Uk General Convective Discussion & Forecasts, 13th March 2013 onwards

[Raidan]

Where in Bristol are you Trikx198?

[AWD]

Cumulonimbus coming my way!

Edit; seems to be passing a little west!

Yes, I've got a similar scene to my west too.

[Raidan]

Grt in thunder and lightning

[AWD]

Thunder in Bristol. No lightning seen yet though.

[Trikx198]

Thunder and lightning and pea sided hail in Bristol!

[AWD]

Thunder and lightning and pea sided hail in Bristol!

Oooooh!! I must be so close, just drizzle here but very dark.

Where abouts in Bristol are you?

[Raidan]

Had head out kitchen window looking north watching the heavy rain with hail mixed in when lightning shot across the sky then boom,hope that's not it.

[AWD]

Got pea sized hail here now too.

Covered everything white in seconds.

Edited March 16, 2013 by AWD

[Raidan]

Its freezing sat in the window but I think that was it haven't seen or heard anything since.

[Raidan]

Just had a hail shower and now moderate rain,no T&L

[East_England_Stormchaser91]

Looking like some intense rain over Derby across to Newark up to Sheffield, any reports of thunder up there folks ?

Edited March 16, 2013 by East_England_Stormchaser91

[Stuart]

Good evening alll

Synopsis:

Large upper low continues to dominate across Britain, with various surface lows developing and dumbelling around the main parent low during Sunday. Notable inter-model differences in placement and intensity of certain shortwaves, and hence highlighted areas are subject to slight shifting - for Ireland the SLGT area may need extended further southwards, while for E/SE England this may need extending either further westwards or shrinking eastwards.

Discussion:

... EAST ANGLIA, SE ENGLAND ...

On the eastern flank of a developing shortwave, with surface low forming and running northeastwards across this area, 300-400 J/kg CAPE may be generated as LSTs reach 7-8C, allowing convective showers to develop. This shortwave is likely to be a mixture of dynamic and convective rainfall (hill snow) with the majority of convection on its eastern flank, as highlighted by the SLGT area. However, difficulty lies with the exact placement and track of the shortwave, and subsequent placement of the SLGT area.

Due to the messy nature, there is likely to be excessive cloud at times and thus sferic activity is likely to be quite isolated/sporadic. As a result, it is questionable as to whether this warrants a SLGT or not, but for now we will issue one for the potential for a few rumbles of thunder and perhaps some small hail in any decent convective cells.

... IRELAND, NORTHERN IRELAND ...

Again difficulty in highlighting the boundaries of the SLGT threat area, and it is possible it may need to be extended/moved further south depending on the final placement and track of the surface low. A few hundred J/kg CAPE will allow scattered showers to form over the area, and with ELTs as low as -40C should be sufficiently deep for a few pulse-type thunderstorms. Small hail is possible in some showers, else severe weather seems unlikely.

... S/SE SCOTLAND ...

Potential for a few convective showers to form during the day, but given weak instability the chance of sferic activity is currently considered too low for a SLGT threat level.

http://www.ukasf.co.uk/storm-forecasts/229

[TheToastPeople]

Just had a pretty good hail shower with several big gust of wind, a setup like this in summer would have been awesome

[Supacell]

Looking like some intense rain over Derby across to Newark up to Sheffield, any reports of thunder up there folks ?

At the time you posted this there was some torrential rain and heavy hail with some approaching pea size, it also turned fairly gusty too. But I heard no thunder and no sferics picked up on any lightning detectors. I was thinking it looked like a thunderstorm outside but the parameters were not condusive for thunderstorms today this far north.

[Big Bird]

Ahh I've waited so long for the convective season in the UK to resume. And now finally the time has come! Everything written here seems to be only about storms confined to the South-West, but around 4:15-4:20 this afternoon a beefy shower over Rugby, Warwickshire brought two brilliant flashes of lightning just as I was coming back from work there. In the summer I would sneer at this type of "storm", but after 203 days of being storm-starved (previous thundery activity observed on the 25th of August) today's event felt like bliss!

[Coast]

Glad to see some of you got convective weather yesterday and lets hope it continues through the Summer.

ESTOFEX have the bulk of the action today just over in France, with maybe something for us along the South coast:

Storm Forecast

Valid: Sun 17 Mar 2013 06:00 to Mon 18 Mar 2013 06:00 UTC

Issued: Sun 17 Mar 2013 05:41

Forecaster: VAN DER VELDE

A level 1 was issued for northwestern France mainly for some chance of tornadoes.

A level 1 was issued for southern Spain and northern Morocco mainly for isolated large hail and severe wind gusts.

SYNOPSIS

A large low pressure system is situated over British Isles and its radius of influence spans entire western Europe. The low is rather old and its frontal systems broken up, the more active systems are two shortwave troughs moving around Ireland into the English Channel. The temperature gradient increases over the Iberian Peninsula as result of cold air advection from the large low towards the south and warm air advection from the subtropics. As slight frontal wave develops and the warm sector is unstably stratified.

An upper cold pool resides east of Poland, cut off from any warm air by the Russian cold airmass.

DISCUSSION

...northwestern France area...

In several models, the better CAPE seems to lie north of the jet, but an overlap between more than 20 m/s DLS and CAPE should be present in the southern half of this level 1 area. The northern half, however, still shows more than 10 m/s bulk shear in the 0-1 km layer, which combined with low LCL heights may favor a tornado if a mesocyclone-bearing storm could form (probably needs the deep shear). Hodographs show modest curvature and helicity, though.

[Coast]

Is it just too far South?

There's a bit of CAPE there:

Surface CAPE over my region:

Plenty of vorticity so maybe something helical will form?

Note the streamlines over Hants and Sussex:

But not bags of shear:

Another long shot but I'll get a bacon sarnie in me, catch up on the F1 GP and get up the Downs!!

[Coast]

SatRep for today:

[AWD]

Looks to be a couple of small cells over South Devon currently,

[Convective]

Areas most likely to see anything I believe today

[Coast]

Tomorrow looks like it could be a good day for funnel and spout activity across central southern England

Been having a look at this week and that was quite good

Mind you I looked out at some good Cb's over The Channel first thing this morning and GFS has a general outlook that might include a rumble or two:

IOW looks favourite from that overview, here's the specifics:

Some mixed CAPE over Hants and Dorset:

Intense area of spout potential and surface CAPE in that region:

Convergence and shear also in Hants area:

Very steep lapse rates along the South coast all day:

Small threat of MCS propagation up through The Channel from lunchtime:

Edited March 18, 2013 by Coast

[Coast]

There's a lot going on over us today!

[Nick F]

A few strikes over sarfwest London recently, just plain old rain here a little further east.

[Coast]

[MP-R]

Friend of mine just put a thunder status on facebook. He's in Egham at the moment. I think it may have been an hour or so ago though.