Convective / Storm Risk Discussion - 14th June 2013 onwards

[Staffordshire]

Just had 3 or 4 rumble with a heavy shower that passed towards Lichfield (Staffordshire should have been lined up perfectly). Big nasty cloud and shower heading in again now.

hi mate, i only got heavy rain off that, not too sure why, remember im not in lichfield.city

[Stuart]

Synopsis:

Upper trough migrates eastwards across the British Isles through Saturday. At the surface, a cold front will clear eastwards through the early morning hours, followed by a very showery/convective scenario.

 

Discussion:

A cold front will migrate eastwards across England and Wales through the night-time hours, at the beginning of the forecast period (forming a wrap-around occlusion over Scotland). Under the left-exit region of the jet on the forward side of the upper trough, some 40-60kt DLS will allow embedded convective elements to develop, with the possibility of occasional broken convective lines/QLCS capable of producing locally very strong gusty winds and short periods of very heavy rain. Low-level helicity generated from backed surface winds ahead of the main surface front, rapidly veering westerly along/behind the front increases the threat of a tornado as the front continues to track eastwards. Isolated lightning/thunder is possible along the cold front, but given expected convective depth to be fairly shallow, this is likely to be rather isolated, if any at all.

Shortly behind the front, a cluster/area of heavy showers is expected to pass through, particularly across Wales and SW England, this having a greater chance of producing local thunder given MLCAPE values of 200-300 J/kg.

Through the day on Saturday scattered showers and a few thunderstorms will become widespread across many parts of Britain, with up to 800 J/kg SBCAPE by afternoon. Particular attention is given to E England where longest land track coupled with best diurnal heating and organisation from 30-50kts DLS is likely to lead to more widespread sferic activity. However, wrap-around occlusion debris with areas of more dynamic rain will tend to result with a rather messy situation in places, reducing surface temperatures (and SBCAPE) locally.
The strongest cells (for organisation and longevity) are expected to be across the Midlands, Lincolnshire and East Anglia during the afternoon, with hail possibly >2.0cm in diameter in any stronger cells. Sufficient low-level helicity may allow for one or two low-topped supercells, capable of producing a tornado. Thus, these aforementioned areas will need monitoring for potential upgrade to SVR threat level through Saturday, although any severe threat should tend to be quite localised.

 

http://ukasf.co.uk/storm-forecasts/250

[robt]

Absolutely ridiculous rainfall in Hatfield, Doncaster in the last 5 minutes. Gone from nothing at all to absolutely barrelling it down, with little bits of hail in there as well..

[Supacell]

Was just rain here by the time the shower arrived. Looks from ukasf as if there will be little lightning activity tonight but tomorrow looking potentially good. Thus my plan will be to sleep tonight and then chase tomorrow, maybe head to somewhere like south Lincolnshire.

[Chris.R]

Heaavy shower just passed

[Harry]

UKASF doesn't like given us anything in the SE corner Boo Dan on UKASF, boooooooooo!!!! lol

 

Still setting my alarm just in case for the front marching through. 

[paul m]

It's looking lively in Lincs'.

Always ruddy lively in Lincs GREEDY BUGGERS

[Summer of 95]

Gone very dark here and wind picking up, had a really heavy shower about 3- any chance here?

[Supacell]

Always ruddy lively in Lincs GREEDY BUGGERS

 

And it looks like Lincolnshire may be the best place tomorrow too.

 

It is a complicated situation as it looks like several areas to watch tonight and tomorrow. At present I would say tonight's front has the potential to bring severe convective weather as it passes through with the risk of hail, damaging convective wind gusts and the possibility of a tornado should any storms develop. As was said earlier by Nick, the potential would have been much better had this come through during daylight. The expectation is that lightning activity will not be high though due to the lack of CAPE.

 

To my eyes it looks as if the post frontal airmass contains a much higher likelihood of lightning. CAPE increases as do lapse rates across western parts  very early in the day and this airmass expands east to be all the way to the east coast by around 7-8am tomorrow morning. We then have another day of heavy showers and thunderstorms but a better chance of severe thunderstorm potential tomorrow.

 

UKASF has their MDT risk across the NE Midlands, Lincolnshire, East Yorkshire and northern East Anglia. GFS lightning wizard charts show the best overlap of shear, helicity and CAPE being across the Midlands and into Lincolnshire and East Anglia through the day (slightly south and west of where UKASF have it).

 

I think this translates to the risk of organised storm activity across the Midlands early on, expanding across Lincolnshire and East Anglia through the afternoon. These storms have the potential to develop into an MCS or possible supercell bringing strong gusts, hail and a tornado risk. Elsewhere the storms should be less organised and less severe but some of the best lapse rates in the UK are further north and so perhaps more lightning across the NE of England later in the day. 

 

If i was to pick an area that looks good to benefit from shear, helicity, good lapse rates, higher CAPE and negative LI indices it could very well be somewhere in a line from Leicester to the Wash through the afternoon and across into East Anglia by evening. 

 

Problem could be cloud hanging around from the nights cold front, although the strong SW winds should help shift this out into the North Sea allowing the sun to give some heating from early on. Storm motion will be fast so for me I think chasing will be hard, but get into a good position ahead of storms it could end up being a very good day

[Convective]

Even looking at the sky now it looks much more energetic than usual. Usually you get these systems arriving and they just appear as one big murky mass of cloud but you can just about make out embedded cumulus and cumulonimbus clouds in this one this evening.

 

Here's the view from WirralCam now. Looking out over Hoylake, Wirral.

 

Edited June 14, 2013 by Convective

[Chris.R]

looking forward to this one, hopefully i'll see something tonight.

[Tom Jarvis]

What time is it due to go through the Sussex area

[Chris.R]

Prolonged heavy showers here now and I did just hear a large distant boom, not sure what it was, sounded like thunder, but it could have been the docs. Didn't notice a sferic before it so don't know.

[Cheshire Freeze]

Radar doesn't look too interesting

[Alex95]

Rain coming down in torrents here.

[Keraunic]

Very sunny with a clear blue sky in Norwich...and still quite breezy. But very pleasant. Dont think we'll have anything tonight by way of storms.

[carl1980]

Showers here for the last few hours,some very dark clouds about had to put the light on a few times

[Alex95]

Hailstones and torrential rain in the last 10 minutes here although it seems to be easing off now a bit.

[Supacell]

Have to admit to being a bit surprised about the lack of anything from Skywarn and Torro considering there is a tornado risk tonight.

[PolarWarsaw]

The radar looks fairly dull to be honest, just looks like a regular weather front.

[Cheshire Freeze]

The radar looks fairly dull to be honest, just looks like a regular weather front.

 

Yep, where is this tornado risk going to pop up from?

[Adi F]

So what thoughts do people have for the south coast this evening and over night? 

[Panayiotis]

Yep, where is this tornado risk going to pop up from?

-

Edited June 14, 2013 by Panayiotis

[Panayiotis]

Tornado risks (according to the 12Z GFS) are between 9PM and 12PM for the SW: With a small risk in the far SW at 9PM then a greater area of risk stretching from Taunton down to Southampton then up to Gloucester.

[virtualsphere]

Looking at the NMM, it seems the convective elements are anticipated to occur later in the night over parts of the S and E.  The chart for 8pm from the 12Z run suggests a fairly wide area of frontal rainfall pretty much as the radar is showing.  Not a lot of change before midnight, but by 3am there are some notably heavier bursts showing, while the overall area of the frontall precipitation has decreased.

 

I did try and post some images but I think it's restricted because it's only available on Extra