Convective Outlook

[Paul Sherman]

So do we all sit tight and see where Paul chases to or make our own minds up?

The only thing I am chasing tonight is my pillow and duvet as the wind and rain rattle the windows

[Coast]

TORRO update from Paul Knightley:

13:45GMT - Tuesday 24th November 2009 - TORRO CONVECTIVE OUTLOOK

A strong cold front will move south-eastwards across the British Isles this afternoon, evening, and tonight. Across England and Wales, this front is expected to be marked by a line of intense rainfall, along with very squally winds and possibly tornadoes. Wind gusts could reach 60mph, perhaps 70mph in places.

Furthermore, a trough may well follow the front during tomorrow morning and early afternoon, mainly across southern parts of Wales and England. Should this occur, it also brings the risk of severe winds and tornadoes.

The situation will be monitored through this afternoon, and a discussion or watch is likely to be issued later.

[dogs32]

www.thisisgloucestershire.co.uk/Gloucestershire-tornado-warning

my God...I think I might do the night shift just in case

camera on standby..batteries charged

COAST!!!!!!!!!!!

Dont let dogs32 see that post - What are you trying to do man

lol...just seen this Paul

Pat tours are starting...book your place with me now for

Rotation Tours...5 places availible

Edited November 24, 2009 by dogs32

[Paul Sherman]

Have you got a Chilli's in Gloucestershire Pat ? If not then I aint coming.....sorry

Back on To tonight, I would think the Netweather Team will issue something in the next few hours reagarding tonights and tomorrow mornings potential.

Paul S

[dogs32]

Have you got a Chilli's in Gloucestershire Pat ? If not then I aint coming.....sorry

Back on To tonight, I would think the Netweather Team will issue something in the next few hours reagarding tonights and tomorrow mornings potential.

Paul S

no..But we have Buffalo Wings..lol

Not the Tornado I was expecting to hit here Paul like I said on the phone..

Maybe this is a good Omen..

How in the world am I suppose to go to bed tonight knowing there is a chance of a Tornado or severe weather..

Its going to be a long night of watching the weather

[SteveB]

Nobody has any warnings up yet regarding tonights developments?. Is it because it is up in the air (if you pardon the pun).

[Coast]

GFS connective gusts for the time frame under consideration:

Current analysis:

[dogs32]

Nobody has any warnings up yet regarding tonights developments?. Is it because it is up in the air (if you pardon the pun).

BULLETIN - EAS ACTIVATION REQUESTED

TORNADO WARNING

NATIONAL WEATHER SERVICE CHELTANHAM GLOS

14.37 PM GMT TUE NOV22 2009

THE NATIONAL WEATHER SERVICE IN GLOUCESTERSHIRE HAS ISSUED A

* TORNADO WARNING FOR...

GLOS COUNTY IN CENTRAL SOUTHERN.

* UNTIL 3.00AM GMT.

* AT 15.00 PM GMT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED

A SEVERE THUNDERSTORM CAPABLE OF PRODUCING A TORNADO. THIS

DANGEROUS STORM WAS LOCATED 10 MILES SOUTHWEST OF CHELTENHAM...OR

11 MILES EAST OF TEWKSBURY...MOVING EAST AT 45 MPH.

REPORT SEVERE WEATHER TO THE NEAREST PAUL SHERMAN,JANE OR DOGS32 LAW ENFORCEMENT AGENCY. THEY

WILL RELAY YOUR REPORT TO NETWEATHER OR THE NATIONAL WEATHER SERVICE.

Sorry Mods and Rocker's back to reality..

I shall hold my silence

Edited November 24, 2009 by dogs32

[Coast]

Nobody has any warnings up yet regarding tonights developments?. Is it because it is up in the air (if you pardon the pun).

TORRO have a preliminary forecast, but I think people want to wait a short while to see how this is likely to go.

TORNADO WARNING

NATIONAL WEATHER SERVICE CHELTANHAM GLOS

@Pat!

[dogs32]

TORRO have a preliminary forecast, but I think people want to wait a short while to see how this is likely to go.

@Pat!

Coast couldnt stop laughing..

I shall be sensible now..and go quietly

[Harry]

I prefer it at night in some ways, at least that way if there is any lightning we should see it!

[weatherobsuk]

Its a shame the BBC have got their facts wrong about the SLW damage in Derby being Tornadic Damage, one forecast I saw earlier even referring to yesterdays event being "sometime last week"

I'd say 70mph is good estimates by the MetO however, CAPE values arent high but the factor with tonights Front is Forcing rather than Convective inhibition, although there will be convective cells embedded within the Squall and accompanying SLW with possible FC/TN activity to suite. Depending on Cloud Cooling heights Sferic activity will also be a likely threat with some hail and CG activity as the Front enters higher terrain to the Central areas of England and Wales.

[Jane Louise]

Oh my!!! A Tornado in Glos tonight!!! I will most certainly be staying up. Has dogs got the message yet lol.

Hey Harry, thanks I still may get my thunderstorm after all if this pans out. Let's hope if this does happen everybody stays safe. Eyes glued to the radar tonight.

[Harry]

Its a shame the BBC have got their facts wrong about the SLW damage in Derby being Tornadic Damage, one forecast I saw earlier even referring to yesterdays event being "sometime last week"

I'd say 70mph is good estimates by the MetO however, CAPE values arent high but the factor with tonights Front is Forcing rather than Convective inhibition, although there will be convective cells embedded within the Squall and accompanying SLW with possible FC/TN activity to suite. Depending on Cloud Cooling heights Sferic activity will also be a likely threat with some hail and CG activity as the Front enters higher terrain to the Central areas of England and Wales.

Precisely - the lively squall line with thunderstorms last Saturday (week and half ago) which brought the Essex tornado was early in the morning (8-9am), and if I remember rightly there wasn't that much in the way of CAPE - the sheer ferocity of the squall line provided enough of the umpf required. This I really think could be worth setting the alarm for - even though of course there could be a downgrade in the next few hours, bearing in mind the 'event' if any is about another 10-12 hours away for many.

[Coast]

So what's going up there at the moment? Herstmonceux 12Z Sounding:

[Ian Fergusson]

Doh! Never mind - will keep the window ajar so if there is any significant winds, it might wake me. With any luck there'll be some sferic activity accompanying it - which may wake me

Will wait and see - fingers crossed

Cheers Paul

SFERICS unlikely Paul - latest MetO NAE and high-res modelling suggest embedded tops on the ANA-front up to only FL 12-14 so we're not expecting a thundery feature to any great degree (if at all). The wind / squall-line / tornadic potential remains the primary interest (as well as rainfall obviously). The prefrontal conveyor will be blowing a steady 60+ kts; marked wind shift as the front passes and there's good agreement in the last NAE / severe weather diagnostic runs for marked low-level vorticity. General rainfall expectations range at 5-10mm under each hour across the front but more for Wales (15mm in 3 hours) . MO high-res model suggests classic ANA-front (rear-sloping) for this one tonight and some lively line convection elements with fairly wide swathe of 50-ish knot squally gusts inland and >60 coastally. In the likes of Bristol / Weston / Glos, you'll find these pick-up markedly between 2100-2300hrs; Swindon along M4 to Reading around 00Z-01Z Wed, with the NAE runs today all consistent in bringing the heaviest precip across Bristol at or soon after midnight. By 05-06Z we expect the whole show will be clearing out of East London and indeed nearly out of Kent (heavy and perhaps thundery showers then tomorrow at times for the south coast and indeed some other areas).

Cheers

Ian

[Harry]

SFERICS unlikely Paul - latest MetO NAE and high-res modelling suggest embedded tops on the ANA-front up to only FL 12-14 so we're not expecting a thundery feature to any great degree (if at all). The wind / squall-line / tornadic potential remains the primary interest (as well as rainfall obviously). The prefrontal conveyor will be blowing a steady 60+ kts; marked wind shift as the front passes and there's good agreement in the last NAE / severe weather diagnostic runs for marked low-level vorticity. General rainfall expectations range at 5-10mm under each hour across the front but more for Wales (15mm in 3 hours) . MO high-res model suggests classic ANA-front (rear-sloping) for this one tonight and some lively line convection elements with fairly wide swathe of 50-ish knot squally gusts inland and >60 coastally. In the likes of Bristol / Weston / Glos, you'll find these pick-up markedly between 2100-2300hrs; Swindon along M4 to Reading around 00Z-01Z Wed, with the NAE runs today all consistent in bringing the heaviest precip across Bristol at or soon after midnight. By 05-06Z we expect the whole show will be clearing out of East London and indeed nearly out of Kent (heavy and perhaps thundery showers then tomorrow at times for the south coast and indeed some other areas).

Cheers

Ian

For clarity - it was me who mentioned hope for thunder

[Coast]

Thanks again for the analysis Ian, for us not so familiar with some of the terms:

Cold Fronts can be devided into two types: Ana and Kata Cold Fronts. These types can be described both in terms of classical frontal theory and in terms of conveyor belts. The main feature which separates the different types of Cold Front is the orientation of the jet relative to the front in the middle and upper levels of the troposphere:

In the case of an Ana Cold Front, the jet axis and dry intrusion are parallel to the frontal cloud band, and form a well pronounced rear cloud edge. In the case of a Kata cold front, the jet axis crosses the frontal cloud band.

www.zamg.ac.at

[Paul Sherman]

Seeing as Ian is around and hopefully he reads this, I would just like to ask a question as it looks like Ian is a qualified Met etc

Why do the Weathermen/Presenters on BBC Keep on mentioning the chance of Mini Tornadoes when the term simply does not exist, a Tornado is a Tornado period and there is nothing "Mini" about it, or another question is are you told to mention the word "Mini" in the broadcast to keep the public from panicking ?

Just curious as to your viewpoint on this subject as it grates most people interested in the weather and not just on this weather forum.

Paul S

[Coast]

Reply back to the question I asked of Kaddy Lee-Preston at BBC South East today (one of Ian's BBC colleagues no doubt!) specifically about Sussex and Kent:

There is a tiny risk for us when the cold front passes between about 3-7am, but the risk is so small - plus you can never predict where is more likely to get one. The main fact will be that we'll all notice some very heavy rain for a time, and some very very strong winds - so it'll sound rough out there whatever!

[BrickFielder]

If anyone is a little confused go read Ian Fergusson post which is spot on in my opinion. Cloud tops will not be that high. High resolution models show a little instability (SBCAPE = 30J/KG) at low levels very close to the front. It is worth mentioning that there are two ways a tornado can form. Firstly from low level horizontal vorticity where wind speeds at 3000 feet are much higher than those at the surface.This requires a strong updraft to lift the vorticity. This will not be the case tonight. The second method is that exsting vertical vorticity whether from orographic conditions or wind curvature in the lowest layers are lifted. This gives very short lived weak tornadoes and it is just possible the conditions might be in place tonight.

Looking at the satellite pictures I am not convinced about line convection but there does look to be some potent squalls coming in behind. Forecast SkewT's tell their own tale. South coast might be the place for paul to head to.

[Coast]

TORRO TORNADO WATCH 2009/013

A TORNADO WATCH has been issued at 17:15GMT on Tuesday 24th November 2009

Valid from/until: 18:00 - 12:00GMT on Tuesday 24th/Wednesday 25th November 2009, for the following regions of the United Kingdom & Eire:

Parts of (see map)

All of England and Wales Channel Islands

THREATS

Tornadoes; wind gusts to 70mph; hail to 15mm diameter; CG lightning (hail/lightning post-cold front)

SYNOPSIS

Strong cold front will move east/south-east across the area tonight. Whilst deep convection is not expected along the front, strongly-forced shallow convection is simulated, with a good chance of LEWP/bowing segments, and misocyclone development. Such development brings the risk of wind gusts of 60-70mph, and short-lived tornadoes. There is a chance of a number of tornadoes overnight.

Tomorrow morning, one or more post-frontal short-wave troughs is expected to race eastwards, especially (but not exclusively) across southern parts. If convection fires on these, hail/thunder/strong winds and (perhaps) tornadoes will be possible - indeed, a stronger tornado (T4) is possible should this convection develop.

The major driving trough is expected to move across late morning into the afternoon. The watch may need to be extended/re-issued at 1200GMT tomorrow.

[dogs32]

News travell's fast...

just had my neighbour knocking on the door telling me that he as seen in a Glos paper news of possible tornado's tonight

hope you are all up to the night shift

Edited November 24, 2009 by dogs32

[chapmanslade]

I'm really pleased to see Ian posting on here as it gives us an extra dimension to our discussions. I was also delighted that Richard Angwin mention on his lunchtime forecast that tonight's front is an ANA cold front. This level of information is great for those interested in the subject and to be honest will fly well above the head of the majority and go un-noticed. My interest in the weather was kindled by Francis Wilson in the 80's who was at the BBC at the time and always gave 'a little bit extra' in his forecasts for those who wanted to listen. Three cheers the for the BBC !

Even Horizon seems to be back to it's old self again recently !

[risk of sleet]

Forecast SKEW-T shows very high values for TT index (Total Totals). 58 - 60 for the UK tomorrow. Can't say I really understand though. SKEW-T HABYHINTS

Some strong gusts this afternoon here and currently.