Convective / Storm Discussion - 22nd October onwards 2013

[carl1980]

Edited October 28, 2013 by carl1980

[Chris.R]

Having some heavy rain and hail showers this morning. missed all the showers yesterday but glad to see we're not today.

[Guest William Grimsley]

There were quite a few heavy showers in Chester, today. There is lots of surface water and spray on the roads, especially, the M56. Also, there is lots of surface water and spray on the roads in Acton Bridge, too.

[Mokidugway]

Beutifull sunset tonight, big sky, lots of colours wish i had my camera with me ..

[Supacell]

I would not be surprised to see a few flashes and rumbles across NW Britain today with a little CAPE along with 30-40knts of deep layer shear and moderate levels of helicity. ELT's around -30c may promote hail up to 1cm in diameter. Estofex meterological charts are showing an area around southern Scotland where hail of 1.5-2cm could occur, although Estofex itself has this area under the 15% lightning which, considering the low risk, would appear about right. There could also be some gusty winds around heavy showers of up to 50mph. 

 

I think there is the chance of some weak thundery showers in the yellow zone with the slight risk of something more organised in the red zone. 

 

 

Tomorrow evening looking interesting in southern coastal areas, especially the IOW eastwards into Kent, Sussex, Essex etc.

Edited October 31, 2013 by Supacell

[Coast]

ESTOFEX covering the Northern half of the UK today with emphasis on Scotland:

 

 

 

Storm Forecast

Valid: Thu 31 Oct 2013 06:00 to Fri 01 Nov 2013 06:00 UTC

Issued: Wed 30 Oct 2013 23:16

Forecaster: GATZEN

A level 1 was issued for parts of western central Norway mainly for excessive precipitation.

 

SYNOPSIS / DISCUSSION

 

Weak geopotential and cool mid-level temperatures will remain over most of the west Mediterranean. Embedded in the weak geopotential, a cut-off low present east of Iberia will slowly dig southward entering northern Algeria. To the east of this trough, southerly winds will lead to low-level warm air advection resulting in steepening lapse rates especially across the Tyrrhenian Sea. Additionally, boundary-layer moisture will be rather rich from the central Mediterranean to the western Balearic Islands, whereas northerly winds advect dry air further west. Latest observations indicate that a weak surface low has formed across the western Balearic Sea with increasing convective activity. Weak vertical wind shear will not support organized convection, but the high coverage and slow storm movement will support isolated excessive precipitation that may affect parts of Italy and Sardinia or Corsica. Additionally, waterspouts are not ruled out near the coasts and along outflow boundaries. The threat seems to be to marginal to issue a threat level at this time.

 

Across the east Mediterranean, mid-level ridging and subsidence will limit the potential of deep moist convection, but isolated storms are not excluded especially in associated with offshore land/sea-breeze fronts during the night and morning hours.

 

Central Europe is dominated by weak lapse rates at the southern flank of the jet stream currently extending from the British Isles to southern Scandinavia. A short-wave trough moving east late in the period will provide strong DCVA from Scotland to the northern North Sea and the European Polar Sea, resulting in steepening lapse rates overspreading the warm sea surface. Showers and thunderstorms will therefore increase in coverage and intensity and thunderstorms are expected to spread eastward reaching Norway. Vertical wind shear is relatively weak and severe thunderstorms are not forecast. However, storms will likely contribute somewhat to the excessive precipitation along the western Scandinavian coasts.

 

 

 

[Summer Sun]

Synopsis

 

Upper trough will track eastwards across northern Britain through today, introducing much colder mid-levels. This atop warm SSTs will promote widespread convection, particularly where shortwave troughs enhance forced ascent.

 

Discussion

 

Convection will be ongoing throughout the forecast period across the highlighted areas, as cold-mid levels (-30C to -33C at 500mb) overspread relatively warm SSTs. The resultant very steep lapse rates, combined with a few hundred J/kg CAPE and ELTs down to -40C, suggests an active day for lightning across the SLGT, most likely in 'waves' as several shortwave troughs cross the area.30-40kts will allow cells to become well-organised, and given 30+kts LLS, local topography and slight coastal veering of surface winds, a funnel or waterspout is possible in this environment. Furthermore, hail perhaps greater than 2.0cm in diameter is possible from the strongest cells, along with the risk of local surface flooding from frequent heavy downpours.

 

http://ukasf.co.uk/storm-forecasts/293

 

[ZONE 51]

I would not be surprised to see a few flashes and rumbles across NW Britain today with a little CAPE along with 30-40knts of deep layer shear and moderate levels of helicity. ELT's around -30c may promote hail up to 1cm in diameter. Estofex meterological charts are showing an area around southern Scotland where hail of 1.5-2cm could occur, although Estofex itself has this area under the 15% lightning which, considering the low risk, would appear about right. There could also be some gusty winds around heavy showers of up to 50mph. 

 

I think there is the chance of some weak thundery showers in the yellow zone with the slight risk of something more organised in the red zone. 

 

31st Oct.PNG

 

Tomorrow evening looking interesting in southern coastal areas, especially the IOW eastwards into Kent, Sussex, Essex etc.

Just looked at radar and lightning and heavy downpours!... (in the areas you indicated)

Keeping watch on thunderstorm risk for S-UK this weekend, could be some surprises I think.

Edited October 31, 2013 by ElectricSnowStorm

[Guest William Grimsley]

Just looked at radar and lightning and heavy downpours!... (in the areas you indicated)

Keeping watch on thunderstorm risk for S-UK this weekend, could be some surprises I think.

 

I'm not sure why people are highlighting tomorrow evening as a possibility. Yes, there will be heavy rain in S England tomorrow night. But, I don't think there will be thundery rain in S England tomorrow night? 

Edited October 31, 2013 by William Grimsley

[Panayiotis]

Are we expecting anything on Saturday? 

[Supacell]

 

 

I'm not sure why people are highlighting tomorrow evening as a possibility. Yes, there will be heavy rain in S England tomorrow night. But, I don't think there will be thundery rain in S England tomorrow night? 

 

 

On earlier runs there looked to be some interest but later runs have shifted this further and further south until now I think any lightning activity later today/tonight would be the other side of the channel. So, on current forecasts you are correct.

[Supacell]

Are we expecting anything on Saturday? 

 

I take it you mean convective-wise, in which case I think thunderstorms are unlikely away from the outside risk around the south and west coasts. A lot of heavy rain for southern parts though during this evening and tonight but it looks mostly dynamic and convective showers tomorrow, but lightning activity low IMO.

Edited November 1, 2013 by Supacell

[Guest William Grimsley]

On earlier runs there looked to be some interest but later runs have shifted this further and further south until now I think any lightning activity later today/tonight would be the other side of the channel. So, on current forecasts you are correct.

Oh right, I didn't hear any mention of showers or thunderstorms later today/tonight on BBC Weather.

Edited November 1, 2013 by William Grimsley

[Jane Louise]

Morning all,

A couple of forecasts for today from Estofex and Dan from UKASF.

 

Storm Forecast

Valid: Sat 02 Nov 2013 06:00 to Sun 03 Nov 2013 06:00 UTC

Issued: Fri 01 Nov 2013 22:23

Forecaster: PISTOTNIK

A level 1 was issued for Ireland and Wales for severe convective wind gusts.

 

SYNOPSIS and DISCUSSION

 

A broad zonal flow covers most parts of Europe, distorted by a progressive, deepening trough and another powerful cyclone which cross the British Isles during the forecast period. Minimal and rather shallow CAPE is forecast in the belt of augmented low-level moisture along its cold front over Northern Portugal, Northern Spain and France, and then again in its wake over the British Isles and the Bay of Biscay, where lapse rates steepen in response to QG lift. Shower activity in these areas may be accompanied by a few lightning strikes. 0-3 km vertical wind shear does not exceed 15 m/s, but the strong background wind field can promote some severe wind gusts even with weakly organized convection over Ireland and Wales (25-30 m/s flow at 850 hPa).

Further downstream, a forerunning frontal wave crosses BeNeLux and Northern Germany but gets dampened by a lack of forcing. Leftover patches of (elevated) CAPE near its crest might allow isolated thunderstorms in the 06 to 12 UTC time frame. However, their northward displacement from the stronger kinematics of the warm sector should preclude any severe weather.

 

Scattered to widespread showers will form in the cool maritime air mass off the Norwegian coast, which is characterized by deep mixing and very weak vertical wind shear. They will barely grow deep enough to produce any lightning.

 

To the South, quiescent conditions prevail over the Mediterranean Sea, but scattered showers are still possible in the range of a decaying upper-level low around Italy. An isolated waterspout is not ruled out, especially along land breeze fronts in the morning hours.

 

http://www.estofex.org/

 

 

UKASF

 

Synopsis

 

Large upper trough will approach from the Atlantic, with axis aligned N-S down western Britain by 00z Sunday. At the surface, a deepening low will track northeast from Ireland to the Borders, and thereafter exiting across the North Sea during the evening hours.

Discussion

 

Behind the wrap-around front, cold mid-levels will overspread warm SSTs, significantly steepening lapse rates and generating a few hundred J/kg CAPE. Numerous showers and a few thunderstorms are forecast to develop across Ireland during the midday and afternoon hours, this activity translating to and becoming more widespread across Irish Sea and Celtic Sea areas, and along adjacent exposed west-facing coasts. Particular attention is given to Pembrokeshire, Devon and Cornwall during the evening and into Saturday night as very steep mid-level lapse rates suggest more widespread lightning activity - potential, perhaps, to upgrade some coastal areas to MDT.

 

An increase in offshore convection is also forecast near the coasts of eastern Scotland, grazing Aberdeenshire and tracking further northwards through the evening towards Orkney, and Shetland after midnight, hence the inclusion of a second SLGT area.

 

In both cases, 30-40kts DLS will allow cells to become well-organised, especially at first, and with strong LLS and SREH, a funnel or waterspout is certainly possible. Dry surface air suggests cloud bases will be quite high, albeit dropping slightly during the evening hours as the surface layers moisten. Some small hail is likely in several stronger cells.

 

http://ukasf.co.uk/storm-forecasts/294

[Nick F]

Storm & Convective Forecast

 

 

Issued 2013-11-02 08:31:34

Valid: 02/11/2013 0800 to 03/11/2013 0600

 

THERE IS A RISK OF THUNDERSTORMS FORECAST

 

Synopsis
A sharpening upper trough with a strong SW'erly jet ahead of it moves off the Atlantic across western Britain today. A deepening surface depression on the forward side of the trough moves NE across N Ireland and S/E Scotland today, with the centre falling to around 976mb off eastern Scotland this evening. An occluding cold front associated with the depression will move N and E across the UK today, lying roughly SW Scotland to CS England by midday, rPm airmass following this cold front will be unstable across Ireland and western UK.

... IRELAND, SW ENGLAND, WALES, N ENGLAND and SW SCOTLAND ...

Apart from convection giving isolated lightning and possible strong wind gusts in squall along cold front moving east, main convective events today will occur in the west as increasingly cold air in the mid-levels overspreads Ireland and western UK today following cold front, which will steepen lapse rates as upper trough moves in from the west. As a result, some shallow instability will develop in the moist air above the still seasonally warm SSTs, with a few 100 j/kg CAPE indicated by GFS in the post frontal rPm airmass. 30-50 knts of deep layer shear and increasing low-level shear reaching > 35 knts suggests organisation of any convection - showers/storms will tend to move through quickly - so although rainfall maybe intense - flooding will not be a big issue unless convection forms trains. Main threats appear to be strong convective gusts (60-70mph) - which has lead me to issue a SLIGHT risk for Ireland and SW UK. Also, given strong LL shear, enhanced instability over seas/coastal areas created by seasonally warm SSTs may provide sufficient buoyancy to allow rotation of updrafts, so one or two isolated waterspouts or tornadoes can't be ruled out.
 

Issued by: Nick Finnis

Edited November 2, 2013 by Nick F

[Mokidugway]

Large cell to my south,mama observed, possable rumble of thunder or was it the wind ?...

[Cloud 10]

Large cell to my south,mama observed, possable rumble of thunder or was it the wind ?...

 

 

Quite a few strikes in the North-West at the moment.

 

[Mokidugway]

Just back from the saturday shop, weather throwing out practicaly everything ,wind ,hail ,rain, thunder, lightening !!!.

[Darandio]

Just back from the saturday shop, weather throwing out practicaly everything ,wind ,hail ,rain, thunder, lightening !!!.

 

Got exactly the same here, but on the east. It's gone utterly mental out here.

[Thundery wintry showers]

Not as spectacular as the 20th October one, but here at Sandhutton in North Yorkshire I've had some thunder and lightning, all of which passed to the south and south-east of here.  That's three thunderstorms from south-westerlies in the space of a fortnight, in October/November, all of which made it over the Pennines- that's got to be an unusual occurrence!

[cheese]

Screw this autumn - sorry, I mean craptumn. Boo.

[IanR]

Thunderstorm just to the east of here at about 16.15 pm  saw about 8 flashes and some rumbles, not as good as the one last week and the one a fortnight ago, which co- incidentaly happened about the same time on a Saturday

[The PIT]

No thunder here but heavy rain and hail

[Cloud 10]

Had a really impressive downpour here around 16.15 with strong winds on the back edge of it

which then electrified as it headed out into the North Sea.

 

Next band of showers just starting now.

[NorthYorkMoorsSnow]

Been lighting loads hear power went off for a few seconds.