Uk Convective General Discussion & Forecasts - May 2012

[Coast]

Morning storm fans!!!

More pictures from me this morning and ESTOFEX to start off:

Storm Forecast

Valid: Mon 30 Apr 2012 06:00 to Tue 01 May 2012 06:00 UTC

Issued: Sun 29 Apr 2012 23:03

Forecaster: TUSCHY

A level 1 was issued for far SW/W-Germany, far NE France, Belgium, Luxembourg and parts of the Netherlands mainly for large hail and strong to severe wind gusts. An isolated tornado event is possible mainly during the evening hours.

A level 1 was issued for parts of CNTRL France mainly for large hail and strong to severe wind gusts. An isolated tornado event is possible.

SYNOPSIS

Large-scale cut-off low is situated over W-Europe with high pressure to the east. Lowering 500 hPa height levels occur over most of CNTRL Europe with increasing probabilities for isolated DMC even beneath the western fringe of the ridge. Progressive wave train of upper troughs still affects far N-/NE Europe with unsettled and cool conditions.

DISCUSSION

... Germany, Benelux, NE France and S-UK ...

20 Z synop data places a tongue of augmented LL moisture just south of the stalling warm front over N-Germany with readings in the lower to mid tens. This air mass advects to the SE in response to a weak thermal low, which drifts to NW Poland during the forecast. Best moisture will reside over Poland, the W-Czech Republic and probably also sneaks into far S-Germany. For the rest, marginal BL moisture with readings of 6-9 °C are expected during the forecast. However, outflow boundaries from convection of last night and other convergence zones on the mesoscale may serve as foci for better dewpoints. Impressive EML plume, which affected CNTRL Europe during the past 2 days, starts to fan out to the N/NW with diminishing intensity. Hence, final CAPE dispersal will be messy with most robust build-up along the moisture axis from Poland to S-Germany. 500 to 800 J/kg MLCAPE are possible with significantly lower values to the west. Again, better LL moisture/CAPE exists over Belgium.

UKASF going with:

Forecaster: Dan

Last Updated: 2012-04-29 21:52:00

Valid: 2012-04-30 00:00:00 - 2012-04-30 23:59:00

Areas Affected:

SLGT: N, C + E Wales, Midlands, Home Counties, SE + CS England

Synopsis:

A vertically-stacked area of low pressure will become centred to the southwest of the British Isles, developing an easterly flow from the continent.

Discussion:

Rising LSTs as a result of diurnal heating, with -24/-25C at 500mb, will result in a few hundred J/kg CAPE. Consequently, a scattering of showers is expected across parts of the Midlands down to the SE, drifting slowly westwards into Wales/West Country towards the evening. It is possible given ELTs down to -40C for sferics, especially given some 25kts LLS and 30-40kts DLS which should allow cells to become organised for a time later in the day, with a heightened chance of perhaps a funnel or tornado developing.

Given PWAT of 16-18mm, there is likely to be some slow-moving heavy downpours. Hail up to 1.0cm in diameter is possible in stronger cells, with convective gusts potentially >35kts. These showers/storms will gradually decay during the evening hours as they continue to drift ever further west/southwest-wards.

Attention thereafter turns to northern France/Belgium as an approaching developing front advects some much higher WBPT westwards across southern Britain on Monday night, increasing moisture convergence. Scattered thunderstorms are expected to develop over these areas late in the afternoon and evening hours, forming multicell clusters and drifting gradually W/NW'wards towards southern Britain throughout the evening. While sferic activity may be high over France/Belgium, as they begin to cross the English Channel/southern North Sea with SSTs ~10C, it is quite likely that the resultant surface inversion will result in such storms becoming rapidly elevated, still with several J/kg MLCAPE initially, but eventually losing the majority of sferic activity as vertical profiles become increasingly saturated.

As a result, most storms will begin to merge into a large area of heavy rain, and given advection of high PWAT this will result in heavy downpours increasing the risk of local flooding given the already saturated ground. There is some considerable model disagreement on areas most prone, but the general consensus appears to be Kent/Sussex and Hampshire northwards into Essex and Suffolk through the late evening and overnight period. Given the elevated nature, this limits the potential for severe weather somewhat, despite significantly high values of shear and helicity over East Anglia in particular.

With an ever-changing forecast with regards to Monday night's event, we may issue an update if necessary.

SkyWarn still have a forecast in operation from the weekend which doesn't cover tonight yet:

SKYWARN UK SEVERE WEATHER WARNING #015

ISSUED: 1730UTC SATURDAY 28TH APRIL 2012 (GJ/SM)

SKYWARN UK HAS ISSUED A SEVERE WEATHER WARNING FOR THE FOLLOWING REGIONS:

ENGLAND

WALES

CHANNEL ISLANDS & IOM

IN EFFECT UNTIL 1200UTC MONDAY 30TH APRIL

DEEPENING BISCAY LOW OVER W FRANCE BRINGING A WARM OCCLUSION WITH HEAVY PRECIP AND GALES NORTHWARD

SEVERE WEATHER IS EXPECTED IMMINENTLY, OR OCCURRING, SOMEWHERE WITHIN THE REGIONS INDICATED. THREATS WITHIN THIS WARNING INCLUDE, BUT ARE NOT LIMITED TO:

HEAVY RAIN...FLOODING...STRONG WINDS...DAMAGING GUSTS

DISCUSSION:

THERE IS STRONG MODEL CONFIDENCE OF A SEVERE WEATHER RISK THROUGH SUNDAY INTO MONDAY. A LOW PRESSURE DEEPENING TO ~990MB FROM W FRANCE INTO THE SW APPROACHES WILL ENTRAIN VERY WARM AND SATURATED AIR FROM THE CONTINENT, WITH PRECIPITABLE WATER VALUES OVER 2.5CM. AS A RESULT RAINFALL ACCUMULATIONS OF UP TO 40MM MAY BE POSSIBLE, PERHAPS GREATER OVER HIGHER GROUND WHERE ENHANCED BY GALE FORCE WINDS. INTENSE RAINFALL IS EXPECTED ACROSS SOUTHERN, CENTRAL AND EASTERN ENGLAND DURING THE MORNING AND OVER HIGHER GROUND OF NORTHERN ENGLAND THROUGH THE AFTERNOON, WITH GENERAL ACCUMULATIONS OF BETWEEN 20MM TO 40MM. SOUTHWEST ENGLAND AND WALES MAY SEE SOME VERY INTENSE RAIN DURING THE EARLY HOURS, WITH PERSISTENT BOUTS OF CONVECTIVELY ENHANCED RAINFALL THROUGH SUNDAY PROVIDING 30MM GENERALLY. AVERAGE WIND SPEEDS THROUGH THE MORNING WILL BE AROUND 40MPH ACROSS WALES AND THE SOUTHERN HALF OF ENGLAND, WITH 50MPH POSSIBLE OVER HIGH GROUND AND EXPOSED COASTS, CONTINUING BUT WEAKENING FURTHER NORTH IN ASSOCIATION WITH THE FRONT INTO MONDAY MORNING. FURTHER GALES ARE POSSIBLE FOR THE CHANNEL ISLANDS LATER SUNDAY INTO MONDAY. CONVECTIVE ELEMENTS WITHIN THE FRONTAL ZONE ACROSS WALES AND SOUTHWEST ENGLAND MAY ENCOURAGE POTENTIALLY DAMAGING GUSTS UP TO 70MPH LOCALLY. OWING TO THE INTENSITY OF THE OCCLUDING FRONTAL SYSTEM OVER THE EASTERN SIDE OF THE WARNING AREA, SURFACE AND CATCHMENT FLOODING IS POSSIBLE. PERSISTENT SHOWERS OF HEAVY RAIN OVER WESTERN AREAS MAY LEAD TO MORE PROLONGED RIVER FLOODING AND FLASH FLOODING DISRUPTING INFRASTRUCTURE. PLEASE MONITOR WEATHER AND TRAVEL INFO AS NECESSARY. THIS WARNING MAY BE UPDATED.

Let me dig out a few more charts and see if we have any potential for tonight and into tomorrow!

[BrickFielder]

I think Estofex largely have it right today when they say.

S-UK was not added to the level 1 due to ongoing concerns of limited CAPE, as clusters of showers/embedded thunderstorms may decrease insolation/diabatic heating. A few marginal hail events are possible. If stronger diabatic heating occurs, the risk of an isolated tornado increases during the evening hours as LL shear intensifies.

Cape is not that impressive and there is a risk of clouding over in the south east corner of the UK.

Forecast SkewT's do show some turning of the winds through the mid layers which would make a slight risk of super cell development if instability was higher.

Low level winds are just a little too brisk for tornado risk and I would see heavy showers being rather isolated. Some thing to watch might be a slight tongue of vorticity moving up from central France through central southern areas(suggested on the EUMET Satellite obversations), although this is likely to shift.

Biggest risk would be localised heavy rain and hail.

I am not quite sure what to make of overnight condiitions either. Surpisingly we may see some instability through the mid levels.

Fax charts show a mixture of frontal and trough conditions and since this is coming in over night we should not expect much in the way of surface based instability (Forecast SkewT's confirm this). Still there may be some surface based convergence which could play a part.

Based on that skewT you would suggest just very wet weather with some instability around the 500mb level but no real instability. The reason why I was looking at this was to see whether was a tornado potential. On the whole the whole thing looks more frontal than convective and it is unlikely to have the necessary updraft potential. Worth keeping an eye on though, as it is hard to predict.

Key risk though would be for very strong wind gusts,and localised flooding.

With trees heavy with leaf forecasters will be keeping a close watch on this.

[Jane Louise]

Hi all,

Here's a nice new clean thread to start off tonights potential it's all looking exciting for tonight. I even think I may stand a chance. Good luck everyone and don't forget to post up your pics.

[SP1986]

No chance of anything in the way of thundery nature here tonight, although there is further south.. the Met-office hint at it on their regional forecasts, yet I'm a little sceptical about their inclusion of the Northwest of England.

[SnowJoke]

Allready a few storms kicking off in the channel towards IOW & a couple of recent sferics to the SW of Swindon. Looks stormy outside, not in the way of dark clouds, but theres a strange sort of calm & alot of turbulence in the upper level cirrus layer which normally proceeds a summer evening & night of storms.

[Wilxy]

Hopefully that cell to my SE will produce some lightning and i might be able to get a good light show in the distance

[Andy Bown]

A very interesting evening with mid level cloud bringing sharp showery rain, warm rain too for a change!

Not at all surprised to see a potent looking cell around the Trowbridge area with the disturbed sky that's here now, just disappointed~

it didn't come 10 miles further South!

I think Salisbury Plain has helped generate the downpours and it gives hope for more interest as the evening/night continues.

[essex coast matt]

The stuff on essex coast looks worse then it is,under the red bit on radar but only light rain at mo here

[liambailey09]

Looks to be some altocumulus passing over, nice mackerel pattern in the sky. Don't won't to be too optimistic about tonights prospects, but it looks quite good for those on the south coast!

[essex coast matt]

modarate rain here now

[Snow and storms]

Sky going dark here now, not exceptionally dark though, just started with small burst of moderate rain, wind gradually picking up

[stormnut]

did look good to my south east. now just gloomy and surprisingly dry. heres hoping for tonight

[stormnut]

could someone please post a european radar. would love to see uf anything is heading this way. come on basildon.....lol

[chionomaniac]

Something building to my SE.

[SP1986]

It's getting windy here, and the rain will come later for sure, but up this way it is never going to be thundery, it rarely is from the southeast, plus it is cooling much too quickly to allow the effects of convection to be long lasting.

[Neilsouth]

could someone please post a european radar. would love to see uf anything is heading this way. come on basildon.....lol

http://www.meteox.com/h.aspx?r=&jaar=-3&soort=satradar

[Harry]

Definitely a muggy thundery feel! Steady rain atm with an iffy looking sky

[Jane Louise]

It's feeling quite stormy around here. very grey sky to my East. I have my eyes glued to the radar in hope that something appears tonight.

[viking_smb]

Only because you want a storm

[legritter]

just spent half an hour posting to a locked forum ,oh well , and i dont even know how to save it ,anyhow my son down in dorset says you can see sheet lightning out over the channel ,its flat calm here at the moment ,something brewing iv seen that sky many times before .im not going to stayed glued to the radar tonight as it nacks you out . i will leave window open a bit and if anything kicks off big time i will here it . i hope the flashes are bright enough and thunder loud enough to make our jackdaws down chimney go elsewhere . just noticed some good action coming in to wiltshire area ,all the best gang and enjoy it IF you get it CHEERS legritter .

[Lauren]

Could someone kindly post what the potential is and where please?

[Lynxus]

I got some darkening skies here!!!!!!

I think its due to t he sun going down though

Could someone kindly post what the potential is and where please?

the metoffice website have it pretty much spot on.

[Harry]

Could someone kindly post what the potential is and where please?

There's no specific post which summarises the chances.

Basically, for our area, the risk of thunder (of which I put at around 20-30%) won't be until later, perhaps between 00z and 04z.

A dynamic and complex atmosphere is overhead, with occasional electric bursts around Channel, with slightly more organised thunderstorms over C/N France. Pulses of moisture are likely to converge in the next few hours, forming an organised band of heavy rain, with some localised torrential downpours with the chance of embedded thunderstorms.

Risk extends from S Wales across the S Coast/M4 corridor region along to Kent/Essex, as far north as Suffolk/Norfolk.

The messages from amateurs to experienced professionals alike has been that this is a very complex setup. Potential thunder but by no means guaranteed.

Keep an eye out of your window this evening and see how things develop.

IMO, the skies have looked conducive for thunder for the past 2-3 hours so fingers crossed

[VillagePlank]

Well, Begium has finally kicked off with numerous cells initiated and forming cells that are producing lightning,

Looks about three to four hours away for the SE, and the track, at the minute is for Essex, and E Anglia. However, I would suspect, given the synoptics that this will veer further West as it approaches, thus hitting E Sussex, W Sussex, Kent, S London (etc) Almost certainly it may pass through and perhaps even head up to the E Midlands.

The moisture feed from this is advected all the way from under a cap hovering over Germany/Poland which is very favourable along with the strong shear and convergence over Benelux; storms will start dissipating (and losing strength) when you start to see cells fanning out. If you haven't had one by then, and the radar shows them the other side of the channel, you're pretty much out of luck. Inote that the cap has broken on the E German border which may mean that the moisture may get used up in situ, rather than advected to Benelux. I guess we shall see.

Happy hunting all

Edited April 30, 2012 by Boar Wrinklestorm

[Jane Louise]

Could someone kindly post what the potential is and where please?

Check out page 1 of this thread Lauren I've just moved the two forecasts that were posted up this morning from Coast and Brickfielder.