Uk Convective General Discussion & Forecasts - April 2012

[Convective]

It is so irritating. Practically everywhere has heard a rumble of thunder except here It's the wrong time of year to be honest here. The sea temperature and air temperature are too similar for anything to blow in..

[Andy Bown]

The London storms muct have something to do with the UHI effect? Even though it's not particularly warm, London will be warmer

than elsewhere.

A much more interesting mid-late pm in West Wiltshire than the previous 3 when we have been 10-20 miles away from storms in

various directions. Right now a developing cell is to the West and the sky is a swirly angry grey/black, seems like the earlier

convergence zone nearer the South coast is now further North - a set up which can deliver big goods for this area although I've

a feeling it may just develop into an area of moderate rain rather than anything thundery - ears are pinned back though lol.

Interestingly humidity is quite low at 58% but it has been quite warm at 15.8c max.

[Robbie Garrett]

Another rumble of Thunder, I am guessing from a cell to my Northwest??? If it gets closer and rumbles/lightning again... that's Number 6 this week and this year and the 3rd today.

Where on earth is this potential coming from !!! Either that or 2012 is going to be a very thundery year. There is minute cape, but no lifted index. HMMMM!!!

Edited April 13, 2012 by Robbie Garrett

[nanu]

Just seen Green Lightning!!!.... due to hailstones in the clouds possibly??.. but no hailstones dropping here yet.

[Rustynailer]

I could not post this yesterday http://www.iwcp.co.uk/news/news/lightning-hits-building-43887.aspx I was working in the woods near by when the storm appeared. we had 4 lightning strikes, 2 of the strikes are in the above link. I can safely say they are the worst 4 lightning strikes I have ever witnessed. It was like a bomb going off, my ears were buzzing. The storm lasted about half an hour, the worst I have been scared by a storm in 46 years...

[Wet'n'Dry]

Afternoon all, the old git here

Just had a minor shower pass but looking to my West is a monster tower, I would guess anyone between Dartford and Chatham is going to get a show, lucky bleeders !!!

[Chris.R]

don't forget me, as i've already said, no thunder here down wind of you Convective, Merseyside is as stormless as the IOM. We get more thunder here in winter than in summer.

[Kookylou]

lovely and sunny here still but the view east is amazing. lots of towers.

[nanu]

well thats moving off.. giving me a beautiful huge double rainbow.

[staplehurst]

Another rumble of Thunder, I am guessing from a cell to my Northwest??? If it gets closer and rumbles/lightning again... that's Number 6 this week and this year and the 3rd today.

Where on earth is this potential coming from !!! Either that or 2012 is going to be a very thundery year. There is minute cape, but no lifted index. HMMMM!!!

CAPE isn't everything my friend... besides there is a few hundred J/kg of it, and I take it you are using GFS LI with it's poor model resolution?

[Robbie Garrett]

CAPE isn't everything my friend... besides there is a few hundred J/kg of it, and I take it you are using GFS LI with it's poor model resolution?

I know that, but you couldn't really have a stable atmosphere and have Thunderstorms surely??

What's the best CAPE forecasts then??

[staplehurst]

I know that, but you couldn't really have a stable atmosphere and have Thunderstorms surely??

What's the best CAPE forecasts then??

It's far from stable!

Taking a look at the 12z Herstmonceux sounding, if you put a surface temperature of 13.3C (as per latest Heathrow observation) you generate 569J/kg CAPE

Herstmonceux already had just shy of 400 J/kg CAPE at 1pm without any modifcations to the tephi, couple that with the low-level convergence - you get your rapid convection...

Edited April 13, 2012 by staplehurst

[Robbie Garrett]

It's far from stable!

Taking a look at the 12z Herstmonceux sounding, if you put a surface temperature of 13.3C (as per latest Heathrow observation) you generate 569J/kg CAPE

Herstmonceux already had just shy of 400 J/kg CAPE at 1pm without any modifcations to the tephi, couple that with the low-level convergence - you get your rapid convection...

Ah my understanding of it's fairly poor, except those thing we learn in aviation.... and that's mostly to scare us from flying in such conditions.

Do you have links to such charts??

Just starting to Shower here, could go bang here shortly. But organisation of this cell looks fairly poor....

[Harry]

Ah my understanding of it's fairly poor, except those thing we learn in aviation.... and that's mostly to scare us from flying in such conditions.

Do you have links to such charts??

Just starting to Shower here, could go bang here shortly. But organisation of this cell looks fairly poor....

Yeah was just thinking that - some huge drops just fallen and it's gone dark! Feels like we're close to round 2 but with such a poor view of the sky I can't make out much.

[MP-R]

I need to seriously move house to London or Southampton it would seem!

For the rest of the year's weather in London it's not worth it.

Gone jet black to the south and east here with very pronounced rain shadows over the Mendips. They have however died down a bit and lost their electrical power as they've moved northwards, which does somewhat contradict what is supposed to happen lol.

[staplehurst]

Ah my understanding of it's fairly poor, except those thing we learn in aviation.... and that's mostly to scare us from flying in such conditions.

Do you have links to such charts??

Just starting to Shower here, could go bang here shortly. But organisation of this cell looks fairly poor....

No worries, there was always a little potential today (wasn't a complete right off) looking at the 0z tephis from last night. Just needed a bit of insolation and surface convergence to develop it.

You can see the Herstmonceux sounding here: http://expert-images.../03882_1312.gif but you'd have to manually draw the new parcel based on your revised surface temperature. I used RAOB which we have at work to draw it quickly.

You can see that tephi already has 328J/kg just with the conditions present when the radisonde was released, so if you add another degree or so during afternoon heating - every little helps...

Edited April 13, 2012 by staplehurst

[Robbie Garrett]

Yeah was just thinking that - some huge drops just fallen and it's gone dark! Feels like we're close to round 2 but with such a poor view of the sky I can't make out much.

I have looked up and the organisation looks a lot better, may go bang any second now....or minute.

No worries, there was always a little potential today (wasn't a complete right off) looking at the 0z tephis from last night. Just needed a bit of insolation and surface convergence to develop it.

You can see the Herstmonceux sounding here: http://expert-images.../03882_1312.gif but you'd have to manually draw the new parcel based on your revised surface temperature. I used RAOB which we have at work to draw it quickly.

You can see that tephi already has 328J/kg just with the conditions present when the radisonde was released, so if you add another degree or so during afternoon heating - every little helps...

Ah thanks for that, looks understandable. But the LI is +2 right??

[Cheshire Freeze]

Convergence in action now.....stuff over Wales heading NE, stuff over NW England heading S and guess who's in the war zone......can see very notable virga to the SW and seemingly getting closer.

[staplehurst]

I have looked up and the organisation looks a lot better, may go bang any second now....or minute.

Ah thanks for that, looks understandable. But the LI is +2 right??

True, but the lifted index is purely the temperature change of a parcel which is taken from the surface to 500mb compared to the actual temperature of the surrounding environment at 500mb. Most of these showers/storms have formed below 500mb today, and although it is a good indication for stability, it's not the best of indices to use in today's case I guess.

Edited April 13, 2012 by staplehurst

[johnholmes]

I really would recommend you storm fans to have a go at being able to use the skew-t diagrams if you are not already able to do so. All the phrases and accronyms that are used to show whether it might shower or hail or thunder are taken from the data available on a skew-t.

Its easy to find a tutorial on this-simply go to the Net Wx Guides and its about the first thing on there-seems pretty popular and if you spot any problems with it please pm me and I'll try and sort it out.

Remember that forecast skew-t's are available both on the free Net Wx list of data and also you can get more from the Extra versions.

[robt]

Got a large bank of cloud forming behind the house (over the Aire Valley and York), possibly a few high tops in there. No sign of any naughty stuff yet from it.

[legritter]

brilliant hvy  hail storm here ,one distant clap of thunder . storms maturing to my s/west ,will that big cluster over devon  make it south of bristol .it looks an interesting early evening  fingers crossed .

[Cheshire Freeze]

Well the developing cell to my west looks like it's going to slip too far south of here......shame because from my window it looks like a bit of a bad boy. Wrexham being pummelled

[Robbie Garrett]

True, but the lifted index is purely the temperature change of a parcel which is taken from the surface to 500mb compared to the actual temperature of the surrounding environment at 500mb. Most of these showers/storms have formed below 500mb today, and although it is a good indication for stability, it's not the best of indices to use in today's case I guess.

Lifted index, is lapse rates in theory isnt it? and those charts you've shown me are the lapse rates for the atmosphere.

Hence why the lower based CB today, compared to the ones that where pretty high based Tue-Thur. Makes sense.

[robt]

This is the one round the back of me, looks like its slipping off towards North Lincolnshire.

Development has probably been aided by the Aire Valley Power Stations..