34 replies to this topic

[Stuart]

Last Updated: 19:59 Wednesday, 3rd August 2011

Valid: 00:00 Thursday, 4th August 2011 - 23:59 Thursday, 4th August 2011



Areas Affected:

Ireland and SW Scotland



Synopsis:

A large and complex area of surface low pressure and its associated frontal systems are expected to dominate the weather across the UK during the course of Thursday. A marked upper trough in association with a surface frontal zone and also in association with a broader mid-level cyclonic feature is expected to move across the UK during the day, bringing extensive frontal cloud, precipitation and behind a more convective situation.

Discussion:

Firstly discussing the majority of the UK and Thursday is expected to be the day of change in terms of producing far more widespread unsettled conditions than of late and also producing a change in air mass as the very warm conditions of late are advected to the east of the country. The UKMO MESO, NAE, WRF and NMM models are signalling extensive frontal cloud across many parts of the UK during the course of the day and as a result convective activity is forecast to be limited across many areas. Some embedded convective activity may develop in association with the eastward moving frontal zones, but this is extremely difficult to highlight and forecast and is nothing more than a low, isolated risk.

It should be noted that there is model wide agreement for a marked region of vorticity to move across parts of England and Wales during tomorrow bringing a zone of heavy or perhaps very heavy rainfall to some areas. So despite a lack of convective activity, some areas of England and Wales are at risk of experience some heavy precipitation.

Moving onto the primary risk areas and that is Ireland and SW Scotland. These areas are forecast to experience a clearance, of sorts, with some solar input expected during the afternoon as the more persistent rain and frontal clouds clear away to the east. A modest 200 to 400j/kg of MLCAPE is forecast across parts of Eastern Ireland and SW Scotland during the afternoon and forecast soundings do signal instability, despite an obvious reduction in surface temperatures and dew points given an air-mass change. As a result there is an isolated risk of some heavy showers and/or thunderstorms developing across the highlight area during the course of Thursday afternoon.

There is very little or no significant LLS, DSL or helicity. As a result convection and thunderstorm activity is not forecast to be severe.

http://www.ukasf.co....rm-forecasts/61

[Jane Louise]

9.40pm Weds

Moderate Risk of Thunderstorms northern half of Eire 09Z-18Z

Slight Risk of Convective Showers (Some thundery) UK regions as per map 12Z-21Z

Fairly high risk of general thunderstorm activity over northern regions of Eire through Thurs as the occluded front wraps around the central low pressure system. Prime risk moderate hail and CG's.

Slight risk of post frontal isolated convective showers in the wake of the initial upper and surface cold front for parts of UK as per map. Some of these could develop some weak sferic activity. Though given the weak height falls in place there will be some uncertainties here. Upper shear profiles slightly more supportive than of late. Particular attention is given to the front left exit region of the jet stream which shows a strong divergent vector from 700 mb upwards. General dynamic lift could be asserted within the region of the southern most yellow risk box running from Bristol Channel through to Lincs. Whilst there is steady increase in vertical speed shear with height the general profiles look fairly straight lined at all levels with minimal convergence right across the board!


Edited by Tony Gilbert 3/8/2011 21:54

http://www.ukweather...w.asp?tid=44260

[CreweCold]

Should be enough instability for some post frontal showers tomorrow, more especially across Northern Ireland. Will rustle up a risk map in a bit

Edited by CreweCold, 03 August 2011 - 21:48 .

[Nick F]

Convective / Storm forecast - Issued 03/08/2011 22:00



Valid: 04/08/2011 10:00 - 05/08/2011 06:00
Headline: ...THERE IS A RISK OF THUNDERSTORMS FORECAST...

Synopsis

A large upper low to the W of the UK will begin to shift eastwards towards the UK, with a surface area of low pressure to the west of Ireland tonight moving across western UK during Thursday with occluding frontal system moving east - clearing the recent hot and humid air away from Ern England.

... NERN EIRE and SCOTLAND ...

Cooler post frontal polar maritime airmass digging in across NW/Nern UK during Thursday above a moist boundary layer will become unstable to surface heating as mid-level lapse rates steepen from the west. Therefore scattered heavy showers and a few thunderstorms are likely to develop.

... ENGLAND ...

Less certainty further south for the risk of a few embedded thunderstorms possibly developing along cold front and also a few storms post cold front. Despite more favourably sheared environment than recent days as jet stream moves in from the W, weak instability/weak lapse rates suggests only isolated sferic activity ... though embedded convection developing ahead/along cold front may yield threat of high rainfall totals in a short space of time and risk of localised flooding - given warm moist airmass ahead of front.

Issued by: Nick F - Forecaster for Netweather

Also can be found here: http://www.netweathe...onvective;sess=

[THE EYE IN THE SKY]

Video of the flash flooding from todays incredible storm from our local paper.

http://www.peterboro...rough_1_2928248

[Blizzards]

THE EYE IN THE SKY, on 03 August 2011 - 22:33 , said:

Video of the flash flooding from todays incredible storm from our local paper.

http://www.peterboro...rough_1_2928248

Hope the flooding wasnt too bad but good you got a good Storm there.

Nice to see some good green grass in the background on that video there too compared to our area where it seems to have gone hard and brown again!

[lewisosd]

Sorry 3rd Aug thread has been closed. Here's a couple of pics I took from yesterdays madness!

Edited by lewisosd, 04 August 2011 - 10:33 .

[CreweCold]

As promised, convective risk for tomorrow........Looks like a large swathe at risk from the map, when in all honesty shower distribution will most likely be far more scattered than is suggested as the map highlights the areas at risk.

Edited by CreweCold, 03 August 2011 - 23:20 .

[ElectricSnowStorm]

Met Office radar snap at 3am

waiting to see what happens as it enters the humid warm airmass across the east! expecting some intense pulses to form with lightning maybe becoming thundery as it moves across towards SE/EA!

Edited by ElectricSnowStorm, 04 August 2011 - 02:23 .

[Surrey]

ElectricSnowStorm, on 04 August 2011 - 02:22 , said:

Met Office radar snap at 3am

waiting to see what happens as it enters the humid warm airmass across the east! expecting some intense pulses to form with lightning maybe becoming thundery as it moves across towards SE/EA! Radar - 3am.PNG

Well no lightnings..but in under two hours from your post its picked its self up a lot!!

Attached Thumbnails

• 

[ElectricSnowStorm]

that looks like the 5am radar, heres is the wider picture of the 5am snap!

just about to upload some new DATA!



-

Met Office Radar-link to site

Edited by ElectricSnowStorm, 04 August 2011 - 04:53 .

[ElectricSnowStorm]

Another day of exciting weather! and thundery or thunderstorm is possibly on the menu for some!

GFS00Z new update run this morning looks good to those that like some action

we have rain developing in the south and some very heavy pulses already forming, i expect embedded thunder or a storm to develop in the main rain zone this morning, also note the heavy rain up western side(see radar snap above) through the day as system moves away then heavy showers and thunderstorms are possible! the charts to me look interesting and im sure GFS is an upgrade this morning for more thundery activity.
anyway il post up the charts as im off now and il be reading and sky waching when i can! must say the rain some areas could cause flooding.

Also if you not seen it their is a Nw storm forecast issued! so another day of weather watching.


looking at this morning....
-NAE-ppn-6am-12pm
-GFS-convection index - 9am
-GFS-ppn-6am-9am
-soaring index/Convective cloud cover-9am
-GFS-vertical velocity 700hpa-9am

and the afternoon and some for the evening..
-GFS-Theta-W 850hpa-3pm
-NAE-Theta-W 850hpa-3pm
-GFS-vertical velocity 700hpa-12pm
-GFS-vertical velocity 700hpa-3pm
-GFS-Lifted index-12pm(note-yellow=unstable air)
-GFS-Lifted index-6pm
-NAE-dew points - 3pm
CAPE - GFS - 3pm

[TomSE20]

I'm sure I was woken up about 20 minutes ago by a rumble of thunder, accompanied by some quite heavy rain, here in S.E.London. Radar shows the real heavy stuff away to the south west, which should be with us in an hour or two but nothing electrical in that.

Regards,
Tom.

[Coast]

Stuart's covered UKASF, so here's ESTOFEX:

Quote

Storm Forecast
Valid: Thu 04 Aug 2011 06:00 to Fri 05 Aug 2011 06:00 UTC
Issued: Wed 03 Aug 2011 21:46
Forecaster: GATZEN
A level 1 was issued for Italy and the Balkans mainly for large hail.

SYNOPSIS

A northern Atlantic trough is associated with a rather strong westerly flow that is directed to western Europe. The delta of this jet is located over central Europe. South-westerly low-level winds will advect moderately warm and rather moist air masses into western and central Europe ahead of a cold front spreading across the British Isles.

Attached Thumbnails

• 

[Coast]

and some other indicators for the day:



MetO interpretation has the opportunities further North:



Mid level aviation charts show it off to the East without touching our shores:



This made me sit up a bit, the KO index for the far SE has a very bright area over me!



This soaring index also has the SE and Scotland covered at the same time:



CAPE isn't great today for the UK and wanders around all over the place:







A bit if shear up the spine of the country later:





Loads of rain!



Note far SE corner again:



Lapse rates to the West and Central band, nothing major:



Have a look at this tornado area to the West of London and the Home Counties this afternoon and the deep layer shear over France:





Not as certain as yesterday, but some may be worrying about the rain and flash flooding more than convective weather and sferics!

[Lauren]

Been raining non-stop since the early hours here.

[Coast]

Lauren, on 04 August 2011 - 10:48 , said:

Been raining non-stop since the early hours here.

I think that's going to be the headline for today, nothing convective so far but I'm keeping an eye out amongst he torrential downpours!

[Purplepixii]

When I went to be at 2am there was very light rain falling (kinda mist-like) but it's been raining heavily since 08:30 here. Wind is gusting every now and then too. Rain has just lessened a bit but I think Coast is right - today is a day of rain rain rain and more rain!

[Coast]

Purplepixii, on 04 August 2011 - 11:03 , said:

When I went to be at 2am there was very light rain falling

I think I know what you're saying, but please don't elaborate!

[Harry]

Purplepixii, on 04 August 2011 - 11:03 , said:

When I went to be at 2am there was very light rain falling (kinda mist-like) but it's been raining heavily since 08:30 here. Wind is gusting every now and then too. Rain has just lessened a bit but I think Coast is right - today is a day of rain rain rain and more rain!

I wouldn't say that, rain should be clearing your area within the next 30-60 mins. Should clear London by around 2ish and then be stubborn along the EA/Kent coast, probably not clearing until evening.

Looks as if showers may develop behind the rain mass given reasonable CAPE/LI's, however likely to be subject to amount of sunshine and heating to get them going. GFS breaking out heavy precip in similar areas to yesterday (around the wash area and slightly further north) with perhaps lighter showers further SE (again, according to GFS)

GFS downgraded CAPE/LI across NI and Scotland so I am less optimistic for fireworks here.

Edited by Harry, 04 August 2011 - 11:41 .