Uk General Convective Discussion & Forecasts, 10th October 2012>

[Bobby]

Big rumble of thunder here, I see some strikes around Wales.

[mikeocarroll]

Lightening and thunder here too in Mid Wales, wasn't expecting that.

[TonyH]

Quite a lot of sferics over Wales, torrential showers, and had two storms so far, and within a warm sector.

[Bobby]

Big overhead thunderstorm now with multiples flashes of lightning including fork lightning, thunder shacking the house and biblical rain. Good fun.

[Chris K]

Quite a lot of lightning activity over Wales at the moment as well as the Bristol Channel. All heading this way I wonder if it will keep up or weaken a bit as it heads inland....

[Supacell]

Thunderstorms inland during January!!! What will we see next.

I think there is a little storm to the NW of here, at least it is showing up on the lightning detector - not sure if it is coming this way though.

[Love Snow]

Sure I've just heared a rumble of thunder

[Love Snow]

Wow double flash of lighting !

[Mark -W-s-M]

Plenty of lightning around here too .

[Raidan]

Reports of thunder and lightning in weston super mare,winterboure,thornbury and stoke gifford,nothing here though!wind is really gusting.

[Mark -W-s-M]

Reports of thunder and lightning in weston super mare,winterboure,thornbury and stoke gifford,nothing here though!wind is really gusting.

Seems to have gone quiet now but certainly does feel a bit more milder out there.

[Stuart]

Storm Forecast

Valid: Sun 27 Jan 2013 06:00 to Mon 28 Jan 2013 06:00 UTC

Issued: Sun 27 Jan 2013 07:30

Forecaster: VAN DER VELDE

SYNOPSIS

The cold continental airmass is losing the battle against the warmer maritime airmass advancing steadily with a fierce westerly flow pattern all over the North Atlantic, driven by a massive 940-ish hPa low south of Iceland. The occluded cold front arcs all the way from Iceland to southern Sweden down to Portugal, and the maritime airmass is unstable, especially at the west coasts of Ireland (with gusts 20-25 m/s, Monday stronger) and the UK. The cold front will also move along with significant vorticity advection into the western Mediterranean, where cyclogenesis takes place, but instability is weak this time. The old system of earlier this week is now petering out around Greece and Turkey, but there is still some convective juice left in it. It may produce some waterspouts.

http://estofex.org/

[Nick F]

Horizontal torrential rain, violent wind gusts, thunder and lightning driving home through SW London after midnight last night, was like driving through RFD in a supercell.

Edited January 27, 2013 by Nick F

[coffee lover]

Torro - the UK's Tornado and Storm Research Organisation

Interesting cell just moving into S Wales, between Port Talbot and Porthcawl - heaviest precip on SW'ern edge - possible low-topped supercell.

Just posted on FB

[Bobby]

Torro - the UK's Tornado and Storm Research Organisation

Interesting cell just moving into S Wales, between Port Talbot and Porthcawl - heaviest precip on SW'ern edge - possible low-topped supercell.

Just posted on FB

Looks intense, some gusty winds and heavy rain from that here along with some sleet and snow mixed in

[Raidan]

I'm very happy just had heavy rain and hail with thunder and lightning,not a storm and not like parts of Wales seen lastnight but it was something so I'm happy!

[Raidan]

More thunder and lightning with the rain,a good start to the year!

[Coast]

Well here it comes, ESTOFEX lead the way today - watch that triple point later:

Storm Forecast

Valid: Mon 28 Jan 2013 06:00 to Tue 29 Jan 2013 06:00 UTC

Issued: Sun 27 Jan 2013 22:21

Forecaster: TUSCHY

A level 1 was issued for parts of Ireland and UK mainly for severe to damaging wind gusts and an isolated tornado risk.

A level 1 was issued for the Netherlands and extreme NW Germany mainly for severe wind gusts.

SYNOPSIS

Most active part of the split polar vortex resides atop the N-Atlantic Ocean which induces active and intense cyclogenesis over a broad offshore area. This pattern shift starts to affect far W-Europe during the overnight hours with rapidly rising mid-level heights spreading east. Once again, a strong impulse along the eastern fringe of the WAA regime races south over the W-C Mediterranean towards N-Africa as a 50 m/s mid-level jet moves S/SE. Out of this impulse, a closed mid-level low evolves over the Gulf of Gabes with unsettled conditions affecting most of the C-Mediterranean.

A weakening cold-core low exits Romania/Bulgaria to the SE and crosses the W-Black Sea while adjacent precipitation shield also moves offshore during the evening hours onwards.

The system of main interest will be an intense 960 hPa depression, which passes Ireland and Scotland to the north. As seen in past events over the N-Atlantic Ocean (past 24-48 h), this cyclone features a strong warm-seclusion process with phase diagrams reflecting an appropriate signature. Back-bent occlusion will be pronounced and probably the main focus for severe wind gusts.

DISCUSSION

... Ireland, UK and the S-North Sea ...

Regarding thunderstorm probabilities, the current focus shifts to the cold front, which is forecast to cross Ireland around noon. Thereafter, the occlusion point builds south (e.g. probably towards C-UK ) until the front exits UK to the east at roughly 18Z. While affecting Ireland and UK, an authentic signal of a rapidly SE-ward building dry slot exists with a tropopause fold and drying at 700 hPa being present. QPF model signals remain mixed, but there will be a low-end chance for a few deeper updrafts / potentially electrified /. Pooling signals like LL convergence, parcel layer depth and 700 hPa instability, the highest probabilities for an isolated thunderstorm event occur over S-Irland and C/S UK between 12-21 Z. Strong UVV max. /exit region of a 55 m/s 500 hPa jet max enter the scene also in time, so current plan is that a forced line of showers/isolated thunderstorms (LEWP) accompany the cold front passage, capable of mixing winds down to the surface. Kinematics are off the chart, so damaging wind gusts and an isolated tornado event are possible. Some better LLCAPE sneaks in from the W and affects C/SW UK during the afternoon and evening hours, probably also increasing the tornado risk somewhat. A broad level 1 was issued, mainly for the severe to damaging wind gust risk with the expected limited DMC activity and to a lesser degree for the low-end tornado risk. In case a better CAPE environment sets-up and/or the frontal line of showers/thunderstorms becomes more vivid than currently forecast, an upgrade may be considered, given 35-40 m/s just atop the PBL.

A more widespread severe to damaging wind gust risk is forecast with the back-bent occlusion, which affects Ireland during the evening hours onwards. Despite a weakening wind field at 850 hPa, well mixed maritime air should assist in downward transport of winds from higher levels and therefore widespread severe wind gusts affect Ireland and UK during the overnight hours. Missing DMC activity means no reflection in our warning scheme.

We expanded the level 1 far east, including the S-North Sea, the Netherlands and extreme NW-Germany for the frontal passage during the latter part of the forecast. The triple point still resides beneath the exit of a 50 m/s mid-level jet maximum and despite gradually decaying instability, expected profiles still reveal a near neutral stratification and remain supportive for an ongoing forced line of showers with sporadic thunderstorm activity. Severe wind gusts will be the main risk although convectively induced gusts may become blurred by the background wind field betimes as convection weakens.

For the rest of Europe, a few spots see some isolated lightning activity, but nothing severe is anticipated.

Then SkyWarn say:

SKYWARN UK SEVERE WEATHER WATCH #007

ISSUED: 0330UTC MONDAY 28TH JANUARY 2013 (GS/GJ)

SKYWARN UK HAS ISSUED A SEVERE WEATHER WATCH FOR THE FOLLOWING REGIONS:

NORTHERN IRELAND

SOUTH SCOTLAND

ENGLAND

WALES

IN EFFECT FROM 0600UTC MONDAY 28TH UNTIL 0600UTC TUESDAY 29TH JANUARY 2013

STRONG COMPLEX CYCLOGENESIS UNDER AN INTENSE ONCOMING JETSTREAM WIND MAXIMUM, INSPIRING STRONG GUSTS WITHIN BOTH THE COLD FRONT AND BENT BACK OCCLUDED FRONT.

THERE IS A POSSIBILITY OF SEVERE WEATHER AFFECTING THE INDICATED REGIONS IN THE TIME PERIOD SPECIFIED. THREATS WITHIN THIS WATCH INCLUDE, BUT ARE NOT LIMITED TO:

GALES...STRONG GUSTS...BRIEF/WEAK TORNADOES...HEAVY RAIN...FLASH FLOODING

DISCUSSION:

THERE IS STRONG PARTNER AGENCY CONFIDENCE WITH GOOD MODEL SUPPORT FOR THE POSSIBILITY OF A SEVERE WEATHER RISK THROUGH MONDAY. A LARGE COMPLEX LOW PRESSURE SYSTEM IS ENGAGED BY AN INTENSE JETSTREAM, DEVELOPING A LOW CENTRE THAT TRANSITS ACROSS THE NORTH OF THE UK. TWO AREAS OF POTENTIALLY SEVERE WINDS ARE GENERATED, ALONG THE FRAGMENTED SURFACE FRONT DURING THE AFTERNOON AND ALSO ASSOCIATED WITH THE BENT-BACK OCCLUSION INTO THE EVENING AND OVERNIGHT. FROM LATE MORNING ONWARDS, THE COLD FRONT CROSSES NORTHERN IRELAND INTO ENGLAND DURING THE AFTERNOON WITH THE SOUTHWESTERN PORTION TRAILING LATER. ALONG THE ENTIRE FRONTAL ZONE, DIRECTIONAL SHEAR IS CONDUCIVE TO ALLOWING DOWNWARD MIXING OF STRONGER THAN 60MPH WINDS TO THE SURFACE; WHILE THROUGH WALES, SOUTHWEST, CENTRAL AND NORTHERN ENGLAND THE FRONT IS EXPECTED TO FRAGMENT AND PROVIDE A FOCUS FOR POSSIBLY STRONGER GUSTS AND BRIEF VORTICES. SLIGHT INSTABILITY ENHANCED BY VERY STRONG FORCING FROM VERY LARGE DLS UNDER THE JET NOSE, AND A STRONG DRY AIR INTRUSION INTO THE MID LEVELS, MAY SUPPORT THE FORMATION OF ISOLATED CONVECTION, ADDING SUPPORT TO THE CHANCES OF TORNADOES. RAINFALL ACCUMULATIONS OF AROUND 20MM, WITH PERHAPS 40MM OVER HIGHER GROUND OF THE WESTERN SIDE OF THE MAINLAND, WITHIN A SHORT SPACE OF TIME MAY CONTRIBUTE TO FLASH FLOODING OR EXCESS SURFACE WATER ESPECIALLY WHERE COMBINED WITH SNOW-MELT AND/OR FROZEN GROUND.

DURING LATE AFTERNOON AND EVENING, THE WRAPPING OCCLUSION OF THE DEVELOPED LOW CENTRE WILL TRANSIT NORTHERN IRELAND, WITH THE POSSIBILITY OF GREATER THAN 50MPH MEAN WINDS AND THE CHANCES OF HIGHER THAN 70MPH GUSTS OVER LAND. THIS RISK EASES SOMEWHAT INTO THE NIGHT, BUT MAY ALSO AFFECT SOUTHERN SCOTLAND ESPECIALLY OVER HIGHER GROUND OR EXPOSED WESTERN COASTS. THIS WATCH MAY BE UPDATED OR UPGRADED. PLEASE MONITOR WEATHER AND TRAVEL INFO AS NECESSARY.

Wow!! The jet is in full strength mode!

Lightning Wizards GFS charts picture the situation well:

Ireland and Scotland in for a battering, but also the East coast on its Exit East:

Tornadoes a strong possibility wrapped up in the winds

Looks to be slightly more to the South on this run

So some big sustained winds:

and gusts (especially on Western and Eastern coasts, but no exclusively):

Maybe the threat of some more TStorms, but I think the wind will be the thing to draw most attention, maybe the our spout or tornado?

Edited January 28, 2013 by Coast

[Liam J]

Expect some locally extreme conditions wherever that makes landfall somewhere over NW England!

[Cheese Rice]

Crazy lightning and thunder here.

[Convective]

Tomorrow looks like the northwest might see something thundery tomorrow as a trough moves through around lunch. Quite a bit of energy around.

[Supacell]

BBC forecast this morning are going with some thundery showers across N England and then what looks like a squall line moving through overnight. I wanted to look at some charts myself but the lightning wizard charts I usually use are stuck at October.

HELP!!! Is this the case for anyone else, or have they moved elsewhere?

[Supacell]

Just had a check as found it is only the Hirlam charts I can't view.

The squall line tonight looks interesting across England and Wales with a fair/large amount of helicity, 40-60knts of DLS along with some steep lapse rates. Tomorrow morning there is 80-100knts of DLS across the central swathe of the country!!! This would translate to a period of very heavy rain, strong convective wind gusts and, although not overly widespread, some lightning and thunder - most prolific over N England.

Shall have another look this evening

[Thundery wintry showers]

Haven't heard any thunder here yet, but there's an impressive cumulonimbus cell just to the north with hail shafts and a fair number of sferics are showing up from it on the N-W radar.

[Chris W]

Haven't seen a convergence line on a fax chart for quite a while. This for Saturday:

http://www.metoffice...oductId/4799126

Edited January 30, 2013 by Chris W