Storms and Convective discussion - September 2023

[viking_smb]

6 minutes ago, Eagle Eye said:

Sorry for the late forecast. Made this earlier today but was waiting for Jay to do the map. Was playing cricket so couldn't help him when making it either. 

Convective Outlook ⚡️ 

A large Theta-E airmass advection will allow for near tropical moisture rates along the Irish Sea and the coasts of Eastern Ireland and western England up to western Scotland. 1000+ J/KG of MLCAPE looks to advect and create showers and storms Wednesday night/Thursday morning, with potentially frequent lightning in some of them. They will move roughly north as it goes into Thursday morning.

 

This kind of saturation and moisture levels tends to allow for very frequent lightning once the cap is broken. If the capping isn't broken then it's a bust but it looks fairly likely to break and so some storms around the previously mentioned coasts could have quite frequent lightning rates.

 

Further into Ireland may see some scattered storms at random points throughout the night. These may have fairly frequent lightning, having good lapse-rates along with near tropical like moisture amounts and fairly good MLCAPE.

 

850's Theta-W at 16°C+ is enough for the elevated storms to form. Lots of elevated CAPE and good hydrolapse rates continue to suggest frequent lightning rates at times possible.

 

The inflow layer is fairly large with good below zero CAPE. Along with good hydrolapse rates and a supportive hodograph, severe hail is quite possible.  Hail could potentially be up to 2 inches but it's probably unlikely to reach it's potential but I suspect some 1.5 inch hail is possible. Some surface flooding is also possible.

Timing wise and it's on Wednesday night, storms should form in the southern part of the Irish Sea and into the SW of England, moving north towards SW Scotland potentially by around mid morning. These storms will be mostly longer-lasting pulse-type reaching 9-10 km before new storms should form after one falls. They might form into a weak but wide MCS with some near severe wind gusts depending on DCAPE strength.

Going off your forecast and other info, I think wales west of swansea will be most at risk 

Edited September 6 by viking_smb

[Eagle Eye]

Just now, Flash bang flash bang etc said:

Tony G at UKWW suggested a lot of hail will melt before hitting people on the ground. So… expect soggy people, albeit unhurt.

Could do. High LCL's weakens entrainment CAPE and with it being so warm sub cloud level, hail won't be as strong as analogs and they might not be accounting for the height. Those 850's aren't really typical for larger hail events. Given the 2 inch analogs, some people might say that my 1.5 inch forecast was very conservative but I think it was actually pretty high end. 

[Marcus_surfer]

It's real muggy here. Hoping to see a few strikes of lightning to my west tonight.

[viking_smb]

Just now, Marcus_surfer said:

It's real muggy here. Hoping to see a few strikes of lightning to my west tonight.

West of swansea will most at risk tonight

[pad199207]

[CoventryWeather]

I know it's not really convective weather, but it was a stunning sunset tonight! My view to the west on my Canon Camera earlier.

Seriously have gone mad with sunsets recently - social media having nothing but sunsets recently! 

[viking_smb]

Just now, CoventryWeather said:

I know it's not really convective weather, but it was a stunning sunset tonight! My view to the west on my Canon Camera earlier.

Seriously have gone mad with sunsets recently - social media having nothing but sunsets recently! 

they did say in the media about Sahara dust making for stunning sunrises and sunsets

[pad199207]

All bark and no bite I’d imagine 

 

[viking_smb]

27 minutes ago, Eagle Eye said:

Could do. High LCL's weakens entrainment CAPE and with it being so warm sub cloud level, hail won't be as strong as analogs and they might not be accounting for the height. Those 850's aren't really typical for larger hail events. Given the 2 inch analogs, some people might say that my 1.5 inch forecast was very conservative but I think it was actually pretty high end. 

the current synoptic chart (18z) and 12 hrs confirms my theory 

[minus10]

55 minutes ago, Eagle Eye said:

Could do. High LCL's weakens entrainment CAPE and with it being so warm sub cloud level, hail won't be as strong as analogs and they might not be accounting for the height. Those 850's aren't really typical for larger hail events. Given the 2 inch analogs, some people might say that my 1.5 inch forecast was very conservative but I think it was actually pretty high end. LCL 

Sorry mate..LCL s?...and re 850s, what would a typical 850 be for larger hail events...assuming your talking about temps at 850....

[Eagle Eye]

8 minutes ago, minus10 said:

Sorry mate..LCL s?...and re 850s, what would a typical 850 be for larger hail events...assuming your talking about temps at 850....

Lifted condensation levels. Entrainment CAPE is calculated using the LCL and equilibrium level. LCL is cloud height. For larger hail events you want cold 850's meaning good low-level lapse-rates. Don't know any specific numbers but it's a reason why spring tends to have the best hail events. Though high CAPE can counteract that 850's being warm scenario. 

Edited September 6 by Eagle Eye

[Marcus_surfer]

Showers gathering to the south. Will they trigger? time will tell

[ChannelThunder]

56 minutes ago, Marcus_surfer said:

Showers gathering to the south. Will they trigger? time will tell

Going by Arome, we can ignore those showers. If it's right, things will start to kick off around Brest soonish and track NNW. There's some cloud moving into that area on the satellite.

[WeatherWatchmanG]

Showers appearing near London, lightningmaps shows a strike just south of London M25 lets see what happens the other storm is out at sea underneath Wales.

[Flash bang flash bang etc]

18 minutes ago, WeatherWatchmanG said:

Showers appearing near London, lightningmaps shows a strike just south of London M25 lets see what happens the other storm is out at sea underneath Wales.

Eh?

[Azazel]

19 minutes ago, WeatherWatchmanG said:

Showers appearing near London, lightningmaps shows a strike just south of London M25 lets see what happens the other storm is out at sea underneath Wales.

There are no showers within 100 miles of London 

[Sprites]

26 minutes ago, WeatherWatchmanG said:

Showers appearing near London, lightningmaps shows a strike just south of London M25 lets see what happens the other storm is out at sea underneath Wales.

Going by the rainfall radar there are no showers south of London ATM.  Some rain in Oxfordshire, and Northants though.

Edited September 6 by Sprites

[ChannelThunder]

20 minutes ago, WeatherWatchmanG said:

Showers appearing near London, lightningmaps shows a strike just south of London M25 lets see what happens the other storm is out at sea underneath Wales.

Lightningmaps is notorious for false strikes that appear temporarily then get removed, which that one has been. London area is far east of the trough tonight so there won't be any storms anywhere near there.

[Ben Sainsbury]

Pembrokeshire will be happy! Like to think most elevated parts of Wales with a view to the Irish Sea should see a few flashes.

Though, main destabilisation anyway judging by models not until dawn now.

Edited September 6 by Ben Sainsbury

[Flash bang flash bang etc]

Another gripping event to etch into the marbled plaque of U.K. storm history

 

[Marcus_surfer]

Can see faint lightning to the west here

[Cheshire Freeze]

Nothing much showing on the radar now, that stuff in SW Wales looks to have petered out.

[Ben Sainsbury]

Purely a spectacle rather than a forecast. But ICON 0z has 3,000 J/Kg of MLCAPE on Sunday across East Anglia. Not seen anything like it.

[Cheshire Freeze]

Looks to me like there's the chance of an atmospheric light show on Saturday night for Wales the Midlands and N England

Also look at this CAPE chart for Sunday!

Edited September 7 by Cheshire Freeze

[ChannelThunder]

Bit of a damp squib overnight then! Arome's been known to overdo it a bit.