Convective weather - 2nd-3rd November 2011

[Chris K]

Hoping for an interesting day tomorrow/tomorrow evening! As others have mentioned, there's some good potential, but will be a day of radar watching to see how things develop during the day. Seriously hope the usual story of, "its coming directly our wa....ohh what...noooo its starting to move NE!", doesn't happen again and miss us by about 10-20 miles haha.

[Nick F]

21z satellite image shows CB clusters off the NW tip of Iberia this evening, this is what is headed our way for tomorrow:

Sferics associated with these clusters too:

[The watcher]

Might be some good photo opportunities for me off the East Coast of NI looking out towards NW England tommorow. Shall check on it in the morning and see how far West it has progressed.

[Chris K]

At the moment, most of the predicted fun by the BBC and Met Office is going to miss me from both sides, The activity in the day looks to cross Cornwall/Devon, then head towards N Ireland, and the stuff during the evening/night across CS England will be just a little too far east and miss me again....hoping this changes! The path of those detected sferics in Nicks post on radar, etc above looks promising so far though. Going to be glued to the radars all day for this last ounce of storm hope.

[Slingfox]

Looks to be some hefty rain moving through at the moment, it's raining cats and dogs outside.

[Nick F]

Ok, going to bite the bullet and issue a moderate risk for Thursday across a lage swathe of southern and western areas, a set-up we don't see too often and more than capable of being ideal conditions for one or two 'nadoes!

Storm & Convective Forecast - Issued 03/11/2011 00:00

Forecast Summary Map

Click for full size

Valid: 03/11/2011 00:00 - 04/11/2011 06:00

Headline: ... THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS FORECAST...

Synopsis

A deep long-wave trough to the west of the British Isles extends south from Greenland to the west of Iberia during the forecast period. At the surface, a deep area of low pressure is expected to be situated to the W of Ireland, with a slow moving cold front across E England and troughs moving north further W in strong southerly flow.

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

A well modified rPm airmass will move in across much of the UK behind cold front clearing east overnight/Thurs morning, with increasingly cold air of the upper trough to the west advecting northeast aloft, while a deeply moist southerly flow advects across England, Wales and Eire towards the surface.

Therefore, increasngly steep lapse rates will spread from SWern UK across much of southern, central and western UK during Thursday - which will allow heavy showers and thunderstorms to spread north during the day. Already CB clusters with sferics are evident across NW tip of Iberia tonight, this area of steep lapse rates/convective activity arriving across SW England/S Wales in the early morning before increasing N and E in coverage during Thursday.

Given rather deep moisture advecting north, which is indicated by GFS to generate several 100 j/kg CAPE combined with a fairly strongly sheared environment with 30-50 knots of deep layer shear and 20-30 knots of low-level shear ... any storms may quickly organise into line segments or perhaps even one or two isolated low-topped supercells capable of producing moderate-large hail (2-3 cm), strong wind gusts (40-60mph), intense rainfall and perhaps one or two tornadoes, even a strong tornado, particularly towards southern and westen coastal areas where SSTs enhance low-level potential of vigorous updrafts. Therefore have issued a slight to moderate risk. Storms may continue after dark into the overnight period into Friday morning, with a continued risk of severe weather.

Issued by: Nick F - Forecaster for Netweather

Can also be viewed here: http://www.netweathe...1e0cf3af0e8e98f

[ZONE 51]

This is an exciting! be amazing to get some action!

The risk of storms is a lot higher than usual with this setup so i would say a high risk of thunderstorms, i also am concerned as its a real risk of tornados here, and of course the other problems of flooding, a night storm could be on the horizon for some, we have darker evenings earlier now so the chances are the storms would still be active late afternoon, and continue late into the night.

Radar 12:20am - Central South - purple colours showing some intense rainfall

Below is the recent lightning activity,

Edited November 3, 2011 by ElectricSnowStorm

[BlueHedgehog074]

Reading the above posts, I think it's safe to say their could be quite a few storm shields getting smashed to pieces tomorrow......

....Especially Jane Louise's! In fact, hers might even explode.

[Raidan]

OMG i just had a well of a fright!!! I heard the rain getting heavier so opened the window and stuck my head out on the off chance something might happen,I stood there for a while but nothing did,I sat back down to look at some radars,All of a sudden i felt something on my arm,It was a massive house spider must of been on the window and crawled on me,I tried to catch it but as it ran my dog stood on it,well its gone now and i think further sky watching will be done with the window SHUT! Good luck all on getting a storm

[ZONE 51]

Ok, going to bite the bullet and issue a moderate risk for Thursday across a lage swathe of southern and western areas, a set-up we don't see too often and more than capable of being ideal conditions for one or two 'nadoes!

Storm & Convective Forecast - Issued 03/11/2011 00:00

Forecast Summary Map

Click for full size

Valid: 03/11/2011 00:00 - 04/11/2011 06:00

Headline: ... THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS FORECAST...

Synopsis

A deep long-wave trough to the west of the British Isles extends south from Greenland to the west of Iberia during the forecast period. At the surface, a deep area of low pressure is expected to be situated to the W of Ireland, with a slow moving cold front across E England and troughs moving north further W in strong southerly flow.

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

A well modified rPm airmass will move in across much of the UK behind cold front clearing east overnight/Thurs morning, with increasingly cold air of the upper trough to the west advecting northeast aloft, while a deeply moist southerly flow advects across England, Wales and Eire towards the surface.

Therefore, increasngly steep lapse rates will spread from SWern UK across much of southern, central and western UK during Thursday - which will allow heavy showers and thunderstorms to spread north during the day. Already CB clusters with sferics are evident across NW tip of Iberia tonight, this area of steep lapse rates/convective activity arriving across SW England/S Wales in the early morning before increasing N and E in coverage during Thursday.

Given rather deep moisture advecting north, which is indicated by GFS to generate several 100 j/kg CAPE combined with a fairly strongly sheared environment with 30-50 knots of deep layer shear and 20-30 knots of low-level shear ... any storms may quickly organise into line segments or perhaps even one or two isolated low-topped supercells capable of producing moderate-large hail (2-3 cm), strong wind gusts (40-60mph), intense rainfall and perhaps one or two tornadoes, even a strong tornado, particularly towards southern and westen coastal areas where SSTs enhance low-level potential of vigorous updrafts. Therefore have issued a slight to moderate risk. Storms may continue after dark into the overnight period into Friday morning, with a continued risk of severe weather.

Issued by: Nick F - Forecaster for Netweather

Can also be viewed here: http://www.netweathe...1e0cf3af0e8e98f

Thought i would show this again! isnt it amazing to see these levels of risk! a very interesting situation developing.

[VillagePlank]

Here's the estofex chart for the day,

[Dorsetbred]

Here we go, sat in the middle AGAIN, whilst to the east I see action, to the west I see action, to my south I see the channel.

Ho hum

[Stuart]

here we go i moved i going miss out

[Staffordshire]

Look like I'm too far east for the rain tonight and to far NE to see a storm today.

[DeepSnow]

Well good luck today, it is looks good for something to develop, fingers crossed for something good as its been too long since I last saw a proper thunderstorm!

[Coast]

Here's the estofex chart for the day,

Here's the detail to go with the map:

Storm Forecast

Valid: Thu 03 Nov 2011 06:00 to Fri 04 Nov 2011 06:00 UTC

Issued: Wed 02 Nov 2011 21:08

Forecaster: GATZEN

A level 1 was issued for the British Isles and northern France mainly for large hail, severe wind gusts, and tornadoes.

SYNOPSIS

The deep Atlantic long-wave trough will slowly enter Iberia during the period. A strong south to south-westerly flow will affect the British Isles, France, the western Mediterranean, and Iberia. The cold front will become mostly parallel to the jet and will be present from the western North Sea to France and the west Mediterranean at Friday morning. Rich low-level moisture is already present along the cold front and will even increase over the west Mediterranean given a moist south-easterly flow and strong low-level convergence. QG lift is likely from the British Isles to the west Mediterranean ahead of the eastward moving trough. This lift is expected to lead to increasing lapse rates that will overlap with the moisture.

DISCUSSION

British Isles, northern France

A tongue of very moist low-level air mass has spread into the British Isles and France and latest observations indicate surface dew points of 14°C. While the cold front crosses the Iberian Peninsula during the day, a frontal wave will be associated with backing surface winds from northern France to the British Isles in the afternoon and evening hours, associated with continuous moisture advection. Lift can be expected through-out the period given the approaching trough and mid-level jet streak as well as the frontal wave associated with warm air masses at low levels spreading northward. As a consequence, steepening lapse rates are forecast and CAPE becomes likely.

The overlap of the rich low-level moisture with strong low-level vertical wind shear (12 m/s 0-1km bulk shear) is clearly indicated by latest models. Main uncertainty will be the lapse rates and the chance of surfaced-based instability as well as the lift that may be rather weak. Current thinking is that showers and thunderstorms will develop rather isolated and will rapidly move northward. Some of these storms are expected to develop into supercells capable of producing large hail, tornadoes, and severe wind gusts. The convective activity will likely last until the night hours.

UKASF's take on today:

Last Updated: 21:55 Wednesday, 2nd November 2011

Valid: 00:00 Thursday, 3rd November 2011 - 23:59 Thursday, 3rd November 2011

Areas Affected:

S & W England, Wales, SW Scotland, Eire

Synopsis:

A large deep (960mb ish) area of low pressure centred several hundred miles west of Ireland will push a waving front across Britain during the day. A mild, humid southerly flow ahead of the front and associated cold air aloft behind the front will enhance the chance of rain and perhaps even some thunder. Several troughs are expected to follow the main surface front enhancing the risk of thunder.

Discussion:

Post cold front a strong southerly flow and unstable airmass with a large upper trough to the west will bring the potential for organised showers with embedded thunder. The risk for some severe weather is also possible given the combination of shear and instablity. DLS values in the region of 40kts along with LLS values around 25kts will overlap SBCAPE values of 400-500j/kg across W England, Wales and perhaps even parts of SW Scotland and Ireland (however shear values will be less in Ireland). Heavy showers will generate from sea-temps, but likely move well inland given strong southerly flow. The potential for some moderate sized hail 1-2cm with organised storms is possible, and perhaps even an isolated tornado, especally where terrian driven convergence boundaries are present.

Autumn post-cold frontal troughs in a strong synoptic flow have a history of producing isolated tornadoes and severe weather events in the UK, so this situation warrents a severe risk.

SkyWarn:

SKYWARN UK SEVERE THUNDERSTORM WARNING #059

ISSUED: 1530UTC WEDNESDAY 2ND NOVEMBER 2011

SKYWARN UK HAS ISSUED A SEVERE THUNDERSTORM WARNING FOR THE FOLLOWING REGIONS:

NORTHERN IRELAND SOUTHWEST SCOTLAND NORTHWEST ENGLAND WALES MIDLANDS SOUTHWEST ENGLAND SOUTHERN ENGLAND

IN EFFECT FROM 0000UTC UNTIL 2300UTC THURSDAY 3RD NOVEMBER 2011

UNSTABLE POST-FRONTAL ENVIRONMENT WITH LOW LEVEL CONVERGENT WARM AIR ADVECTION ENHANCING CONVECTION SEVERE THUNDERSTORMS ARE EXPECTED, OR OCCURRING, SOMEWHERE WITHIN THE INDICATED REGIONS IN THE TIME PERIOD SPECIFIED. THREATS WITHIN THIS WATCH INCLUDE, BUT ARE NOT LIMITED TO:

HEAVY RAIN...HAIL...STRONG GUSTS...FUNNELS...TORNADOES...FLASH FLOODING...LIGHTNING

DISCUSSION:

THERE IS GOOD MODEL CONSENSUS OF A POSSIBLE SEVERE THUNDERSTORM EVENT WITHIN THE WATCH AREAS THROUGH THURSDAY. A COLD FRONT TRANSITS THE UK OVERNIGHT SLOWING OVER EASTERN ENGLAND, BEHIND WHICH 500MB TEMPS AS LOW AS -25C WILL ENCOURAGE WIDESPREAD CONVECTION MOSTLY INITIATING OVER SURROUNDING SEAS AND ADVECTING INLAND. LOW LEVEL WARM AIR IS ADVECTED UNDER A DEEP WIND PROFILE, WITH POSSIBLE SHORTWAVING AND RESULTANT CONVERGENT ZONES THROUGH THE IRISH SEA, IN LEE OF COASTS, PENINSULAS AND HIGH GROUND, AND THROUGH CENTRAL ENGLAND. 0-6KM DEEP LAYER SPEED SHEAR IS SUFFICIENT TO ENHANCE UPDRAFT STRENGTH AND HEIGHT, WITH EQUILIBRIUM LEVELS HIGHEST OVER NORTHERN IRELAND. LOW LEVEL DIRECTIONAL SHEAR IS SUPPORTIVE OF ORGANISED CONVECTION, WITH INCREASED POTENTIAL FOR FUNNELS, TORNADOES UP TO T2 AND STRONG CONVECTIVE GUSTING. PRECIPITABLE WATER IS UP TO 2.5CM SO CORES MAY BE HEAVY WITH POTENTIAL FOR FLASH FLOODING, ESPECIALLY FOR TRAINS OF STORMS. HAIL IS ALSO A CONCERN. THIS WARNING MAY BE UPDATED.

TORRO:

TORRO TORNADO WATCH 2011/008

A TORNDAO WATCH has been issued at 22:10GMT on Wednesday November 2 2011

Valid from/until: 00:00 - 18:00GMT on Thursday November 3 2011, for the following regions of the United Kingdom & Eire:

Parts of (see map)

Eire N Ireland England Wales S Scotland IoM Channel Is

THREATS

Tornadoes; wind gusts to 65mph; hail to 25mm diameter; CG lightning

SYNOPSIS

A cold front will move north-eastwards tonight, introducing a returning polar maritime airmass, which has been strongly modified (warmed/moistened) in the lower levels, whilst remaining cold aloft. A large upper low to the west and high to the east will promote a strong southerly flow throughout the depth of the troposphere. One or more shortwave upper troughs will rotate around the low, and these are likely to promote some backing of the low-level flow ahead of them. The unstable airmass will move into the more south-western parts of the risk area overnight, and then up the Irish Sea, extending north and east tomorrow.

There is some uncertainty to the instability within the airmass, and how far inland instability will move, given seasonally weak insolation during Thursday. Also, low-level cloudiness may be fairly extensive, further complicating the forecast. However, given model indications of several hundred J/Kg of CAPE within a fairly strongly sheared (both deep layer and low-level), a risk of severe weather is indicated.

The highest risk would appear to be close to southern and western coastal parts of England and Wales, and throughout Eire/N Ireland, given closer proximity to the upper low. However, the brisk flow is likely to bring the risk inland, and there is a chance a new watch will be needed for areas further east and north during the day, and the risk may extend well into tomorrow night.

Enough shear is forecast to support organised convection, including the risk of supercells. Strong winds and fairly large hail are possible. There is also the risk of tornadoes, perhaps quite strong, should storms become well-rooted into the boundary layer. There is a suggestion of a push of stronger low-level winds for a time during the morning and into the early afternoon around the Irish Sea, especially into eastern Eire and across N Ireland, especially the eastern half. This could enhance the tornado risk although it must be stressed that mesoscale features during the day tomorrow are currently hard to pinpoint.

It is worth noting that similar synoptic set-ups in the past at this time of year have yielded various forms of severe convection, including tornadoes.

[Jane Louise]

Good luck all. It's going to be a good day! All setup now and waiting in anticipation!

[wimblettben]

I must admit that I will be very dissapointed if nothing comes this time around as I am right in the MODERATE RISK zone!!!

Heck they have even issued a tornado warning!

[A.J]

Look like I'm too far east for the rain tonight and to far NE to see a storm today.

Really?...all the forecasts & model consensus infer we're in a good shout of a thunderstorm today/tonight!....What are you basing your assumptions on?......or is it a bit of classic reverse psychological warfare against mother nature? :winky:

[SteveB]

Theres some lively looking showers to the south west of me, I would imagine if you're in Bridgwater or Taunton it chucking it down.

Hopefully it will get to me as it seems to be moving in a northerly direction with a slight easterly montion which might take it to the west of me.

[MP-R]

Some huge towering cbs above the plaguing low cloud below to the southwest. Fingers crossed for later.

[Coast]

Here's my round up of some of the other information available:

The UKMO chart from 21st OWS has it slap bang over the middle of the SW and Wales:

GFS:

Lapse rates:

Tornado possibilities:

The new hi-res, HiRLAM charts much the same, maybe a little further inland:

Wow, those lapse rates!

and rain:

Hard to pick out the specific area under threat:

Looks like the SW, and Wales, South coast up to Portsmouth + some of the Midlands under fire from hail, high wind gusts, maybe some lightning and even a tornado threat! Going to be keeping an eye on the radar and detectors today.

[richep]

No rain at the moment steve

[Nick F]

Some lively thunderstorms recently passing over the Channel Islands looking at radar and sferic plots - probably headed north towards Dorset coast. Wouldn't be suprised if that's a storm across northern Somerset too at the end of the line extending NW across SW Wales and onto Ern Ireland - which is likely a trough heading north.

[SteveB]

No rain at the moment steve

It must be further down from you then, maybe minehead area!