Convective / Storm Risk Discussion - 21st June 2013 onwards

[Tempest]

What is an anaprop please. Thanks

[Sprites]

What is an anaprop please. Thanks

This is when the weather radar shows rainfall, but it is an error as it isnt really raining. Happens more often in High pressure, can also be caused by wind blowing millions of insects together.. lol

[paul m]

BBC news saying anywhere between London Northwards could get a storm but the Lightning indicator over Lincs....Meh im going to cry

[Bluebreezer54]

This is when the weather radar shows rainfall, but it is an error as it isnt really raining. Happens more often in High pressure, can also be caused by wind blowing millions of insects together.. lol

 Yep. It's a false radar return ( anomalous propagation ). Im not quite sure that millions of wind blown insects play a part though ?!

Edited July 13, 2013 by Bluebreezer54

[NorthNorfolkWeather]

Obviously all lying in this morning.  BBC weather just talking about showers anytime after 16:00 and rumbling "Anywhere from the South East of England, all the way to Yorkshire".  Looks quiet either side of that through.

 

NMM Shows it starting in the North but some heavy stuff further South later.  Tomorrow Looks like London gets some heavy.

showers

 

NMM for 17:00 today

Edited July 13, 2013 by NorthNorfolkWeather

[Gordon Webb]

Forecast for the Midlands is the chance of an isolated heavy shower during the afternoon , Thunder does not even get mentioned

 

Met office site has the thunderstorm symbol for Wednesday in the London area

[Mesoscale]

its all well and good having that kind of Cape and LI but if theres nothing to trigger it then its worthless.

[VillagePlank]

BBC Breakfast just forecast slow and intense thunderstorms!

[Ben Sainsbury]

Forecast for the Midlands is the chance of an isolated heavy shower during the afternoon , Thunder does not even get mentioned

 

Met office site has the thunderstorm symbol for Wednesday in the London area

Not surprised fairly large amounts of cape and precipitation widespread across southern England. In my personal opinion this could be a better opportunity for a wider area of the UK.

[Gordon Webb]

a better opportunity you say on Wednesday but the Cape and LI are lower so I assume other elements come into play on Wednesday

its all well and good having that kind of Cape and LI but if theres nothing to trigger it then its worthless.

 

You just have to look at Northern England yesterday to see that was the case

[Ben Sainsbury]

a better opportunity you say on Wednesday but the Cape and LI are lower so I assume other elements come into play on Wednesday

Capping doesn't look too much of a problem. But the cape values shown still looks to be decent.

However I'm only a 14 year old boy, I don't know everything!

Edited July 13, 2013 by interestingweather

[AWD]

Oooh, maybe Wednesday then;

I'll enjoy it while it lasts! lol.

[NorthNorfolkWeather]

Good grief, most people seem to have taken their "Unhappy Pills" this morning.  There will be a slight destabilisation of the atmosphere with that cold front coming south before it just fades away.

 

As for further South temps heading to 32 will produce some intense ground heating, if that can burst through the cap, there'll be some fun.

 

In the meantime

[Ben Sainsbury]

Is Estofex ever going to unleash their forecast with a lvl 3 over us;)?

[Gordon Webb]

Good grief, most people seem to have taken their "Unhappy Pills" this morning.  There will be a slight destabilisation of the atmosphere with that cold front coming south before it just fades away.

 

As for further South temps heading to 32 will produce some intense ground heating, if that can burst through the cap, there'll be some fun.

 

In the meantime

 

I'm not unhappy about this forecast

 

As I'm sure most are aware by now Thunderstorms terrify me so this is not a bad forecast even if the BBC still like to focus the showers/storms at my location which does have me a little concerned

[johnholmes]

the predicted ascent for Doncaster at various times shows how the atmosphere is probably going to change between now and 18z, the 12z issue is obviously the most unstable. Perhaps not enough at the surface unless some kind of 'trigger' action is around, sea breeze into the Manchester basin or in Lincs/E Yorks, a minor trough developing due to the intense surface heating. Perhaps a prob 20-30% of an isolated storm in various places, nothing widespread on that ascent. Anything that did form would be quite intense.

Best you look to any forecast by Nick F for a more general UK guide and probably better informed than myself anyway.

Doncaster upper air data

http://www.netweather.tv/secure/cgi-bin/premium.pl?action=cskew;sess=2ff6e70647a8dfc6d7bae64061a01105

simply type your nearest town in

Edited July 13, 2013 by johnholmes

[VillagePlank]

Heathrow, 12z, today,

 

 

Small convective potential (K=24) today despite today's large instability forecast (LI=-7) Given strong surface heating I'd expect some showers to form with some of them being thunderstorms (TT=49) Where storms do form - and they are likely to be sparse - they will be quite long lived, slow moving, and maybe hail and frequent lightning, (CAPE=1550j/kg) and certainly some very heavy rain is possible with perhaps up to an inch in some places.

 

I think you'd be lucky to catch one in the SE corner. More losers in this area than winners, today. North East coast of England favoured today, although virtually any of England could see one.

Edited July 13, 2013 by Sparkicle

[VillagePlank]

[Coast]

ESTOFEX say:

 

 

 

 

... British Isles ...

 

Isolated to scattered afternoon thunderstorms are likely under anticyclonic influence. Both instability and shear will be too weak for an augmented severe weather threat.

 

 

 

showforecast.cgi.png

 

Sorry, snap!!! :lol: 

[East_England_Stormchaser91]

ESTOFEX say:

 

 

 

 

Sorry, snap!!!

Ah yessssss, knew they'd do it! 

Would be more close to banking on a storm now they've issued a warning, they are balls accurate most of the time. 

Temp is currently rocketing at the moment, proper heatwave feeling like old times!

[VillagePlank]

I don't think GooFus has a great handle on this. Compare the following,

 

 

(I know one is for Herstmonceaux the other is for Heathrow, but that's all I can get for free!)

[Coast]

Let me chuck a few charts up so you can poke around them and see what you think:

 

Big dollops of CAPE available according to GFS:

 

 

 

Lower level CAPE not up to much:

 

 

 

Someone's put a huge blanket down over the Home Counties this afternoon!! :lol: 

 

 

Lapse rates very encouraging 

 

 

 

Not a lot of moisture though:

 

 

But some helicity:

 

 

You can see the trend with GFS as to where it would place anything, but can inhibition be overcome?

 

 

It looks confined to coastal areas, so maybe a bang and flash later this afternoon!

[VillagePlank]

I am hoping that the CIN is what's going to do it for us in the SE, Coast: V strong surface heating with moderate CIN. Hmmmm, I hope it can hold out until about 2pm ....

[Bobby]

There's plenty of CAPE but it will it be utilized. Need some kind of trigger such as a convergence zone or uplift over upland areas I think. Not sure the cold front will be enough. Perhaps the Pennines could be a good spot today, near the coasts too if see breezes can create a convergence. Otherwise the odd isolated thundery shower could be the case. If there's the trigger and the cap gets broken there's lots of CAPE so any storms could quite decent I'd say.

 

NMM has a convergence zone inland off the south coast, going up to London, might be useful:

 

Edited July 13, 2013 by Bobby

[Coast]

I am hoping that the CIN is what's going to do it for us in the SE, Coast: V strong surface heating with moderate CIN. Hmmmm, I hope it can hold out until about 2pm ....

 

Yep:

 

 

 

I think Dan over at UKASF has it about right (morning if you're in here Dan):

 

 

 

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 ...

 

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.