Storms and Convective discussion- 7th August onwards

[Osca31]

What a crazy night. One of the longest lasting ,active storms I have ever seen.Started here about 8.30pm then it was just constant strobe lightning and deep thunder for hours on end. It was still flickering away at 4.00am this morning,extraordinary!

[Guest]

@Paul Sherman Has the CoS been broken this morning? 

[Typhoon John]

Lots of cloud coming in from the storm that crossed the channel overnight. I'm pretty thankful it's hiding the sun and keeping it cooler than it would otherwise have been.

[nanu]

1 minute ago, Typhoon John said:

Lots of cloud coming in from the storm that crossed the channel overnight. I'm pretty thankful it's hiding the sun and keeping it cooler than it would otherwise have been.

Almost under that.. and its pretty dark,, which is nice! anything to block that orange ball today is a bonus.

[Paul Sherman]

3 minutes ago, Alderc said:

@Paul Sherman Has the CoS been broken this morning? 

Nope just a little bit of larger convective rain drops then a steady rainfall which the sand (arid desert) garden looks like it enjoyed

So about 10 mins of steady rainfall and skies are now clearing from the SE for the Oven to go back upto around 200c for 7 hours 

[Justin1705]

5 minutes ago, Typhoon John said:

Lots of cloud coming in from the storm that crossed the channel overnight. I'm pretty thankful it's hiding the sun and keeping it cooler than it would otherwise have been.

Not for long tho hehe. After that clears through lots of sun as shown on Satellite another hot day. But you are right its cool this morning. Looks like E london Essex  could get a nice shower all Be it not thundery. But yes a nice interlude.

Edited August 11, 2020 by Justin1705

[Chris.R]

I am quite concerned that wrf wants a sea-breeze starting this  afternoon. Worried  that will put me out of the game.

[Justin1705]

Just now, Justin1705 said:

Not for long tho hehe. After that clears through lots of sun as shown on Satellite another hot day. But you are right its cool this morning. Looks like E london Essex  could get a nice shower all he it not thundery. But yes a nice interlude.

 

[Justin1705]

So guys. I know this is really gonna Aggravate us Southerners. But Arome seems confident in this elevated cruddy stuff right now maybe organising and strengthening towards the wash and grimsby area. All i can say is at least there is something further east. Rather. than watching everyone in the west get the action

[Gordon Webb]

Estofex Important bit

(2) Great Britain, Belgium, rest of France, Switzerland, N Italy:
The capping inversion on top of the moist boundary layer and limited synoptic lift could keep the storm coverage rather low, but the conditional severe weather risk is notably enhanced once storms initiate. The main risk is excessive rain due to plentiful low-level moisture and slow storm motion. However, steep lapse rates in the "Spanish plume" also enhance the risk of large hail and severe downbursts even in the absence of noteworthy vertical wind shear.
Confidence in surface-based storms is limited in England (where the ratio between capping and lift deteriorates), and in general turns very low in coastal areas. Elevated activity on top of the sea breezes or in the warm air advection regime in Great Britain can still bring some heavy rain, but the other risks are significantly lower.

[Summer Sun]

Day 1 Convective Outlook

VALID 06:00 UTC Tue 11 Aug 2020 - 05:59 UTC Wed 12 Aug 2020

ISSUED 07:06 UTC Tue 11 Aug 2020

ISSUED BY: Dan

... SUMMARY ...

• A few isolated elevated thunderstorms will be possible E Scotland and E England during Tuesday daytime
• Elevated showers/thunderstorms possible over SW England during Tuesday daytime
• Depending on strength of the cap, isolated to scattered explosive thunderstorms will be possible in parts of England and Wales by late afternoon into the evening - many areas within the SLGT will remain void of lightning. Any storms that do develop pose a threat for large hail and flash flooding
• An increase in thunderstorm coverage, primarily elevated, is expected from Cumbria northwards across a swathe of Scotland during Tuesday night
• A few scattered elevated showers/weak thunderstorms will be possible over the Channel Islands / English Channel on Tuesday night

... DISCUSSION ...

Decaying MCV over Scotland on Tuesday morning has considerably worked over the environment last night. However, with a PV lobe aiding ascent, there is an ongoing risk of some sporadic lightning on its eastern flank from elevated convection through the morning as it continues to lift north and ultimately offshore. The same instability plume extend SSE-wards across eastern England, and continues to run a risk of a few isolated elevated thunderstorms developing this morning/early afternoon - some model guidance suggests this perhaps most likely from East Anglia across the East Midlands to Yorkshire. There may also be an uptick in elevated activity across central/eastern Scotland during the afternoon hours on the tail end of the morning MCV. other elevated showers/thunderstorms may also drift from the Brest peninsula towards SW England through the day.

Elsewhere, it may be rather quiet for much of the day with an EML covering much of England and Wales and acting as cap to surface-based convection. Diurnal heating will lead to 1,000-2,000 J/kg CAPE building through the day, essentially once again creating a loaded-gun environment. Surface dewpoints may mix out a little, especially towards southern and eastern England where the hottest conditions are most likely. Nonetheless, it seems likely dewpoints of 19-20C will be fairly widespread, especially late afternoon and into the evening. The slack surface pattern will lead to several convergence zones developing, and these combined with orographic forcing will be crucial in providing forced ascent given the lack of any upper support. Forecast profiles suggest air temperatures of 32-33C in SE England to 29-30C in Wales will be required to break through the capping inversion. Where this in conjunction with low-level convergence occurs, explosive deep convection could evolve by late afternoon and more especially into the evening hours almost anywhere in England, Wales and southern Scotland.

NWP guidance varies drastically as to where these convergence zones may develop, in part related to the events from Monday night, and so it is difficult to pinpoint specific areas where storms could fire. Bulk shear is a little on the weak side (15-20kts), but steep mid-level lapse rates and significant CAPE (fast upward motion) suggests that where storms do develop, the threat for large hail exists in the most organised cells (2-4cm in diameter). Inverted-V profiles suggests localised wind gusts of 40-50mph may occur, and with PWAT of 40-45mm and storm motion of ~15mph prolonged torrential downpours could lead to flash flooding. A SVR has been issued primarily for the threat of large hail and flash flooding, and to a lesser extent for damaging winds.

Most surface-based storms will probably only last a couple of hours given the strong cap in place and lack of notable forcing aloft - however, the shortwave associated with elevated thunderstorm activity over SW England today may allow thunderstorms that do erupt over Wales and the West Country to persist through the evening hours as they track northeast across the Midlands. There is better agreement on a developing shortwave running northeast from the Irish Sea into northern England and Scotland on Tuesday evening and night, and this may lead to another wave of elevated thunderstorm clusters over these areas during the overnight period, with any activity across central and southern Britain generally quite isolated through this time.

http://www.convectiveweather.co.uk/forecast.php?date=2020-08-11

[Mitch the motorbike storm]

13 minutes ago, Justin1705 said:

So guys. I know this is really gonna Aggravate us Southerners. But Arome seems confident in this elevated cruddy stuff right now maybe organising and strengthening towards the wash and grimsby area. All i can say is at least there is something further east. Rather. than watching everyone in the west get the action

the south east isnt matching the first pic

[davehsug]

That ribbon of rain (not that it's actually reaching the ground), just isn't moving , just snaking around. Very strange watching it on the radar. 

[Dan the Man]

50,000 lightning strikes over the UK last night, for what it's worth. Probably just the aperitif in comparison to what is coming down the track later this week...

[claret047]

30 minutes ago, Paul Sherman said:

Nope just a little bit of larger convective rain drops then a steady rainfall which the sand (arid desert) garden looks like it enjoyed

So about 10 mins of steady rainfall and skies are now clearing from the SE for the Oven to go back upto around 200c for 7 hours 

You are very lucky Paul.

We have not even had one drop of rain. I raise your Sahara with my Chilean coastal desert!

[Harry]

WRF-NMM from tomorrow through until Friday looks sensational with very high instability and potentially numerous rounds of storms

[East_England_Stormchaser91]

Interesting forecast once again. Once this elevated stuff clears, temperatures should rocket. Possibly Cambridge area down to the Home Counties again to break the cap by mid-late afternoon. There’s also less of a breeze from the NE here, so that should also help. 

[Lauren]

Some light rain this morning to cool things down a bit but looks like no storms. BBC only forecasting storms for Thursday.

[Paul Sherman]

3 minutes ago, claret047 said:

You are very lucky Paul.

We have not even had one drop of rain. I raise your Sahara with my Chilean coastal desert!

[Gordon Webb]

27 minutes ago, Summer Sun said:

Day 1 Convective Outlook

VALID 06:00 UTC Tue 11 Aug 2020 - 05:59 UTC Wed 12 Aug 2020

ISSUED 07:06 UTC Tue 11 Aug 2020

ISSUED BY: Dan

... SUMMARY ...

• A few isolated elevated thunderstorms will be possible E Scotland and E England during Tuesday daytime
• Elevated showers/thunderstorms possible over SW England during Tuesday daytime
• Depending on strength of the cap, isolated to scattered explosive thunderstorms will be possible in parts of England and Wales by late afternoon into the evening - many areas within the SLGT will remain void of lightning. Any storms that do develop pose a threat for large hail and flash flooding
• An increase in thunderstorm coverage, primarily elevated, is expected from Cumbria northwards across a swathe of Scotland during Tuesday night
• A few scattered elevated showers/weak thunderstorms will be possible over the Channel Islands / English Channel on Tuesday night

... DISCUSSION ...

Decaying MCV over Scotland on Tuesday morning has considerably worked over the environment last night. However, with a PV lobe aiding ascent, there is an ongoing risk of some sporadic lightning on its eastern flank from elevated convection through the morning as it continues to lift north and ultimately offshore. The same instability plume extend SSE-wards across eastern England, and continues to run a risk of a few isolated elevated thunderstorms developing this morning/early afternoon - some model guidance suggests this perhaps most likely from East Anglia across the East Midlands to Yorkshire. There may also be an uptick in elevated activity across central/eastern Scotland during the afternoon hours on the tail end of the morning MCV. other elevated showers/thunderstorms may also drift from the Brest peninsula towards SW England through the day.

Elsewhere, it may be rather quiet for much of the day with an EML covering much of England and Wales and acting as cap to surface-based convection. Diurnal heating will lead to 1,000-2,000 J/kg CAPE building through the day, essentially once again creating a loaded-gun environment. Surface dewpoints may mix out a little, especially towards southern and eastern England where the hottest conditions are most likely. Nonetheless, it seems likely dewpoints of 19-20C will be fairly widespread, especially late afternoon and into the evening. The slack surface pattern will lead to several convergence zones developing, and these combined with orographic forcing will be crucial in providing forced ascent given the lack of any upper support. Forecast profiles suggest air temperatures of 32-33C in SE England to 29-30C in Wales will be required to break through the capping inversion. Where this in conjunction with low-level convergence occurs, explosive deep convection could evolve by late afternoon and more especially into the evening hours almost anywhere in England, Wales and southern Scotland.

NWP guidance varies drastically as to where these convergence zones may develop, in part related to the events from Monday night, and so it is difficult to pinpoint specific areas where storms could fire. Bulk shear is a little on the weak side (15-20kts), but steep mid-level lapse rates and significant CAPE (fast upward motion) suggests that where storms do develop, the threat for large hail exists in the most organised cells (2-4cm in diameter). Inverted-V profiles suggests localised wind gusts of 40-50mph may occur, and with PWAT of 40-45mm and storm motion of ~15mph prolonged torrential downpours could lead to flash flooding. A SVR has been issued primarily for the threat of large hail and flash flooding, and to a lesser extent for damaging winds.

Most surface-based storms will probably only last a couple of hours given the strong cap in place and lack of notable forcing aloft - however, the shortwave associated with elevated thunderstorm activity over SW England today may allow thunderstorms that do erupt over Wales and the West Country to persist through the evening hours as they track northeast across the Midlands. There is better agreement on a developing shortwave running northeast from the Irish Sea into northern England and Scotland on Tuesday evening and night, and this may lead to another wave of elevated thunderstorm clusters over these areas during the overnight period, with any activity across central and southern Britain generally quite isolated through this time.

http://www.convectiveweather.co.uk/forecast.php?date=2020-08-11

I was quite happy until that bit about storms possibly tracking across the midlands

[ChannelThunder]

What a funny looking CW Outlook today  

Another day of roasting with little chance of storms commences!

[Flash bang flash bang etc]

Just now, Harry said:

WRF-NMM from tomorrow through until Friday looks sensational with very high instability and potentially numerous rounds of storms

Forgive me but just how many times before have we seen this? They can’t even predict today because it’s so uncertain - so I really have doubts about anything expected past midnight tonight to remain as good as it has done in recent days.

I’m just waiting for tomorrow’s comment in the forecast write ups about activity in the SE being “limited by _______” (insert anything you want in the blank)

[sparky1972]

Sth Lincs storm shield in full effect, lol, sun trying to poke through but this high level crud is going to keep the temps surpressed and the easterly breeze still keeping things on the fresh/cooler side.

[Calayte]

Another day of interesting forecasts, but I guess it will all come down to nowcasting again!

[Flash bang flash bang etc]

12 minutes ago, Dan the Man said:

50,000 lightning strikes over the UK last night, for what it's worth. Probably just the aperitif in comparison to what is coming down the track later this week...

Over the northern parts of the UK.
 

I see on twitter they are trying to suggest the whole UK got the storm last night that was quite clearly nowhere near the south