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Uk General Convective Discussion & Forecasts, 24th August '12>


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#1 Nick F

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Posted 24 August 2012 - 06:24

A new thread as the other was running to 38 pages.

To start the ball rolling I have issued a forecast for today (below), looks to be some potential for storms across southern Britain today with passage east of quite an active occluding front this afternoon and evening ahead of slow moving but fairly deep low near Sern Ireland. I'm sure Coast will post up the other forecast available:


Valid: 24/08/2012 06:00 - 25/08/2012 06:00
Headline: ... THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FORECAST...

convmap_240812.jpg

Synopsis
A fairly deep depression just SW of Ireland will track slowly east today (Friday), associated occluding front will move east across England and Wales this PM, by 00z Sat the low around 995mb expected off SW Ireland with occluded front lying Anglesey to Suffolk.

... S IRELAND, S ENGLAND, WALES, MIDLANDS, E ANGLIA ...

Fairly moist boundary layer (dew points 14-16C) in vicinity occluded frontal zone, as moist Tm air is entrained into low circulation, is indicated by GFS to yield 300-600 j/kg MLCAPE during frontal passage across Sern Britain today PM. Dry air slot at 500mb indicated by GFS to over-run the frontal zone will further enhance convective activity. Embedded thunderstorms are therefore possible with passage of the front. Fairly strong low-level shear (20-25 knts) is indicated along with low LCLs (as low as 600m) in vicinity of front - so surface-based storms with potential to develop mesocyclones that spawn one or two tornadoes can't be ruled out - so have included a SLIGHT risk. Otherwise, storms may produce marginally severe hail, strong wind gusts and torrential downpours with a risk of localised flooding. Storms may continue overnight along southern coastal counties.

Tornadoes seen to date:


Fredericksburg (TX) 01/05/07, Stafford (KS) 05/05/07, Medicine Lodge (KS) 06/05/08, Hooker (OK) 05/05/08, Stuttgart (AR) 10/05/08, Big Spring (TX) 14/05/08, Sielbert (CO) 21/05/08, Hoxie (KS) 22/05/08, Collyer (KS) 22/05/08, Dighton (KS) 23/05/08, Ness City (KS) 23/05/08, Ellis (KS) 23/05/08, Quinter (KS) 23/05/08, Pratt (KS) 26/05/08, Kearney (NE) 29/05/08, Aurora (NE) 29/05/08.

#2 Coast

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Posted 24 August 2012 - 06:35

Owwww, do they mean us?

Storm Forecast

Posted Image

Valid: Fri 24 Aug 2012 06:00 to Sat 25 Aug 2012 06:00 UTC
Issued: Thu 23 Aug 2012 23:04
Forecaster: TUSCHY
A level 1 was issued for SE Ireland mainly for heavy rain.

A level 1 was issued for parts of W/SW UK and NW France mainly for a few tornado events, marginal hail and strong wind gusts.

SYNOPSIS

Brisk SW-erly flow pattern continues over most of W/C-Europe. This assists in the set-up of an active baroclinic boundary, which runs from S/C France to Poland. Numerous disturbances graze that boundary and cause scattered to widespread thunderstorm initiation. Hot and dry conditions prevail over the Mediterranean. A strong depression enters the forecast area from the west with unsettled conditions affecting Ireland and UK.

... W/SW-UK, parts of Ireland and parts of NW France ...

A strong 995 hPa depression moves from Ireland to W-UK. Attendant well structured cold front enters the forecast area from the west during the day with a slow eastward motion forecast. A pronounced dry slot overtakes the cold front and assists in an active thunderstorm period mainly within the highlighted 50% lightning area. Those storms evolve within an environment with strong directional shear (e.g. 15 m/s LL shear and 200 J/kg SRH-1) and LCLs well below 1000 m. A few tornado events are possible next to strong wind gusts and marginal hail. The severe risk decreases after sunset although some surface based convection may persist over N-France. Strong shear still supports an isolated better organized thunderstorm event with strong wind gusts and an isolated tornado event. Hence the level 1 was expanded all the way to NE France.

An occlusion wraps around the depression's center with an augmented probability for training thunderstorm activity mainly over S-Ireland. Heavy rain will be the main hazard as modified subtropical air wraps around the center of the depression.


Well that backs Nick F's view and UKASF also going with:

Moderate
Forecaster: Dan
Last Updated: 2012-08-23 21:34:00
Valid: 2012-08-24 00:00:00 - 2012-08-24 23:59:00

Posted Image

Synopsis:

Upper trough approaches from the Atlantic, with a deep surface low at the surface. A plume of high ThetaE is advected around the centre of the low in associated with a cold front/occlusion complex. Some convection is expected embedded along and behind the front.

Discussion:

Cold front/occlusion migrates northwards and eastwards across England, Wales and Ireland with embedded convective elements likely. Favourable lapse rates and a few hundred J/kg MLCAPE may allow some sporadic sferic activity to occur, more likely over SW England, S Wales and S Ireland.

20kts DLS and >25kts LLS may allow some line convection to occur along the front, and with backed surface winds a funnel or weak tornado is possible, especially along the south coast where backed winds are heightened due to the onshore component. Hail up to 1.5cm in diameter is possible from stronger cores embedded within the line.

Scattered convective showers/storms are also expected behind the main front.

... S IRELAND ...

Behind the front, under the centre of the low with light and variable winds (and thus low-level convergence), >900J/kg CAPE is possible as cool mid-levels (-17/-18C at 500mb) overspreads the area. Sferic activity could be quite widespread here for a time during the afternoon and evening hours, provided there is enough insolation to generate surface-based convection. It is worth noting that the MDT is purely dependent on sufficient cloud breaks.


Hmmmm, some agreement then?! Nothing yet from SkyWarn or TORRO, here's a few charts to ponder:

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There's that CAPE in the SW:

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Just getting into the South and South East reaches by dark:

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Note the hotspot over Portsmouth/IOW?

Posted Image

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Not so much surface base CAPE:

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Lapse rates are still up at 21Z

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Plenty of rain!

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Extensive tornado threat area!

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Helicity right over the South coast:

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Isolated thunderstorms in The Channel and over SW England (Come on Jane Louise!!!)

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Still going up through the Midlands and heading NE into the night!

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Time to update your radar subscriptions if you haven't already!!

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#3 Jane Louise

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Posted 24 August 2012 - 07:19

Oh Coast, surely it has to happen for me today!this summer has been another let down for me. I almost took up stamp collecting lol. I must admit I do have a good feeling about today so once again it's fingers crossed and plenty of radar watching.I live in hope lolPosted Image
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#4 Stuart

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Posted 24 August 2012 - 07:30

Good Luck jane this could be your day

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#5 Jane Louise

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Posted 24 August 2012 - 07:34

Good Luck jane this could be your day


Well, thank you kind sir.Posted Image I really do hope so.It's been a long time lol.
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Please come visit us at the Storm Enthusiasts group we'd love to hear your storm stories and more!! Posted Image
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#6 Paul

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Posted 24 August 2012 - 07:44

A quick look at the nmm today show some fun and games are possible!


Heavy rain moving northeast
nmm1.png

TT index indicating severe storms are possible.
nmm2.png

Plenty of energy on offer
nmm3.png

Will anyone get to see something like this?! (Photo by Dave Powell from day 1 of our Arizona lightning chase tour)
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#7 Stuart

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Posted 24 August 2012 - 07:59

after the weekend let down here i going give up for the year now Posted Image

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#8 TEITS

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Posted 24 August 2012 - 08:21

Personally im looking forward to tomorrow when it looks as though widespread storms are possible. All im expecting today is a band of heavy rain moving across my region this evening.

July 23rd 2013
 

lightning_1.jpglightning_2.jpglightning_3.jpgCapture.jpg

 

 

 

 

 


#9 Nick F

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Posted 24 August 2012 - 08:58

Been a few strikes down in Cornwall, so certainly some embedded strong convection in the rain band across the SW atm. Usual multiple stikes off the eastern England coast over the North Sea - don't know what it is about that area - but it seems to be a good place. Storm chase on a North Sea Oil Rig anyone?
Tornadoes seen to date:


Fredericksburg (TX) 01/05/07, Stafford (KS) 05/05/07, Medicine Lodge (KS) 06/05/08, Hooker (OK) 05/05/08, Stuttgart (AR) 10/05/08, Big Spring (TX) 14/05/08, Sielbert (CO) 21/05/08, Hoxie (KS) 22/05/08, Collyer (KS) 22/05/08, Dighton (KS) 23/05/08, Ness City (KS) 23/05/08, Ellis (KS) 23/05/08, Quinter (KS) 23/05/08, Pratt (KS) 26/05/08, Kearney (NE) 29/05/08, Aurora (NE) 29/05/08.

#10 Supacell

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Posted 24 August 2012 - 09:03

Will anyone get to see something like this?! (Photo by Dave Powell from day 1 of our Arizona lightning chase tour)
davepowell2.jpg


I would love it if I could get a capture like that.

Those NMM charts you show have the area of storm risk much covering a wider area and further north with things even flirting with my area by later this evening. I wasn't expecting north of about Worcestershire to Suffolk today but maybe I should start recharging my camcorder.
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#11 Robbie Garrett

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Posted 24 August 2012 - 09:06

Nothing thundery till tomorrow according to the latest TAF's for the Southeast.

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#12 ajpoolshark

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Posted 24 August 2012 - 09:10

yep, camera on charge currently.....I might slip out for a birthday chase today (I'm 21 for the second time, work it out Posted Image ) so a big storm would round off the day nicely! Posted Image
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#13 Robbie Garrett

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Posted 24 August 2012 - 09:14

yep, camera on charge currently.....I might slip out for a birthday chase today (I'm 21 for the second time, work it out Posted Image ) so a big storm would round off the day nicely! Posted Image


Happy 52nd Birthday aj :)

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#14 Chris W

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Posted 24 August 2012 - 09:16

I had a quick look this morning and it looks pretty good around here tomorrow in terms of CAPE/LI and the wrap-around occlusion passing over, added to the Met Office yellow warning and mention of thunderstorms for the North West. As for today it looks from UK Weather World's charts as if there's an area of CIN passing from Pembrokeshire in this direction later in the day - how much of a factor might this be in terms of storms making it to Cheshire this evening? Weather Underground has Chester slated for a thunderstorm late evening with an 80% chance of precipitation.

#15 Kain

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Posted 24 August 2012 - 09:17

Happy Birthday Aj :)

Lets hope we get something today as a gift :p

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#16 gottolovethisweather

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Posted 24 August 2012 - 09:29

Happy Birthday Aj Posted Image

Lets hope we get something today as a gift Posted Image


How about this for AJ's birthday. Posted Image

The Lightning Star.gif

At risk of straying slightly off topic here so....... Back on topic, do you folk not think that the cloud detritus will affect the situation for storms, as I must say it's damn cloudy here and not excessively warm either. Posted Image

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#17 Staffordshire

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Posted 24 August 2012 - 09:48

yep, camera on charge currently.....I might slip out for a birthday chase today (I'm 21 for the second time, work it out Posted Image ) so a big storm would round off the day nicely! Posted Image

happy birthday mate! hopefully the gods will give you somethong good hey... and that would mean getting me too maybe... :p

Edited by Staffordshire, 24 August 2012 - 09:49 .

The weather always pays its debts.

#18 Costa Del Fal

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Posted 24 August 2012 - 09:54

yep, camera on charge currently.....I might slip out for a birthday chase today (I'm 21 for the second time, work it out Posted Image ) so a big storm would round off the day nicely! Posted Image

Happy Birthday mate! Have a good one and I hope Mother Nature delivers for you! She did for me on 28th June, 2 days before my bday! :D

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#19 AWD

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Posted 24 August 2012 - 09:55

Rain looks very showery in the SW/South Wales currently with the heavier, more organised rain in the channel heading for the South Coast!
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#20 gottolovethisweather

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Posted 24 August 2012 - 09:59

Happy Birthday mate! Have a good one and I hope Mother Nature delivers for you! She did for me on 28th June, 2 days before my bday! Posted Image


And to think in past years, we use to get several 28th June's in one season. A different risk area to what we've seen in recent weeks so maybe it's the South and the Midlands turn for once. Mind you, I expect the Lincoln area will strike lucky for a change.

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Finally, two quotes from two very different recent Winters.

"Wasn't it enough that we lived through the coldest December for over 100 years that no one alive has experienced?" and "Wasn't it enough that we lived through the wettest December - February for over 250 years that no one alive has experienced?"