping inversion and lead to explosive development in a loaded-gun environment, especially when aided by low-level convergence near the surface low centre and a PV lobe arriving from the English Channel.

Should deep convection occur, the backed low-level winds north of the surface low and modest flow aloft will create 20-30kts DLS which may be sufficient for organisation and perhaps supercellular mode. Given the substantial CAPE (1,000-1,500 J/kg) and steep mid-level lapse rates, very frequent lightning and large, damaging hail 2-4cm in diameter would be possible (although possibly shrinking somewhat in size as it falls through the hot surface air before reaching the ground). PWAT near 40mm and storm motion of ~20mph brings the risk of prolonged torrential downpours and flash flooding. Should storms exhibit supercellular characteristics, then they may deviate to the right of the mean flow and slow their forward speed. Given the large T-Td spread, cloud bases may initially be quite high, around 6,000ft - but due to a combination of storm processes, northward movement into less-hot air and nocturnal cooling of the boundary layer, cloud bases may steadily lower during the evening hours. Backed low-level winds will create 20-30kts LLS, which may bring the risk of an isolated tornado if cloud bases can lower substantially. Otherwise, inverted-V profiles suggests the risk of strong downburst winds 45-55mph. A SVR has been issued primarily for the threat of large hail and flash flooding, and to a lesser extent for strong winds and an isolated tornado.

The greatest risk of severe thunderstorms appears to be initially close to the M4 corridor and SE Wales, shifting northwards into the south / central / west Midlands and east Wales during the evening, and then NW England / Irish Sea later. However, as storms run north into an increasingly capped environment, they may become more elevated in nature. Much of this depends on how strong the cap is during Monday afternoon...

... NORTHERN ENGLAND / SOUTHERN SCOTLAND - MONDAY EVENING / NIGHT ...

As the shortwave ejecting north from France arrives during the evening hours, existing thunderstorms over the Midlands and/or new thunderstorms over NW England will likely grow upscale into a complex of primarily elevated thunderstorms over Cen N / NW England, while migrating northwards through the night towards southern Scotland. Lightning could be quite frequent in the strongest cells, and the threat of localised flooding exists from prolonged downpours. Some hail and gusty winds are also possible.

... ENGLISH CHANNEL - MONDAY NIGHT ...

A few other elevated showers/thunderstorms may be possible in parts of western mainland Scotland, and perhaps also exiting northern France and across the Channel Islands / English Channel towards S / SE England during the overnight period.

http://convectiveweather.co.uk/forecast.php?date=2020-08-10

 

[DIS1970]

Not too much on the go here, still bright, temp at 27.7C, appears to breaking out just north and west of Wolves.

Edited August 10, 2020 by DIS1970

[SP1986]

Interestingly some pronounced sea breezes have set up in coastal Northwest England... I presume that means surface based storms at least are out of the question for coastal areas. Elevated storms still possible, but the temperature here is plummeting now... I think within the hour it'll be below 20C so I'm not sure my locality will see any storms based on this but might get a few rumbles from elevated stuff as it trundles north.

[Shane]

Plenty of audible thunder in the distance think the shower it is coming from is just going to skim Telford, well north Telford. Kids are in the garden waiting for the heavy rain lol! 

[Gordon Webb]

4 minutes ago, DIS1970 said:

Not too much on the go here, may just be outside the firing line, may be wrong, but it looks like it's just to the NW, of Wolves - at the moment.

well the met office 4pm storm warning only has Wolverhampton just in the southern edge of the zone so perhaps you'll be unlucky

[SalopWatcher]

passed through in about 15-20 mins, but some close strikes and really loud thunder. A total direct hit for Shrewsbury, seems to be degrading slightly on radar as it moves north to be honest.... 

Great show though! 

[Eagle Eye]

A Nice celebration of the Viking God Of Thunder on Thursday

[StormChaseUK]

Up the Long Mynd. 

Rumbles to North, very high up though. Excellent for nighttime flashes but not much good for daytime 

[Shane]

1 minute ago, SalopWatcher said:

passed through in about 15-20 mins, but some close strikes and really loud thunder. A total direct hit for Shrewsbury, seems to be degrading slightly on radar as it moves north to be honest.... 

Great show though! 

Heard the thunder from it, did not see any lightning. My eldest was pretty upset, only 7 and he wanted to see lightning I have given him the thunderstorm bug lol!! 

[BugboyMike]

Hinckley is hovering around 30 degrees now. Towers started going up. This looks promising to be honest

[GeordieX9v]

Rubbish in NE6

[SarahWxm]

6 minutes ago, SalopWatcher said:

passed through in about 15-20 mins, but some close strikes and really loud thunder. A total direct hit for Shrewsbury, seems to be degrading slightly on radar as it moves north to be honest.... 

Great show though! 

Don’t dash my hopes and dreams here! lol 

[ChannelThunder]

Dan's update, coupled with that lengthy towering Ac Cas line to my south, has given me hope. But it's the hope that makes it harder to swallow when it doesn't lead to anything!

[Flash bang flash bang etc]

Over near Kenilworth and it’s a roaster! Think there might be something elevated building overhead  

[SalopWatcher]

2 minutes ago, Shane said:

Heard the thunder from it, did not see any lightning. My eldest was pretty upset, only 7 and he wanted to see lightning I have given him the thunderstorm bug lol!! 

Think I might have got on a lucky angle and saw three bolts across the sky... with almost instant thunder... 

Wonder with these temps to the south if there might be another round later... 

[TJS1998Tom]

Looks like I'm too far East for this one, if it was dark I'd probs see lightning from a distance. Unless more are due tonigh t 

[Gordon Webb]

5 minutes ago, Xanderp009 said:

A Nice celebration of the Viking God Of Thunder on Thursday

would've been better if your used Thorsday instead of Thursday

[SalopWatcher]

1 minute ago, SarahWxm said:

Don’t dash my hopes and dreams here! lol 

Still producing occasional thunder, but compared to half a n hour ago, the cells not as intense ATM. Fingers crossed it picks back up. 

[alexisj9]

1 minute ago, Lance M said:

Dan's update, coupled with that lengthy towering Ac Cas line to my south, has given me hope. But it's the hope that makes it harder to swallow when it doesn't lead to anything!

I'm still not in the update lol. East Kent is doing badly this year. But at least we got a decent light show, may get another tonight. 

[TJS1998Tom]

I'm guessing more storms will develop later tonight?

[Gord]

Hmmm...the sky suddenly seems to be getting darker overhead here.

[SarahWxm]

3 minutes ago, SalopWatcher said:

Still producing occasional thunder, but compared to half a n hour ago, the cells not as intense ATM. Fingers crossed it picks back up. 

Hope the hills round here perk it up lol. Looks grey towards your way atm. 

[UKSupercell]

I'm holding off on driving north atm actually. Monitoring the Cambridge cell and atm it doesn't look like it's particularly intensifying. NW Wales is having a light show but that's far too far for me to reach from South Bucks now. 

[Neilsouth]

6 minutes ago, alexisj9 said:

I'm still not in the update lol. East Kent is doing badly this year. But at least we got a decent light show, may get another tonight. 

Can't believe how bad its been this year! Yet all that flooding we had in the early part

[Gord]

Blue skies seeping back in from the southeast as the darker developing cloud moves towards the northwest.

Obviously right on the fringe of any development here. I think places northwest of here could be in for more corkers looking at the way the clouds just keep building overhead and then moving off northwest.

Edited August 10, 2020 by Gord