Uk Convective General Discussion & Forecasts, 11th July 2012>

[Raidan]

Dry slot,just showers,living here that sounds spot on.

[Chris K]

I'm going to be pessimistic again and say our area around Bristol will be brewing the showers rather than seeing the thundery downpours. It's just one of the familiar types of set-ups again. Areas to our E, NE and SE look like having the better chance as showers will likely develop more as they head inland along convergence zones. Perhaps we MAY see something if showers started developing in Cornwall/Devon then head NE towards us?

By no means am I writing anything off - I'm just going with the dodgy gut instinct looking at the models and past similar set-ups. Certainly some areas may see some lively action! There is good potential there for most of Southern half of England and it will be a case of watching the radars and skies during tomorrow. Good luck to those living away from this impenetrable storm bubble.

Who knows we might finally see something here in Bristol/South Glos, but I'm not interested until I see stuff happening on radar!

[Harry]

Tomorrow will very much be a wait and see day IMO...some will get slammed and be in for a right treat...others will get sod all.

If anyone gets what I witnessed yesterday evening, you'll be most satisfied

[Keraunic]

Ipswich didn't even get a snifter on Wednesday even though it looked good at times. Ah well, tomorrow is another day......again.

[Chris W]

Looks like maybe there's a chance here tomorrow from the 12z GFS, we'll see - ever the optimist! I also see there's been something mildly stormy crossing the Lleyn Peninsula into Gwynedd tonight.

Edited July 12, 2012 by Chris W

[East_England_Stormchaser91]

Next week could be looking better, as there looks to be some heat possibly building. Heat is the key ingredient to get fierce, proper storms on the go.

[Harry]

Next week could be looking better, as there looks to be some heat possibly building. Heat is the key ingredient to get fierce, proper storms on the go.

Of course heat helps (enables higher moisture content) but its not THE critical ingredient IMO.

Dry air sitting on top of heated, humid air, followed by a trigger to cause explosive Cb development, finished off with a nice, well sheered atmospheric profile....now that's lush!!! Often, plumes we get lack sheer and we often lack triggers.

Fingers crossed for a repeat of 28th June

[Norfolk Sheep]

Ipswich didn't even get a snifter on Wednesday even though it looked good at times. Ah well, tomorrow is another day......again.

Once again I think EA will have to be satisfied with "showery bursts of rain" which will become fully blown TS when they hit the coast and naf off into the N Sea I would say August is usually a better month but it hasn't been for the last 4 years

[SimonP]

Regarding Friday's potential, UKASF have gone with a moderate risk:

Synopsis:

On the forward side of a marked upper trough, cool mid-levels will overspread an area of high WBPT and ThetaE. Consequently, destabilisation will occur under any prolonged insolation, leading to scattered or organised convection.

Discussion:

... E WALES, S MIDLANDS, HOME COUNTIES, LONDON, E ANGLIA, SE ENGLAND ...

A marked low-level convergence is forecast along the surface low axis in a WNW-ESE orientation. As a result, a line of heavy showers and thunderstorms will develop where any insolation can allow CAPE values of ~700J/kg to occur. It is along this line that the greatest sferic activity is expected, hence a MDT threat level for coverage.

During the afternoon this line will very slowly drift southwards, but due to the very slow storm motion and PWAT ~25mm, flash flooding is a distinct possibility locally given the already saturated ground. Despite rather weak shear, given low LCLs (dewpoint depressions typically only 2-3C) a few funnels or weak CZ-type tornadoes may occur. Slight dry air aloft may allow some small hail to fall in any stronger cores.

This line is likely to persist well into the evening hours, although diminishing CAPE as a result of falling LSTs will probably result in a decrease of sferic activity.

... SW AND CS ENGLAND, WEST COUNTRY ...

To the south of this marked convergence, a few scattered showers and thunderstorms are likely to form with 600-800J/kg CAPE. Depending on insolation and local seabreezes, another low-level convergence may allow a separate line of showers/storms to form from the SW peninsula towards the M4 corridor, in a WSW-ENE orientation.

Slow storm motion and PWAT ~25mm will increase the risk of local flooding from prolonged downpours, while small hail is likely in any stronger cores.

... ...

Main concerns are excessive cloudiness, and hence lack of any sufficient insolation. Also, the exact positioning of convergence zones may differ slightly in reality compared to current NWP due to the final position of the associated surface low.

In addition, ESTOFEX have included a chunk of the UK under a 15-% thunderstorm area, and have included the following text:

... Rest of the lightning areas ...

Weak shear and low to moderate SBCAPE allow scattered to widespread showers and thunderstorms (pulsating) to evolve during the daytime hours. Main hazard will be heavy rain due to slow storm motion. LL moisture values not excessively high, but especially over C-UK, backbuilding activity is possible. For now, no level 1 was included.

Next to the aforementioned risk, marginal hail and strong wind gusts accompany strongest storms.

Full UKASF forecast can be found here: http://www.ukasf.co....m-forecasts/194

Full ESTOFEX forecast can be found here: http://www.estofex.o...ormforecast.xml

Edited July 12, 2012 by SimonP

[Norfolk Sheep]

Ha ha! Norwich out of the risk zone, quelle surprise!

[SimonP]

Since my last post, Estofex have updated the forecast slightly - now placed CS England under a 50% thunderstorm area and updated the text to read:

... Rest of the lightning areas ...

Weak shear and low to moderate SBCAPE allow scattered to widespread showers and thunderstorms (pulsating) to evolve during the daytime hours. Main hazard will be heavy rain due to slow storm motion. LL moisture values not excessively high, but especially over C-UK, backbuilding activity is possible. Low LCLs and enhanced backing along a strong convergence zone may assist in a few funnels/isolated tornado reports over C-UK (mainly within the 50% lightning area). For now, no level 1 was included.

Next to the aforementioned risk, marginal hail and strong wind gusts accompany strongest storms.

Edited July 12, 2012 by SimonP

[AWD]

Good start to the day here, plenty of broken cloud and sun is now shining high. We have all the ingredients here today, so if we don't get it today, then we won't get it!!

[Nick F]

Valid: 13/07/2012 07:00 - 14/07/2012 00:00

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

Synopsis

A large upper vortex covers much of NW Europe, with cold pools and various troughs in its circulation. At the surface, a shallow low pressure system lies across S England during Friday.

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

Unseasonably cold mid-levels coupled with surface heating of a moist boundary layer will again create steep lapse rates across England and Wales. Increasing cloud breaks/insolation will help destabilise the airmass further through the day and will likely yield around 400-800 j/kg SBCAPE - so scattered thunderstorms are likely to develop. Vertical shear will be rather weak, so storm will generally be dis-organised - however, a wind convergence zone is indicated from N/mid-Wales across The Midlands to East Anglia this afternoon, so storms may organise and back-build along this zone and pose a threat of prolonged downpours with a risk of localised flooding. Storms may also be accomapnied by isolated moderate-size hail and gusty winds. A few funnels or even an isolated tornado can't be ruled out along the wind convergence zone.

Issued by: Nick F - Forecaster for Netweather

[Raidan]

Expected to wake up to a overcast sky this morning but as AWD has said the sun is out and clear skies,I'm still going for a no show of storms but a good start to the day and a little bit of excitment creeping in.

[Karl83]

Come on Bristol, make it our turn today! Nice to see the sun again!

[Coast]

Since my last post, Estofex have updated the forecast slightly - now placed CS England under a 50% thunderstorm area and updated the text to read:

A good place to start for today then.

... Rest of the lightning areas ...

Weak shear and low to moderate SBCAPE allow scattered to widespread showers and thunderstorms (pulsating) to evolve during the daytime hours. Main hazard will be heavy rain due to slow storm motion. LL moisture values not excessively high, but especially over C-UK, backbuilding activity is possible. Low LCLs and enhanced backing along a strong convergence zone may assist in a few funnels/isolated tornado reports over C-UK (mainly within the 50% lightning area). For now, no level 1 was included.

UKASF:

Synopsis:

On the forward side of a marked upper trough, cool mid-levels will overspread an area of high WBPT and ThetaE. Consequently, destabilisation will occur under any prolonged insolation, leading to scattered or organised convection.

Discussion:

... E WALES, S MIDLANDS, HOME COUNTIES, LONDON, E ANGLIA, SE ENGLAND ...

A marked low-level convergence is forecast along the surface low axis in a WNW-ESE orientation. As a result, a line of heavy showers and thunderstorms will develop where any insolation can allow CAPE values of ~700J/kg to occur. It is along this line that the greatest sferic activity is expected, hence a MDT threat level for coverage.

During the afternoon this line will very slowly drift southwards, but due to the very slow storm motion and PWAT ~25mm, flash flooding is a distinct possibility locally given the already saturated ground. Despite rather weak shear, given low LCLs (dewpoint depressions typically only 2-3C) a few funnels or weak CZ-type tornadoes may occur. Slight dry air aloft may allow some small hail to fall in any stronger cores.

This line is likely to persist well into the evening hours, although diminishing CAPE as a result of falling LSTs will probably result in a decrease of sferic activity.

... SW AND CS ENGLAND, WEST COUNTRY ...

To the south of this marked convergence, a few scattered showers and thunderstorms are likely to form with 600-800J/kg CAPE. Depending on insolation and local seabreezes, another low-level convergence may allow a separate line of showers/storms to form from the SW peninsula towards the M4 corridor, in a WSW-ENE orientation.

Slow storm motion and PWAT ~25mm will increase the risk of local flooding from prolonged downpours, while small hail is likely in any stronger cores.

Main concerns are excessive cloudiness, and hence lack of any sufficient insolation. Also, the exact positioning of convergence zones may differ slightly in reality compared to current NWP due to the final position of the associated surface low.

No updates from SkyWarn or TORRO yet today, so on with some charts:

Interesting crossover in the South according to the aviation chart this morning:

GFS has performed reasonably well this last couple of weeks, here is their take on today from Lightning Wizard:

CAPE through the central band:

Shear along the Channel coast:

Convergence right through the home counties and into EA:

Terrific rain through France!

SBCAPE and spout zone features through that central band again:

Low level apse rates highlight a watch area for me:

France is messy as hell today!

But do we also get some action?

In the simple overview from GFS, if you want thunderstorms, here's where they think you should get them:

Anywhere in a 50 miles radius of London maybe today then? (maybe stretching that a little West and East during the day?)

[Norfolk Sheep]

Why is there a patch of drizzle right over my postcode? Did I do something wrong in a past life?

[Lynxus]

Good luck everyone.

While im slap bang in some warning areas im not expecting anything as gloucester seems to have a great way of displacing any approaching storm.

stay safe

Warm and sunny here at the moment. Blue skies.

Edited July 13, 2012 by Lynxus

[richep]

I'm willing to put money on Somerset missing out on any storm activity today. Too far west I think, as per usuall .!.

[SteveB]

I'm willing to put money on Somerset missing out on any storm activity today. Too far west I think, as per usuall .!.

Agree, not a chance in hell for us today.

[Cloudwatcher]

Not going to get anything here today. Day has started cool, overcast with 100% cloud cover that looks like its in for the day.......and drizzle. Lots of drizzle!

[NO LONGER POSTING]

Sunny here and clouds already bubbling up!

[SimonP]

Thanks for the usual charts, Coast! Always good to see.

Here's another forecast, this from Tony Gilbert over at UKww:

Moderate Risk of Scattered Thundery Showers 12Z-21Z all central and Southern UK regions

Prime Risk CG's and Slight Risk of Funnel Cloud/ Weak Tornado Development.

Following on from Paul's forecast and in agreement.

Confidence Level; Medium

Low pressure moves slowly eastward with deep upper trough gradually overspreading region through the afternoon and evening. Occluded front and surface trough to the south expected to initiate rain and convective showers across many parts within the white box zone today.

A weakly sheared environment right across the board today though with a line of strong convergence marked yellow box running from N.Wales through to Essex expected to initiate lift and low level vorticity with the chance of one or two FC events possible. GFS now predict dry mid level incursion across central region. This may increase buoyancy of any lifted parcel later today around N.Hants and Cambs region. Though some concerns today regarding solar heating as according to WRF a thick layer of elevated cloud expected to move north from the continent reducing surface temps.

All in all this outlook has some specific detail which could undermine the results and my posting is only now added due to the forecast dry incursion which was not there last night. Additional concerns regarding how much instability will develop along the expected line of convergence today. Though, it should be noted that the forecast convergence vector looks optimised to create the best chance for close nit circulations! Some scope for continued storms Southern coast up until mid night as further convection possible along English Channel.

Still quite overcast here at the moment; hoping lack of insolation isn't going to be an issue. Plenty of time, however!

[legritter]

I'm willing to put money on Somerset missing out on any storm activity today. Too far west I think, as per usuall .!.

i was thinking the same 30min ago ,sun was out ,and sat having first fag and coffee ,had a gut feeling that somerset would be the breeding ground again .hey bingo black as night and light rain ,wind gone flat ,the potential is there im sure ,the trigger could come this afternoon .im confident the weather will be making the news later but moth nature only knows at present ,bring it on . i think today just wont be cells forming with heavy downpours but organised areas of hvy rain ,would love to be a fly down at exeter met office ,i can tell you from wording of todays forecast ANYTHING IS POSSIBLE CHEERS LEGRITTER N SOM .

[AWD]

What started out as a sunny and bright morning as now turned progressively cloudier now. I can see areas just to the south of the main rain band doing well today, pretty sure it's not guna happen here though.