25th into 26th Aug 2011 - Storm/convective Forecast Discussion And Reports

[Wet'n'Dry]

wow! we have a stunning orange sky to the west and a beautiful rainbow to the east

I got a double rainbow here, not bad but the photo I got is a bit washed with the orange tint in the clouds! Also started to rain here.

[Lancashire Lass]

Well that was er...refreshing. 36mm/hr. Even with a waterproof jacket and a brolly I'm still drenched.

[Tim B]

Went to the window just now to check on this cloud burst when a huge forked bolt shot over the cloud base right as I twitched the blind, made me jump. Loud too.

[Lancashire Lass]

The sky is extremely dark to the south of me and what was a hint of orange sunset to the West of me has now been replaced by grey.

[cyclonic happiness]

I got a double rainbow here, not bad but the photo I got is a bit washed with the orange tint in the clouds! Also started to rain here.

Was it all the way across the sky?

[Wales123098]

stuff bubbling up here from no where in Cardiff.

[Kookylou]

stuff bubbling up here from no where in Cardiff.

really?

[staplehurst]

Can't see any excitement for tonight? Just hours of persistent and heavy rain? Can't see much, if any ,lightning potential sadly

[Liam Ellis]

stuff bubbling up here from no where in Cardiff.

Saw some bubbling to the East earlier on - anything to the West or South?

[Jane Louise]

Ukasf forecast for tomorrow folks.Good luck everyone.Even I stand a chance tomorrow I'm going to be near the Worcestershire border.

Areas Affected:

MODERATE: Wales, WC England

SLIGHT: much of W & S Britain, E Ireland

Synopsis:

An area of low pressure will move across SE England during the morning along with another frontal wave bringing a round of heavy rain to parts of E Anglia. Otherwise a broad area of low pressure will encompass much of the British Isles with cold air aloft bringing an unstable airmass across all areas.

Discussion:

Another complex day across Britain weather-wise, early on an area of rain with some localised flooding potential will move across E Anglia with totals in excess of 50mm (2 inches) possible in places. Large model uncertainty over the afternoon period as to whether this area of rain moves off into the North Sea as indicated by the GFS, or whether it moves back into E Britain during the afternoon (indicated by the NAE). Either way, it appears large amounts instablity will be limited with this frontal wave/developing triple point and lightning is unlikely to occur within it. *The caveat being that there is some very modest deep layer shear (DLS) 20kts and any larger updrafts that develop could last long enough to allow for some hail and gusty winds.

The main potential for thunder will happen further west (and transfer eastwards throug the afternoon) as 500mb temperatures approach -24C in places. CAPE levels in excess of 800j/kg across parts of Wales will be the focal point for the Moderate risk, with thunderstorms most widespread through the afternoon in reaction to surface heating. ELTs near -40C indicate tops of storms could reach 25-30 thousand feet giving suffiecent depth for lightning in most showers that develop in this area. Much like Thursday DLS and LLS are very low in the highest instablity regions meaning storms will generally be pulse variety and bring very little threat of severe weather (other than some frequent lightning and small hail (~1cm).

http://ukasf.co.uk/storm-forecasts/84

[Hathers]

That's the first time I think I've been in the orange area on the ukasf map. Should I be excited by this or not?

[Wales123098]

Ukasf forecast for tomorrow folks.Good luck everyone.Even I stand a chance tomorrow I'm going to be near the Worcestershire border.

Areas Affected:

MODERATE: Wales, WC England

SLIGHT: much of W & S Britain, E Ireland

Synopsis:

An area of low pressure will move across SE England during the morning along with another frontal wave bringing a round of heavy rain to parts of E Anglia. Otherwise a broad area of low pressure will encompass much of the British Isles with cold air aloft bringing an unstable airmass across all areas.

Discussion:

Another complex day across Britain weather-wise, early on an area of rain with some localised flooding potential will move across E Anglia with totals in excess of 50mm (2 inches) possible in places. Large model uncertainty over the afternoon period as to whether this area of rain moves off into the North Sea as indicated by the GFS, or whether it moves back into E Britain during the afternoon (indicated by the NAE). Either way, it appears large amounts instablity will be limited with this frontal wave/developing triple point and lightning is unlikely to occur within it. *The caveat being that there is some very modest deep layer shear (DLS) 20kts and any larger updrafts that develop could last long enough to allow for some hail and gusty winds.

The main potential for thunder will happen further west (and transfer eastwards throug the afternoon) as 500mb temperatures approach -24C in places. CAPE levels in excess of 800j/kg across parts of Wales will be the focal point for the Moderate risk, with thunderstorms most widespread through the afternoon in reaction to surface heating. ELTs near -40C indicate tops of storms could reach 25-30 thousand feet giving suffiecent depth for lightning in most showers that develop in this area. Much like Thursday DLS and LLS are very low in the highest instablity regions meaning storms will generally be pulse variety and bring very little threat of severe weather (other than some frequent lightning and mall hail (~1cm).

http://ukasf.co.uk/storm-forecasts/84

woo !! Yeah there was storms bubbling up in Cardiff, there to the north now. Look at the radar.

[staplehurst]

That's the first time I think I've been in the orange area on the ukasf map. Should I be excited by this or not?

If you look here: http://ukasf.co.uk/content-12/Criteria it suggests the orange area is for a 36-70% chance of lightning to occur. I'd give my left arm to be in the orange area!

[Jane Louise]

woo !! Yeah there was storms bubbling up in Cardiff, there to the north now. Look at the radar.

Yes, I've got my eye on those lol unfortunately I'm still in Cheltenham at the moment and I know there's no way they'll ever come here lol. Hope you get something your way.

[Chris K]

I'm only just inside the orange area. I have a bad feeling its going to be one of those 'so near yet so far' days. Will be another day of radar watching

[Jane Louise]

Just had an email from Torro:

There's still some potential for tonight up till morning...fingers crossed.

TORRO CONVECTIVE DISCUSSION 2011/015

A TORRO CONVECTIVE DISCUSSION has been issued at 20:30GMT on Thursday 25th August 2011

Valid from/until: 20:30GMT - 09:00GMT on Thursday 25th/Friday 26th August 2011 for the following regions

Parts of (see map)

SW England

Central S England

SW Midlands

Wales

S & E Eire

THREATS

Isolated tornadoes; CG lightning; heavy rain; hail; gusty winds

DISCUSSION

Upper low moving in from the west towards the area. Numerous showers and a few thunderstorms are circulating around it. Low-level shear on the eastern side of the low may be sufficient for isolated tornadoes and gusty winds, especially close to the coasts, where instability will be higher. Later in the night, winds will become light in the west. Local convergence zones may then set-up, perhaps with isolated torndaoes - again, the coasts may be most at risk.

Deep layer shear is stronger across the eastern part of the area for the next few hours - more organised cells may affect this area for a time, with a tornado risk

Further east, heavy rain will develop, perhaps with thunder across Kent and E Anglia later in the night. At this stage, severe weather looks unlikely with this, but it will be monitored.

Tomorrow, conditions will be monitored for further discussions as there currently looks to be a reasonable chance of convergence-zone tornadoes across parts of England and Wales.

Forecaster: RPK.

http://www.torro.org.uk/site/forecast.php

[Wales123098]

Yes, I've got my eye on those lol unfortunately I'm still in Cheltenham at the moment and I know there's no way they'll ever come here lol. Hope you get something your way.

Thanks:)

[Staffordshire]

I'm just on the east side of the orange zone (maybe a mile) but if the showers are moving from east-west they should get me.

[Marcus_surfer]

Lightning can be seen to my west, quite bright flashes, and that cell looks quite heavy by pembrokeshire

[Sprites]

Some jelly fish and midlevel cumulus here at sunset, looked like a mid level storm may be lurking later..

[Jane Louise]

Estofex is in now and I'm sure Coast and Nick F will be around at some point to post up theirs

I'm getting really excited now for tomorrow there is so much potential there.

http://www.estofex.org/

Storm Forecast

Valid: Fri 26 Aug 2011 06:00 to Sat 27 Aug 2011 06:00 UTC

Issued: Thu 25 Aug 2011 20:40

Forecaster: GROENEMEIJER

A level 2 was issued for NE Netherlands, NW Germnay and S Denmark for damaging winds, large hail and to a lesser extent for tornadoes.

A level 1 was issued for the remainder of Denmark, much of Germany, for E, central and S France, Switzerland, and for the remainder of the Benelux countries for severe wind gusts and large hail.

SYNOPSIS

A deep trough over the western Atlantic with its North-South directed axis over the Irish Sea, moves evolves into a separate upper level low located over north-central France on Saturday morning. Ahead of the system a cold front, intially stretching from a surface low over the southern North Sea to the Massif Central, moves eastward into central parts of Europe.

DISCUSSION

... Benelux, Denmark, Germany...

Ahead of the front pronounced northward advection of warm air takes place. Friday morning, a diffuse warm frontal zone is located from the W Netherlands into N Germany.

Ahead of the front between 1000 and 2000 J/kg of CAPE will generally be available. A strong southerly jet that is particularly well-defined at 700 hPa, with wind speeds 20 - 30 m/s. This will provide wind shear that is more than sufficient for storm organization. The best overlap of wind shear and CAPE is in the morning and early afternoon across the level 2 area, where the jet crosses the warm sector of the surface low over the North Sea.

We expect convection to be ongoing near and just east of the surface low over the Benelux countries and the German Bight. Models suggest that surface-based storms will develop across the level 2 area during the late morning and early afternoon. Upon interacting with the strong wind shear, these storms may easily become severe warranting the level 2. Bowing features with severe wind gusts are the most likely mode. Some large hail, will be possible given the substantial CAPE. The development of a isolated tornado or two cannot be discounted either given the high moisture and the substantial low level shear.

Further south, forcing for upward motion during mid-day expected to be rather weak if at all present, as a slack shortwave ridge passes from the south. This, in combination with a relatively strong cap, will probably suppress convection to a large extent during the day. Following the ridge, convection is again expected to move in from eastern France during the evening hours.

The overall parallel orientation of the shear and the front is expected to limit the severe threat to a great extent. Severe wind gusts are nevertheless possible where bowing features develop, and some large hail may occur as well.

... France and Switzerland...

As the front moves eastward, it appears not to be very active across the northeastern quarter of France because of upper-level ridging. Only Isolated convection is expected in the upward branch of the frontal circulation. During the afternoon, upper-level forcing should increase from the south, and convective coverage is expected to increase across SE France. With around 1000 J/kg of MLCAPE in place and 20-30 m/s deep-layer shear, a few supercell or bowing storms with severe winds gusts and large hail will probably form. The storms will move into SW Germany during the evening.

[Purplepixii]

Ooooh I like the central southern england (coastal)Torro warning! Hubby says if he wakes up in the morning to find I've covered the car in armour-plating he'll know why (ok, I watch too many storm-chasing programs!!)

Heavy rain has just started up here, I've been watching it approach on Meteox. Just waiting for my cat (aka "soggy moggy") to come running into the house from outside squeaking a lot to tell me it's raining...

[Wales123098]

http://www.bbc.co.uk/news/uk-wales-south-east-wales-14670371 I don't know if anyone has posted this but storm caused damages in S.Wales earlier

[Norfolk Sheep]

I'll just have to be satisfied with light to moderate rain for the next 12 hrs

[staplehurst]

I'll just have to be satisfied with light to moderate rain for the next 12 hrs

I'm expecting a bit more than light to moderate lol!!