Uk General Convective Discussion & Forecasts, 10th October 2012>

[weatherobsuk]

We just had a storm lasting some 25 minutes at 04:20am in the western Peak District in association with a localised LEWP. On average there was some 4-lightning strokes per minute, even now 20 mins afterwards the bedroom light is browning out due to distant strikes. Quite a unexpected surprise and definitely goes to show here in the UK it can do almost anything at any time.

[Coast]

ESTOFEX forecast just offshore, but worth noting for the dialogue:

Storm Forecast

Valid: Thu 31 Jan 2013 06:00 to Fri 01 Feb 2013 06:00 UTC

Issued: Wed 30 Jan 2013 23:25

Forecaster: PISTOTNIK

A level 1 was issued for the Netherlands, Belgium and parts of Germany for severe wind gusts.

SYNOPSIS

To the South of an almost endless chain of deep cyclones from the Northern Atlantic via the British Isles into Scandinavia, a pronounced zonal flow continues over much of Europe. An occlusion which rapidly moves eastward across North-Central Europe provides a possible focus for a strongly forced convection event.

Meanwhile, a subtropical ridge extends into most of the Mediterranean region and presents it with calm and dry weather.

DISCUSSION

...North-Central Europe...

The occluded frontal system of a mature low over Scotland gets reinforced in the left exit region of a jet streak (60 m/s at 500 hPa) as it moves from the English East coast via Germany into Poland in the 06 to 18 UTC time frame. The accompanying signal in the surface fields seems subtle, as it is dwarfed by the overall strong pressure gradient. However, the combination of a strong background wind field and slightly backed surface winds is sufficient to drive the 0-3 km storm-relative helicity into the 200-300 m^2/s^2 range, overlapped by synoptic lift support and neutral to marginally unstable profiles in the lower troposphere.

The lack of a pronounced frontal structure and the slantwise orientation of the vorticity lobe to the mid-level flow suggest that a convective line (if any) will soon give way to a small flock of shallow multicells as the dominant convective mode. Showers and isolated thunderstorms are expected to make landfall in Belgium and the Netherlands around 10 UTC and to move into Northwestern Germany in the following hours, and they might attain briefly rotating updrafts in this helical environment. Sub-severe soft hail is locally possible and even an isolated tornado is not ruled out. However, all in all this threat is limited by a lack of low-level buoyancy and by a displacement of the deepest instability (further North) from the strongest vertical wind shear (further South). The only uniformity in this highly dynamic setup is the strong low-level wind field (30-35 m/s at 850 hPa), which makes the severe wind threat solid enough to issue a level 1 area, even though the majority of convection will be too shallow for electrification.

The favourable overlap of strong vertical wind shear, lift support and marginal instability is quite limited in space and time, hence the wind risk will taper off in Central Germany, Poland and the Czech Republic in the late afternoon and evening hours. A further involvement of convection becomes doubtful, too.

[Kain]

Just had a thunderstorm here in Bridgnorth, lasted about 15 minutes. Nice thing to wake me up this morning!

On a side note, I'm not a relgious man in any shape or form, but yesterday a good friend of mine passed away. He often laughed at me going out filming the storms....I swear it was one last gift from him for me. Yeah I know it wasn;t...but I would like to think it was!

[Chris K]

Just had a thunderstorm here in Bridgnorth, lasted about 15 minutes. Nice thing to wake me up this morning!

On a side note, I'm not a relgious man in any shape or form, but yesterday a good friend of mine passed away. He often laughed at me going out filming the storms....I swear it was one last gift from him for me. Yeah I know it wasn;t...but I would like to think it was!

Sorry to hear about your friend. Here's hoping for an extra thundery 2013 for you, to remember him whilst experiencing one of the awes of nature

Edited January 31, 2013 by Chris K

[NW Leeds Russ]

Just seen a flash of lightning in Leeds city centre. Very heavy shower too and gusty winds.

Anyone else reported anything? Cell seemed to be over NW Leeds?? Shame not at home...

[Coast]

ESTOFEX keeping us up to date for today:

Storm Forecast

Valid: Mon 04 Feb 2013 06:00 to Tue 05 Feb 2013 06:00 UTC

Issued: Mon 04 Feb 2013 00:38

Forecaster: TUSCHY

SYNOPSIS and DISCUSSION

The active branch of the polar vortex reorganizes, so cold and unsettled conditions continue over most of Europe, although the air mass features mostly low-end moisture values. A cut-off development atop the C/E-Mediterranean results in better moisture along its eastern fringe which increases thunderstorm chances somewhat from the S-Ionian Sea into the Aegean Sea.

This pattern will be a quiet one for thunderstorm development although a few areas were highlighted for some isolated activity. The thunderstorms will be sub-severe although convection over Ireland, UK, Belgium/the Netherlands and far NW Germany may be accompanied by strong to isolated severe wind gusts given strong LL flow. Marginal hail will be another issue given rapidly cooling lower/mid troposphere.

[IanR]

just heard thunder

[Kain]

Sferics in bridgnorth

Nice to see abit of lightning at night!

Edited February 4, 2013 by Kain

[Stuart]

i see no 1 posted this

Synopsis:

Broad upper trough will continue to dominate the North Atlantic to the west of Britain. In the post-occlusion environment, slight cooling aloft increases the rather limited risk of convection in places.

Discussion:... SW ENGLAND, S WALES ...

A couple hundred J/kg CAPE may develop during the afternoon hours on Friday, if sufficient insolation can allow surface temperatures to reach 12-14C. Local convergence and orographic forcing may assist in producing a convective shower or two, deep enough (ELTs down to -25C or so) for sferic activity. This is a very low probability setup, with only a 10-20% chance or so of occurring.

Major concern is slower clearance from frontal system over CS/SE England, providing excessive cloud cover and limited insolation. A nose of warm air aloft will also be present at ~700mb, such that even if parcels could be lifted from the surface this would provide a capping inversion, hence T2 ideally need to be >13-14C or so. For now we highlight the area as a SLGT, but stress a very low probability of occurrence.

... W / SW IRELAND ...

A slightly better chance (not guaranteed) across W-C Ireland during Friday afternoon for a few scattered convective showers to develop in the post-frontal environment. A few hundred J/kg CAPE should be generated with any decent insolation, and such showers should have sufficient depth (ELTs down to -40C) for sporadic sferic activity. Organisation is likely to be poor given lack of speed shear, but relatively low LCLs coupled with slight low-level directional shear may allow a brief funnel to develop.

S and SW Munster have been included in the SLGT for potential mid-level instability late in the evening and into the early hours of Saturday, but again lightning activity with this is considered a low probability.

http://www.ukasf.co.uk/storm-forecasts/225

[Raidan]

Thanks for that Stuart,not going to get my hopes up but something of interest to keep a eye on.

[Stuart]

Synopsis:

Broad upper trough continues to be located to the west of Britain over the Atlantic, while a shortwave migrates slowly northeastwards across SW England. Slight cooling aloft coupled with mild LSTs will increase chances of convection.

Discussion:

... SW ENGLAND, S WALES, S IRELAND ...

Several hundred J/kg CAPE will generate by Saturday lunchtime and into the afternoon, and combined with low-level convergence and orographic forcing will allow scattered showers and a few weak thunderstorms to develop in places. Convection should be sufficiently deep (ELTs down to -30C) for some occasional sferic activity in any stronger cores. There are indications of a convergence zone forming in a W-E orientation to the south of the M4 corridor, over southern coastal counties.

Very little shear means convection will be poorly organised, and consequently relatively short-lived. Cold air aloft will be sufficient such that any stronger cores may produce some small hail up to 1cm in diameter. Showers will decay by evening as diurnal heating subsides.

http://www.ukasf.co.uk/storm-forecasts/226

[Jane Louise]

i see no 1 posted this

Synopsis:

Broad upper trough will continue to dominate the North Atlantic to the west of Britain. In the post-occlusion environment, slight cooling aloft increases the rather limited risk of convection in places.

Discussion:... SW ENGLAND, S WALES ...

A couple hundred J/kg CAPE may develop during the afternoon hours on Friday, if sufficient insolation can allow surface temperatures to reach 12-14C. Local convergence and orographic forcing may assist in producing a convective shower or two, deep enough (ELTs down to -25C or so) for sferic activity. This is a very low probability setup, with only a 10-20% chance or so of occurring.

Major concern is slower clearance from frontal system over CS/SE England, providing excessive cloud cover and limited insolation. A nose of warm air aloft will also be present at ~700mb, such that even if parcels could be lifted from the surface this would provide a capping inversion, hence T2 ideally need to be >13-14C or so. For now we highlight the area as a SLGT, but stress a very low probability of occurrence.

... W / SW IRELAND ...

A slightly better chance (not guaranteed) across W-C Ireland during Friday afternoon for a few scattered convective showers to develop in the post-frontal environment. A few hundred J/kg CAPE should be generated with any decent insolation, and such showers should have sufficient depth (ELTs down to -40C) for sporadic sferic activity. Organisation is likely to be poor given lack of speed shear, but relatively low LCLs coupled with slight low-level directional shear may allow a brief funnel to develop.

S and SW Munster have been included in the SLGT for potential mid-level instability late in the evening and into the early hours of Saturday, but again lightning activity with this is considered a low probability.

http://www.ukasf.co....m-forecasts/225

Cheers Stu fingers crossed

[Supacell]

Agreed on the possibility of a few sferics amongst weak thundery showers that could develop across SW England, Wales and the West Country in the milder air (temperatures up to 13-14c).

The most likely place would appear to be north Devon, Somerset, South Wales and around the Bristol channel. The wind convergence line showing below could very well be a focal point for this convection.

As mentioned above, cold air aloft could bring a risk of hail in these showers. With weak CAPE/LI values and very little wind shear I would not expect organised activity/widespread sferic activity but worth a mention all the same - especially along the convergence line.

Estofex not in agreement however with the storm risk remaining well to the SW of the British Isles

http://www.estofex.org/

[Raidan]

Although a low risk but a risk all the same,Had planned to meet my mum and sister in Bristol Centre for mothers day meal but on the off chance something may crop up have decided to go to a pub in Cleavdon that way I'm by the Bristol Channel.

[SteveB]

Agreed on the possibility of a few sferics amongst weak thundery showers that could develop across SW England, Wales and the West Country in the milder air (temperatures up to 13-14c).

The most likely place would appear to be north Devon, Somerset, South Wales and around the Bristol channel. The wind convergence line showing below could very well be a focal point for this convection.

As mentioned above, cold air aloft could bring a risk of hail in these showers. With weak CAPE/LI values and very little wind shear I would not expect organised activity/widespread sferic activity but worth a mention all the same - especially along the convergence line.

Estofex not in agreement however with the storm risk remaining well to the SW of the British Isles

http://www.estofex.org/

Local BBC forecast confirms your prognosis

[Coast]

A new thread to kick off the 2013 season here: