Stormy Wednesday 15th August 2012

[Lynxus]

Rapid development over south wales now.

Shockingly fast to be honest.

[Paul]

Plenty happening today, so here are a few tools to keep you up to date.

Firstly Nick issued a detailed look at the storm risk overnight - he's forecasting a slight risk of severe storms in parts of England and Wales:

http://www.netweather.tv/index.cgi?action=convective;sess=

Rain radar (link works for both subscribers and free radar users)

http://www.netweather.tv/index.cgi?action=radar;sess=

ATD lightning detector

http://www.netweather.tv/index.cgi?action=lightning;sess=

[gottolovethisweather]

Sferics now just popped up over Waterford area in Southeastern Ireland, within the main rain band.

Edited August 15, 2012 by gottolovethisweather

[Coast]

Morning all!!!

I'll just round up what other dedicated sites are saying to kick off:

ESTOFEX have no forecast for Europe today, not sure if that's because they are waiting to see what's going on or not, but quite unusual considering? (All bold type has been emphasised by me)

UKASF go with a severe forecast:

Storm Forecast Severe

Forecaster: Dan

Last Updated: 2012-08-14 22:22:00

Valid: 2012-08-15 00:00:00 - 2012-08-15 23:59:00

Synopsis:

A deepening area of low pressure approaches from the Atlantic. Ahead of the cold front, strong WAA will allow a plume of significantly high ThetaE to advect northwestwards across the British Isles. There is potential for severe convection ahead/along the cold front.

Discussion:

A strengthening jet will move northwards across southern Britain, driving an active frontal boundary northwards as a surface low deepens to the southwest of Ireland. Within the warm sector, a substantial plume of very high ThetaE is expected, which should destabilise with the approach of the cold front.

As is often the case with frontal destabilisation in plume events, there is some uncertainty as to how widespread such convection will be. General thinking is along the cold front, with 40kts DLS and 30kts LLS, LEWP/bowing segments may form, with locally torrential rain and occasional lightning. With such shear values and substantial backing of surface winds, bowing segments would also be capable of producing a weak to moderate tornado. Rather saturated vertical profiles may inhibit frequency of lightning somewhat, hence only a SLGT for the majority.

If there is any sufficient insolation within the warm sector, it is possible that isolated convection may form ahead of the main cold front. If this is the case, then such convection may benefit from 700-800J/kg CAPE, coupled with ample shear and helicity with backed surface winds, and possibly resulting in a supercell capable of producing moderate hail and a tornado. However, this scenario is heavily dependent on sufficient cloud clearance, which is questionable.

Also, there are indications in most models of the eastern portion of the cold front becoming a zone of broken convection (mainly East Anglia and South East England), which would benefit better from ample shear and helicity to intensify into scattered thunderstorms or supercells, with a heightened risk of hail and a tornado. PWAT values of >40mm would be more than capable of producing local flooding from cell backbuilding.

The SVR has been introduced for excessive precipiation, strong gusty winds in downdrafts and the threat of a tornado (although spot locations will always have a low probability). Conditions will be monitored throughout Wednesday, and an update may be necessary.

SkyWarn:

SKYWARN UK SEVERE THUNDERSTORM WARNING #049

ISSUED 0815UTC WEDNESDAY 15TH AUGUST 2012 (GJ)

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

SOUTHERN ENGLAND MIDLANDS EAST ANGLIA NORTHEAST ENGLAND

IN EFFECT UNTIL 2100UTC WEDNESDAY 15TH AUGUST 2012

DESTABILISATION OF A STRONG PRE-FRONTAL PLUME WITH FAVOURABLE CONDITIONS FOR SUPERCELLS SEVERE THUNDERSTORMS ARE EXPECTED IMMINENTLY, OR OCCURRING, SOMEWHERE WITHIN THE INDICATED REGIONS IN THE TIME PERIOD SPECIFIED. THREATS WITHIN THIS WATCH INCLUDE, BUT ARE NOT LIMITED TO: HEAVY RAIN...FLASH FLOODING...STRONG GUSTS...MODERATE HAIL...FUNNELS/TORNADOES

DISCUSSION:

THERE IS GOOD MODEL AND PARTNER CONFIDENCE OF THE OCCURRENCE OF SEVERE THUNDERSTORMS THROUGH WEDNESDAY. THE APPROACHING COLD FRONT BEING OVERTOPPED BY THE NOSE OF A STRONG JET WILL ENCOURAGE DESTABILISATION OF A VERY WARM AND MOIST PLUME OF CONTINENTAL AIR. LOW LEVEL CONVERGENCE AND VEERING WINDS COMBINED WITH STRENGTHENING DLS WILL PROVIDE A FAVOURABLE ENVIRONMENT FOR WELL ORGANISED CONVECTION, WITH SUSTAINED SUPERCELLS POSSIBLE AHEAD AND WITHIN THE FRONTAL ZONE OVER THE WARNING AREAS. INSTABILITY ON THE ORDER OF 700-1000J/KG CAPE WILL GENERATE STRONG UPDRAFTS, MAKING MODERATE TO LARGE HAIL AND TORNADOES POSSIBLE RISKS. LATER IN THE AFTERNOON THE SURFACE FRONT MAY DEVELOP CONVECTION INTO A LEWP OR BROKEN BOWING SEGMENTS, WITH ATTENDANT WIND AND TORNADO RISK. EASTERN AREAS OF THE FRONTAL ZONE APPEAR MOST AT RISK, WHILE WESTERN ENGLAND MAY SEE SOME STRONG CONVECTIVE ENHANCEMENT OF THE FRONT. THIS WARNING MAY BE UPDATED. PLEASE MONITOR WEATHER AND TRAVEL INFO AS NECESSARY.

TORRO's forecast is dated yesterday but does include today's with the proviso, like all the others, of an update as things happen:

TORRO CONVECTIVE OUTLOOK issued on Tuesday August 14th at 12:50GMT

A rapidly deepening depression will approach south-western parts of the British Isles overnight, and will push a plume of moisture and reasonably steep lapse rates across many places on Wednesday. Wind shear will be sufficient for organised convection, especially across England and Wales. However, the evolution of the activity is unclear at the moment. If precipitation is widespread along the cold front (which seems quite likely given the strong ascent) then embedded thunderstorms, perhaps an MCS, with strong winds and heavy rain, seems likely. If there is a lot of frontal activity it may be than overall convection is rather limited.

However, if the activity is somewhat more broken then well organised multicells and supercells may develop, mainly across England, on Wednesday. A risk for severe winds and perhaps a tornado would exist, along with reasonably large hail.

Conditions will be monitored and a discussion or watch may be issued in due course.

21st OWS:

Aviation weather:

It might be a bit too close to start putting specific charts up as radar/detector viewing is probably order of the day now! I'll go and have a look anyway and might put up some interesting ones if they stand out!

Fingers crossed for stormy, but not damaging weather !!!!

[Stuart]

look like a lot going on today the rain wont get here tell later on this evening

[tara303]

Took the dogs for a walk at just after 6 this morning, the mid level clouds were lit from underneath, giving them an angry red glow, and it was completely still and ominous. A ver light breeze now, but feeling close an oppressive - anyone give a forecast for around the heathrow area???

[Methuselah]

Cheers for that, Robin...The excitement is building!

[twister2005]

Very stormy looking sky here today :-) maybe this is going the day :-)

[Bluebreezer54]

.....Give me strength!!....What a daft thing to post mate....There is plenty of interest, due in part to your 'heads up'...This specialist thread is proof of that!.... so with that in mind, get that bee out of your bonnet and start posting!!

I second that AJ. For what its worth I value Weather09's input as much as anyone elses.

In the meantime lets look forward to what are showing signs of being a few interesting days ahead.

[Nick F]

Sferics over Channel Islands and Cherbourg Peninsula near/along cold front, so definately some embedded storms possible as the front moves NE later this morning/afternoon across England and Wales. Alot of mid-level cloud in the warm sector across Sern England ahead of the front - so severe potential seems likely to be limited. However, sunshine across the Midlands, northern and eastern England could allow sufficient surface CAPE to build to allow some severe storms to develop this afternoon as forcing increases from the SW ahead of the front.

Have updated my storm forecast this morning with a few tweaks, but mainly the same as issued last night:

http://www.netweather.tv/index.cgi?action=convective;sess=

[jessandjon]

here in south cornwall all we have had is heavy rain not much wind just looks like an autunm day? so i take it there is no chance of a strom for me it will just blow over and the rest of you will get one

[smoggyjester]

the rain has just reached here quite light at the moment but the wind is picking up and the dark clouds have been replaced by a milky grey colour sky which seems to be getting a little darker

[Aaron]

Well the sun is shining here and it's a warm 19.5c, so that might aid things further on

[AWD]

It's quite a low for August!

Some very heavy rain over the South West now!

This from Matt Hugo

Edited August 15, 2012 by Active Weather Dude

[NorthNorfolkWeather]

It's quite a low for August!

Some very heavy rain over the South West now!

There are 2 beasts of lows on that chart, look at the one over Ukraine!!

Interesting discrepancies between national weather and local weather on BBC, National says just heavy rain for the East, Local news showed Storms.

Whatever happens, after 15:00 please, the Red Arrows are at Cromer carnival this afternoon.....

[Biggin]

Cloud cover not allowing sun to heat up my area atm

EDIT sun breaking through !!

Edited August 15, 2012 by Biggin

[TheToastPeople]

Dew point at 17c here and very humid, Got high hopes for today the charts are superb, such a beast of a system for the middle of summer! Cant decide if i should walk to a high point with the camera or hide away inside today!?

[DeepSnow]

Cloudy here, had some heavy rain a while ago but its stopped for now, don't think it will be too long before the main band of heavy rain is here although I doubt there will be much in the way of storms down here!

[Coast]

A few charts just to illustrate some of what might be about today, but to be honest, we are into radar territory now:

CAPE not exceptional on land, but other factors are probably at work today to give us an interesting period.

Shear on the edge cuts right through the UK as it circulates around the low:

Convergence all over the place:

Spout chances for later in the day and into tomorrow?

Of course, it's going to rain, a lot!!!!!! (maybe some hail too)

Streamlines:

Very messy and extensive shear maybe giving rise to a fledgling tornado or funnel?

and convective gusts across the West and South West

Good chances of MCS developing in the West and moving through?

Please keep everything crossed for the possibility of Tstorms!!!!!

10M wind in the SW late afternoon and Western Scotland late afternoon and maybe a while beyond that:

[Harry]

Storms already igniting over France...interesting indeed! So so so upset I'm going to be in meetings between 1pm and 2.30pm today....the window when if anything is likely to happen, it will!!!!!!

[jessandjon]

i wonder if the lightning i see in the channel will reach plymouth

[smoggyjester]

rain now getting heavier

http://www.isleofwightweather.co.uk/live_storm_data.htm

lightning getting going over the channel too

Edited August 15, 2012 by smoggyjester

[Coast]

Sferics on their way, will they get to us on the South coast this morning?

[smoggyjester]

Sferics on their way, will they get to us on the South coast this morning?

i do hope so

[Walkinglad2013]

Sky looking very tropical this morning but very sunny and hot in Leeds.

Temperatures are soaring in West Yorkshire.

Very high humidity. Some cumulus and high level cloud developing.