Convective Outlook & Discussion Mon 6th July 09

[Tony Gilbert]

10pm Sun

Moderate Risk of General Thundery Showers 06-21Z UK & Eire

Slight Risk Severe Thunderstorm Southern Ireland, Wales and Southern UK 06-18Z

Slight Risk of Strong Tornadoes Southern UK, Wales, E.Anglia and South Midlands 06-18Z

Probably the most serious forecast that I have posted to the UKWW so far this year;

Deep break away upper trough moves east through Monday increasing lift with steep lapse rates at all levels. Moderate divergent upper jet stream further increases lift with primary focus to the front left exit region. Increasing low level jet at 850mb establishes strong low level shear. Models currently develop high CAPE values as heavy surface moisture advects east mixing with mild air from the south. Potential instability is utilised as dry incursion pushes through inline with the predicted surface trough. Strong vertically stacked PVA max builds over Wales and moves east adding to stronger convective potential.

Quite a day in store with potential for non severe convective gusts of around 30kts based on mean average values from 800mb to 600mb. Threat of large hail and defined risk of one or more strong tornado events are possible.

Particular attention is given to southern UK late in the day where the low level jet is shown to increase and overrun lighter winds at surface. Whilst winds would seem to be straight lined the speed shear should compensate to increase low level field vorticity. Upper winds are strong but show only slight increase with height hense a SLIGHT risk of Severe Thunderstorms is expected ATM.

This situation will require close monitoring through Monday for a possible upgrade.

[Roger J Smith]

I agree, it's looking quite active. People oop north might not be out of the running either because the stacked low is drifting slightly north of due east (currently it is southwest of Galway, Ireland) and it tracks across the Irish Sea mid-day and northern England later in the day. Today, the heaviest showers with this feature in Ireland were around Galway to the northeast of the centre. Another area of developing heavy showers can be seen in the southwest around Kerry and west Cork (county).

For people reading this in Ireland, don't write off the northerly flow on the backside of this feature, because sometimes that can generate its own active hail storms with the lower freezing levels.

My estimate is that in the UK, the best chances for severe weather will be in the central Midlands on a line from about Leamington Spa to Hull. I think there would be pretty good chances everywhere south of that, and slowly decreasing chances anywhere north, but this is where I foresee the most active storms developing. It may be quite a chaotic radar by mid-day though, if it's anything like what was seen in Ireland today.

[Nick F]

Netweather storm forecast for tomorrow, slight chance of severe storms over parts over Sern UK tomorrow, but storms likely almost anywhere:

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

Could be one of the most interesting days of the year so far from a severe perspective.

[TEITS]

Sounds like I need to charge my camera batteries ready for tomorrow.

Just want to say thanks to the above posters because I love reading these technical posts even though I don't fully understand them. <_<

Certainly hoping to see a tornado as unusually for the Peterborough area we haven't seen one this year!

[Wales123098]

http://www.raintoday.co.uk/

seems to be spirlaling round like a hurricane

[Greeny]

Netweather storm forecast for tomorrow, slight chance of severe storms over parts over Sern UK tomorrow, but storms likely almost anywhere:

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

Could be one of the most interesting days of the year so far from a severe perspective.

Yeah I'm excited about later on todays prospects (yes its gone midnight ) Seems like alot of potential all over the UK, shame I have to work tomorrow, would have been better if today was tomorrow and tomorrow was today but thats your luck. I should be on the road though. I love this time of the year with temps as they are more heat means more moisture held in the air and potentially more likely to be severe storms and a better chance of the gust front phenominum <_< Cape and LI values at a higher level too.

http://www.raintoday.co.uk/

seems to be spirlaling round like a hurricane

Yeah I noticed that earlier nice rotating weather system :lol:

[Phil UK]

Not particulary experienced myself in this field, TEITS But tomorrow (Ok, today for the pedantic! ) looks like it will go bang big time.

Thanks again Mr Gilbert, Nick F and Roger J Smith. (The latter being spot on with Thursday night/Friday morning storms).

Phil. (Goodnight, sleep well, camera batteries charged in order to see a cell). <_<

[Roger J Smith]

Yes, the rotation of the stacked low has been quite evident all day watching the Irish radar, the centre is now just west of Shannon and I expect it will be fairly easy to spot on radar all the way across the British Isles next 24 hours.

Sometimes over land these features get filled up with convection and you can only spot them from an animated version of radar, so keep that in mind, but usually they retain a relatively dry circular core of either stable strato-cu or even a clear patch.

Somebody mentioned on the Irish weather forum that Galway had seen a lot of rain all day long but there had been no thunder heard with it. I think this will begin to change when the system gets over the warmer land surface of eastern Ireland and Great Britain (has the name of our blessed island home been changed since I left? I would hate to speculate).

[❄️❄️❄️❄️❄️❄️❄️❄️❄️]

Smack bang in the middle of a 'slight risk' but i wont get my hopes up. Too many let-downs these past few weeks

[dogs32]

Met

Amber warning's issued at 03.59

Central, Tayside & Fife Heavy Rain 0535 Mon 6

SW Scotland, Lothian & Borders Heavy Rain 0535 Mon 6

Northern Ireland Heavy Rain 0540 Mon 6

Wales Heavy Rain 0250 Mon 6

Heavy Rain 0600 Mon 6

North West England Heavy Rain 0245 Mon 6

South West England Heavy Rain 0600 Mon 6

[gpspete]

My bus is fueled up camera batteries charged up laptop ready wireless networking ready which way do I go north to Birmingham west to south wales or sit on the Birdlip or South to Coast for todays best chance

[Lynxus]

Morning all,

Well well, what a lovely day we have today to watch

Ive been in cornwall ( near St austal ) the passed week and we had plenty of sunshine and one evening we even had tunder yay!

Lets hope today brings some fun considering im now back at work booo.

I like the metoffice warnings for today.

http://ukasf.co.uk/index.php?name=storm have a warning out and so do estofex.

Wicked.

[Marcus_surfer]

Just had a torrential downpour with a flash of lightning and bang of thunder thrown in

[Godot]

Radio Four mention rotating cloud in the forecast for Wales and the SW this morning. The day ahead certainly looks interesting.

[Tony Gilbert]

8.10am Mon

UPDATE

As per earlier forecast with enhanced tornado risk zone (blue box) 15Z-18Z

Additional risk box added Scotland for enhanced risk of Convergence Zone Tornadoes.

Based on the most recent model update there would appear to be an enhanced risk for tornadoes this afternoon from north Dorset arcing through to E.Anglia where surface vector is reduced increasing LL shear. Upper dry air incursion times in nicely and pushes in from the west creating an arcing line of isolated strong convective cells. It is within this line that severe weather potential today will peak.

It is however noted that due to lack of any considerable veer at surface the risk for meso derived tornadoes today remains SLIGHT. A reminder that the broad coverage box does not mean that everyone in that box will see a storm today, but just that there is a defined risk. In fact I do not expect the thundery activity to be widespread in nature!

[Coast]

ESTOFEX going along with it today for all of us:

Storm Forecast

Valid: Mon 06 Jul 2009 06:00 to Tue 07 Jul 2009 06:00 UTC

Issued: Sun 05 Jul 2009 18:22

Forecaster: TUSCHY

A level 1 was issued for NE/E Spain mainly for large hail and severe wind gusts.

A level 1 was issued for parts of Italy, Slovenia and S-Austria mainly for large hail and excessive rain.

A level 1 was issued for NE-France, Belgium, the Netherlands and extreme NW-Germany for large hail and severe wind gusts.

SYNOPSIS

A large-scale trough over NW-Europe moves slowly towards the east with warm and unstable conditions over parts of the N-Mediterranean and SE-Europe. Cold and stable conditions are present over NE-Europe due to a northeastward moving upper trough.

DISCUSSION

... Ireland, United Kingdom and Scotland ...

Upper trough slides eastwards and crosses the area from the west. Cold mid-levels and hence moderately steepened lapse rates at mid-levels, adequate boundary layer moisture, weakly capped atmosphere and numerous east/northeastward moving convergence zones will cause an active thunderstorm period with widespread initiation. Marginal hail and strong wind gusts with isolated high rain amounts are expected. Another concern is an augmented funnel/tornado risk next to convergence zones and over S/SE UK, where LL shear is slightly enhanced. Thunderstorms decrease in coverage and intensity after sunset due to the diabatically driven nature of those storms.

... Rest of the highlighted areas ...

Neither shear nor instability are adequate for a more significant severe risk. Isolated large hail is possible over central Poland and E-Germany/W-Czech Republic next to strong wind gusts

and the UKASF bring the potential for joy to us all:

Storm Forecast Issued: 2009-07-05 19:14:00

Valid: 2009-07-06 00:00:00 - 2009-07-06 23:59:00

Regions Affected

All of the United Kingdom and Ireland

Synopsis

Again, an area of LOW pressure will be the dominant feature of the weather across the UK on Monday, although this time now centred over southern Scotland at 12z GMT. The eastward shift of the area of LOW pressure therefore shifts the 'potential' for thunderstorms further eastwards to cover all of the UK. Four main focal areas for thunderstorms are merged into one large THUNDERSTORM area on the map - thunderstorms during the early hours across Germany and Holland in particular, combined with thunderstorms over Norway, the UK and the Low Countries during Monday daytime. Numerous showers will be present even at daybreak across quite a few areas of the U.K. thanks to embedded troughs and fronts within the anticyclonic flow around the area of LOW pressure. Throughout the day the showers will become increasingly widespread with thunderstorms also very likely. Slow-moving torrential downpours may cause local flash flooding, particularly in central and western parts where the showers will be most frequent. Hail is also very likely to accompany the showers and thunderstorms. There is an enhanced risk of a tornado developing, particularly from the Midlands southwards. Given the favourable conditions, multicells may develop. Showers and thunderstorms will persist well into the night, but are likely to become more isolated in nature.

Everyone happy then?

[Stuart]

Good morning to just seen I have a Weather Warning out for my area but i know what will happen like a few times storms will move to the east of me but i hope i see my 2nd storm today

[TonyH]

Several torrential showers this morning, one now lasted 15 minutes so far, no thunder, very dark.

[Harry]

Left my house this morning with a mature/weakening Cb moving straight at me. Think it was weakening, brought nothing more than a downpour!

Good start though - bring it on!!!

Has to be the first time I have seen a UK chart (let alone more than one) showing a thunder watch for the whole of the UK.

[Paul Sherman]

Just back from a Weekend away in Cork/Kerry where the weather was pretty active at times and just in time by the looks of things. Had the 1st Shower of the day rattle through, No Sferics with it but some heavy Precip. Another band now moving NE From the South Coast should affect the South East in the next few hours.

Could be a Good day if Tony's forecast pans out

Paul S

[Lynxus]

How / where are these meant to come from?

Are these storms home grown today and moving up from the SW / W ? Im having problems trying to see the big picture here today. Maybe im still hungover..

[Harry]

How / where are these meant to come from?

Are these storms home grown today and moving up from the SW / W ? Im having problems trying to see the big picture here today. Maybe im still hungover..

All going to be homegrown I think today Lynxus - quite an active area of L pressure sitting slap bang over the UK! Already a mass of showers across Wales, three pronounced bands lining up across the S and several across the N!

Direction though on this occasion not all SW to NE - they will all be rotating around the L pressure - so across the S storms/showers will probably move SW/W to NE/E, across the N from SE/E to NW/W

[Lynxus]

All going to be homegrown I think today Lynxus - quite an active area of L pressure sitting slap bang over the UK! Already a mass of showers across Wales, three pronounced bands lining up across the S and several across the N!

Direction though on this occasion not all SW to NE - they will all be rotating around the L pressure - so across the S storms/showers will probably move SW/W to NE/E, across the N from SE/E to NW/W

I see,

Fair enuf.

Will just have to wait and see today then

Theres some very big convective cloud about . No showers yet.

-G

[Callie]

Gone very dark here, the wind is picking up and now raining slightly.

Correction to the rain, now coming down steadily from a westerly direction.

Callie

[gpspete]

I know it may be slightly off topic but look at these nssl mesonet chasers cars in us

http://www.nssl.noaa.gov/observations/imag...bilemesonet.jpg wow