Convective / Storm Discussion - 8th September onwards 2013

[Jane Louise]

New thread for Autumn  carry on here please.

[VillagePlank]

There is a risk of thunderstorms, today.

 

Potential develops across Eastern England (CAPE=400j/kg) in a moderately unstable atmosphere (KI=27,LI=-2); showers that do develop have reasonably good prospects of storm formation (TT=53) enhanced by up to 20m/s DLS shear (1-6km, no LLS)

 

 

There is some risk of large hail, and whilst storm chances are best in East England, rainfall totals are likely to be highest across the Southern part of Britain with up to 19mm falling on already saturated ground. There seems to be no risk of convective gusts, but strengthening winds from low pressure developing out in the North Sea, may cause problems later and overnight (and bring more rain) especially near to Eastern coasts.

 

Best chances look to be Lincolnshire and Norfolk, with slightly less risk across Kent, Essex, and E Sussex.

 

More from the 6z, later.

Edited September 9, 2013 by Sparkicle

[Coast]

UKASF (morning Dan!) have the following for today:

 

 

 

Synopsis

 

Sharp upper trough will lie almost stationary, with axis from eastern Scotland to the Netherlands. Through Monday it will begin to (once again) form a cut-off upper low. The associated cool mid-levels atop warm SST/LSTs will promote another day of convective activity across the British Isles.

Discussion

 

... S SCOTLAND, N ENGLAND, E MIDLANDS, E ANGLIA ...

 

Showers will be ongoing over the Irish Sea and North Sea through the early morning hours, as a result of warm SSTs. Therefore some offshore (and nearshore) lightning is possible at the beginning of this forecast period, particularly near the coast of Norfolk for example. Diurnal heating through Monday will allow showers to become more widespread over inland areas, as several hundred J/kg CAPE is generated. Showers will begin to form over northern England and southern parts of Scotland through the morning, and will gradually expand southeastwards across the East Midlands and eventually East Anglia by mid afternoon onwards. 20-40kts DLS, greatest further south, will allow cells to become organised at times, and given ELTs down to -20 to -30C some sporadic lightning is possible. Enhancement from coastal convergence along North Sea coasts may briefly increase lightning activity as showers near the coastline, and subsequently move offshore. Given also coastal convergence, a few funnels or brief waterspouts may form. Some hail, perhaps locally >1.5cm in diameter, is possible in any stronger cells.

 

 

... S WALES, WEST COUNTRY, S MIDLANDS, HOME COUNTIES, SE ENGLAND ... 

 

Models are struggling in the placement of a frontal wave due to run across northern France, with the most recent runs shifting this slightly further north compared to previous guidance. The net result is some uncertainty in the potential convective development over these aforementioned areas. Nonetheless, most models suggest an area of showers or showery rain (mixture of convective and dynamic rainfall) will run progressively eastwards across these areas, but given rather low/weaker instability, little (if any) lightning activity is expected with these showers - the exception being perhaps for Kent, Sussex and Essex later in the afternoon where instability begins to increase from the north.

 

 

In all areas, showers will decrease in coverage through the evening hours as daytime heating subsides and LSTs fall rapidly, although they will continue over the southern North Sea in particular overnight, providing a continued risk of sporadic coastal lightning from Yorkshire southwards to Kent etc.

 

 

 

[Coast]

GFS charts for reference:

 

 

That patch from East Anglia up through to the Humber looks interesting later this afternoon:

 

 

Very interesting:

 

 

 

 

 

The GFS general overview says it all I think:

 

[Nick F]

THERE IS A RISK OF THUNDERSTORMS FORECAST

 

Vaild Time: 09/09/2013 0730z to 10/09/2013 0600z

 

 

Upper and surface low over the North Sea will drive a slack but unstable N/NW flow across eastern Britain during Monday.

 

... SE SCOTLAND, N and E ENGLAND ...

 

Upper low and its associated cold mid-level air overspreading the eastern side of Britain will create steep lapse rates. Although lingering morning cloud cover may hamper convection ... weak convergence along the east coast along with insolation from any cloud breaks will allow some low-topped thunderstorms to develop within the steep lapse rate environment. Although vertical shear will be weak, storms maybe accompanied by hail, torrential rain and gusty winds. A few funnels or even a weak tornado can't be ruled out with more buoyant updrafts along surface convergence lines.

 

 Issued by Nick Finnis for Netweather.

Edited September 9, 2013 by Nick F

[poseidon]

Interesting to see how this pans out. It's raining steadily here with grey skies and MO says it will continue until evening, so prospects for diurnal heating don't look great, although the weather does looks better further north. I was surprised we didn't get more action yesterday, as some very nice cells around. Saw one coming down the M11 with mammatus.

Edited September 9, 2013 by poseidon

[Coast]

NMM TT index looking good for areas already highlighted in here:

 

 

 

 

 

[NL]

Vigorous convection occurring here in the NE,  lightning detectors are already showing storms breaking out in Northumberland and North Yorkshire.

[poseidon]

Vigorous convection occurring here in the NE,  lightning detectors are already showing storms breaking out in Northumberland and North Yorkshire.

 

Vigorous rain and grey cloud going on here in Essex.

[Coast]

Vigorous convection occurring here in the NE,  lightning detectors are already showing storms breaking out in Northumberland and North Yorkshire.

 

Is it all offshore though?

 

[NL]

According to NW lightning overlay showing sporadic lightning inland, even Carlisle has had lightning....but will it snow there come winter?..

NW 5min radar.

[The PIT]

A storm to the North East of us or Thundery shower otherwise Sheffield shield holding very well just allowing short light to moderate showers through. Radar showing plenty of shower build up but we need some some sun to get them temps up to provide more fuel.

[ChezWeather]

Quite a few cells knocking about now... 

[Methuselah]

Hard to believe, I know - but there's absolutely zilch over here...

[Supacell]

Quite a few cells knocking about now... 

 

There are indeed, and within our area too. I have my eye on the cell near Glossop.

[Summer Sun]

Thunder over Darlo as I type

[johnholmes]

one flash noted about 10 minutes ago, did not hear anything but the radar shows a pretty potent area of echoes with attendant lightning indications just N/NE to here moving SE.

An earlier shower had no elctical activity but puddles on the roads when returning about 1450, maximum rate shown as 26.6mm at 1300.

[Captain Shortwave]

Hard to believe, I know - but there's absolutely zilch over here...

Same, exactly the same conditions as yesterday, convection cap then followed by developing sea breeze resulting in it being cloudy most of the day and then the sun coming out as the cloud is forced back inland. Not a shower in sight

[The PIT]

Only trace conditions here so far. Sheffield shield doing it's normal job.

[P-M]

Heard a couple of bangs of thunder earlier in Newcastle - seemed to be coming way over the to west of the City though not overhead.

[Guest William Grimsley]

There is some big thunderstorms over N and NE England, at the moment!

[ChezWeather]

Looks very dark to my NW, heavy rain starting as well 

[The PIT]

Heavy Shower right now a little hail no thunder or lightning that'll be for Chesterfield and Dronfield no doubt.

[Guest William Grimsley]

Some lucky people, today. I wish.

[reef]

Currently under a heavy shower right now and just had a clap of thunder.

 

There's been quite a rapid drop in temperature too from around 17.1C half an hour ago to 13.0C at the moment.

 

1.8mm so far with a rain rate of 20.2mm/hr