Uk Convective General Discussion & Forecasts - April 2012

[Lewis]

strict met definition-up to 5mm is small, and yes after over 50 years of weather observing its fairly easy to make estimates.

Was just pulling your leg John.

We had some decent sized hail here yesterday and day before. Quite amazing how quickly it accumulated on the ground, was scenes of winter for a time, until of course the rain washed it all away.

[Eskimo]

I wouldn't dismiss anything at this stage! You have to realise that the SW is an entirely different kettle of fish...the SW counties are relatively narrow and surrounded by a body of water on either side. In addition, the central area is relatively high ground (the moors). The result is convergence of air, causing showers/thunderstorms not only to develop, but stick around AND continue to grow...this means that the SW is exposed to a higher threat of flooding and disruption, hence the yellow warning. The absence of a warning elsewhere does not mean that showers or thunderstorms are unlikely - there have been no warnings over the past three days yet I've had storms/downpours on each day!

Cu are now readily building around the London region, after the slow start caused by the dense fog and low cloud this morning! This has meant that the Sun has had to work a lot harder today so a much later initiation than the past few days. Sadly, it means a narrow window too, but certainly not out of the question!

Don't get me wrong, I'm not dismissing any opportunity of thundery activity, it's just the areas in which the Metoffice are calling London & the South-East, Southampton is nowhere near the South-East and especially London!

[robt]

well that shower-see radar just east of dn4, was perhaps about the sharpest one of this spell, 10 minutes of smallish hail, about 5mm diameter, as I walked along, soon taking shelter under a large fir tree, most grass was white over and it was starting to settle on parts of the pavement before it turned to rain. As to the cloud type, irrespective of the 12z prog I commented on from Net Wx for the skew-t for Doncaster, it had to be a large Cu(2) and probably extending into a Cb(3) for the hail to occur. I can't see the cloud tops yet as its still masked by other CuSc.

I'm up in DN7, and from guestimates (and the fact its covered by the CuSc rolling behind), its at least 15000ft+ to the top of the Cu. It missed me by a matter of about a mile (saw it pass just west of me then go east slightly). Think theres a Cb in there somewhere, but the back end of the shower system has covered it.

[Robbie Garrett]

Don't get me wrong, I'm not dismissing any opportunity of thundery activity, it's just the areas in which the Metoffice are calling London & the South-East, Southampton is nowhere near the South-East and especially London!

It's a fairly poor system for the general joe, but people that use it on a regular basis such as councils etc are fairly aware of it.

As someone that's keen into weather, your best bet is to take a look at the METARS and TAFS or sign up to the following website http://www.metoffice....uk/aviation/ga

It gives detailed information that covers better areas and regions, and can be more specific in detail. As Harry says, the South West is probably a breeding ground today, and all it's babys will be kids by the time they get to the South East, so this area cannot be ruled out.

An occluded front, giving areas Isolations till 18Z of 7km SHRA with isolations of +SHRA and +TSRA with SEA COT AND LAN TL 21Z

Edited April 13, 2012 by Robbie Garrett

[Lewis]

Would you say todays triggers for the thunderstorms/cells (more so for the South of the country) is due to a sea-breeze convergence, along with a little bit of CAPE?

Kind of scratching my head a bit. We have some towers here, certainly more than the magic 18,000 feet mark. Just don't have the trigger to turn these localized cells electrical in nature.

Just realized there's a trough on the FAX charts, should be around the South now, that's another trigger.

Edited April 13, 2012 by UK Storm Chasers

[robt]

Would you say todays triggers for the thunderstorms/cells (more so for the South of the country) is due to a sea-breeze convergence, along with a little bit of CAPE?

Kind of scratching my head a bit. We have some towers here, certainly more than the magic 18,000 feet mark. Just don't have the trigger to turn these localized cells electrical in nature.

I'm watching a few bits and pieces to the NE of me (over the Yorkshire Wolds direction that are definitely towering up to that height. Need to do a little bit more looking to work out what exactly has gone on though.

[johnholmes]

I'm up in DN7, and from guestimates (and the fact its covered by the CuSc rolling behind), its at least 15000ft+ to the top of the Cu. It missed me by a matter of about a mile (saw it pass just west of me then go east slightly). Think theres a Cb in there somewhere, but the back end of the shower system has covered it.

yes its still covered by CuSc so I'm unable to see the part I was under, looking round the rest of the skyline and there is nothing more than Cu (2) showing.

[Cheshire Freeze]

Small cell popped up around Preston on the 2.30 radar.....the pokier cells are quite scattered today as John has pointed out. Been dry all day here.

[Tim B]

There's small cells all around Lancashire now but at the moment they are just rain showers, had a few already.

[Lewis]

After having a quick look at the models, humidity levels, along with a higher upper 850 temps, can see why the south are getting them.

I reckon tomorrow's going to be the same, colder uppers digging southwards, with the South of the UK bringing in some milder upper 850's from the near continent (to the SE) moisture levels supportive, along with a much higher CAPE and LI, so perfect recipe for thunderstorms for Southampton/Pompey area, right along the South Coast line. Cornwall/Devon coasts could be in for some serious stuff, with a small chance of thunderstorms running through the Bristol channel, heading into central southern parts, and maybe later the home counties.

[johnholmes]

Wx Online have the Watnall 12z available and tops, with T and Td as they were here just prior to the shower, show 8-10,000ft for the majority of tops with a few with 13C and 5-6C Td to 14,000ft and a small prob of 16-17,000ft.

Edited April 13, 2012 by johnholmes

[Kookylou]

looking like Cardiff escaping at the moment. Everything seems to be up in the Brecon Beacons.

[Cheshire Freeze]

There's small cells all around Lancashire now but at the moment they are just rain showers, had a few already.

Yes, they're mostly lacking any real height with the odd one ascending far enough to produce some small hail.

[johnholmes]

The showers over the SW are partly due to convergence of the surface winds along with the higher ground of Exmoor and Dartmoor providing an additional trigger.

I also suspect that those setting off in this area and into Lincs are partly due to a similar set up, low level wind covergence in places and the higher ground of the Wolds.

[Raidan]

Fourth day of lovely sunshine and convection but based on recent days I not expecting anything thundery today.

[Lewis]

Next Tuesday is looking very good.

I know a long time away for thing's to change, more especially so with it being a low pressure system, and the angle/position will most likely change greatly but here it is;

[Cheshire Freeze]

The showers over the SW are partly due to convergence of the surface winds along with the higher ground of Exmoor and Dartmoor providing an additional trigger.

I also suspect that those setting off in this area and into Lincs are partly due to a similar set up, low level wind covergence in places and the higher ground of the Wolds.

The upland parts of north and Mid Wales are seeing development too as I suspected, most likely due to convergence as has been advertised by the GFS. The situation for N England looks rather messy and disorganised atm.

[SteveB]

I'm just loving this weather at the moment, even though I have not really had a proper thunderstorm, I saw some lightning in the distance yesterday & had some beefy showers with pea size hail 2 day's in a row.

[robt]

Overview of the UK at 1130UTC this morning. The stuff over SW Wales looks a bit interesting.

[Cheshire Freeze]

Things seem to be destabilizing slightly from the north here with some darker bases becoming evident. The sky is very congested however so spotting cloud structures isn't the easiest today.

[Herefordweather]

Looks very dark towards South/South East Wales from here.

[Aaron]

The showers developing in the dales contain hail

[robt]

Had a couple of showers develop virtually over the back of the house in the last 15 minutes. One has moved towards Scunny, the other is currently over me giving a little bit of drizzle.

Edited April 13, 2012 by robt

[Purplepixii]

Confirm thunder & lightning in Fareham again, woohoooooooooooooooooooooooo!!

[MP-R]

The sky has a lovely 'warm, slightly humid, summer afternoon' look to it with what one would call popcorn towers. I can see a long line of cbs over Wales, probably the stuff over the Brecon Beacons but so far it's just a lovely day here with sunshine overhead. Congrats to those with thunder and lightning already today.