Uk Convective General Discussion & Forecasts, 27th June 2012>

[Deluxe]

Good morning all The sun is out here (sort of) Should be a fun day, whatever happens! Amazing to hear talk of supercells and the possibility of a strong tornado somewhere today Stay safe!

Edited June 28, 2012 by Polar Thole

[Supacell]

So close to that monstor cell across South Wales but its tracking just west of me. Hopefully something develops right over me. Can see lightning in distant mind you!

If it can hold together then it looks to me like it is set to hit West Birmingham, maybe Wolverhampton area.

Edit: Actually Telford would be a better guess.

Edited June 28, 2012 by Supacell

[Coast]

So, sorry if this is repeating earlier posts and info, here are a few pictures and words from other sites all in one place:

Storm Forecast

Valid: Thu 28 Jun 2012 06:00 to Fri 29 Jun 2012 06:00 UTC

Issued: Wed 27 Jun 2012 22:28

Forecaster: GATZEN

A level 2 was issued for the Benelux countries mainly for large hail and severe wind gusts.

A level 1 was issued for portions of the northern British Isles mainly for tornadoes.

A level 1 was issued for the central and southern British Isles mainly for large hail.

SYNOPSIS

An Atlantic trough moves into western Europe pushing a ridge into central Europe. An elevated mixed layer currently across France will spread north-eastward on Thursday, and rich boundary-layer moisture is expected underneath the cap from eastern France to eastern England and the Benelux countries. Over eastern Europe, rather cool/dry air will remain.

DISCUSSION

The Benelux region

The nose of the warm low-level air will move into the Benelux countries ahead of the surface cold front. Moisture pooling and diurnal heating will result in CAPE around 2000 J/kg given the elevated mixed layer spreading northward. Additionally, strong vertical wind shear will be in place.

Favorably veering profiles and rather isolated convection in the afternoon hours pose a threat of supercells capable of producing large or very large hail and maybe a tornado. Later in the period, a linear MSC may develop ahead of the cold front. The increasing low-level jet is forecast to increase the potential of severe wind gusts with this MCS that will spread into western Germany. Excessive rain is also not ruled out.

British Isles

Warm air advection will continue during the night and morning hours from England into Scotland. This warm air is characterized by steep mid-level lapse rates. The warm air advection will increase, and a low-level jet is expected to strengthen on Thursday ahead of the approaching cold front.

Latest satellite images indicate widespread convective/stratiform clouds spreading eastward ahead of the approaching trough and associated jet streak. Until the morning hours, these clouds will spread across much of the forecast area. During the day, especially the southern portions will be placed below the anticyclonic flank of the approaching jet streak, and weak forcing may result in rather strong daytime heating.

Furthern north, QG forcing will be stronger. Elevated storms in the warm air advection regime may root to the boundary-layer in the noon and afternoon hours. Storm motion vectors close to the cold front are expected to result in a squall line with excessive rain the main threat. The severe wind threat is expected to be rather low given the expected slow propagation of the squall line.

Further north, storms are expected to be more isolated. Although instability will be weak, these storms may organize given strong vertical wind shear. Mesocyclones will pose a threat of tornadoes.

Across the southern British Isles, weak QG forcing will remain through-out the period. Along the cold front, some storms may evolve especially during the the second half of the day, when low-level heating and rather rich moisture will result in CAPE of 1000 J/kg. Strong vertical wind shear will overlap with this instability, and storms that form will rapidly organize. The potential of supercells is expected to decrease from the west during the day, and mostly multicells are forecast, capable of producing large hail and strong to severe wind gusts. However, supercells are not ruled out especially across the eastern portions where larger hodographs will persist well into the afternoon hours ahead of the cold front. Isolated very large hail may be possible when supercells indeed will form. The convective activity will decay during the evening hours in the wake of the surface cold front.

SKYWARN UK SEVERE THUNDERSTORM WATCH #033

ISSUED: 1500UTC WEDNESDAY 27TH JUNE 2012 (SG/GS/GJ/SM/DH)

SKYWARN UK HAS ISSUED A SEVERE THUNDERSTORM WATCH FOR THE FOLLOWING REGIONS: ALL AREAS UK

IN EFFECT FROM 0000UTC THURSDAY 28TH UNTIL 0300UTC FRIDAY 29TH JUNE 2012

MATURE STALLED LOW PRESSURE TO THE WEST AND WAVE IN THE BISCAY AREA ENCOURAGING A VERY WARM PRE-FRONTAL PLUME OVER THE UK, WITH STRONG INSTABILITY AND FAVOURABLE SHEAR FOR ORGANISED THUNDERSTORMS

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:

HEAVY RAIN...FLASH FLOODING...HAIL...STRONG GUSTS...FREQUENT LIGHTNING...FUNNELS/WEAK TORNADOES

DISCUSSION:

THERE IS GOOD MODEL AGREEMENT ON THE POSSIBLITY OF A SEVERE THUNDERSTORM INTO AND THROUGH THURSDAY WITHIN THE WATCH AREAS. A MATURE LOW PRESSURE SYSTEM STALLED TO THE WEST OF IRELAND BECOMES DEVELOPED THROUGH THE DAY BY A THE CYCLONIC JET ROUNDING TO THE SOUTH, WITH A WAVE DEVELOPED NEAR PORTUGAL MOVING THROUGH THE BISCAY AREA. TO THE EAST OF THIS, AN ELEVATED MIXED LAYER FROM IBERIA INTERACTS WITH DEEP MOISTURE CONVERGENCE OVER NW FRANCE AND IS ENCOURAGED NORTHWARD OVERNIGHT. THIS MAY GENERATE STRONG MIXED LAYER INSTABILITY OF WELL OVER 1000J/KG CAPE, WITH THE APPROACHING JETSTREAM NOSE PROVIDING SOME DIRECTIONAL SHEAR ORGANISATION FOR HIGH-BASED UPDRAFTS. THIS COULD LEAD TO MODERATE TO LARGE HAIL SIZES AND VERY HEAVY RAIN CORES ACROSS THE SOUTHWEST AND SOUTH OF ENGLAND DURING THE EARLY HOURS, SPREADING ACROSS THE MIDLANDS AND WALES BY LUNCHTIME AHEAD OF THE COLD FRONT.

BETTER MOISTURE CONVERGENCE THROUGH THE PROFILE AROUND IRISH SEA AREAS AND MIDLANDS TO NORTHERN ENGLAND, TOGETHER WITH FAVOURABLE WIND SHEAR, WILL PROVIDE A FOCUS FOR ORGANISED AND STRONG CONVECTION WITH SUSTAINED SUPERCELLS POSSIBLE. THERE ALSO EXISTS A RISK OF LARGE HAIL, FREQUENT LIGHTNING AND EXCESSIVE RAINFALL FOR THESE AREAS THROUGH THE AFTERNOON, ALONG WITH THE POSSIBILITY OF FUNNELS AND TORNADOES. THERE IS A POSSIBILITY OF THIS PATTERN EVOLVING INTO A MCS LATER IN THE AFTERNOON INTO SCOTLAND, THOUGH THERE IS ALSO EQUAL POSSIBILITY OF ISOLATED AND ORGANISED STORMS HERE WITH SIMILAR ATTENDANT THREATS.

FURTHER SOUTH ACROSS THE EAST MIDLANDS, EAST ANGLIA AND SOUTHEAST THERE IS LESS FORCING AND MOISTURE WHICH MAY PRECLUDE THE RISK OF SEVERE THUNDERSTORMS. HOWEVER INSTABILITY ALONG AND AHEAD OF THE FRONT IS DEPENDENT UPON DAYTIME HEATING AND MAY GENERATE ISOLATED STRONG CONVECTION WHICH, GIVEN A FAVOURABLE SHEAR PATTERN, COULD LEAD TO SHORT-LIVED SUPERCELLS CAPABLE OF PRODUCING LARGE HAIL AND STRONG GUSTS, WITH TORNADOES ALSO A POSSIBILITY. THIS WATCH MAY BE UPDATED OR UPGRADED. PLEASE MONITOR WEATHER AND TRAVEL INFO AS NECESSARY.

Severe

Forecaster: Dan

Last Updated: 2012-06-27 21:58:00

Valid: 2012-06-28 00:00:00 - 2012-06-28 23:59:00

Areas Affected:

SVR: SE Scotland/Borders, NE Eng, Yorkshire, E Mids, East Anglia

MDT: NE Eng, Yorkshire, E Mids, N Cambs/W Norfolk

SLGT: Majority of United Kingdom, excluding NW Highlands and N Isles

Synopsis:

Upper trough gradually approaches from the west, allowing a plume of high WBPT and very high ThetaE to advect northwards across Britain. Destabilisation will occur on the plume axis during the passage of a pronounced shortwave trough, with potential for severe convection over Lincolnshire, Cambridgeshire and Norfolk during the afternoon.

Discussion:

Several areas of interest exist during this forecast period, with varying levels of severity.

From the start of the forecast period through to daylight, indications are that elevated thunderstorms will develop over the English Channel/move northwestwards from northern France as the moisture plume destabilises with the approach of a shortwave. These mid-level showers/storms will tend to merge as they cross SW England and across the Irish Sea to Ireland. >40kts DLS coupled with >25kts would suggest some organisation of such storms into multicells or elevated supercells, sustaining such storms for quite a long period of time.

>800J/kg MLCAPE also highlights reasonably frequent lightning with these storms at first, although the exact interaction of such storms with long sea tracks leaves us with a cautious SLGT level for sferic coverage for the time being - this may be upgraded to MDT if necessary. Other than very heavy rain, with PWAT values near 36mm locally, generally due to the elevated nature of storms severe weather is unlikely.

This general area of thundery rain will then move north across the Irish Sea, grazing both Ireland/Northern Ireland and western parts of Britain during the day on Thursday, with ever-decreasing values of MLCAPE. Nevertheless, it is quite probable that lightning activity will continue throughout the day as cells remain sustained with decent shear available.

Across the rest of England and Wales, a few mid-level showers will migrate northwards later in the night and first thing Thursday morning, although significant WAA in the mid-levels will provide strong capping, thus most showers will be light with a low probability of thunder/lightning. Capping is strongest towards SE England, and weaker towards the NorthWest.

Behind these showers, conditions should improve with some patchy insolation expected as cloud cover begins to break. Dewpoints of ~17C and surface temps of 22-27C are simulated by most models, and will be substantial enough to generate some surface-based convection.

Initially this will take place over eastern England, east of the Pennines with the plume axis and approach of a shortwave, combined with topographical forcing. Initially numerous thunderstorms are forecast to develop from ~12z onwards, with forecast soundings suggesting ample shear (typically 40kts DLS, 30kts LLS) and some helicity (>300m^2/s^2). This would generate an environment, coupled with 1000-1300J/kg CAPE, capable of producing multicells or supercells, with the potential for a tornado.

However, due to the weakly-capped environment it is likely that mass forced ascent will quickly merge such storms into a linear formation along the trough, eventually forming an MCS producing frequent lightning and possibly some large hail (locally >3cm). PWAT of up to 39mm also increases the risk of flooding from torrential downpours.

This line will continue to move quickly northeastwards, wrapping back into eastern Scotland during the evening so increasing sferic activity is expected here during the evening.

It is not clear where the southeastern edge of such line will be, with some inter-model disagreements. Current thinking is south Lincolnshire southwards will be in a more-capped environment, and here such storms that develop will be more scattered and less likely to merge into any linear structures. Indeed, by adjusting forecast soundings to realistic T and Td values, 1800-2000J/kg CAPE is potentially available, with a slight cap being broken by combination of rising LSTs and the approach of a shortwave.

Thus, in a zone from northwest Essex to southern Lincolnshire, a few scattered surface-based thunderstorms are expected to form in the early-mid afternoon hours, rapidly moving northeastwards. Given such CAPE values, combined with >40kts DLS, >25kts LLS and >250m^2s^-2 helicity, then a few discrete supercells are possible, especially in southern Lincolnshire across The Fens to West Norfolk.

Veering wind profiles with height, and a substantial increase in speed shear with height suggest the potential for one or two severe thunderstorms, with rotating mesocyclones. With forecast dry air aloft, such storms will be capable of producing hail 3-4cm in diameter (up to golf ball), frequent lightning, with local flooding possible given PWAT values approaching ~40mm, although fast storm-motion should ease this risk somewhat. If the cap can be broken to generate such storms, then this is borderline our threshold for EXTRMLY SVR. Low LCLs as a result of relatively low dewpoint depressions (generally ~7C) with such shear values poses a significant tornado risk. Convective gusts may be as high as 50-60mph, and outflow boundaries may pose a focus for breaking the cap downstream and generating new cells.

Storms will rapidly move northeastwards, generally clearing by 18z.

In SE England, capping appears to be too strong, and the surface flow not backed enough, to generate any noteworthy convection, although some uncertainty remains.

Nothing again from TORRO - come on you guys!!!

21st OWS:

GFS general forecast:

Its all gone East and North!

But look at the area around Lincolnshire and surrounding counties later!!!

Lapse rates mark the area I'd be looking closely at today:

Owww I'm loving these ones!!

Good helicity here:

MCS?

HiRLAM, as for what seems like an age, still have things more central/to the West:

But they do have it large!!!!!

Lapse rates show an area slightly more to the South than GFS, I'd take that indicator selfishly and would love this to be an area of potential today!!!

Same messy atmosphere with any amount of shear and tornado possibilities, but big hail seems on the cards today!!!

In conclusion, a great set of charts, a great set of possibilities throughout the UK and many people I'm sure, will be happy with today's weather!!!

Good luck everyone!

[SteveB]

Nice storm going off in the Welsh marches area.

Nothing except rain last night.

[Alex95]

there's something big somewhere. Can hear sferics every second about 100-200 miles away.

There has been a lot of lightning in the Irish Sea within the last hour, as well as from the thunderstorm in Wales - both are about 100-150 miles from you I would say. Thunderstorms keep developing on the western edge of that lot in the Irish Sea - I wonder if Cumbria or SW Scotland will get lucky this morning!

[A.J]

Morning all!.....look at that lovely multicell cluster heading through the welsh borders!..Very active indeed!....Just run the radar loop and finger crossed it's look like a head on collision with me in about an hour or so

[P-M]

Very uninspiring local forecast here just now, load of rubbish actually hardly even mentioned the warning or thundery downpours (he might be right about the NE though) Well today has started so lets see what happens! Good luck everyone ;-)

[Weather-history]

Interesting how the band of rain when it left the NE coast of England,it increased in intensity over the North Sea.

[Coast]

Have to say all the BBC national and local forecasts I have seen are having none of it for today?

[Dan the Man]

I gather than ESTOFEX L2 warning was forecasted over the SE a few days ago!

Moisture pooling and diurnal heating will result in CAPE around 2000 J/kg given the elevated mixed layer spreading northward. Additionally, strong vertical wind shear will be in place.

Favorably veering profiles and rather isolated convection in the afternoon hours pose a threat of supercells capable of producing large or very large hail and maybe a tornado.

[Ian Ballinger]

If it can hold together then it looks to me like it is set to hit West Birmingham, maybe Wolverhampton area.

Edit: Actually Telford would be a better guess.

I have everything crossed

[Staffordshire]

another cell firing up just south of this one, more likely to hit brum

[weatherobsuk]

A slow-moving developing MCS system, not close enough so that precip smothers any storm structure but not far away either to scupper any visual lightning. Preferably within the in/outflow boundary and along any dryline. Not too much to ask of today is it

[I remember Atlantic 252]

Morning all!.....look at that lovely multicell cluster heading through the welsh borders!..Very active indeed!....Just run the radar loop and finger crossed it's look like a head on collision with me in about an hour or so

looks like missing here to the west? more in line with gnosall/telford area

[Alex95]

That storm is really getting going now over Wales which is a good sign for the rest of us later. I also expect those showers in the Channel to turn thundery this morning, in fact I'm surprised they haven't already considering the Irish Sea was active earlier.

[Supacell]

Morning all!.....look at that lovely multicell cluster heading through the welsh borders!..Very active indeed!....Just run the radar loop and finger crossed it's look like a head on collision with me in about an hour or so

It does look like heading your way AJ - so you may not be "stuck in the middle near Crewe" after all

Looks like cells developing behind it and it is backbuilding. Could this be our first MCS of the day on the mainland?

[Deluxe]

Cmon Carol get on with the weather, this isn't cbeebies!

Edited June 28, 2012 by Polar Thole

[picog]

We have thunder and lightening here now from the cell on the Welsh borders. It's getting very dark and ominous. Dogs cowering.

[Cheshire Freeze]

It does look like heading your way AJ - so you may not be "stuck in the middle near Crewe" after all

Looks like cells developing behind it and it is backbuilding. Could this be our first MCS of the day on the mainland?

No but I'll still be stuck in the Middle IN Crewe! Lol

[Coast]

Its starting!!!!

*** NexStorm TRAC Report generated 28/06/2012 08:18:32

Tracking 1 thunderstorms from IoW

-------------------------------------------------------

Thunderstorm ID B-3698 detected 08:08

Storm location bearing 322.7 dgr distance 157 mi

Last recorded activity 08:17

Intensity class Weak

Intensity trend No change

Current strikerate 4/minute

Peak strikerate 4/minute

Total recorded strikes 12

Cloud-Ground strikes 4 - 33.33%

Intracloud strikes 8 - 66.67%

-- Strike type distribution --

Positive Cloud-Ground [+CG] 0 - 0.00%

Negative Cloud-Ground [-CG] 4 - 33.33%

Positive Intracloud [+IC] 6 - 50.00%

Negative Intracloud [-IC] 2 - 16.67%

-------------------------------------------------------

*** TRAC Report end - NexStorm V1.8.0.7025:PCI

http://www.isleofwig..._storm_data.htm

[A.J]

looks like missing here to the west? more in line with gnosall/telford area

It'll be a close call Mark, but it's building on it's flanks, very organized matey, should certainly get some lightning/thunder...look at the lightning spread Mark, that is one really active storm cluster, it's tapping into a hell of a lot of low level moisture advecting into the region...I was chatting with W09 via pm last night and we both were eye-ing up this possible scenario with considerable interest for the midlands around breakfast....The storm parameters for this morning/afternoon are about as good as you can get in the UK!

[Static Prevails]

Hopefully as this builds it will eventually hit me. Even if it doesn't, the cell to the south east of this may have more of a chance.

[PolarWarsaw]

I think that'l miss here to the west by around 5-10 miles. Hopefully some distant lightning though. This isn't the cold front is it? Hopefully just a back burner to a collection of storms.

[SteveB]

Yes, a nice little cell has just popped up behind the one in the welsh marches near Newport.

Already producing lightning.

Hopefully something can develop behind the one over newport near to me..

[Chris.R]

That must be one hell of a storm. I can hear several sferics a second now, it's almost constant.