Uk General Convective Discussion & Forecasts, 28th August 2012>

[Coast]

... Southern UK ...

Hmmmm, I would have said that was the lesser risk area of the day, but these guys have a better grip than I do! I still say Ireland, Scotland and West cost then through the North and Midlands into Humberside in a broad sweep through the country and over the day.

[Convective]

I also would of said southern areas are less likely to see the thundery activity..? Oh well, suns trying to come out here, strong and warm, heres hoping!

[Coast]

TORRO now the last ones to come through with:

TORRO TORNADO WATCH 2012/008 AND CONVECTIVE DISCUSSION 2012/016

A TORRO TORNADO WATCH AND CONVECTIVE DISCUSSION have been issued at 0800GMT on Wednesday 29th August 2012 Valid from/until: 0800GMT – 2359GMT on Wednesday 29th August 2012 for the following regions of the United Kingdom & Eire:

TORNADO WATCH:

Far eastern Eire N England Midlands SW England Wales

CONVECTIVE DISCUSSION

Much of Scotland IoM Central Eire N Ireland

THREATS

TOR WATCH: Tornadoes; hail to 30mm diameter; wind gusts to 60mph, CG lightning

DISCUSSION: Wind gusts to 50mph; isolated tornadoes; hail; CG lightning

SYNOPSIS

Large upper trough to the west of the British Isles will drift eastwards today. Ahead of this, a cold front is moving eastwards, followed by a well-mixed polar maritime airmass. A mixture of shear and curvature vorticity is enhancing shower activity within this airmass, with thunderstorms already detected. Along the cold front, some line convection has developed around SW England, and this may continue eastwards today, bringing some gusty winds and a small risk of a tornado.

Behind the front, numerous showers and a few thunderstorms are expected across most of the rest of the discussion area. Across central and south-western parts of the area wind shear will be sufficient for storms to organise into lines and perhaps supercells, with an associated wind threat. Reasonable low-level shear suggests isolated tornadoes will be possible too.

Elsewhere, whilst shear will be weaker, reasonable low-mid level buoyancy means strong storms are possible, although more of a pulse nature. Isolated tornadoes where low-level convergence develops will be possible.

[Kain]

Hmmmm, I would have said that was the lesser risk area of the day, but these guys have a better grip than I do! I still say Ireland, Scotland and West cost then through the North and Midlands into Humberside in a broad sweep through the country and over the day.

Agreed. Not entirely sure what they are seeing and we ain't, but I bow down to the experts I guess. I know it's bloody dark this morning and rarther muggy. I'll be glad when this front passes by so I can turn the livingroom light off!

Edited August 29, 2012 by Kain

[Coast]

MCS off the SW coast?

[Evening thunder]

ESTOFEX do partly have southern areas less likely to see thundery activity, see the 50% probability of lightning within 40km of a point misses the SE. They just suggest if something develops it will have a more favourable environment to do something severe. Still only 5% probability within 40km of a point looking at the key though.

Had some very heavy/torrential rain here a short while ago. Radar showed it even heavier to my north though I would expect the main thunderstorm risk to be further north today. Maybe one or two storms will get going over the SW peninsula this afternoon with some CAPE although maybe a less chance here than the ESTOFEX map suggests if I was predicting it.

[Lynxus]

I can only assume they are expecting convection behind the main band? To me that band doesn't seem too interesting... Well.. Nothing above the normal...

Edit:

yeah this looks most likely.

The showers/storms out in the sea between Wales and Dublin are showing some intense sferic activity.

Edited August 29, 2012 by Lynxus

[Darren Bown]

A couple of thundery showers in Wales now. Things are kicking off early, hoping they do as I have work at 130 til 1030 today.

[Nick F]

Have upgrade to a SLIGHT risk for Eire, S Scotland, Wales and much of England - see update in bold:

Valid: 29/08/2012 09:30 - 30/08/2012 06:00

Headline: ... THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FORECAST...

Synopsis

Deep upper trough to W of the British Isles Tues night will begin to shift eastwards across the UK on Wednesday. Surface depression to W of Ireland will drift NE and expected to be centred close to the N coast of Ireland around 998mb by 12z Weds, while associated occluding cold front lies Whitby - Bournemouth with unstable post frontal airmass following with troughs in the flow moving east.

*UPDATE 0930Z WEDS 29TH AUGUST*

Have issued a broad SLIGHT risk area to cover Eire, England, Wales and S Scotland. Linear convection has developed along cold front, risk of isolated lightning along with strong wind gusts and perhaps an isolated tornado exists with this convection.

Unstable polar maritime airmass following front will be conducive for numerous showers and thunderstorms to move northeast across much of the UK through the day. Organised band of storms are noted near/along short-wave trough approaching western mainland UK - pronounced dry slot overspreading western UK along with sufficient deep layer and low-level shear suggests organised bands of storms capable of producing strong wind gusts, hail to 2cm or more in size, flash flooding and also a threat of tornadoes where surface winds back ahead of troughs.

... PREVIOUS DISCUSSION ...

... ENGLAND, WALES, SCOTLAND and EIRE ...

Some potential exists for linear convection to develop with passage of occluding cold front which is indicated to be overlapped by fairly strong DL Shear (40-50knts) and low-level shear (15-20 knts) ... which suggests a strong wind gust threat and perhaps a tornado can't be ruled out. However, there is uncertainty over whether any strong/deep convection will occur - with GFS unkeen on the idea, so will not highlight a severe risk area.

Otherwise, post frontal airmass will be characterised by steep low-mid level lapse rates as colder mid-level air (at or below -20C) spreads in from the west with arrival of upper trough. Steep lapse rates, surface heating, large scale ascent and forced ascent near troughs will favour the development of widespread heavy showers and thunderstorms which will spread NE from fairly early on in the west across most areas by the afternoon following frontal rain pushing east. Overlap of strong jet stream across increasingly unstable post frontal airmass over England and Wales suggests storms could organise into bands - particularly near shortwave troughs moving in - with a risk of localised flooding from prolonged torrential downpours along with strong wind gusts and perhaps hail locally to 2cm or more in size with stronger storms.

Over Ireland, backing winds ahead of approaching surface low moving in close to the W/NW may enhance low-level shear with a tornado or two not ruled out with any stronger cells here.

[AWD]

Courtesy of Ian Fergusson:

http://t.co/v2mbbQ1n

UKMO-UK4 model of convergence zones 4pm; indicative of where heavy showers are more likely after AM rain clears:

[Jane Louise]

I can remember it was around this date back in 2003 we had quite a severe storm in Cheltenham. I wonder if this will be a repeat of then now that the storm-shield has broken here lol but the main thing is of course that everybody keeps safe whatever Mother nature throws at us.

[Chris K]

Will be interesting to see if anything develops. Although if it happens before 1600 I won't see anything, being stuck in this flourescent lit building of delight known as the office.

Edited August 29, 2012 by Chris K

[SalopWatcher]

Just to the north east of a storm over montgomoryshire ATM... suspect I just herd a distant rumble from it, but might just sweep to the west of me. Going very dark to the west.

EDIT - Defo louder rumbles from the west... pitch black sky..

Edited August 29, 2012 by SalopWatcher

[legritter]

think i will change my name from Legritter to Big spot ,WE HAVE VERY BIG SPOTS AGAIN ,GONE VERY DARK AND flat calm .main band of rain now moved away ,but some impressive clouds to my west .not expecting much till after mid day here ,but charts and data do look very juicy .some nice action building out west ,lets hope it holds together for later .cheers

[Karl83]

Courtesy of Ian Fergusson:

http://t.co/v2mbbQ1n

UKMO-UK4 model of convergence zones 4pm; indicative of where heavy showers are more likely after AM rain clears:

Is this good mate? My untrained eye says we may see a lil action today?

[BrickFielder]

Mixed bag of opportunities today making it difficult to predict.

Firstly the front is likely to be convective in the lower layers possibly leading to some line convection. The risk here would be for weak tornadoes due to the sheared environment. The problem is that mid level lapse rates do not steepen until after the front has passed, updraft strengths are likely to be modest due to lack of insolation. Main risk for me would be persistent heavy rain.

There is also a risk of a few back edge storms developing mainly across Wales and into Northern parts. Here mid level lapse rates are better but cloud cover will limit surface temperatures. The environment may be still relatively wind sheared so a weak tornado could not be ruled out.

I am just not that convinced that you will get too much apart from heavy rain from the frontal band.

There should be plenty of lift through the zero degree isotherm which might increase the hail risk.

Second possibility is post frontal storms developing. There is some evidence that this is happening but this is likely to affect more central and northern areas I think where lapse rates are highest. Wind shear drops off and you start to have problems with convergent winds aloft.

There is a suggestion of a trough on the fax charts and vorticity charts but it looks rather weak. Radar and Satellite pictures do show some potential though.

The third potential has a significant number of conditions which suggest a limited impact but is worth exploring a little. This is for central areas through the night.

There is a little instability, mid level lapse rates are still steep and low level winds show some veering.

Here is the problem though.

That is elevated convection and there is no real lift in the lowest layer. Mid level winds are weak suggesting those veering low level winds will make little difference. The risk here I think might be a bit of a lightning show and some slow moving heavy rain.

Its difficult to assess and you are better of watching the radar from here on.

[AWD]

Is this good mate? My untrained eye says we may see a lil action today?

I'm not too confident about anything today, think cloud cover maybe a problem for us here.

Chart above does show something of a channel streamer though. Worth just keeping an eye on the radar through the afternoon!

[windshadow]

No rain, blue sky with thunder..Very strange, although it is looking very dark over to sea.

[gottolovethisweather]

Some active cells which are producing sferics are chasing the frontal band across the country right now, currently heading into West Wales and other parts of the West. Also, to my eyes, there could be some convectiveness kicking in along the front, maybe, maybe not? This squall feature aforementioned will be shortly stretching North through North of Newbury down to the Isle of Wight and into the English Channel. I feel it may pep up as it heads further East.

Edited August 29, 2012 by gottolovethisweather

[joanna1971]

Wool woop seen my first two flashes of fork , black here but it's skirting to my west

[gottolovethisweather]

persisting down here now.

[SalopWatcher]

So frustrating, the cell went just to my west, skirting the town, but giving some brilliant loud booming thunder and a couple of flashes... a really low cloud at the centre of it all look menacing... now showing sferics on Netweather radar as it leaves town to the northish....

Closest strikes to me this year, at less than 9 miles away.

Start of things to come??

[gottolovethisweather]

persisting down here now.

A rain rate of 115.2mm/hr just achieved with 3.2mm falling between 1150BST and 1151BST, yikes!

[smoggyjester]

just got very windy and absolutely bucking it down

[Snowmadsam]

Thunder here now....dog freaked out (like scooby doo!)