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

[Nick F]

A new thread as the other was running to 38 pages.

To start the ball rolling I have issued a forecast for today (below), looks to be some potential for storms across southern Britain today with passage east of quite an active occluding front this afternoon and evening ahead of slow moving but fairly deep low near Sern Ireland. I'm sure Coast will post up the other forecast available:

Valid: 24/08/2012 06:00 - 25/08/2012 06:00

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

Synopsis

A fairly deep depression just SW of Ireland will track slowly east today (Friday), associated occluding front will move east across England and Wales this PM, by 00z Sat the low around 995mb expected off SW Ireland with occluded front lying Anglesey to Suffolk.

... S IRELAND, S ENGLAND, WALES, MIDLANDS, E ANGLIA ...

Fairly moist boundary layer (dew points 14-16C) in vicinity occluded frontal zone, as moist Tm air is entrained into low circulation, is indicated by GFS to yield 300-600 j/kg MLCAPE during frontal passage across Sern Britain today PM. Dry air slot at 500mb indicated by GFS to over-run the frontal zone will further enhance convective activity. Embedded thunderstorms are therefore possible with passage of the front. Fairly strong low-level shear (20-25 knts) is indicated along with low LCLs (as low as 600m) in vicinity of front - so surface-based storms with potential to develop mesocyclones that spawn one or two tornadoes can't be ruled out - so have included a SLIGHT risk. Otherwise, storms may produce marginally severe hail, strong wind gusts and torrential downpours with a risk of localised flooding. Storms may continue overnight along southern coastal counties.

[Coast]

Owwww, do they mean us?

Storm Forecast

Valid: Fri 24 Aug 2012 06:00 to Sat 25 Aug 2012 06:00 UTC

Issued: Thu 23 Aug 2012 23:04

Forecaster: TUSCHY

A level 1 was issued for SE Ireland mainly for heavy rain.

A level 1 was issued for parts of W/SW UK and NW France mainly for a few tornado events, marginal hail and strong wind gusts.

SYNOPSIS

Brisk SW-erly flow pattern continues over most of W/C-Europe. This assists in the set-up of an active baroclinic boundary, which runs from S/C France to Poland. Numerous disturbances graze that boundary and cause scattered to widespread thunderstorm initiation. Hot and dry conditions prevail over the Mediterranean. A strong depression enters the forecast area from the west with unsettled conditions affecting Ireland and UK.

... W/SW-UK, parts of Ireland and parts of NW France ...

A strong 995 hPa depression moves from Ireland to W-UK. Attendant well structured cold front enters the forecast area from the west during the day with a slow eastward motion forecast. A pronounced dry slot overtakes the cold front and assists in an active thunderstorm period mainly within the highlighted 50% lightning area. Those storms evolve within an environment with strong directional shear (e.g. 15 m/s LL shear and 200 J/kg SRH-1) and LCLs well below 1000 m. A few tornado events are possible next to strong wind gusts and marginal hail. The severe risk decreases after sunset although some surface based convection may persist over N-France. Strong shear still supports an isolated better organized thunderstorm event with strong wind gusts and an isolated tornado event. Hence the level 1 was expanded all the way to NE France.

An occlusion wraps around the depression's center with an augmented probability for training thunderstorm activity mainly over S-Ireland. Heavy rain will be the main hazard as modified subtropical air wraps around the center of the depression.

Well that backs Nick F's view and UKASF also going with:

Moderate

Forecaster: Dan

Last Updated: 2012-08-23 21:34:00

Valid: 2012-08-24 00:00:00 - 2012-08-24 23:59:00

Synopsis:

Upper trough approaches from the Atlantic, with a deep surface low at the surface. A plume of high ThetaE is advected around the centre of the low in associated with a cold front/occlusion complex. Some convection is expected embedded along and behind the front.

Discussion:

Cold front/occlusion migrates northwards and eastwards across England, Wales and Ireland with embedded convective elements likely. Favourable lapse rates and a few hundred J/kg MLCAPE may allow some sporadic sferic activity to occur, more likely over SW England, S Wales and S Ireland.

20kts DLS and >25kts LLS may allow some line convection to occur along the front, and with backed surface winds a funnel or weak tornado is possible, especially along the south coast where backed winds are heightened due to the onshore component. Hail up to 1.5cm in diameter is possible from stronger cores embedded within the line.

Scattered convective showers/storms are also expected behind the main front.

... S IRELAND ...

Behind the front, under the centre of the low with light and variable winds (and thus low-level convergence), >900J/kg CAPE is possible as cool mid-levels (-17/-18C at 500mb) overspreads the area. Sferic activity could be quite widespread here for a time during the afternoon and evening hours, provided there is enough insolation to generate surface-based convection. It is worth noting that the MDT is purely dependent on sufficient cloud breaks.

Hmmmm, some agreement then?! Nothing yet from SkyWarn or TORRO, here's a few charts to ponder:

There's that CAPE in the SW:

Just getting into the South and South East reaches by dark:

Note the hotspot over Portsmouth/IOW?

Not so much surface base CAPE:

Lapse rates are still up at 21Z

Plenty of rain!

Extensive tornado threat area!

Helicity right over the South coast:

Isolated thunderstorms in The Channel and over SW England (Come on Jane Louise!!!)

Still going up through the Midlands and heading NE into the night!

Time to update your radar subscriptions if you haven't already!!

Latest SatRep:

[Jane Louise]

Oh Coast, surely it has to happen for me today!this summer has been another let down for me. I almost took up stamp collecting lol. I must admit I do have a good feeling about today so once again it's fingers crossed and plenty of radar watching.I live in hope lol

[Stuart]

Good Luck jane this could be your day

[Jane Louise]

Good Luck jane this could be your day

Well, thank you kind sir. I really do hope so.It's been a long time lol.

[Paul]

A quick look at the nmm today show some fun and games are possible!

Heavy rain moving northeast

TT index indicating severe storms are possible.

Plenty of energy on offer

Will anyone get to see something like this?! (Photo by Dave Powell from day 1 of our Arizona lightning chase tour)

[Stuart]

after the weekend let down here i going give up for the year now

[TEITS]

Personally im looking forward to tomorrow when it looks as though widespread storms are possible. All im expecting today is a band of heavy rain moving across my region this evening.

[Nick F]

Been a few strikes down in Cornwall, so certainly some embedded strong convection in the rain band across the SW atm. Usual multiple stikes off the eastern England coast over the North Sea - don't know what it is about that area - but it seems to be a good place. Storm chase on a North Sea Oil Rig anyone?

[Supacell]

Will anyone get to see something like this?! (Photo by Dave Powell from day 1 of our Arizona lightning chase tour)

I would love it if I could get a capture like that.

Those NMM charts you show have the area of storm risk much covering a wider area and further north with things even flirting with my area by later this evening. I wasn't expecting north of about Worcestershire to Suffolk today but maybe I should start recharging my camcorder.

[Robbie Garrett]

Nothing thundery till tomorrow according to the latest TAF's for the Southeast.

[A.J]

yep, camera on charge currently.....I might slip out for a birthday chase today (I'm 21 for the second time, work it out ) so a big storm would round off the day nicely!

[Robbie Garrett]

yep, camera on charge currently.....I might slip out for a birthday chase today (I'm 21 for the second time, work it out ) so a big storm would round off the day nicely!

Happy 52nd Birthday aj

[Chris W]

I had a quick look this morning and it looks pretty good around here tomorrow in terms of CAPE/LI and the wrap-around occlusion passing over, added to the Met Office yellow warning and mention of thunderstorms for the North West. As for today it looks from UK Weather World's charts as if there's an area of CIN passing from Pembrokeshire in this direction later in the day - how much of a factor might this be in terms of storms making it to Cheshire this evening? Weather Underground has Chester slated for a thunderstorm late evening with an 80% chance of precipitation.

[Kain]

Happy Birthday Aj

Lets hope we get something today as a gift

[gottolovethisweather]

Happy Birthday Aj

Lets hope we get something today as a gift

How about this for AJ's birthday.

At risk of straying slightly off topic here so....... Back on topic, do you folk not think that the cloud detritus will affect the situation for storms, as I must say it's damn cloudy here and not excessively warm either.

[Staffordshire]

yep, camera on charge currently.....I might slip out for a birthday chase today (I'm 21 for the second time, work it out ) so a big storm would round off the day nicely!

happy birthday mate! hopefully the gods will give you somethong good hey... and that would mean getting me too maybe...

[Costa Del Fal]

yep, camera on charge currently.....I might slip out for a birthday chase today (I'm 21 for the second time, work it out ) so a big storm would round off the day nicely!

Happy Birthday mate! Have a good one and I hope Mother Nature delivers for you! She did for me on 28th June, 2 days before my bday!

[AWD]

Rain looks very showery in the SW/South Wales currently with the heavier, more organised rain in the channel heading for the South Coast!

[gottolovethisweather]

Happy Birthday mate! Have a good one and I hope Mother Nature delivers for you! She did for me on 28th June, 2 days before my bday!

And to think in past years, we use to get several 28th June's in one season. A different risk area to what we've seen in recent weeks so maybe it's the South and the Midlands turn for once. Mind you, I expect the Lincoln area will strike lucky for a change.

[Evening thunder]

Oh look, there's been a storm just sat in the North Sea for hours on end with seemingly not much CAPE there and average looking charts.. that's unusual!

[Eskimo]

The phenomenon known as North Sea Convection.

[East_England_Stormchaser91]

If only the North Sea fuelled us our storms like that all the time !

[gottolovethisweather]

I'm not quite sure but I think this little number approaching from the English Channel could be organising itself a wee bit more. Let's see what happens as it comes ashore. It certainly looks full of potential on the radar and the latest satellite image. Will this be interacting with any other usuable features such high cape, fronts etc. I estimate it affecting the Poole area within the next 20-30 minutes and should then trundle itself into other parts of Hampshire/Berkshire/Essex. Good lightning potential, surely?

[The PIT]

Mmmm looking like another possible dead duck. The front overall doesn't look very active but time will tell. Warming up her some convection going onnow whether this will do a local brew is another matter.