Convective / Storm Discussion - 4th October onwards 2013

[virtualsphere]

Im glad to see that ESTOFEX and other members have come up to the same conclusion as me for tomorrow! Should definitely be an interesting day, and Im keeping my eye out for tornadoes! 

 

Good luck - not often we see both a Level 1 and the bold 50% lightning yellow area over us in Wales! 

[Supacell]

For the Midlands the forecasts are not appearing on the same page. BBC/Met Office show heavy precipitation through the night and the wording from the met office indicates this could be thundery. NAE agrees on heavy precipitation overnight, although I can't tell if it will be thundery or not. GFS keeps the Midlands mostly dry tonight but shows a good chance of storms today (where BBC/Met office just show rain for today).

 

So, I have no idea if the Midlands can expect storms. The forecasted Level 1 from Estofex and the storm forecasts from other agencies are more to the SW, certainly looks an interesting day if you are in the southwest.

[Coast]

2013102306_201310212001_1_stormforecast_xml.png

 

Specifically for us:

 

 

DISCUSSION

 

W France, S and SW England and Wales...

 

Showers and thunderstorms are expected to occur throughout the forecast period. As they are embedded in a strong SW-flow and 0-1 km bulk shear in the range of 10-15 m/s is expected, significant low-level rotation may develop in some storms and a few short-lived tornadoes or waterspouts may occur. Some risk of isolated non-tornadic severe wind gusts will also exist.

 

 

UKASF have:

 

 

 

Synopsis

 

A similar setup to the weekend, with an upper ridge clearing eastwards, allowing an upper longwave trough to nudge northeastwards towards Britain, separated by a strong southerly jet. Cooling aloft, behind a surface cold front, atop a fairly warm, moist surface airmass will result in some convective chances.

Discussion

 

Despite a surface cold front erractically clearing eastwards (with potential frontal wave during the afternoon across East Anglia and southeast England), the surface airmass remains fairly warm and moist, characterised by dewpoints of 13-14C. Mid-levels will begin to cool from the west as the upper trough approaches (-19C at 500mb), which will steepen lapse rates given warm SSTs (and LSTs in response to diurnal heating). Scattered showers and a few thunderstorms are likely to form, initially over land within the SLGT given some low-level convergence/orography aiding development. Later in the afternoon, and more especially into the evening, a shortwave trough is likely to bring a line of broken convection across many parts of SW England, Wales, CS England and S Ireland, with some embedded thunderstorms possible.

 

However, instability is not as impressive as that during the last weekend, so despite reasonable CAPE (600-800 J/kg, higher over nearby Atlantic), lightning may not be as widespread/active as the past few days. Nonetheless, ELTs down to -40C suggests there will be some occasional lightning in places, with particular focus over western Ireland where the deepest instability will be present. 30-40kts DLS (25-30kts in lowest 1km), with backed (southerly) surface winds and low LCLs increases the potential for a tornado, with the strongest cells perhaps exhibiting supercell-like characteristics with strong, gusty winds. Hail locally >1.5cm in diameter is possible, along with local flash flooding from several heavy downpours. Again this setup is borderline SVR given the tornado and hail potential, and will need to be monitored closely - particularly along southern coasts.

 

 

So similar areas, but less chances than the weekend?

[Coast]

GFS going with:

 

 

 

 

Plenty of CAPE:

 

 

 

Shear and convergence in a number of areas:

 

 

 

Lots more rain:

 

 

 

Oww that's a messy old day convectively: 

 

[chionomaniac]

Interesting radar characteristics of the storm south of Cork. Supercell? It may clip SW Ireland.

[ItIsGee]

this one?

[chionomaniac]

this one?

Yep, but its faded as its travelled north.

[ItIsGee]

i am close to north wales today, what are the odds of something firing? not really looked at any forecasts or models due to work but i believe there is a chance of something today!

[Coast]

NMM TT index has a great swathe of the West (and North) in contention:

 

Edited October 22, 2013 by Coast

[SalopWatcher]

Got the day traveling around Mid-wales for work, so might be well placed for any action. Looks an interesting day. If I see anything will post updates 

[Coast]

 

SKYWARN UK SEVERE THUNDERSTORM WARNING #034

ISSUED: 0000UTC TUESDAY 22ND OCTOBER 2013

 

SKYWARN UK HAS ISSUED A WARNING FOR SEVERE THUNDERSTORM CONDITIONS AS FOLLOWS:

POTENTIALLY STRONG AND DAMAGING TORNADOES - SOUTHWEST AND SOUTHERN ENGLAND, WALES, MIDLANDS AND CHANNEL ISLANDS

STRONG, POTENTIALLY DAMAGING WIND GUSTS - SOUTHWEST AND SOUTHERN ENGLAND, WALES, MIDLANDS AND CHANNEL ISLANDS

HEAVY RAIN LEADING TO A RISK OF FLOODING - SOUTHWEST ENGLAND, WALES, MIDLANDS

 

IN EFFECT UNTIL 2200UTC TUESDAY 22ND OCTOBER 2013

 

UNSTABLE ENVIRONMENT ALONG AND BEHIND A WAVING COLD FRONT, WITH STRONG SHEAR AND LIKELIHOOD OF MESOCYCLONE DEVELOPMENT.

 

DISCUSSION:

 

THERE IS STRONG MODEL AND PARTNER AGENCY CONFIDENCE IN THE LIKELIHOOD OF A SEVERE THUNDERSTORM RISK THROUGH TUESDAY. A ROBUST WARM AND MOIST FEED OF LOW LEVEL AIR FROM THE SOUTH WILL REMAIN DESPITE A WAVERING COLD FRONT MOVING EAST THROUGH THE FIRST PART OF THE DAY. THE ENVIRONMENT WILL BECOME UNSTABLE MID MORNING WITH CAPE OF AROUND 500J/KG INCREASING TO MAXIMUM 1000J/KG BY LATE AFTERNOON, WITH POCKETS OF DEEP MOIST CONVERGENCE ALLOWING FOR STRONG CONVECTION TO OCCUR BOTH ALONG THE REAR OF THE FRONTAL ZONE AND ACROSS THE POST-FRONTAL ENVIRONMENT. FURTHER NORTH AND EAST CONVECTION IS EXPECTED TO BECOME ELEVATED, BUT FROM THE SW APPROACHES AND INLAND THROUGH THE WARNING AREAS ORGANISED SURFACE-BASED CONVECTION WITH LOW LCLS IS VERY LIKELY. GIVEN DIRECTIONAL SHEAR ALONG A KINKED FRONTAL ZONE AND INCREASING 0-3KM HELICITY WITH SHORTWAVES BOTH IMMEDIATELY AFTER THE FRONT AND LATER INTO THE EVENING, THERE IS SCOPE FOR MESOCYCLONIC DEVELOPMENT WITH UPDRAFTS, LEADING TO TORNADOGENESIS IN AN ENVIRONMENT FOR SUSTAINING STRONG VORTICES. THE MOVEMENT OF THE COMPLEX LOW CENTRE DRAPED OVER THE NW OF THE UK WILL GENERATE THE POST-FRONTAL SHORTWAVE FROM LATE AFTERNOON INTO EVENING, AND ENCOURAGE A STRONGER LOW LEVEL JET. THE RISK OF TORNADOES AND STRONG CONVECTIVE GUSTS ARE HIGHER IN THIS PERIOD, THOUGH LIKELY WITH ANY STRONG UPDRAFT THROUGH THE WARNING PERIOD.

 

PRECIPITABLE WATER VALUES OF AROUND 2.5-3CM AND A HIGH FREEZING LEVEL WILL ALLOW FOR VERY HIGH RAIN RATES FROM ORGANISED CORES, THOUGH WITH THIS A LACK OF SIGNIFICANT HAIL OR ICING PERHAPS NOT FOREWARNED BY LIGHTNING. FLASH FLOODING IS A PRIMARY CONCERN, THOUGH GIVEN RECENT RAINFALL THE GROUND WILL LIKELY BE SATURATED IN MANY AREAS SO RAPID RUN-OFF AND SHARP RIVER CATCHMENT FLOODING ARE ALSO A POSSIBILITY. RIVERS THEMSELVES MAY BECOME SWOLLEN, LEADING TO POSSIBLE LONGER TERM FLOODING PROBLEMS IN WESTERN AREAS. THIS WARNING MAY BE UPDATED. PLEASE MONITOR WEATHER AND TRAVEL INFO AS NECESSARY.

 

 

http://www.skywarn.org.uk/current.html

[Coast]

Then there's that rain:

 

 

Yellow warning of Rain

 

Issued at: 

1152 on Mon 21 Oct 2013

 

Valid from: 

0005 on Tue 22 Oct 2013

 

Valid to: 

1500 on Tue 22 Oct 2013

 

Further heavy rain will affect much of South West England and South Wales on Tuesday, clearing during the afternoon.  The public should be aware of the risk of disruption due to localised flooding. Periods of heavy rain will continue to affect many south western parts of the UK during Tuesday, bringing a risk of minor disruption due to river and surface water flooding. Total rainfall during Monday and Tuesday will exceed 60 mm in the wettest spots, mostly over higher ground, with many places seeing 20 to 30 mm. 

 

The more persistent rain will clear to showery conditions during Tuesday afternoon, though there is uncertainty over precise timings of this clearance.

 

 

http://www.metoffice.gov.uk/public/weather/warnings/#?tab=warnings&map=Warnings&zoom=5&lon=-3.50&lat=55.50&fcTime=1382396400&regionName=sw

[Mapantz]

Morning! I see the showers are ganging up just out of the radar shot at the moment, certainly looking interesting as we head through today.  

[Coast]

Batten down the hatches, the Atlantic is on the attack!

 

 

Jet stream is all over the place

 

 

Edited October 22, 2013 by Coast

[Jane Louise]

It seems rather quiet on here today. Are we just waiting for the fun and games to start or are we just maybe a little over excited at the potential and it may not happen lol. Time will tell later I suppose.

[Mapantz]

It seems rather quiet on here today. Are we just waiting for the fun and games to start or are we just maybe a little over excited at the potential and it may not happen lol. Time will tell later I suppose.

 

I see the MO have extended their yellow warning to all southern counties until 6am tomorrow. It sure will be lively but who will be the lucky ones? Or unlucky if you look at it another way. :lol:

 

All eyes on the radar later this afternoon. 

[Jane Louise]

I see the MO have extended their yellow warning to all southern counties until 6am tomorrow. It sure will be lively but who will be the lucky ones? Or unlucky if you look at it another way.

 

All eyes on the radar later this afternoon. 

Always a case of hit or miss  in these kind of set-ups. But I'm hoping we all see something if it pans out! I've not got a weather warning as of yet lol South Gloucestershire has but I know I will later on I'm sure of it  lol.Fingers crossed .

[weatherobsuk]

Beeb becoming ever more confident of some squally (potential SLW damaging) showers moving across the country overnight, as usual with these things it'll be hit and miss.

[Nick F]

Storm & Convective Forecast

Issued 2013-10-22 11:29:52

Valid: 22/10/2013 1200Z to 23/10/2013 1200z

 

 

THERE IS A SLIGHT RISK OF SEVERE WEATHER FORECAST

 

Synopsis

A deep warm and moist southerly surface flow and southwesterly flow in the mid to upper levels continues across northwest Europe today ahead of upper-level trough just W/SW of Ireland, cold front clears eastern Britain early this afternoon followed by an unstable rPm airmass with a shortwave trough that will swing in from the southwest approaches this afternoon/evening across SW Britain.

... S IRELAND, SW and S ENGLAND, WALES, THE MIDLANDS and N ENGLAND ...

GFS indicates several 100 j/kg CAPE this afternoon across the above areas ... as lapse rates steep in response to colder air feeding in aloft with approach of upper trough atop of unseasonably warm and moist southerly flow. Scattered heavy showers and isolated thunderstorms are possible this afternoon in the increasingly unstable rPm airmass moving in across these areas, with storms perhaps increasing in coverage this evening and overnight towards southwest and southern Britain, as a shortwave troughs moves in from the southwest - which will provide additional forced ascent.

Strong southwesterly flow aloft and winds backed southerly at the surface will produce reasonably strong vertical shear, GFS indicates 30-40 knots of deep layer shear and 25-30 knts of low level shear, so storms could develop rotating updrafts that can lead to an enhanced risk of isolated tornadoes developing. Storms will also be capable of producing excessive rainfall totals leading to flash flooding, hail and strong wind gusts. A SLIGHT risk has been issued for tornadoes and excessive rainfall.

 

Issued by: Nick Finnis

 

[liambailey09]

Very much enjoying being on the south coast (moved from herts), Sunday morning was pretty intense and to hear about a possible tornado over on hayling island I was surprised. Very strong wind and torrential rain along with a few rumbles of thunder. Looking forward to today's risk, got a decent view from my flat to the south west. 

[weatherobsuk]

Batten down the hatches, the Atlantic is on the attack!

 

 

Jet stream is all over the place

 

 

 

8 injured yesterday when a flight from New York to Dublin encountered severe turbulence whilst on the descent into Ireland, the Atlantic truly is making its presence felt this past week.

 

http://www.dailymail.co.uk/news/article-2470257/Severe-turbulence-injures-8-New-York-Dublin-flight.html

[staplehurst]

Beeb becoming ever more confident of some squally (potential SLW damaging) showers moving across the country overnight, as usual with these things it'll be hit and miss.

 

That's code for tornado potential...

[Coast]

That's code for tornado potential...

 

 

Which increases as we go through the evening and into tomorrow first thing along the South coast according to GFS:

 

Edited October 22, 2013 by Coast

[Supacell]

Local radio forecasting thunder, lightning, hail, squally winds and torrential rain for early hours of the morning here. I have no access to charts again so could someone tell me if this is likely? I know the south and west are at risk but this far north???

[Paul]

Nick's issued a storm forecast for the next 24 hours - slight risk of severe storms..

 

http://www.netweather.tv/index.cgi?action=convective;sess=