Convective/Storm Discussion

[Jane Louise]

Estofex forecast is looking good

I'm wondering whether any of us storm starved may get any thunderstorms from this:

http://www.estofex.org/

[Coast]

Estofex forecast is looking good

Morning Jane Louise! I'll stick that forecast in here for anyone who hasn't caught it, much of the Southern half of the UK is under a watch with some under a level one:

Storm Forecast

Valid: Thu 12 Nov 2009 06:00 to Fri 13 Nov 2009 06:00 UTC

Issued: Wed 11 Nov 2009 20:17

Forecaster: GATZEN

A level 1 was issued for portions of England and Wales mainly for severe wind gusts and for a lower extend for tornadoes.

SYNOPSIS

A broad trough over Europe moves north-eastward, while warm air advection sets in over western Europe ahead of an Atlantic trough. This is associated with a strong mid-level jet streak spreading into western Europe. At lower level, a strong jet will advect moist air across the Bay of Biscay and the British Isles late in the period. Further east, most of Europe is dominated by dry air masses. Over the Turkey region, rather moist low-level air mass is present in the range of the trough.

DISCUSSION

Portions of England and Wales

Models agree on the development of a strong mid-level jet streak spreading into the northern Bay of Biscay in the evening hours, and strong QG forcing will be present in the warm air advection regime ahead of the surface cold front of low pressure over the Atlantic Ocean. A 25 m/s low-level jet is forecast by latest numerical models leading to strong low-level vertical wind shear, while the low-level mixing ration may reach more than 8 g/kg in the south-western portions of the British Isles. Weak instability is forecast due to differential warm air advection in an air mass characterised by nearly moist-neutral lapse rates. Together with strong linear forcing along the cold front, a shallow line of convection is forecast to develop in the evening hours. North of the mid-level jet, deeper convection will likely evolve cold pools due to melting of graupel and snow, helping the convection to organise. Bowing elements are expected, associated with severe wind gusts and possibly tornadoes in the range of embedded mesocyclones. The convective line will rapidly spread into the North Sea late in the period, where the potential of deep convection decreases due to weaker low-level moisture.

Here's TORROS take on it:

Over the next few days, the British Isles are at risk from severe weather, mainly in the form of high winds and heavy rain. Some of the strong winds are likely to be associated with severe convection, and there is a slight risk of tornadoes in a few places.

The first risk, albeit fairly small, will be on Thursday afternoon and evening, as a cold front moves eastwards. There are some indications that across southern and central parts of England and Wales, line convection may develop in a region of reasonable low-level shear...thus, misocyclones may develop, enhancing the chance of strong winds and isolated tornadoes.

A more vigorous set of fronts will cross the British Isles through Friday and Friday night. The cold front and triple point of this system may be areas where convection is possible. With strong winds throughout the atmosphere, changing in direction with height, a few tornadoes may be possible, along with some strong wind gusts. The system will also produce strong winds away from convection too.

A few charts for today:

and later in the day:

Current SatRep analysis:

An interesting few days coming up for us storm lovers, who knows what or when we will actually get!!!

[Jane Louise]

Morning Coast

It's certainly looking good. Just hope everyone keeps safe whatever the weather prevails. Lots of radar watching to do over the next couple of days. could be quite interesting!

[Methuselah]

Morning Coast

It's certainly looking good. Just hope everyone keeps safe whatever the weather prevails. Lots of radar watching to do over the next couple of days. could be quite interesting!

Do hope you get something this time, JL...In the mean-time, there'll be no lamppost-watching duties to keep us all away from the radar! :lol:

[Nick F]

My eyes are drawn to late tomorrow evening when the cold front+triple point moves across England

... GFS/Lightning Wizard charts for 00z Sat show strong DL-Shear (up to 100 Knts) and LL-shear as the front moves through, so convection is likely to form a squall line with embbedded mesocyclones with the potential for tornadoes and strong damaging wind gusts:

06Z GFS DLS and LLS charts:

What may limit this potential, is lack of instability, though dry air intrusion on the rear side of the cold front will maybe compensate by increasing potential instability.

Further severe potentials over the weekend too as the deep low moves across Sern England with strong shear and potential instability likely during the low's passage bringing threat of damaging convective gusts and risk of a tornado or two.

[Devon-Nelly]

Thats amazing strong windshear forecast for us tommorow under the white area nearly! and being under the level 1 on ESTOFAXs storm forecast wow lol :lol:

Glad im off work the next couple of days, it will be intreasting to see what happens we've had nearly 3 inches of rain so fair this month already and October was very wet as well.

Just started chucking it down here now

[weatherobsuk]

TORRO are forecasting a risk of T2/3 Tornadic activity from 1300-0100 today in the Midlands and all across the South as the Cold Front moves East. Also a risk of CG Lighting and Hail within the precip cores.

[Harry]

TORRO are forecasting a risk of T2/3 Tornadic activity from 1300-0100 today in the Midlands and all across the South as the Cold Front moves East. Also a risk of CG Lighting and Hail within the precip cores.

One I've just read suggests a threat of T3-4 tornadoes!! Confirms reports of thunder this morning in Devon.

[Coast]

Sorry, just got back from the workshop where we've been converting the Coastmobile......

[weatherobsuk]

I'd imagine the TORRO T3/4 forecast is for Tomorrows outlook with the Wind Shear, CAPE and Squall Line expected. But the risk of T2/3 tornadoes is still a significant risk to anyone unaware of any convective activity overnight tonight.

[Coast]

TORRO are forecasting a risk of T2/3 Tornadic activity from 1300-0100 today in the Midlands and all across the South as the Cold Front moves East. Also a risk of CG Lighting and Hail within the precip cores.

Worth looking at the detail of that one, thanks SJ

A TORRO TORNADO WATCH has been issued at 13:50 GMT on Thursday 12th November 2009

Valid from/until: 13:50 - 01:00GMT on Thursday 12th/Friday 13th November 2009 for the following regions

**NOTE THAT THIS IS AN UPGRADE FROM THE PREVIOUS DISCUSSION***

Parts of (see map)

S Wales Midlands S England E Anglia

THREATS

Tornadoes; wind gusts to 65mph, heavy rain; occasional CG lightning; hail

DISCUSSION

Cold front is moving E across the British Isles at present. A jet streak approaching SW England will overspread the front in the south through the afternoon and evening. Differential cooling is likely to allow some convection to develop - in addition, a forced line may develop aided by rear inflow/cold pool generation. Thus, a generally shallow convective line but with deeper convection embedded may result. This seems to be occurring in places, with a recent report of thunder in E Devon. Shallow line convection will bring the risk of isolated, largely weak tornadoes, but any deeper convection brings the risk of a stronger tornado (T3-4), given the low-level moisture and shear.

[Jane Louise]

Sorry, just got back from the workshop where we've been converting the Coastmobile......

Lol

Do hope you get something this time, JL...In the mean-time, there'll be no lamppost-watching duties to keep us all away from the radar!

Thank you Pete. Fingers crossed as always.

[Methuselah]

Lol

Thank you Pete. Fingers crossed as always.

You're welcome, JL...With all that potentially unstable air (of a cold origin?) coming all that way round in the Atlantic, you 'could' be in line for something??

Maybe - here too!

[Jane Louise]

You're welcome, JL...With all that potentially unstable air (of a cold origin?) coming all that way round in the Atlantic, you 'could' be in line for something??

Maybe - here too!

Hi Pete

My area is also in the slight severe thunderstorm risk tonight. Time will tell if anything happens! although I wouldn't want it severe lol Just a rumble of thunder will do me for now after being so storm- starved lol

Good luck for up your way too.

[TonyH]

21mm most of which fell between 12-1500 this afternoon.

Lots of flooding on the roads and lanes, torrents coming from fields and tracks.

If we get more heavy rain tomorrow it looks bad over here.

[A.J]

Intense downpour here, very heavy rainfall!

tell me about it!...just driven back from Walsall, and the M6 was at a standstill, could barely see a damn thing!

[Costa Del Fal]

We had about 20 minutes of non stop torrential rain. The drains couldnt cope for a while and traffic slowed right down. Going to be very interesting over the next few days!

[Coast]

OK then, so the storm is almost on us and what are the other severe weather sites forecasting?

Storm Forecast

Valid: Fri 13 Nov 2009 06:00 to Sat 14 Nov 2009 06:00 UTC

Issued: Thu 12 Nov 2009 21:22

Forecaster: TUSCHY

A level 1 was issued for parts of the Bay of Biscay, UK, Scotland and Ireland mainly for severe wind gusts and to a lesser extent for tornadoes.

SYNOPSIS

An extensive baroclinic zone has established between 10-40°W and 40-50°N. This region will be the setting for a rapidly developing depression and phase diagrams of numerous model data indicate a warm core seclusion with this feature. Slow forward motion during the rapid intensification stage (until 18-21 UTC) gives way to a more rapid NNE-ward motion during the night hours, as a strong jet ejects out of the base towards the north. At the surface, a cold front pushes eastward, trailing over the Atlantic with a more aggressive propagation over Irlenad, UK and Scotland.

Ridging downstream affects central Euorpe with cold/stable conditions over far east/northeast Europe.

... Bay of Biscay, NW-France, extreme NW Spain and N-Portugal ...

Aforementioned warm seclusion is in full progress west of Irleand and assists in a rapidly strengthening wind field at all levels over the area of interest. In fact, 20-30m/s 0-3km shear does not reflect at all the strength of the overall wind field with 45m/s at 700hPa, increasing to outstanding 65m/s at 500hPa, approaching the Bay during the day from the NW. The increasingly negative tilt of the upper trough axis and the gradually increasing inertial advective wind component along the base of the trough causes overall jet strength to decrease during the evening and night hours, with one stronger branch exiting the area to the north (UK) and a re-developing one along the zonally aligned baroclinic zone over the Atlantic.

Overall synoptic pattern and intense LLJ (40m/s at 850hPa), pumping rapidly mixing/thinning tongue of subtropical air towards the north, probably establishes an extensive warm conveyor belt (WCB), running from extreme NW-Spain/N-Portugal all the way to NW-France and UK. WAA keeps atmosphere neutral/stable with moist adiabatic ascent and there is no risk for deep, moist convection. However, a region for isolated, deep convection could evolve along the back (west side) of the WCB, as the cold front and somewhat drier/cooler

upper-level air approaches from the west. Another feature, which fosters this scenario is the split front appearance in forecast model data/cross sections of the cold front itself. Given the magnitude of the LL wind field, at least a level 1 was issued due to the limited coverage of showers/very isolated thunderstorms. The main risk of this activity will be confined to the NW-Bay, NW-France and extreme SW-UK. Overall environment with low ELs and weak updrafts is hostile enough for not even issuing a low probability thunderstorm area.

... United Kingdom, Scotland and Ireland...

The outlook for UK turns out to be even more complex in respect of the degree of thunderstorm coverage. The WCB with more stratiform rain ought to keep the atmosphere very moist and stable for vertical ascent, so the main focus for convection arises during the evening hours, when the cold front draws near from the west. Overall set-up looks promising for a flare-up of convection during the cold front passage over S/central UK as surface cold front gets topped by WAA above 5-6km AGL with aforementioned 65m/s streak at 5km covering SW-UK during the sunset-midnight hours. Despite the unfavorable placement of the front beneath the indirect thermal jet circulation, overall diffluent upper streamline pattern and left exit of a streak at roughly 3km, crossing SE-UK during that time, point to adequate conditions for low-topped convection. Forecast soundings indicate some LL CAPE release and the possibility for storms to evolve in roughly 30-40m/s 0-5km shear (even stronger, if deeper convection verifies). Speed and directional shear, low LCLs and NE-ward racing vorticity lobe create a favaorbale environment for a strongly forced convective line (LEWP-type) with damaging wind gusts and tornadoes possible. Model discrepancies are still high, so new model data has to be evaluated to determine the final severe weather risk. A coarse level 1 was issued, but if the forced line with embedded thunderstorms verifies, a level 2 may be needed.

Another area of concern arises over SE-Ireland and east/northeastwards at 15 UTC onwards, as the triple point of the warm/cold front and occlusion approaches from the SW. Enough instability for stronger and more persistent updrafts and forcing/shear in the extreme range indicate a severe wind gust and tornado risk and an isolated strong tornado event can't be ruled out. This risk spreads northeastwards, affecting S-Scotland thereafter. Decreasing instability onshore may be delayed by the left exit of the 50-60m/s mid-level streak and hence the level was expaned well towards the north.

... South of Ireland and extreme W/SW-UK 21 UTC onwards ...

The intensification of the depression just to the WSW of Ireland will be already in the end pahse and occlusion starts. GFS and ECMWF are in line with the overall scenario, whereas the rest of the model pool is still oscillating around their solution. For now, we stick with the American/European model solution, which sounds quite reasonable, as both models had the most persistent scenario during the past few runs. A back-bent occlusion starts to wrap around the center beneath a pool of drier high-tropospheric/low stratospheric airmass, covering the center of the depression. A rapidly intensifying sting-jet event is forecast to unfold at roughly 21 UTC onwards, affecting the offshore areas south of Ireland. Model output forecast wind speeds indicate gusts in excess of 35-40m/s, which sounds reasonable, given 40-45m/s at 850hPa and a well mixed postfrontal airmass. This evaporatively cooled air is not favorable for deep convection and therefore the damaging wind gusts risk is not reflected in our risk level forecast, but damaging and potential life-threatening wind gusts in excess of 35m/s affect SW-UK after 03 UTC and spread eastwards thereafter.

Just for the sake of completeness, the last similar event (although not comparable in respect of forcing and wind speed) was severe extratropical cyclone Klaus over the far S-Bay of Biscay. A few thunderstorms occured in a similar environment offshore and onshore, so the risk for isolated showers/thunderstorms can't be ruled out completely. An upgrade may be needed, if this concern increases

Storm Forecast Issued: 2009-11-12 21:40:00

Valid: 2009-11-12 23:00:00 - 2009-11-13 22:59:00

Regions Affected

Wales, Southwest England, western Scotland and parts of Northern Ireland & NW England (all of the UK is included in the WATCH)

Synopsis

Two main and deep areas of LOW pressure, one to the northwest and one to the southwest of the UK, will dominate the weather on Friday. The cold front will clear eastwards from eastern England at the very start of this forecast period, with a risk of a tornado across the far southeast. This front will linger along the English Channel for much of the daylight hours, before moving back north again over England and Wales during the afternoon and evening hours as a new depression approaches.

The main timeframe for convective activity will be the late afternoon, evening and night hours both along the cold front of the approaching depression and also behind in the much more unstable airmass. The cold front poses a risk of embedded cells over Southwest England and Wales between 18z-00z, and also a risk of a moderate tornado and severe wind gusts. This then shifts eastwards after the expiry of this forecast period.

Behind the cold front, numerous showers and thunderstorms will affect Ireland and western coasts of England and Wales, as a result in the difference between land and sea surface temperatures. There appears to be a risk of a tornado if cells become organized.

Numerous showers and isolated thunderstorms will also affect western Scotland and the Northern Isles mainly during daylight hours. This forecast may be updated if necessary during Friday due to the complex setup.

TORRO TORNADO WATCH 2009/008

A TORRO TORNADO WATCH has been issued at 13:50 GMT on Thursday 12th November 2009

Valid from/until: 13:50 - 01:00GMT on Thursday 12th/Friday 13th November 2009 for the following regions

**NOTE THAT THIS IS AN UPGRADE FROM THE PREVIOUS DISCUSSION***

Parts of (see map)

S Wales Midlands S England E Anglia

THREATS

Tornadoes; wind gusts to 65mph, heavy rain; occasional CG lightning; hail

DISCUSSION

Cold front is moving E across the British Isles at present. A jet streak approaching SW England will overspread the front in the south through the afternoon and evening. Differential cooling is likely to allow some convection to develop - in addition, a forced line may develop aided by rear inflow/cold pool generation. Thus, a generally shallow convective line but with deeper convection embedded may result. This seems to be occurring in places, with a recent report of thunder in E Devon. Shallow line convection will bring the risk of isolated, largely weak tornadoes, but any deeper convection brings the risk of a stronger tornado (T3-4), given the low-level moisture and shear.

So general agreement of soemthing going on today, but a complicated and uncertain outcome even at this stage. It's certainly very messy on the charts and the only certaintity is lots of rain and high winds:

Eyes on the radar today

[dogs32]

Model discrepancies are still high, so new model data has to be evaluated to determine the final severe weather risk. A coarse level 1 was issued, but if the forced line with embedded thunderstorms verifies, a level 2 may be needed.

Coast

Interesting!!

level 2 could be issued if the TS evolve....

Edited November 13, 2009 by dogs32

[Neilsouth]

Has nobody mentioned the bollo*ed up forecast? , i watched it last night (met and sky) and it was different for today... Heaviest rain was due to pile up southern ireland and western england , with lighter but still heavy rain towards the east. I wake up this morning and its a bloody monsoon outside , with slight flooding in my garden. I check the radar and the heaviest rain is towards the south and south east!!!

We look at models day after day and into FI yet the next day is wrong!

Edited November 13, 2009 by neilsouth

[Coast]

We look at models day after day and into FI yet the next day is wrong!

I have to say all the media forecasts I've seen for the last couple of days have been there or thereabouts on the money, with general agreement with models and amateur forecasts / observations.

[Azores Hi]

Regardless of forecast or not, it really is rather wet out there at the moment, notably so.

[dogs32]

sferics firing off out towards the rain band

[Neilsouth]

I have to say all the media forecasts I've seen for the last couple of days have been there or thereabouts on the money, with general agreement with models and amateur forecasts / observations.

Why do i always get that from either staff or forecasters , yet the general view of my own family and normal members is different. I'm going to record these forecast's one day and actually prove it once and for all!

[Lynxus]

Sferics are on the increase to the SW of the UK.

Fingers crossed for some good shiznit later