Uk Convective General Discussion & Forecasts - April 2012

[Stormyking]

Hi all, I haven't posted on here for a long time and for that I apologise I been too busy! But tonight I felt like was a good time to return to posting as we had one of the most incredible looking storm structures and colours of it was just beautiful! There was only 2 cg's and 2 cracks of thunder but also so much rain and hail! But here is a couple of pictures I took of the beautiful thing!

Edited April 11, 2012 by Stormyking

[NO LONGER POSTING]

Roll on tomorrow...One clap of faint thunder and 2 heavy showers..

[Neilsouth]

Can I PLEASE request a favour ?

Between 1.30 and 2.30 a very heavy shower passed over whitstable/herne/herne bay and dropped alot of hail and intense rainfall!. Some of the grass started to go white and there was flooding in parts, what was also very noticable was a temp drop to just 2C it went from 7.5C down to 2C and it looked very sleety/slushy in the hilly parts of herne, kent.

What I need is a radar image of that time and any reports of such a low temp?

[Tim B]

Probably in the late 90s, I didn't see a chart for it... but we had Thunderstorms all night long, constant thunder and lightning every 2-3 seconds.

95, I remember the storms that year well.

[Eskimo]

Can I PLEASE request a favour ?

Between 1.30 and 2.30 a very heavy shower passed over whitstable/herne/herne bay and dropped alot of hail and intense rainfall!. Some of the grass started to go white and there was flooding in parts, what was also very noticable was a temp drop to just 2C it went from 7.5C down to 2C and it looked very sleety/slushy in the hilly parts of herne, kent.

What I need is a radar image of that time and any reports of such a low temp?

I can give you the meteox archive for the radar image, just add your time and date

http://www.meteox.com/hist.aspx?URL

[Lewis]

Can I PLEASE request a favour ?

Between 1.30 and 2.30 a very heavy shower passed over whitstable/herne/herne bay and dropped alot of hail and intense rainfall!. Some of the grass started to go white and there was flooding in parts, what was also very noticable was a temp drop to just 2C it went from 7.5C down to 2C and it looked very sleety/slushy in the hilly parts of herne, kent.

What I need is a radar image of that time and any reports of such a low temp?

Hello,

Noticed no reply has been made by one of the experienced forecasters, and I'm sure if I hazard my idea and it's wrong someone will correct me.

First thing is the equipment you was getting your temp reading from exposed to the ice deposits left from the hail stone, as this could have had an impact on the reading, if not....

I'm almost certain a cold front passed through today, so the temperatures ahead, and behind would be have a pretty stark contrast. Could be 12-13c ahead of the cold front, and 7-8c behind the cold front.

Another thing is that when you have convective showers, the freezing level 9 times out of 10 will automatically drop considerably especially in such setups like today with upper 850's not too high to that of our normal warm/moist uppers we get in summer that is associated with our proper thunderstorms.

Don't forget it get's super chilled up there like a freezer

Hope what I said makes sense, that or I need to read more books lol.

[Neilsouth]

Thanks both

[johnholmes]

Can I PLEASE request a favour ?

Between 1.30 and 2.30 a very heavy shower passed over whitstable/herne/herne bay and dropped alot of hail and intense rainfall!. Some of the grass started to go white and there was flooding in parts, what was also very noticable was a temp drop to just 2C it went from 7.5C down to 2C and it looked very sleety/slushy in the hilly parts of herne, kent.

What I need is a radar image of that time and any reports of such a low temp?

Can I PLEASE request a favour ?

Between 1.30 and 2.30 a very heavy shower passed over whitstable/herne/herne bay and dropped alot of hail and intense rainfall!. Some of the grass started to go white and there was flooding in parts, what was also very noticable was a temp drop to just 2C it went from 7.5C down to 2C and it looked very sleety/slushy in the hilly parts of herne, kent.

What I need is a radar image of that time and any reports of such a low temp?

do you not have Net Wx radar?

Drops in temperature at this time of year can be very noticeable and have been mentioned on a couple of days by the duty forecaster on BBC. I doubt that area saw any snow, it can be difficult at a distance to decide white being hail or snow, hail is the most likely given the conditions today at the surface and in the upper air.

Re the radar, well worth checking it out for that area at the time you mention.

[Nick F]

Storm & Convective Forecast - Issued 11/04/2012 22:00

Valid: 12/04/2012 00:00 - 13/04/2011 00:00

Headline: ... THERE IS A RISK OF THUNDERSTORMS FORECAST...

Synopsis

Upper trough will continue to sit across the UK on Thursday, with surface low pressure close to eastern UK drawing an unstable slack polar flow across much of the UK.

E IRELAND, ENGLAND and WALES

Airmass across the UK will again become unstable to surface heating in the strong April sunshine on Thursday, thanks to cold polar air aloft with a low freezing level creating steep lapse rates. GFS generates 300-500 j/kg CAPE across central, southern and eastern England and eastern Ireland - so here we are likely to see the greatest risk of thunderstorms developing - accompanied by hail and gusty winds. Though isolated thunderstorms are possible elsewhere across England and Wales. Like Wednesday, light winds aloft will mean storms will be slow-moving, bringing locally high rainfall totals in a short space of time leading to the risk of localised flooding. Storms should fade after dark.

Issued by: Nick F - Forecaster for Netweather

[Convective]

Probably in the late 90s, I didn't see a chart for it... but we had Thunderstorms all night long, constant thunder and lightning every 2-3 seconds.

But recently, on the 28th June, there was about the same cape and negative lifted index you'd get in the tornado alley/states. (2000-3500) (LI -5 to - 7) But it's not all about the CAPE/LI - from what I learnt in my aviation training you need the following

1. Deep instability in the atmosphere such as that once the air keeps rising it will continue to rise, such as a steep lapse rate with warmer air in the lower levels and cold air in the upper levels.
   
2. A high moisture content - so high dewpoints
   
3. A trigger action, such as air rising from a front forcing the air aloft. A mountain forcing the air alof, or from strong heating of the air in contact with the airs surface, this is evident in the jungles in africa. Check out Sat 24, they get Thunderstorms daily. Or the heating of the lower layers of a polar air mass as it moves to lower latitudes (i.e towards the equator)
   

Various other things such as shear help provide thunderstorms.

I see.. Thanks for that!

I doubt I will see anything tomorrow.. nothing yesterday and nothing today apart from before. I opened the conservatory door to let some air in and heard a very faint but intense/ deep rumble of thunder. It must of originated from Dumfries and Galloway!

[Lewis]

Thanks both

Hope these help

[Nick F]

Re: the large drop in temperature, I suspect downdrafts in the storms would have brought cold upper air sinking to the ground - thus the sudden drop in temps. The freezing level is fairly low atm the polar airmass, around 1000 metres.

I agree with John though that the sleety/slushy deposits are most likely to be melting soft hail.

[Robbie Garrett]

Issued by: Nick F - Forecaster for Netweather

One thing I've noticed, is the CB's are very high based, probably 3800ft, 4800ft. Rain that falls, doesn't actually fall it is mostly virga. Annoyingly this shows up on the radar as rainfall doesn't it??

The southeast only had max 2mm rainfall on 24hrs ending 2100 on Tuesday. Wednesday is similar at 3mm

95, I remember the storms that year well.

Those are the ones, I at 2 years old ran out of my bed at the time and into my nan and grandads haha!! Scared the crap out of me.

The late 90s where very similar though, constant night time MCS, and these where very very windy and scary.

[Aaron]

Storm & Convective Forecast - Issued 11/04/2012 22:00

Valid: 12/04/2012 00:00 - 13/04/2011 00:00

Headline: ... THERE IS A RISK OF THUNDERSTORMS FORECAST...

Synopsis

Upper trough will continue to sit across the UK on Thursday, with surface low pressure close to eastern UK drawing an unstable slack polar flow across much of the UK.

E IRELAND, ENGLAND and WALES

Airmass across the UK will again become unstable to surface heating in the strong April sunshine on Thursday, thanks to cold polar air aloft with a low freezing level creating steep lapse rates. GFS generates 300-500 j/kg CAPE across central, southern and eastern England and eastern Ireland - so here we are likely to see the greatest risk of thunderstorms developing - accompanied by hail and gusty winds. Though isolated thunderstorms are possible elsewhere across England and Wales. Like Wednesday, light winds aloft will mean storms will be slow-moving, bringing locally high rainfall totals in a short space of time leading to the risk of localised flooding. Storms should fade after dark.

Issued by: Nick F - Forecaster for Netweather

Cheers again Nick. Tomorrow is looking like the last day for true convection potential in these parts, the past two days have proved to be disappointing as usual.

[Costa Del Fal]

GFS 18z is not that good for tomorrow now. Still OK but downgrades potential a bit.

Saying that the GFS often undercooks potential. I notice on the 18z this evening, it has shown there was much more CAPE etc today than earlier runs have shown.

Edited April 11, 2012 by Blizzards

[Sprites]

The free netweather sferics map seems to more accurate than the previous version, Dundee had more strikes than Cambridge too... , nice skies earlier ,but no thunder here yet...

[lewisosd]

Ah sprites! Nice to be back in storm season! Current downgrades on potential as usual but I still have a good feeling about tomorrow. Some lovely cloudscapes around today and had two slushy hail showers in Stowmarket. No thunder heard unfortunately.

[Robbie Garrett]

Just for fun!!

[Sprites]

Ah sprites! Nice to be back in storm season! Current downgrades on potential as usual but I still have a good feeling about tomorrow. Some lovely cloudscapes around today and had two slushy hail showers in Stowmarket. No thunder heard unfortunately.

yes its early in the year, have to make the most of our convective days, hope you are healthy for youre stormchase marathon..

[Neilsouth]

Regards to the large drop in temp... hail sleety nature this was reported

http://theweatherout...worth-Kent.aspx

! no wonder if it dropped to 2c!

3cm of hail fell in 10 minutes. It was absolute carnage. The car thermo dropped from 7c to 2.5c at its peak and yes there was wet snow at the end of the thunderstorm too.

The 3cm cover was from hail and not snow but it just goes to show how cold uppers can get dragged right down to the surface under such large convective and thundery cells.

- Thanks to everyone for the info by the way

Edited April 11, 2012 by Victor Meldrew

[A.J]

Decent convection has already initiated over the west midlands...had two heavy showers already this morning, with more developing over north wales pushing into the cheshire gap...Definitely a promising start to the day

[multi cellular thunderstorm]

Got a good feeling about today. For some reason when I got up and looked outside I felt like I was in America on the storm chase. I think it's the feeling of anticipation and the early convection and the fact that I'm wearing a t-shirt that I haven't worn since I was last out there!

Also good to see the Met Office mention thundery showers in the text forecast again, which they had removed from the forecast last night.

Another day of radar and sky watching to come

[Eskimo]

What's on offer today folks?

[Eskimo]

Cumulus is starting to initiate over Central England.

[Coast]

What's on offer today folks?

ESTOFEX say:

Storm Forecast

Valid: Thu 12 Apr 2012 06:00 to Fri 13 Apr 2012 06:00 UTC

Issued: Wed 11 Apr 2012 17:00

Forecaster: GATZEN

SYNOPSIS

Cold mid-level air masses are present over most of Europe. The through center with the coldest air and well-mixed lapse rates up to 400 hPa is situated across the North Sea region and will expand into Scandinavia during the period. The low geopotential also extends into Iberia, while a ridge is situated over the east Mediterranean.

In the cold air, steep low-level lapse rates can evolve in response to diurnal heating. Best low-level moisture is situated along a broad frontal boundary from the Iberian Peninsula to the Alps, the northern Balkans, and the Baltic States, where a couple of convergence zones exist.

British Isles, northern France, Benelux, Germany

Within the deep polar air mass, diurnal heating will likely result in thunderstorms. The best synoptic forcing is expected across Germany at the cyclonically sheared flank of a mid-level jet streak. Weak vertical wind shear is expected and well-organized storms are not forecast. Marginally severe hail is not ruled out given the low wet-bulb zero.

21st OWS have:

Reasonable chance of more lightning today

Maybe it's my areas turn later this afternoon?

Good luck everyone!