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

[TEITS]

As I expected absolutely nothing here, infact I haven't even seen a drop of rain all day. Like I said this morning tomorrow is the day with potential and im really looking forward to it.

[LeeKay]

'Summer lightning' 40 mins ago, several flashes all with 15 mins or so.

Quite a few hefty downpoars too over the past 2 hours, looks like another one is heading on its way.

[NUT]

Fascinating again why it seems normally when it would be dying off the activity? seems to be increasing at end of the day! Been quite a trend that this summer

[Allseasons-Si]

It looks like lincolnshire is in the firing line at the minute lol.

Edit,it is throwing it down here,but no lightning.

Edited August 24, 2012 by allseasons-si

[matt_in_dudley]

'Summer lightning' 40 mins ago, several flashes all with 15 mins or so.

Quite a few hefty downpoars too over the past 2 hours, looks like another one is heading on its way.

No way! I missed it, i went to the gym lol!! Grrrr!!!

[AWD]

Bring on the storms!!!!!!

[Coast]

So, BH weekend and traditional weather to look forward to, but what's in store for storm fans today?

ESTOFEX say:

Storm Forecast

Valid: Sat 25 Aug 2012 06:00 to Sun 26 Aug 2012 06:00 UTC

Issued: Fri 24 Aug 2012 21:57

Forecaster: TUSCHY

SYNOPSIS

Embedded in a belt of agile westerlies, a strong mid/upper wave moves in from the west .... from the Bay of Biscay (start of the forecast period) towards W-Germany (end of the forecast period). At 500 hPa, no pronounced ridge signature is seen over Europe despite a warm anomaly over SE Europe, where stable and hot conditions prevail. Cooler air infiltrates towards N-Europe, where unsettled conditions occur.

The northern fringe of the Mediterranean marks the boundary between hot and muggy conditions to the south and cooler/drier air to the north. This boundary features an elonagted cold front, which runs from Belarus all the way to Portugal (with a wavy structure along the Alps and gradually dissolving over the Iberian Peninsula).

DISCUSSION

... Parts of the Ukraine and far S-Belarus ...

A warm sector stretches over the highlighted area. Attendant air mass is well mixed with a daytime driven lowering of surface dewpoints. BL moisture is maximized along the wave (cold front over W/NW Ukraine and warm front over N-Ukraine), where moisture pooling boosts surface dewpoints into the upper tens. An EML is situated atop the Balkan States all the way into the Ukraine. Overlap of the EML atop the aforementioned boundary layer moisture features roughly 800 J/kg MLCAPE in the warm sector and up to 1.5 kJ/kg MLCAPE along the boundaries. Not much background forcing is forecast, so CI will be bound to surface temperatures, exceeding the convective temperature threshold and the orography/boundaries. Hence, isolated CI is forecast in the warm sector with scattered CI along the boundaries itself. 20 m/s DLS and similar values in the lowest 3 km assist in well structured multicells/isolated supercells (due to locally augmented SRH-3) with large hail and strong to severe wind gusts. An isolated bowing segment with an enhanced severe wind risk is possible but weak forcing keeps this risk rather low for now.

... UK ...

With 500 hPa temperatures dropping to at or below -20 °C atop a moist maritime BL air mass assists in moderate SBCAPE of roughly 800 J/kg during peak heating. This amount of CAPE is enough to support a few strong and probably isolated severe thunderstorms with marginal (isolated large) hail and heavy rain. However it is tough to pinpoint the area of highest activity, as CI will be dictated by mesoscale features. Hence, no level will be added for now. Storms decrease in coverage and intensity after sunset.

UKASF:

Synopsis:

Sharp upper trough migrates northeastwards across the British Isles with a surface low tracking across central Britain. Within the central circulation, widespread showers and thunderstorms are forecast.

Discussion:

Wrap-around occlusion over northern and southwestern England will bring outbreaks of rain at times, with the potential perhaps for a few embedded thunderstorms.

General focus however will be within the central circulation of the low, beneath the upper trough. Cool mid-levels (typically -17/-18C at 500mb) combined with diurnal heating will result in locally >1000J/kg CAPE, with widespread showers and thunderstorms forming, the most frequent sferic activity being during the afternoon and early evening hours.

However, despite favourable lapse rates, with the jet over northern France there is rather poor DLS, and therefore cells may be rather unorganised, short-lived and thus resulting in 'pulse-type' storms. Best organised cells will be in areas with low-level convergence within the trough axis.

Some 20kts LLS combined with low LCLs (600m or so) may result in a funnel or weak tornado, especially within the vicinity of low-level convergence zones. As a result of poor DLS, hail is only likely in any stronger cores where updraft/downdraft separation is prolonged, with a local event potentially up to 2.0cm in diameter possible given dry air aloft.

Main severe weather is the risk of local flash flooding given PWAT values >25mm combined with very slow storm motion within the centre of the low. One main concern is rather excessive cloud cover in the low centre which may inhibit deep convection somewhat.

Nothing from TORRO or SkyWarn, here are the charts!

Widespread MLCAPE:

and SBCAPE with some spout activity:

Lapse rates OK, swirl of activity coming in up The Channel and through France:

Rain, more rain!

Some (low?) hance of a tornado in the SE?

Flow:

But what does it all mean? STORM CHANCES all day!!!?

[VillagePlank]

Estofex have a discussion open about the UK,

... UK ...

"With 500 hPa temperatures dropping to at or below -20 °C atop a moist maritime BL air mass assists in moderate SBCAPE of roughly 800 J/kg during peak heating. This amount of CAPE is enough to support a few strong and probably isolated severe thunderstorms with marginal (isolated large) hail and heavy rain. However it is tough to pinpoint the area of highest activity, as CI will be dictated by mesoscale features. Hence, no level will be added for now. Storms decrease in coverage and intensity after sunset."

It's not hard to see why [London, Heathrow]

Most of England are under moderately warm and moist theta-e, which gives the scope of the risk, I think,

Which areas are most likely to get 'lucky' ? Well, for a start, I think if you are close to the theta-e 40C line in the above chart you are in for a shot, today, but what else?

I'd have to say The West Midlands all the way East to East Anglia, perhaps down as far south as London, are the most favoured locations forecast This is by diurnal heating; other places may have other triggers (such as the North Down's giving orographic lift - so I am expecting some hefty showers, with some thunder mixed in today) A reasonable chance of some imports for the E Sussex (Hastings to Bournemouth) later in the day as Northern France, and particular the Channel will support offshore t/storms during this afternoon.

Almost everyone has a chance today, and, don't forget this forecast says where the storms will form, not where they'll end up. If I had to give it a guess - I suppose I would be travelling to Birmingham, today, but general indices support thunderstorms almost anywhere in England; perhaps not the far far SW, though, and north of Manchester.

Happy hunting,

Edited August 25, 2012 by Boar Wrinklestorm

[Coast]

Nothing yet, but plenty of rain on the way:

[VillagePlank]

Last nights Herstmonceaux ascent,

It seems to me that only the K-index on this 'prevented' some rather remarkable thunderstorms overnight. Once again, the 12z ascent will be essential viewing for those interested in the SE, today. Certainly a great way to start the day

Edited August 25, 2012 by Boar Wrinklestorm

[Coast]

Last nights Herstmonceaux ascent,

It seems to me that only the K-index on this 'prevented' some rather remarkable thunderstorms overnight. Once again, the 12z ascent will be essential viewing for those interested in the SE, today. Certainly a great way to start the day

Hmmm, don't remind me please BW!!!!!! Fingers crossed for a better day today and Herstmonceux is only 4 miles away from me!

[VillagePlank]

Hmmm, don't remind me please BW!!!!!! Fingers crossed for a better day today and Herstmonceux is only 4 miles away from me!

From what I can tell it looks like the lapse rate simply wasn't high enough (part of KI is the difference between 850hPa C, and 500 hPa C) GFS always seems to overcook KI, yesterdays 18z forecast was for KI = 26, when it ended up being less than 15.

[Harry]

Hmmm, don't remind me please BW!!!!!! Fingers crossed for a better day today and Herstmonceux is only 4 miles away from me!

Well I'm heading down to Dymchurch to spend time with the folks today.

Niggling feeling I would much better placed at home tody but hey ho, mother nature has been a largely perpetual disappointment for me this year so I'll be buggered if I'm going make my plans on the back of weather charts!!!

Good luck all!!

[Supacell]

Thick with fog here this morning, but from some of the models I am too far north today. However, some still have my area within the risk zone.

Currently no sferics on the mainland with just the odd one as the continuous thunderstorm over the North Sea clings on for dear life. Today is very hard to pick a target area for chasing as a very large area is at risk.

I want to chase today, and my kids want me to take them on their first storm chase, but having two kids with me I do not want to put them through the ordeal of travelling too far. For that reason I am thinking Lincolnshire/South Yorkshire as a possibility (although I am aware of the powerful storm shield that has plagued Lincolnshire this summer ).

[Stuart]

Good luck today all

[Nick F]

Valid: 25/08/2012 06:00 - 26/08/2012 06:00

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

Synopsis

Low over Wales will drift slowly east across central England on Saturday, clearing into the N Sea by 00z Sunday.

... ENGLAND, WALES, SW SCOTLAND and S IRELAND ...

Moist surface air (current dew points of 14-15C) circulating around low moving east across England today, cooling mid-level temperatures and surface heating will create steep lapse rates and an unstable airmass across much of the southern and central Britain today. GFS indicates 300-900 j/kg SBCAPE across a wide area of England and Wales, so surface heating will allow scattered, locally strong, thunderstorms to develop. Although deep layer shear will be weak, locally strong instability/updrafts may allow formation of marginally severe hail (perhaps >2cm) and the slow moving nature of storms over central and eastern England may bring the risk of localised flash flooding ... therefore have issued a SLIGHT risk of severe weather. Wind convergence indicated across the Midlands and eastern England this afternoon combined with light winds aloft and low LCLs may allow funnels or even a few weak tornadoes to develop. Storms will fade after dark with the onset of diurnal cooling

Also can be found here: http://www.netweather.tv/index.cgi?action=convective;sess=

[Kain]

Please tell me that ain't the same storm in the north sea chugging along from yesterday?! Blimey..

[Supacell]

Looks like winds are converging between Bradford and Manchester according to http://www.xcweather.co.uk/

And some showers breaking out in that area. Can the storms develop this early?

[The PIT]

Please tell me that ain't the same storm in the north sea chugging along from yesterday?! Blimey..

Err no. Radar doesn't shows two isolated strikes in North Sea so definitely not the same one from yesterday although that did chug around for a while. Weather here doesn't seem to know whether to go with convection or just fizzle out. Earlier heavy shower has now turned into steady drizzle.

[Staffordshire]

Looks like i could be in for a shot today! Apart from 30 secs laat night and about 2-3 mins last wednesday? i havent seen even heavy rain since june 28th let alone a storm so heres hoping!

[johnholmes]

The Watnall 00z suggests decent convection in this area with tops well into levels for at least a risk of TS?

[East_England_Stormchaser91]

Please tell me that ain't the same storm in the north sea chugging along from yesterday?! Blimey..

Did the fishermen invent some sort of widespread thermal heating in the North sea or something yesterday?! I have never seen a storm last that long out to sea, especially round here, they normally die as soon as they intercept the sea!

[East_England_Stormchaser91]

I can already see some beefy tops sprouting up already. Thought I heard sferics from that potent looking cell developing near Grantham, might just be other interference though.

[Kain]

Did the fishermen invent some sort of widespread thermal heating in the North sea or something yesterday?! I have never seen a storm last that long out to sea, especially round here, they normally die as soon as they intercept the sea!

No idea but it certianly lasted nearly all day! I wish we had them like that inland!

[Allseasons-Si]

Morning all

some nice convection going on around here and there is some nice towers developing to my south,

good luck all that catch a storm.

Edit,really dark to my south.

Edited August 25, 2012 by allseasons-si