Uk Convective General Discussion & Forecasts, 16th August 2012>

[The PIT]

I can't see anything for the east tonight but it will be a good study for the rain shadow effect.

[Darren Bown]

It's still intensifying, seen the one flash earlier, but that was more than I expected!

[Supacell]

Has the netweather radar gone down?

EDIT: Back on now. Could have been my internet again.

Edited August 17, 2012 by Supacell

[IanR]

It's still intensifying, seen the one flash earlier, but that was more than I expected!

to be honest i didnt even expect anything electical, one flash is a bit of a joke though,ah well at least we got that 90 minute night distant lightning show on monday , cant see any more electrical here tonight, but on a rare occasion i could be wrong

[SP1986]

im sure im living in a bubble, I just havent seen these flashes.. not sure what's going on. Again there was rain, some moderate to heavy but no thunder or lightning. This summer is increasingly infuriating in terms of storms, for me.

[Tim B]

There's been some lightning here amongst this heavy rain over the last hour though it's not showing on the detector.

[shadowfax]

Absolutely torrential now, but no flashes or bangs!

[The PIT]

im sure im living in a bubble, I just havent seen these flashes.. not sure what's going on. Again there was rain, some moderate to heavy but no thunder or lightning. This summer is increasingly infuriating in terms of storms, for me.

Don't worry all they saw was fireworks from a distance. LOL.

[Allseasons-Si]

is that anoprop S of london in the channel or is there something developing?

[Allseasons-Si]

Don't worry all they saw was fireworks from a distance. LOL.

probably can see the lightning just off west of ireland lol,

[Allseasons-Si]

Ok,a broader picture,there is some nice radar returns SW of cornwall,no sferics as of yet but keep a peeping eye.

anyone in for a long night?

I ain't waiting for something not to happen tonight,off to bed to hopefully catch something early morning.

[Chris D]

I

I saw that too, I thought I was imagining it!

You're joking, I missed it!!! Dammmm

Well, at least its not struck my house lol.

Edited August 17, 2012 by Chris D

[Buckster]

18z seems to have pushed the action a bit further east and south for Sunday darn what a surprise

here's hoping for an improvement in the morning

[paul m]

Seems to have got warmer outside after the shower passed over

[Darren Bown]

It's so stuffy, the wind has completely stopped, another pulse of rain in SW but it's getting late.

[NorthNorfolkWeather]

absolutely throwing it down in biblical/apocalyptic amounts here right now - typical welsh weather

Sorry about the really late reply, but you'll know when it's biblical, it will flood in Merthyr

[NorthNorfolkWeather]

Is this a Pub run image or what, look at the LI

[AWD]

Is this a Pub run image or what, look at the LI

Just imagine a cold front sweeping in from the west against that!!!

Shame it is quite possible that for many, it will all go to waste though!

[AWD]

I have been asking my local weather forecaster, Ian Fergusson, what his/meto's views are on any potential storms this weekend on twitter.

Here is the Convo

Me - high Cape, high Theta plume, high Dewpoints, waving front somewhere around us, Meto see any chance of T-Storms this weekend?

Ian - yes jst been discussing all that issue in detail with UKMO. Interesting times

Me - anything interesting come from those talks?

Ian - Potential issues Sun re developments 4 W Country. Something of loaded gun set-up; expect AcCas showers AM, poss T-storms PM. Other key element for Sun is convergence zone forcing deep convection on N/NW flank of the heat low coming N out of France. This largely unmodified NAE 12z Sun frame hints at enhanced shower/storm threat v last model run: http://t.co/cBmpBvAS. On face value, dry lower levels in Sun profiles inhibit sfc convection but likely to moisten-up after AcCas plume showers.

[john pike]

updated fax chart for sunday 12hr

[AWD]

It's the area between the warm front and the heat low coming out of France that I think is the main focus for storm activity.

[IanR]

woken by a couple of flashes and rumbles here during the night, didnt amount to much though

[Supacell]

Using the GFS models: Not looking quite so good for today now for thunderstorms in England and Wales, although N Scotland still looking favourable for a while (moreso early in the day). There is some favourable CAPE elsewhere but looks like the cap will be too strong unfortunately. Not sure what the temperature would have to be to get through the cap, i would imagine the temperature required is higher the further SE you go (but even 30c which is forecast may be too low here). The really hot weather is confined to EA and the SE with temps of 21-24c across the rest of the country. Although feeling humid, i just don't think that will be high enough to spark anything today.

GFS seems to model some elevated storms moving into the SE overnight. The front also reinvigorates over the SW, but as with last night and yesterday, i do not see much sferic activity in this. I would imagine best storm chance would be in the SE and EA.

Tomorrow is changing all the time but looks to be a better chance for storms than today. Some models have the Midlands best, others the SE... so i'll wait and see.

Overall its complicated and perhaps i am a bit out of my depth trying to forecast. For this reason I am awaiting one of the more experienced and knowledgeable members to post up there thoughts before decided on whether to chase this weekend.

[Coast]

ESTOFEX have an area over the UK, but I'm not sure it constitutes anything to get excited about today?

Western Europe...

Some isolated high-based storms may develop very locally across eastern Spain. These should be isolated and non-severe.

Some mostly elevated convection may occur on the western boundary of the elevated mixed layer across the eastern Atlantic Ocean and Bay of Biscay offshore of France and Spain, and across Brittany. Coverage is expected to remain very low as a lift will be minimal.

Some surface-based convection may form during the day across Britain. Although the storms would develop in a strongly-sheared flow their development is uncertain enough not to warrant a threat level at this time.

UKASF:

Synopsis:

Sharpening upper trough will be present to the west of Britain as a thermal ridge builds to the east. In-between the two, a strong jet will be aloft with a waving surface cold front beneath, associated with a plume of very high ThetaE. Several foci for convection exist, with the most widespread sferic coverage expected over the N and NW of Scotland.

Discussion:

... N SCOTLAND ...

To the north of the waving cold front, with a rather slack surface flow, local convergence zones will form and a few showers and thunderstorms will develop. 600-800J/kg CAPE will provide the most frequent lightning over the NW Highlands, and possibly along the Moray coast where the best low-level convergence and DLS is present.

Dry air aloft will allow hail to fall in any stronger cores, potentially >1.5cm in diameter. PWAT in the upper 20s mm combined with slow storm motion may result in local flash flooding, but only after considerable moistening of the mid and lower layers has taken place since forecasting soundings are very dry. Showers/storms are expected to decrease in coverage and migrate eastwards during the afternoon hours.

... IRELAND, N IRELAND ...

A few hundred J/kg CAPE will develop in response to diurnal heating, allowing a few showers to form. Rather poor CAPE will result in weakly-electrified storms.

... ENGLAND, WALES ...

Along a waving frontal boundary, which is classified by a plume of high ThetaE, some occasional pulses of elevated convection may form, moving northeastwards along the front, which itself will migrate slowly eastwards during the day.

While up to 1000J/kg MLCAPE would allow elevated storms to become quite electrically active, the rather isolated and 'sporadic' nature of storm distribution due to local plume destabilisation means we are unable to highlight any specific areas for MDT coverage level. Also, PWAT is forecast to be up to 42mm, but rather dry mid and lower levels will require sufficient moistening for excessive rainfall to become a problem at the surface.

SkyWarn:

SKYWARN UK SEVERE THUNDERSTORM WATCH #051

ISSUED: 1310UTC FRIDAY 17TH AUGUST 2012 (GJ/GS)

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

MIDLANDS NORTHERN ENGLAND

IN EFFECT FROM 1310UTC FRIDAY 17TH UNTIL 1200UTC SATURDAY 18TH AUGUST 2012

SHORTWAVE ENHANCEMENT OF AN ACTIVE FRONTAL BOUNDARY WITH MOISTURE CONVERGENCE ENHANCING INSTABILITY IN A FAVOURABLE SHEAR PROFILE

THERE IS A POSSIBILITY OF SEVERE WEATHER AFFECTING THE INDICATED REGIONS IN THE TIME PERIOD SPECIFIED. THREATS WITHIN THIS WATCH INCLUDE, BUT ARE NOT LIMITED TO:

HEAVY RAIN...STRONG GUSTS...TORNADOES...FLASH FLOODING

DISCUSSION:

THERE IS GOOD MODEL AND AGENCY CONFIDENCE IN THE POSSIBILITY OF A SEVERE THUNDERSTORM-RELATED RISK THROUGH FRIDAY INTO SATURDAY. THIS WATCH IS INTENDED TO COMPLEMENT WATCH #050 FOR GENERAL RAINFALL ACCUMULATIONS. SATELLITE AND RADAR IMAGERY SUGGEST THAT BEHIND THE CURRENT RAIN MASS, CONVECTIVE ACTIVITY MAY BE MORE FRAGMENTED AND ISOLATED LATE AFTERNOON, EVENING AND OVERNIGHT, THOUGH IT MAY ALSO BECOME A TRAIN OR LINE-OUT OF CELLS. GIVEN DIRECTIONAL SHEAR BECOMES MORE FAVOURABLE AS A SHORTWAVE IMPULSE RUNS UP THE FRONTAL BOUNDARY, THERE IS A POSSIBILITY OF ORGANISED CONVECTION AND SOME ROTATION, LEADING TO POSSIBLE STRONG GUSTS AND TORNADOES WITH THE STRONGER UPDRAFTS AND HEAVIER CORES. INSTABILITY IS LIMITED BY CLOUD COVER, BUT ADVECTED PLUME AIR SOUTH OF THE BOUNDARY RISING INTO DEEP MOISTURE CONVERGENCE MAY HAVE SUFFICIENT POTENTIAL FOR VERY INTENSE RAINFALL IN A SHORT SPACE OF TIME, LEADING TO FLASH FLOODING AND EXCESS SURFACE WATER. THE SATURATED ATMOSPHERE MAY PRECLUDE A HAIL RISK, AND STIFLE LIGHTNING ACTIVITY EXCEPT WHERE FULL HEIGHT CUMULONIMBUS OCCUR. THIS WATCH MAY BE UPDATED OR UPGRADED. PLEASE MONITOR WEATHER AND TRAVEL INFO AS NECESSARY.

SKYWARN UK SEVERE WEATHER WATCH #050

ISSUED: 1145UTC FRIDAY 17TH AUGUST 2012 (GS/GJ/SM)

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

WALES SOUTHWEST ENGLAND NORTHWEST ENGLAND

IN EFFECT FROM 1200UTC FRIDAY 17TH UNTIL 1500UTC SATURDAY 18TH AUGUST 2012

ACTIVE FRONTAL ZONE WITH ALONG A VERY MOIST AIRMASS GENERATING SUBSTANTIAL RAINFALL

THERE IS A POSSIBILITY OF SEVERE WEATHER AFFECTING THE INDICATED REGIONS IN THE TIME PERIOD SPECIFIED. THREATS WITHIN THIS WATCH INCLUDE, BUT ARE NOT LIMITED TO:

HEAVY RAIN...PERSISTENT RAIN...FLASH FLOODING...RIVER FLOODING

DISCUSSION:

THERE IS INCREASING MODEL AND AGENCY CONFIDENCE IN THE POSSIBILITY OF A SEVERE WEATHER RISK THROUGH FRIDAY INTO SATURDAY. EXPECTED HEAVY RAIN INTO THE SOUTHWEST WILL BE FOLLOWED BY FURTHER PULSES OF HEAVY SHOWERS AS IT DRIFTS SLIGHTLY NORTHWARD ALONG A SOUTHWEST TO NORTHEAST AXIS. PERSISTENT RAINFALL GENERALLY SHOULD PROVIDE ACCUMULATIONS OF AROUND 20-30MM IN THE PERIOD, BUT A STRONG DEEP WIND FIELD BENEATH THE JET COULD ENHANCE THESE ACCUMULATIONS OVER HIGHER GROUND TO POSSIBLY ABOVE 50MM, SOME OF WHICH MAY BE IN HEAVIER BURSTS. AS A RESULT, SOME FLASH FLOODING IS EXPECTED WITH FURTHER POSSIBILITIES FOR CATCHMENT AND RIVER FLOODING WHERE OVER-SATURATION OF THE GROUND CAUSES RAPID RUN-OFF. THIS WATCH MAY BE UPDATED OR UPGRADED, FURTHER ALERTS ARE POSSIBLE. PLEASE MONITOR WEATHER AND TRAVEL INFO AS NECESSARY.

So anything from mild to wild?!!!! 21st OWS has it going straight over Scotland:

Aviation mid level chart has it everywhere else!

The band of CAPE through the top of the SE corner of England passing through London looks good:

The red dotted line here showing what may be the best area of potential?

with some chances of tornadoes or helicial activity of sorts?

Doesn't look particularly encouraging for thunderstorms though today:

[AWD]

An update from Ian Fergusson suggests "approx Gloucester into the Midlands" at threat of Sunday PM storms!

Lots of shear mid-levels upwards; potential for torrential downpours Sun PM but areal scope for these remains uncertain. Convergence the trigger, with added moisture on frontal boundary. Latest run consistent re threat approx Glos into Midlands.