Convective / Storm Risk Discussion - 21st June 2013 onwards

[Jax]

had cloud build here too, sadly all for nought.

[johnholmes]

Hi John and thanks for the informative post, just one question if I may ? I have heard the term 'heat low' mentioned several times in the last few days but despite researching I still have no idea what this is, and what causes it. Can you help please ? Cheers. BB54

I'll tryUsually the term is associated with a low that develops over Iberia due to the intense heating there. It is due to this heat causing pressure to fall, hot air is less dense than colder air. As it rises so the pressure at the surface falls, hence heat low?hope that helps

[Summer Sun]

Synopsis:

 

A large anticyclone over the east Atlantic continues to dominate the weather across the British Isles for the foreseeable future. A weakening cold front drifts slowly southeastwards across northern Britain during Saturday, while in the upper levels a slight troughing in the overall pattern will migrate southwards across eastern England.

Discussion:

 

... YORKSHIRE, EAST MIDLANDS, W EAST ANGLIA ...

* Updated at 14:18BST to extend SLGT further north in light of recent developments *

From the start of the period, large values of (capped) MLCAPE will be present, drifting slowly southeastwards across northern/central Britain associated with a zone of increased ThetaE / moisture advection. Through Saturday daytime, significant diurnal heating will lead to the development of 1000-1700+ J/kg SBCAPE over these areas, albeit heavily capped. Slight weakening aloft, coupled with seabreeze convergence and possible local topographic features may break the cap locally, allowing a few isolated thunderstorms to form during the afternoon over Yorkshire and Lincolnshire, and possibly further south later in the afternoon and evening, although the signal for this in NWP output is weaker. A general southward-drift of such isolated thunderstorms is expected.

Shear is rather meagre, so severe weather will be limited, but given the large potential instability, some moderate-sized hail up to 3.0cm in diameter and large rainfall accumulations over a small area (given PWAT values >30mm and slow-storm motion) are possible - the risk of moderate hail being greatest if any isolated cells can develop in the southern half of the SLGT risk area (where the point probability of thunderstorm development is lower than further north).

These isolated thunderstorms will gradually decay through the mid/late evening as diurnal heating eases, although given large MLCAPE values over southern England it is possible that one or two may become elevated through the late evening hours.

 

http://ukasf.co.uk/storm-forecasts/253

 

[johnholmes]

why on earth have you posted the above so late at night, its already done and finished with?

[Coast]

Fingers crossed for Wednesday for us. Still a long way to go though.

 

Glad to see some had storms yesterday! GFS Free atmosphere for London shows Wednesday right through to Friday with a slight risk:

 

[Nick F]

I suspect again that, despite GFS CAPE charts painting lots of greens and yellows each day across much of the UK during the coming week, warmed parcels of unstable air will be prvented from rising far by a stout inversion - particularly the further south you are. Though later in the week we may see the cap broken across northern, central and western areas, with help of sea breeze convergence and orographic lift.

[Stuart]

I hope you right nick not had 1 storm here this year

[TEITS]

Looks like we might have to wait until Wednesday for some more storm action. The GFS yesterday was spot on for my location.

[Bobby]

We've had some good storms here this year, on the 26th January! Multiple overhead storms in one day with fork lightning and everything. Better than any summer thunderstorm I can remember for ages. Had some big storms early May 2011 also including a down-burst with winds I estimated at ~100mph. Picked up cast iron garden chairs and table and threw them 30ft across the garden and rain/hail so intense it looked like a whiteout blizzard. Was scary.

 

Don't seem to get storms in actual summer anymore though. Can't even remember the last time.

Edited July 14, 2013 by Bobby

[Ben Sainsbury]

Lots of cumulus has recently been developing?

[Ben Sainsbury]

And it's actually trying to develop upwards, anyone else experiencing this currently?

[Bobby]

There's lots of cumulus here too but I think there's too strong a cap for them to get high enough to amount to anything.

[MP-R]

Lots of cumulus has recently been developing?

 

I can see them too out to the northwest, one of which is trying to spread a little. Certainly feels ripe for a storm.

[Methuselah]

It's here, too...moving roughly west to east...

[Panayiotis]

This is the situation in Cardiff (looking NE), I have been watching these clouds develop over the last hour and some of the cumulus clouds do start to tower however as Bobby said they seem to 'collapse' due to strong capping.

You can also see the clouds develop on the radar in S.Wales but they dont seem to come to anything, hopefully we get something decent next week (how many times hve we said that!)

http://www.sat24.com/en/gb

Edited July 14, 2013 by Panayiotis

[Methuselah]

Aye, P; these descending airmasses can be very misleading?

[Kookylou]

This is the situation in Cardiff (looking NE), I have been watching these clouds develop over the last hour and some of the cumulus clouds do start to tower however as Bobby said they seem to 'collapse' due to strong capping.

You can also see the clouds develop on the radar in S.Wales but they dont seem to come to anything, hopefully we get something decent next week (how many times hve we said that!)

http://www.sat24.com/en/gb

I just popped on to see if anyone else had noticed them! Will probably spend my day with hopes up constantly checking the sky!

[Tom Jarvis]

I am about to get a flight from Glasgow to Exeter and have got a window seat will hopefully be able to see some storms fireing

[Bluebreezer54]

I'll try

Usually the term is associated with a low that develops over Iberia due to the intense heating there. It is due to this heat causing pressure to fall, hot air is less dense than colder air. As it rises so the pressure at the surface falls, hence heat low?

hope that helps

Yes it does, thanks John.

[nitro_deluxe]

Parts of SE Wales, Weston/ Bristol zone maybe favourable for a little very localised action?

[Michelle Baker]

Hope Bristol see's something! Windy and clouding over

[nitro_deluxe]

Hope Bristol see's something! Windy and clouding over

Portishead, half decent band - maybe a good vantage point today? Been there just the once many moons ago, few storms en route via the M5

[MrNooo]

A lot of cu around here, some building up very nicely, especially over towards the Marlborough Downs direction

[Ben Sainsbury]

Very nice looking cloud structure looking north from Bristol. Very high, explosive cloud and another developing cloud to my south east!

[nitro_deluxe]

Hottest part of the day fast approaching - case of now or never

Not quite perhaps as many storms as yesterday, and even then we had only two maybe three discreet areas of convective ppn..in the UK.

Good-luck, chances very slim for many virtually nil for here. Then again dining al fresco later, no complaints if I'm honest!