Convective / Storm Discussion - 5th August onwards 2013

[Nick F]

Storm & Convective Forecast - Issued 2013-08-12 08:47:27

Headline: ... THERE IS A RISK OF THUNDERSTORMS FORECAST ...Valid: 12/08/2013 0900z to 13/08/2013 0600z 

Synopsis

Broad upper trough covers the UK, North Sea, Low Countries and Scandinavia. Surface low pressure centred over Norway will pull an unstable northwesterly flow across northern Britain during Monday.

... SCOTLAND and N ENGLAND ...

Cold mid-level temps across N Britain (-20C to -25C at 500mb) creating steep lapse rates with surface heating and large-scale ascent will support the development of scattered heavy showers and thunderstorms across Scotland and N England this afternoon, the greatest risk of a thunderstorm probably towards the N Sea coasts. Vertical shear will be rather weak, so no organised severe weather is anticipated. Storms may produced localised flooding, hail and gusty winds.

Issued by: Nick Finnis

 

[alr1970]

There's a disctictly autumnal feel to the weather in Manchetser this morning, with a cool NWerly flow over the warm Irish Sea producing lots of showers over the region. Some sharp ones but all very brief as thery blow through.

[I Cumbria Marra I]

yesterday and today have been the most convective days this year lol, no thunder but a few heavy showers.

[Jax]

Storm activity this year seems a lot less than normal or is it just me?

[Summer Sun]

Apparently this is not Photoshopped!

 

 

http://www.nydailynews.com/sports/more-sports/lightning-strikes-bolt-reclaims-100-meter-title-article-1.1423894

 

Yep it true - http://www.bbc.co.uk/sport/0/athletics/23658871

[NL]

Just had a short sharp (ouch.!) shower, no rumbles of thunder as yet but I can see some large cumulus nimbus in the making just to the north-west of here.

[IanR]

Storm activity this year seems a lot less than normal or is it just me?

No its not just you at all, its been  THE worst ever this year, 2 thunder days in total here,,, well below average

 

someone mentioned 2010 being worse , well it wasn't here , one of the best storms in years happened that year. as well as as a few smaller 'thundery' showers

[Thundery wintry showers]

Some sharp showers here today and interesting Cb cloud formations, no thunder though.

[NL]

Three cracks of thunder heard but no lightning observed. Some impressive cloud structure here, even saw pileus cloud in some of the larger Cb's.

[Cloud 10]

Three cracks of thunder heard but no lightning observed. Some impressive cloud structure here, even saw pileus cloud in some of the larger Cb's.

 

 

Took this picture about 17.30 of a cell to my NE,which gave those rumbles.

 

[Allseasons-Si]

Evening all,hope you are all well,not been on for a bit

 

anyways,just found another video clip from my achives(11/03/2008),it's only a minute long but there is some nice booms off one lightning(TURN IT UP).

 

 

[Coast]

Three cracks of thunder heard but no lightning observed. Some impressive cloud structure here, even saw pileus cloud in some of the larger Cb's.

 

Took this picture about 17.30 of a cell to my NE,which gave those rumbles.

 

Looks like the little convective weather forecast for yesterday was in a bout the right spot then  

[Nick F]

Thursday shows potential for some warm airmass heavy and thundery downpours across Ireland, England, Wales, southern/eastern Scotland.

 

We pull in a warm and humid Tm airmass from the SW in a warm sector overspreading many areas which looks to become unstable to surface heating and with large scale ascent looking possible in the cyclonic flow - UKMO shows trough moving east across England and Wales:

 

 

GFS shows instability mainly across ireland and Scotland atm, but more widespread instability may develop over England and Wales too IMO.

 

Friday shows cooler but unstable well-modified Pm flow pushing east behind cold front clearing the SE in the morning, so storm potential likely across northern and western areas in particular.

Edited August 13, 2013 by Nick F

[Supacell]

Well this storm season so far has been characterised by a very quiet, uninspiring period up to mid July with very little storm activity and much lower than normal - actually the poorest start to a season I can remember. Then a very good active period from the 22nd July through to about the 5th August which brought almost daily thunderstorms (not always in the same place of course). Since then it has turned rather quiet and uninspiring again.

 

Although the storms I saw in that active 2 week period were quite special it would be nice to have a bit more before we head into Autumn. Thursday not looking so good to me now, with the best possibility of storms now transferring to Friday but this looks only a slight risk with the best parameters for storm development pushing off to the SE a little early in the day for my liking.

 

What we need is another reload of heat and sunshine (which we may get towards the latter third of August) and then another thundery breakdown (which we may also get) but for the reliable it still looks generally rather quiet convective wise.

Edited August 14, 2013 by Supacell

[Coast]

GFS, looking ahead to Saturday night into Sunday:

 

 

Dare it enter the Triangle of doom?

[Guest William Grimsley]

Thursday shows potential for some warm airmass heavy and thundery downpours across Ireland, England, Wales, southern/eastern Scotland.

 

We pull in a warm and humid Tm airmass from the SW in a warm sector overspreading many areas which looks to become unstable to surface heating and with large scale ascent looking possible in the cyclonic flow - UKMO shows trough moving east across England and Wales:

 

PPVJ89.png

 

GFS shows instability mainly across ireland and Scotland atm, but more widespread instability may develop over England and Wales too IMO.

 

Friday shows cooler but unstable well-modified Pm flow pushing east behind cold front clearing the SE in the morning, so storm potential likely across northern and western areas in particular.

I was questioning Thursday and Friday as being days of showers/thunderstorms! Especially Thursday with the humid air being drawn in in front of a weather front. Friday, is much fresher but still unstable like you said so there could be some more showers/thunderstorms then especially down here in Devon.

[Stuart]

Synopsis

Upper ridging exits across the North Sea, with a series of upper trough axes migrating eastwards across the British Isles through the forecast period. At the surface, a waving cold front will erratically move eastwards, with a warm, humid airmass advected across England and Wales within the warm sector, characterised by WBPT greater than 16C.

 

Discussion... N/NE SCOTLAND ...

To the north of the main waving frontal boundary, the left exit of the jet aloft combined with diurnal heating and shortwave troughing may allow a few scattered showers to develop, with perhaps one or two thunderstorms given several hundred J/kg CAPE and ELTs below -15C. Main focus is between 11z-20z.

... WEST COUNTRY, MIDLANDS, EAST ANGLIA ...

Within the warm sector, some insolation will generate a couple hundred J/kg CAPE, which combined with low-level wind confluence may allow a line of scattered heavy showers to form from the SW peninsula northeastwards across the northern Home Counties to northern parts of East Anglia. Instability is rather meagre, so it is uncertain how electrically active this convection will be. For now we remain with an ISOL to flag the potential.

... NORTHERN IRELAND, REPUBLIC OF IRELAND ...

During the afternoon and evening, a new frontal wave will track northeastwards across eastern parts of Ireland. To the north, and along the back edge of the cold front, some convection is possible with embedded thunderstorms in places. If any discrete cells can develop during the afternoon over Ulster then some small hail is possible in any stronger cores.

Increasing baroclinicity combined with 30-40kts DLS may allow convective cells to form more linear segments, perhaps developing into a QLCS or squall line for a time. Slightly curved hodographs with some low-level speed and directional shear combined with low LCLs suggest the potential for a tornado.

 

http://ukasf.co.uk/storm-forecasts/273

[Coast]

ESTOFEX missing us out completely today:

 

 

 

GFS showing something way up to the North of Scotland later this afternoon:

 

[Coast]

NMM has some CAPE and negative lifted indices across Northern England for much of the afternoon:

 

 

 

But the TT index coincides with GFS and has the potential right up in Northern Scotland:

 

 

 

 

 

 

 

[nitro_deluxe]

Certainly some very heavy rain expected in places today, whole area gradually sliding SE overnight into Fri am.

Unlikely to be sparky though...wish to be proven completely wrong of course.

[Supacell]

I think this evening and into the night deserves some interest for the NW of England, N Wales and possibly the SW of Scotland. Although I haven't the time to post all the charts the fronts moving in overnight develop a triple point which is currently moving towards the SW of Ireland and swings NE across Ireland and then the aforementioned areas of our mainland by this evening/early night time hours. This could be a focal point for some potentially severe weather.

 

Although SBCAPE is fairly poor, there is predicted to be around 30-40 knts of 1-8km DLS, plenty of helicity, deep parcel layer depths, high PWAT values (up to 40mm) and low LCL's all combining across the NW of England and N Wales in particular. This would bring a definite risk of organised convective activity accompanied by torrential downpours, especially in any convective pockets, but also the slight possibility of a tornado. There would be a risk of localised flooding and gusty winds but lightning activity, although not ruled out, would not be very prolific.

 

Main risk looks to be late evening/early night hours in the NW with the best parameters looking to separate as the frontal zone moves south and east.

Edited August 15, 2013 by Supacell

[nitro_deluxe]

Nice one ^

Showers really cranking up in places now, active looking area just offshore near Skegness at the mo.

[conor123]

Some heavy downpours just north of here causing howling winds at the moment, thundery look about them but moving fast and away.

[Stormraider]

Thought I heard a rumble from the shower to my north. Conor123 can you confirm?

[conor123]

Nope definitely no rumbles here, just the odd spot of rain.