Storms and Convective discussion - September 2023

[StormLoser]

Hey, what happened to the SE's weather warned storms? Have they gone already?  I must have missed them whilst having my breakfast cuppa. 

[Sparkiee storm]

Not a direct hit here but managed to see 1 flash and rumble with it with some decent rain. Good to see a little something.

Edited September 26, 2023 by Sparkiee storm

[Flash bang flash bang etc]

28 minutes ago, StormLoser said:

Hey, what happened to the SE's weather warned storms? Have they gone already?  I must have missed them whilst having my breakfast cuppa. 

Yeah it was all talk - the squall here was a grey cloud. Lol sums this year up really

[Windblade]

Yeah, clouding over a bit here but nothing substantial/stormy looking at all. Tbh I expected as much. All the action seems to be out west/north west (as usual).

Edited September 26, 2023 by Windblade

[alexisj9]

21 minutes ago, Flash bang flash bang etc said:

Yeah it was all talk - the squall here was a grey cloud. Lol sums this year up really

We were never expecting a squall down here this morning just a few well scattered small elevated showers, they obviously haven't built here, but Dover was east of the very small risk any way.

[Metwatch]

The backend of the torrential rainfall about an hour ago. 

Some small signs of mid level instability, otherwise just an unnecessary deluge for this morning's commute, 16mm recorded in about 90 minutes. 

[Windblade]

Warm and sunny now. 24c. Still, nice weather for going out this late in September. 

[CoventryWeather]

Heavy rain here this morning, some nearing torrential for a small period too. As stated above, pretty pointless, must be way above average rainfall now here. 

[Metwatch]

Heavy shower passing over Coventry just now, weakened as it passed over the city, but the congestus looked quite nice. 

[WeatherArc]

18 hours ago, WeatherArc said:

Just come across this good vid from the severe thunderstorm outbreak we had 2 weeks ago, i believe this was the storm near Holbeach, absolute insane shelf on that thing 

Sounds like continuous thunder as well, quite rare for the uk and indicative of a very powerful storm. 

Some more vids/tweets i found, this time from the storm that developed over mid wales and tracked eastwards. Im not sure if the thing was supercellular, however the amount of lightning it was putting out was just incredible. Nothing better than a completely isolated storm with a complete lack of any other storms/clouds around it.  Certainly a reminder that when things come together the UK can have storms that rival those on the Continent and US.

 

Even found a view from a plane!

 

[WeatherArc]

This could be very interesting, extremely high 3cape (180+) combined with  600+ m2 s-2 of storm relative helicity, would be very easy to stretch and tilt updrafts even if they are low topped storms, definite tornado risk in Ireland and possible parts of Wales and Scotland depending on instability. 

 

 

[Eagle Eye]

Convective Outlook 

A warm front initially moves through Ireland and perhaps dipping down into SW England and lifts up through the UK, perhaps strongest in parts of Scotland. This occurs during the morning for western parts and eventually leaves Eastern parts late afternoon. Some rain may linger behind it, this is Storm Agnes, coming from a rapid cyclogensis with a low pressure system so severe wind gusts of 100+ km/h on Irish coasts and western UK coasts are possible. Along with widespread 50+ km/h inland with the back edge of the warm front. 

 

Behind the warm front, showers could well form in parts of Ireland moving onto some portions of the western UK. This mainly occurring in the afternoon and evening, these may have the risk of sparodic lightning more than the warm front along with flooding similar to the front. They may come with their own storm related wind gusts of 80+ km/h, mainly on the coasts.

 

DLS may be enough for some stretching of surface vorticity to result in an isolated brief tornado or two. Given that strong DLS, a Supercell cannot be ruled. They may form more organised in Northern Ireland and move into SW Scotland for momentum exchanges to result in small hail and again that slightly heightened risk of an isolated tornado.

 

Edited September 26, 2023 by Eagle Eye

[Eagle Eye]

 

 

Been a deceptively thundery year

[WeatherArc]

53 minutes ago, Eagle Eye said:

 

 

Been a deceptively thundery year

I was have been wondering the past few weeks what our place on that chart would be, for me in the midlands anyway im not that surprised 2023 ranked so high. 

May had a few active days and June featured pretty much storms every weekend for my area including a very powerful MCS on June the 11th. 

If it wasn't for July and August we would probably of beaten 2020, of course September has also been incredibly active.

Certainly been an amazing year for homegrown storms. 

Edited September 26, 2023 by WeatherArc

[Eagle Eye]

Given the streamwise vorticity already in place, any storm that can latch onto the surface flow behind the frontal system will likely be able to increase the momentum into the storm at a steady rate. The extreme LLS with backing winds is quite rare for the British Isles and if enough DCAPE can force enough energy downwards to rapidly increase 3CAPE, specifically in the lowest sector of cloud development then there may be potential for a strong tornado. 

 

Given all that directing of shear, a Supercell is definitely possible. This is especially likely in the middle and southern sectors of the possible line, where there appears to be better stretching and veering of the low-level winds and directing of mid-upper level winds are better, aiding possible Supercellular development. SBCAPE is quite low for Supercellular development, however this appears to be acting on the models as a possible low CAPE/high shearing scenario, with just about weak enough forcing for it not to upscale too much compared to previous events in the past. 

The updraft could well be centred away from the draft given the winds available so some good pictures of the storms are also possible. So if you're in the path, possibly might need your camera for this afternoon and into evening. 

[minus10]

32 minutes ago, Eagle Eye said:

Given the streamwise vorticity already in place, any storm that can latch onto the surface flow behind the frontal system will likely be able to increase the momentum into the storm at a steady rate. The extreme LLS with backing winds is quite rare for the British Isles and if enough DCAPE can force enough energy downwards to rapidly increase 3CAPE, specifically in the lowest sector of cloud development then there may be potential for a strong tornado. 

 

Given all that directing of shear, a Supercell is definitely possible. This is especially likely in the middle and southern sectors of the possible line, where there appears to be better stretching and veering of the low-level winds and directing of mid-upper level winds are better, aiding possible Supercellular development. SBCAPE is quite low for Supercellular development, however this appears to be acting on the models as a possible low CAPE/high shearing scenario, with just about weak enough forcing for it not to upscale too much compared to previous events in the past. 

The updraft could well be centred away from the draft given the winds available so some good pictures of the storms are also possible. So if you're in the path, possibly might need your camera for this afternoon and into evening. 

I think i know what cape is but Dcape and 3cape ?

[jmp223]

Dcape is downward available convective energy 3cape, is cape value below 3km I believe?

Higher DCAPE values (>1000 j/kg) have been associated with increasing potential for strong downdrafts and damaging outflow winds.

Edited September 27, 2023 by jmp223

[emmett garland]

Could we see a tornado 

[Eagle Eye]

1 hour ago, minus10 said:

I think i know what cape is but Dcape and 3cape ?

Downwards CAPE and CAPE up to 3KM.

[Frosty hollows]

1 hour ago, emmett garland said:

Could we see a tornado 

Crikey! You know it's serious when Estofex have a level 2 for the British isles!

[alexisj9]

1 hour ago, emmett garland said:

Could we see a tornado 

Having read the text, the possibility is there, it's a level two for strong wind gusts, and the t word. Don't see that often for the UK.

[Liam Burge]

1 hour ago, emmett garland said:

Could we see a tornado 

"The combination of high low-level streamwise vorticity and low cloud bases points to the risk of tornadoes, including strong tornadoes"

[Metwatch]

Very funky cloudscapes sent from Plymouth this morning, almost asperitas like! 

[Snow Queen one]

Currently in Conwy.  Heavy rain here no wind yet.

[ChannelThunder]

Got some really pretty mid level instability coming in ahead of Agnes. Photos when I'm home 

Edited September 27, 2023 by ChannelThunder