Uk General Convective Discussion & Forecasts, 24th August '12>

[Bobby]

We had one almighty downpour in the morning (after some further heavy downpours overnight that left 10mm) that desposited 7.5mm at a 80mm hour rain rate. The rest of the day was dry and breezy. No thunder or lightning though, again.

[AWD]

The North has potential for some activity midweek, but otherwise it is looking like a lengthy stormless period coming up now

[Chris K]

The North has potential for some activity midweek, but otherwise it is looking like a lengthy stormless period coming up now

Yea it does seem like for a while now there will be little storm activity. Best bets now really is if there is any breakdown to the potential warmer spell the models are still currently showing from next weekend.

Personally though, I can't remember many notable thunderstorms occurring during September. It's still possible of course!

Edited August 26, 2012 by Chris K

[Supacell]

Yea it does seem like for a while now there will be little storm activity. Best bets now really is if there is any breakdown to the potential warmer spell the models are still currently showing from next weekend.

Personally though, I can't remember many notable thunderstorms occurring during September. It's still possible of course!

I find the storm season lasts until about the end of September and I saw some very good storms during September 2006 but that was after a very hot summer. Having said that I have been out storm chasing in October before now and seen some decent storms.

So I don't think its over yet (i hope not) but agree on a quiet period coming up.

[MP-R]

Indeed, 2006 produced some good thunderstorms, as did October. 2000 was another good one, and most other Septembers have at least had a day with thunder in them - I think only 2003 and 2009 fail on that one here.

Perhaps another 23rd September 2010 type event might occur next month?

[Chris.R]

The only time I have ever had thunder in september was 2010 and maybe 2006 as far as I can remember, otherwise, september is a rather stormless month here. O yeah, I forgot, most months are stormless here!

[Chris.R]

what was I thinking

[Coast]

ESTOFEX Level 1 for Ireland, Western areas and all of Scotland:

Storm Forecast

Valid: Mon 27 Aug 2012 06:00 to Tue 28 Aug 2012 06:00 UTC

Issued: Mon 27 Aug 2012 05:03

Forecaster: SCHLENCZEK

A level 1 was issued for W UK and parts of Ireland for severe wind gusts and tornadoes.

SYNOPSIS

While cool and stable conditions prevail over central Europe, a plume of hot and moist air is advected into SW Europe. A destabilization of this airmass may allow isolated severe convection over Spain and S France on Monday evening/ night.

Remnants of a very hot and unstable airmass over Ukraine will provide favorable conditions for severe thunderstorms with large hail and severe wind gusts over E Romania and central/ eastern Ukraine. Most of the activity will be tied to a cold front which separates hot and moist air in the east from a cool airmass further west.

Frontal convection can also be found along a cold front which belongs to a low pressure system W of Scotland. Although not much lightning is expected, a few severe weather events such as tornadoes and severe wind gusts are still possible.

Another region with a chance of thunderstorms is found over the Baltics and W Finland where low-end instability and rather low vertical shear are present. Besides the possibility of a funnel / weak tornado, no severe weather is expected.

DISCUSSION

...Ireland and UK...

Some hundred J/kg of CAPE are forecast along the cold front of a strong low pressure system which slowly translates to the northeast. Strong winds at lower levels (20 m/s at 850 hPa) may support a few severe wind gusts if additional evaporative cooling accelerates the downdraughts. Due to strong LL winds and therefore some LL shear and locally enhanced SRH, an isolated tornado event is also possible.

UKASF go with the same area but a slight forecast:

Synopsis:

Broad upper trough will be located to the west of Britain, with various shortwaves running anticlockwise around the base. Beneath the trough, a deep surface low will be centred west of the Hebrides, with an associated occluded front moving erratically eastwards across the British Isles during the day. Convection is expected behind the front, primarily over Ireland.

Discussion:

A strong jet aloft will allow >50kts DLS, with the bulk of this (30-45kts) in the lowest km. As a result it is possible that, with ELTs only -10C or warmer, some low-topped line convection may occur on the back-edge of the front with the potential for a few bowing segments. Given the shallow nature of such convection, lightning activity is rather unlikely and is considered too low for a SLGT coverage level at this time.

In the wake of the front, cool mid-levels (-19/-20C at 500mb) will overspread Ireland, Northern Ireland and western Scotland, steepening lapse rates and generating 500-600J/kg CAPE. Showers and a few thunderstorms are likely, more especially in the late afternoon and evening hours with the progression of a shortwave.

Given up to 70kts DLS/20kts LLS, showers/storms are likely to become well-organised into linear clusters, with the threat of backbuilding/shower training enhancing the risk of local flooding. Low LCLs (occasionally <600m) with sufficient LLS may allow a funnel or weak tornado to occur. Stronger cells may also produce hail up to 1.5cm in diameter.

Showers may affect the Isle of Man and Irish Sea coasts through the evening hours as the occlusion (and following shortwave) continue to migrate eastwards.

TORRO and SkyWarn are having a lie in, here some stuff that may or may not be applicable:

MLCAPE isn't huge:

Surface CAPE to the West:

Shear over the Irish sea:

Lapse rates are well down in the West:

More rain (lots of it!)

Lots of helicity and shear could bring a tornado threat to the West coast of the UK:

Slight chance of thunderstorms?

[IanR]

does this mean there is a chance of seeing some dusk lightning over the Irish sea like a few weeks ago from North West England ?

[Chris.R]

I'd like to think so, but I think that the CAPE isn't there today and the setupp isn't quite the same is it?

[weatherobsuk]

Looks to be all heading Northeast from what i'm looking at on RADAR

[Supacell]

does this mean there is a chance of seeing some dusk lightning over the Irish sea like a few weeks ago from North West England ?

Certainly looks to be a possibility from around 9pm into the first part of the night as lapse rates increase from the west and some MLCAPE moves in from the west behind the front (charts at midnight)

Although ELT's around -30 don't favour frequent sferic activity so I think it would be fairly sporadic. Could see a few flashes though

[Cloud 10]

Nice sharp back edge on the cold front which is starting to clear Ireland.

A pretty miserable bank holiday monday for many,although The Wizard Of Oz

is on this afternoon so at least a guaranteed tornado!

[Chris W]

I'm quite surprised to see a level 1 covering here from Estofex though it has been pretty gusty this morning - wouldn't say anything particularly damaging but the winds are strong. Little in the way of rain.

There is a line of sharp showers at the rear of the frontal cloud that looks quite interesting - over Northern Ireland and moving ENE, but I'm not expecting much in terms of storms. That said, with CAPE and a trough passing over the Irish Sea tonight is something actually possible tonight?

Wednesday is looking interesting, GFS currently modelling a fair amount of CAPE with accompanying LI values as the next low moves through with an occluded front and a couple of troughs.

Edited August 27, 2012 by Chris W

[Convective]

Would love to see some more oversea lightning tonight.. But even better, I would love a thunderstorm! I am slap bang in the middle of all the forecasts.

[slinky1989]

I'm on holiday near Milford haven atm and am surprised to see this area covered for a storm forecast!

Is the threat mainly for later after the front has passed?

[in the vale]

Some sharp sferics showing up on radar and lightning detector off the Irish / NI coast - heading East on the back edge of the front. Was slightly surprised to see them survive once they crossed into the Irish Sea. There may be something later across N. Wales / NW England. Worth keeping an eye on.

[I Cumbria Marra I]

wouldnt be surprised if 50+mm has fallen today, its been lashing down for since about 10am

[Chris.R]

Having a nice squall here with very heavy rain and strong winds as the coldfront moves through. One of these with hail and thunder like the irish sea squalls of autumns of old tonight would be nice please?

[The watcher]

Crazy looking sky outside right now and I think I hear Thunder in the distance. Could this be the first storm for near 2 years?

[in the vale]

Looks like the main activity is now headed towards S Scotland / N England. Stranraer may be in for some fun. That's me bust again. No TStorms here for at least 4 years now. Forgot what they look like!

[The watcher]

Something brewing at the back edge of the precipitation just passing Belfast, a small but very strong core just developed in the past 15-30 minutes.

[AWD]

Still looking promising for something on Wednesday for western and northern parts of the UK.

Then there is some isolated going's on IMBY, someone upstairs playing me around??

[The watcher]

Well, a distant Rumble heard about 40 minutes ago, but nothing since. The drought continues.

[IanR]

Some sharp sferics showing up on radar and lightning detector off the Irish / NI coast - heading East on the back edge of the front. Was slightly surprised to see them survive once they crossed into the Irish Sea. There may be something later across N. Wales / NW England. Worth keeping an eye on.

the clouds here seem to be moving south to north, i assume this will push any thundery showers if they form into scotland rather than the NW of england ?