Uk Convective General Discussion & Forecasts, 3rd July 2012>

[Jane Louise]

Well folks, looks like there could be a lot of fireworks in the coming days and not just for the 4th July !

So here's a new thread to start the ball rolling and I wish you loads of luck .. Also if like me, you don't get your storm then please head over to the 'No storms club' where you can rant and rave as much as you want! Now let's keep this thread cheerful as there's some good storm potential to look forward to. Keep safe and enjoy.

[Sainsbo]

Netweathers "Will it thunder?" is giving 60% for my town - There's hope! ;D

[SimonP]

UKASF's forecast is out for 4th July: http://www.ukasf.co....m-forecasts/188

... SCOTLAND, N ENGLAND, MIDLANDS, EAST ANGLIA ...

In the broad warm sector under a ThetaE ridge and behind an occlusion/ahead of a cold front, slight backing of surface winds will allow low-level convergence to occur. As a result, 500-700J/kg CAPE will generate showers and a few thunderstorms during the afternoon and early evening, in response to diurnal heating in a humid airmass.

ELTs down to -40C suggest convection will be deep enough for lightning, but very weak speed shear means that storms will be disorganised and pulse-type in nature, going through various phases of peaks and troughs in sferic activity, with some backbuilding likely at times. Current thinking is that these will be primarily inland, so some eastern coasts are likely to stay shower/storm free. Dry air aloft will also allow hail to occur in some showers/storms, perhaps a local event with diameter up to 2.0cm.

Given backing of surface winds, there exists the potential for a funnel or weak tornado, especially if any surface convergence develops. Also, a combination of slow storm motion and PWAT of up to 32mm could lead to local flooding from any prolonged heavy downpours.

Showers/storms will generally decrease in coverage and intensity during the evening hours as daytime heating subsides. Major concern is excessive cloud cover in a broad, moist warm sector which may inhibit insolation and subsequent convection...

... IRELAND, W NORTHERN IRELAND ...

Behind the cold front, cold mid-levels (~-22C at 500mb) will overspread Ireland under an eastward-moving upper trough, steepening lapse rates as diurnal heating takes place. Thus numerous showers and thunderstorms will develop with up to 900J/kg CAPE and ELTs down to -40C.

Very light, variable surface winds will result in slow storm motion, and with PWAT values around 24mm, local flash flooding may result from prolonged heavy downpours. Else, very weak shear will result in poorly organised convection, which will see showers/storms decreasing in coverage during the evening hours as diurnal heating subsides.

... KENT, EAST SUSSEX, EAST ANGLIA ...

Most models simulate advection of high WBPT and ThetaE during the evening/overnight hours from NE France/BeNeLux and across the North Sea, possibly grazing coastal portions of Kent and East Anglia. As such, MLCAPE values of 800-900J/kg may provide some primarily offshore lightning from elevated convection during the late evening and overnight period (beyond this forecast period). PWAT of ~36mm may cause a local flooding event in east Suffolk/Norfolk if any cells manage to move onshore for a period of time.

[Jane Louise]

My Netweather storm risk is looking good for tomorrow but there's no mention of the 'T' word from the Met office for my area . Nothing from Estofex again tonight I think they've all gone on holiday or have gone storm chasing lol.Looking forward to Nick F and Brickfielder's forecasts and all the lovely charts Coast and a few of you other members post up. Thank you to all for keeping us updated.

[Liam J]

Did somebody mention STORMS... Excited doesn't quite cover it

[mattyk1985]

With rain forecast for most of the day round here, I can't see convection getting going. I hope i'm wrong.

[Cheshire Freeze]

I think a lot of the CAPE showing on the GFS for tomorrow is the result of a fairly saturated profile with fairly high humidity? I think a limiting factor tomorrow will be extensive cloud cover which could preclude storm development for quite a few of us!

Therefore I would deem tomorrow as a slight risk of scattered thundery showers.

[Liam J]

My fears exactly, overcast skies are going to do zilch for convection. Slightly worrying, but I'm not to bothered about tomorrow atm because Thurs/Friday are looking much better for convective potential.

[Liam J]

A few charts from the latest NMM model run, CAPE & LI, Vertical vorticity and where the NMM thinks the ppn will be falling come Wednesday afternoon.

Southern Scotland & N/NW England are looking a good bet for some action the risk then stretching down the spine eastwards towards Linconshire, we shall see.

[Supacell]

I have netweather extra lite but does anyone know where to find the MLCAPE charts?

[Mesoscale]

I have netweather extra lite but does anyone know where to find the MLCAPE charts?

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

[Supacell]

Bit of a downgrade overall for my area on the 0z GFS and NMM. To be expected i suppose.

[AWD]

The GFS 0z has downgraded Cape quite significantly across many areas over the next few days now, with just small amounts over smaller areas of the country.

[mattyk1985]

Still chance for it to upgrade the next few days though.

There is still extensive cloudcover here things are very dull, so i'm not confident about today at the minute.

[Supacell]

The GFS 0z has downgraded Cape quite significantly across many areas over the next few days now, with just small amounts over smaller areas of the country.

It seems to have happened every day this week. I am hoping the 06z can bring it back again but if not i am fearful that this spell is all talk and no trousers. At the weekend there was a good storm chance showing every day this week, but as yet there has been nothing of note anywhere in the country. And now the downgrades continue for this week

Still potential, but i'm just becoming ever more concerned that this is not going to happen. Tomorrow now looks the best day for my area, but tbh i will believe that when it is still showing within 6 hours!

[Coast]

Morning all. Looks like today could be the first of a few opportunities around the country and although not everyone will be favoured, we should be happy for those that are surely? So I'll start my usual long drivel with a look at what other people are thinking about today's prospects: You've just gotta love ESTOFEX eh?

Storm Forecast

Valid: Wed 04 Jul 2012 06:00 to Thu 05 Jul 2012 06:00 UTC

Issued: Wed 04 Jul 2012 06:26

Forecaster: GATZEN

A level 1 was issued for northern France and the British Isles mainly for excessive precipitation.

SYNOPSIS

A rather weak mid-level flow affects Europe ahead of low geopotential centred to the west of the British Isles. With southerly winds ahead of this trough, warm air advection is forecast over a broad region. A cold front enters south-western Europe during the period.

DISCUSSION

The western Balkans, the Alpine region, Italy, France, the British Isles, and southern Germany

In the broad warm air advection regime, current soundings indicate steep lapse rates in the eastern parts and neutral to slightly unstable lapse rates in the western portions. Rich low-level moisture will be present and CAPE will reach from 500 J/kg in the north-west to about 3000 J/kg across the Balkans. The instability will be mostly uncapped in the northern parts while the capping will increase near the Mediterranean Sea and across the central and eastern Balkans.

Convective initiation is forecast given the large-scale support by warm air advection. Storms are expected especially across the Alps and from central France to the British Isles along and ahead of a surface cold front from the west. Although large-scale vertical wind shear is weak, local enhancement of the low-level helicity may support some supercells capable of producing very large hail. Excessive precipitation and large hail are also forecast with the stronger pulse storms.

Main threat will shift from excessove precipitation in the nothern and western parts to large hail in the southern and eastern portions. Severe wind gusts seem to be most likely given inverted-v profiles

Nothing from TORRO yet, here's Staplehurst's UKASF forecast, which differs from ESTOFEX's areas slightly, but I'm liking it for my part of the World!!

Forecaster: Dan

Last Updated: 2012-07-03 20:03:00

Valid: 2012-07-04 00:00:00 - 2012-07-04 23:59:00

Synopsis:

Slow-moving upper low approaches from the Atlantic, with cold mid-levels in it's core. This low becomes cut-off as main jet focus shifts into Iberia. Ahead of the cold front, in a broad warm sector, two pulses of WAA are expected, with advection of ThetaE.

Discussion:

... SCOTLAND, N ENGLAND, MIDLANDS, EAST ANGLIA ...

In the broad warm sector under a ThetaE ridge and behind an occlusion/ahead of a cold front, slight backing of surface winds will allow low-level convergence to occur. As a result, 500-700J/kg CAPE will generate showers and a few thunderstorms during the afternoon and early evening, in response to diurnal heating in a humid airmass.

ELTs down to -40C suggest convection will be deep enough for lightning, but very weak speed shear means that storms will be disorganised and pulse-type in nature, going through various phases of peaks and troughs in sferic activity, with some backbuilding likely at times. Current thinking is that these will be primarily inland, so some eastern coasts are likely to stay shower/storm free. Dry air aloft will also allow hail to occur in some showers/storms, perhaps a local event with diameter up to 2.0cm.

Given backing of surface winds, there exists the potential for a funnel or weak tornado, especially if any surface convergence develops. Also, a combination of slow storm motion and PWAT of up to 32mm could lead to local flooding from any prolonged heavy downpours.

Showers/storms will generally decrease in coverage and intensity during the evening hours as daytime heating subsides. Major concern is excessive cloud cover in a broad, moist warm sector which may inhibit insolation and subsequent convection...

... IRELAND, W NORTHERN IRELAND ...

Behind the cold front, cold mid-levels (~-22C at 500mb) will overspread Ireland under an eastward-moving upper trough, steepening lapse rates as diurnal heating takes place. Thus numerous showers and thunderstorms will develop with up to 900J/kg CAPE and ELTs down to -40C.

Very light, variable surface winds will result in slow storm motion, and with PWAT values around 24mm, local flash flooding may result from prolonged heavy downpours. Else, very weak shear will result in poorly organised convection, which will see showers/storms decreasing in coverage during the evening hours as diurnal heating subsides.

... KENT, EAST SUSSEX, EAST ANGLIA ...

Most models simulate advection of high WBPT and ThetaE during the evening/overnight hours from NE France/BeNeLux and across the North Sea, possibly grazing coastal portions of Kent and East Anglia. As such, MLCAPE values of 800-900J/kg may provide some primarily offshore lightning from elevated convection during the late evening and overnight period (beyond this forecast period). PWAT of ~36mm may cause a local flooding event in east Suffolk/Norfolk if any cells manage to move onshore for a period of time.

SkyWarn's forecast also not out yet (expected around lunchtime) so here are a few other indicators to think about:

Getting on for the darker hours according to 21st OWS, I'll take that!

Heavy blobs of red lightning possibilities!!!

Taking the hi-res versions of Lightning Wizards charts:

East Anglia into The Wash seems the place to be as the afternoon turns to evening:

(or Southern Ireland if your'e there!)

You beauty!!

GFS showing substantially more CAPE and a wider coverage:

I'll take GFS's solution please!

So what does it all mean???? If you go with HiRLAM, a very slight risk day and mainly in the East or central parts. If you go with GFS you get:

So it's down to some nail biting, radar watching and detector scanning. I think the chances are good for some today, maybe NW England and Ireland to start off with then possibly an isolated threat further East in the early hours of the evening?

[Harry]

Coast, as ever your efforts are most appreciated!! Not least because I'm off sick today for the first time in just under 5 years with suspected tonsillitis (hoping the GP will confirm in the next couple of hours). I got a tripod from my parents for graduation over the weekend so timing couldn't better really......just need a storm, preferably a night

[Coast]

Muggy as hell out there today. Dewpoints and humidity way up again:

http://www.netweathe...type=maxd;sess=

Coast, as ever your efforts are most appreciated!! Not least because I'm off sick today for the first time in just under 5 years with suspected tonsillitis

Cheers H!!! I'm only collating what other people are showing, so you can draw your own conclusions. Hope you recover from your illness and it doesn't mean you have to take the whole (convective) week off eh?????

[Supacell]

That cheers me up a bit Coast. The problem seems to be a lack of agreement between the forecasting models which makes it difficult to pinpoint an area. I am liking estofex though, with a level 1 and the 50% lightning risk from an IMBY point of view.

I guess its a case of radar watching - which makes chasing very difficult if dealing with pulse storms. Still, at least there are opportunities and some of us should be lucky. Still looking for a 06z GFS upgrade though before i feel overly confident.

[Cloudwatcher]

Definitely nothing on the cards for us here today, and not exactly hopeful for thurs or fri. Yet again we have 100% cloud cover inhibiting any convection. And we have the drizzly mess that has characterised our weather pretty much all year. Good luck to everyone else but for us I fear this week was always a non-starter....

[Harry]

I must do whatever the fine doctor decrees....I know pretty much everyone that has it stays off work...not sure if contagious or what!?!?!

[P-M]

Also just to add to the forecasts Tony Gilbert on UK Weatherworld has this to say:

Slight Risk of Thundery Showers Eastern Eire and UK 12Z-19Z

Confidence Level; Medium

Weak low pressure west of UK moves slowly east. Short wave upper trough remains stationary over southern Ireland increasing mid level lapse rates (primarily Ireland). Pre frontal Surface trough and cold front expected to bring some rain and showers to most part throughout today. Some of these showers may turn thundery where sufficient insolation exists ahead of any frontal boundary. Fairly weak shear will exist across all regions and any convection over the UK will lie heavily on isolated pockets of stronger solar heating. Positive conditions today will be the moist boundary layer overlayed by dry air within the mid levels.

A small chance of some funnel cloud observations today (as per red boxes). The risk for FC's is based on the GFS and WRF predicted convergence zones under regions of moderate CAPE values. The prime region for this looks to be SW Ireland where we should also see some moderate hail falls. Whilst there is a small risk of hail today with any convection, the risk would seem less likely based on relatively weak upper lapse rates and elevated freezing level.

Full text and map can be found here: http://www.ukweatherworld.co.uk/forum/index.php?/topic/92123-convective-outlook-weds-4th-july-2012/page__pid__810064#entry810064

[Coast]

Just checking a few online sources and I suspect the main possibility for today in mainland UK will be into the evening and maybe overnight, may be interesting to see what France sends us later!!!

The next few days generally give us:

The best bits from GFS so far are:

[Aaron]

At least it places a lightning symbol right above my house, that's all that matters

[Lewis]

Won't share me forecasts then.

Simples