Convective / Storm Discussion - 27th July 2013

[weatherobsuk]

The London Athletics down at olympic park could get interesting in a few hours from now.

[NOAJOA]

well it could be an interesting drive from brighton to lymington...

[Harry]

Very warm (hot) and humid...going up and up and up!!!

[rich1974]

Ok I can see it coming...I take it back BBC Weather men, just a tad late...er very late as I didn't plan anything this morning as the weather was looking kack.

[Stuart]

SKYWARN UK SEVERE THUNDERSTORM WARNING #026
ISSUED: 1130UTC SATURDAY 27TH JULY 2013 (SG/GJ)

SKYWARN UK HAS ISSUED A WARNING FOR SEVERE THUNDERSTORM CONDITIONS AS FOLLOWS:
HEAVY RAIN LEADING TO A RISK OF LOCALISED FLOODING - SOUTHEAST ENGLAND

IN EFFECT UNTIL 2300UTC SATURDAY 27TH JULY 2013

MOIST, UNSTABLE AIRMASS AND FRONTS TO PROVIDE POTENTIAL FOR SEVERE THUNDERSTORMS AND LOCALISED FLOODING.

DISCUSSION:
THERE IS GOOD MODEL OUTPUT, RADAR AND SATELLITE OBSERVATION AGREEMENT ON THE LIKELIHOOD OF A SEVERE THUNDERSTORM RISK THROUGH THE PERIOD. A MOIST, VERY UNSTABLE AIRMASS OVER THE SE REGION OF THE UK WILL BE MOVING UP FROM THE CONTINENT WITH A DEVELOPING LOW PROVIDING LIFT INTO SEVERAL HUNDRED J/KG OF MLCAPE ALLOWING FOR THUNDERSTORMS TO DEVELOP WIDELY WITH A NOTABLE AREA TOWARDS SOUTH EASTERN ENGLAND. THESE COULD FORM ORGANISED ELEVATED STORM CELLS GIVEN STRONG MID TO UPPER LEVEL SHEAR. LOCALISED SURFACE FLOODING IS A CONCERN WITH RAINFALL ACCUMULATIONS POSSIBLY EXCEEDING 40MM WITHIN FEW HOURS. PLEASE MONITOR WEATHER INFO AS NECESSARY, AND AVOID TRAVEL IF POSSIBLE.

SPOTTER ACTIVATION IS REQUESTED AND SPOTTERS ARE REQUESTED TO REPORT ALL FACTORS EXCEEDING ACTIVATION CRITERIA.

**** alerts contd below ****

SKYWARN UK SEVERE WEATHER WATCH #025
ISSUED: 0930UTC SATURDAY 27TH JULY 2013 (SG/GJ)

SKYWARN UK FORECASTS THE POTENTIAL FOR SEVERE WEATHER AS FOLLOWS:
HEAVY RAIN LEADING TO A RISK OF LOCALISED FLOODING - SOUTHERN ENGLAND, MIDLANDS, EAST ANGLIA, NORTHERN ENGLAND, SOUTHEAST AND EASTERN SCOTLAND

IN EFFECT FROM 1000UTC SATURDAY 27TH UNTIL 1200UTC SUNDAY 28TH JULY 2013

DEVELOPING LOW UNDER STRONG FORCING FROM AN ONCOMING JET NOSE, INGESTING A VERY MOIST AND UNSTABLE ELEVATED PLUME FROM THE CONTINENT

DISCUSSION:
THERE IS GOOD MODEL AND PARTNER AGENCY CONFIDENCE IN THE POSSIBILITY OF SEVERE WEATHER RISKS THROUGH THE PERIOD. A STRONG REINFORCEMENT OF THE JETSTREAM FROM THE SSW ENCOURAGES THE DEVELOPMENT OF A LOW ALONG THE BOUNDARY OF A VERY MOIST AND UNSTABLE CONTINENTAL AIRMASS. HEAVY AND PERSISTENT RAINFALL IS EXPECTED TO DEVELOP CLOSE TO THE SOUTH OF THE UK, AFFECTING ANYWHERE FROM DORSET EASTWARDS AND UP THROUGH THE MIDLANDS DURING SATURDAY WITH ACCUMULATIONS OF UP TO 40MM WITHIN 6HRS LIKELY BUT 20MM WIDELY. OVERNIGHT THE LOW MOVES NNE OFFSHORE WITH A TRIPLE POINT DEVELOPING OVER THE EAST MIDLANDS AND MOVING UP THE EASTERN SIDE OF NORTHERN ENGLAND AND SCOTLAND. RAINFALL IS LIKELY TO BE SHORTER BUT POTENTIALLY INTENSE, WITH 20-30MM POSSIBLE WITHIN A COUPLE OF HOURS. FURTHER SE ACROSS EAST ANGLIA AND POSSIBLY SOUTHEAST ENGLAND, THE VERY WARM AND UNSTABLE MIXED LAYER IS EXPECTED TO FOSTER DEVELOPMENT OF ELEVATED CONVECTION WHICH, GIVEN HIGH PRECIPITABLE WATER VALUES OF 3-4CM, MAY PROVIDE INTENSE RAINFALL IN A SHORT SPACE OF TIME, ALSO LEADING TO FLASH FLOODING. THERE REMAINS SOME UNCERTAINTY IN THE LOCATION OF THE HEAVIEST RAINFALL TOWARDS THE SE, AND UPGRADES TO THIS WATCH MAY BE ISSUED. PLEASE MONITOR WEATHER AND TRAVEL INFO AS NECESSARY.

SPOTTER ACTIVATION IS REQUESTED AND SPOTTERS ARE REQUESTED TO REPORT ALL FACTORS EXCEEDING ACTIVATION CRITERIA.

 

http://www.skywarn.org.uk/current.html

[Guest William Grimsley]

Just recieved 4.2 mm of rainfall so far today at Newton Poppleford and a flash of lightning with two gun shots of thunder!

[Dan the Man]

Big difference from previous storm events in the last couple of years has been the absence of the jet - not today. Strong upper level winds straight across central England.

[NOAJOA]

Big difference from previous storm events in the last couple of years has been the absence of the jet - not today. Strong upper level winds straight across central England.

sorry, bit of an amateur at this, what difference does that make to the storms?

[Harry]

The most stunning mackerel sky I have ever seen here!!!

[Phantom2]

temp has now dropped to 19c from 24c, humidity has shot up by 20% in the last hour ..amazing changes in such a short space of time

[dave48]

The most stunning mackerel sky I have ever seen here!!!

 

http://www.keraunos.org/

 

Upgraded forecast for extreme storms for NE France, first I have seen from them, think you are in a good spot mate to catch the edge.

[MrSunshine]

widely 26C in S-East now (according to XCWeather)

 

27.2 here in Wigan in the North West of England.

[Harry]

sorry, bit of an amateur at this, what difference does that make to the storms?

In the most basic sense a storm with no jet often struggles to organise into something more severe. The jet can help separate the up draughts from the down draughts allowing much larger storms to form. If the conditions are right it can lead to the up draught actively rotating leading to supercell development. There'll be much fuller explanations I'm sure in the offing!!

[Andy Bown]

All the models, all the forecasts, and did any of them predict storms into the Wet Country this afternoon?

Don't think so!

The weather is in charge of what it does and it looks like doing something pretty amazing in many areas today/tonight!

[Dan the Man]

Think if there was a TORCON index for Northern France, it would be about a 6/7 right about now?

[The PIT]

Ahhh I see the channel of death is at work. Will the storm make it across?

[NOAJOA]

In the most basic sense a storm with no jet often struggles to organise into something more severe. The jet can help separate the up draughts from the down draughts allowing much larger storms to form. If the conditions are right it can lead to the up draught actively rotating leading to supercell development.There'll be much fuller explanations I'm sure in the offing!!

 

ah ok, yes that does make sense, thank you

Ahhh I see the channel of death is at work. Will the storm make it across?

yes i can see that it seems to have kind of stopped from where i am, very eerie outside though

[IanR]

27.2 here in Wigan in the North West of England.

Dont expect any thunderstorms here though, them days are gone

[Summer Sun]

Synopsis:

 

Atlantic trough continues to approach and pivot towards the British Isles from the west through Sunday, lowering heights and providing some cooling aloft. Destabilising plume along a frontal boundary will continue across eastern Britain and the North Sea at first, with the focus of convective weather shifting to central and western areas during Sunday daytime with a fairly active day expected.

 

Discussion:

 

... EAST ANGLIA, EAST MIDLANDS, NE ENGLAND ...

Frontal wave/instant occlusion continues to track northwards through the early hours of Sunday morning, with the potential for some embedded elevated convection/thunderstorms, particularly across eastern parts of East Anglia. Most thunderstorms will tend to be offshore and over the North Sea by 06z. Main threats will be locally large rainfall totals (given PWAT values 30-40mm) and occasionally gusty winds in any elevated thunderstorms.


... IRELAND, NORTHERN IRELAND, SCOTLAND, WALES, MIDLANDS, SW, CS, NE + NW ENGLAND ... 

Ongoing showers/thunderstorms are likely across the Celtic Sea through the early morning hours. Through Sunday, diurnal heating and cool air aloft will generate 700-1000 J/kg CAPE across Britain, and near 1500 J/kg across Ireland/Northern Ireland. Consequently, with the passage of a couple of shortwave troughs, numerous showers and thunderstorms are forecast to develop, particularly over areas with notable upslope flow and/or low level convergence. 20-30kts DLS (25kts in lowest 1km) will enable cells over western Britain to become reasonably well-organised and long-lived.

Such instability can potentially produce hail between 2.0-3.0cm in diameter in any stronger cores, and PWAT values of 25-30mm coupled with heavy downpours and 'shower training' over similar areas may result in some local flash flooding.

 

http://ukasf.co.uk/storm-forecasts/262

[Casper]

Swindon does look like a good location at the moment, those storms in Normandy are heading NNE. Fingers crossed everyone.

[MR CB]

Ahhh I see the channel of death is at work. Will the storm make it across?

 

No - it has lost a lot of lightning activity since leaving the French coast. The cells behind maybe of more interest. I had a look out to sea and most of it breaking up into other cloud types. Nothing more than brief thundery rain but seems to be stronger to its western side...please reinvograte!

[MrSunshine]

Dont expect any thunderstorms here though, them days are gone

 

We live in hope! Might go up Billinge Hill tonight to see if I can catch any sheet lightning. 

[Neilsouth]

Ahhh I see the channel of death is at work. Will the storm make it across?

 

I've noticed this too, it's killing it right off!

[Supacell]

where you heading later mate?

Not sure yet. Current thoughts are to stay around here as doesn't look too shabby around the East Mids later on. SE England too far this evening as not free until 5 which is about the time the SE will be seeing there storms.

[NOAJOA]

ok, I'm off to hampshire, hoping theres a chance of storms there too! Good luck everyone!