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Severe T-Storm Risk UK & IRL June 29th-July 7th

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Author Topic: Severe T-Storm Risk UK & IRL June 29th-July 7th  (Read 6901 times)
Martin Mc Kenna
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Maghera, N. Ireland

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« Reply #120 on: July 06, 2009, 10:26:16 am »

Moderate Risk of General Thundery Showers 06-21Z UK & Eire

Slight Risk Severe Thunderstorm Southern Ireland, Wales and Southern UK 06-18Z

Slight Risk of Strong Tornadoes Southern UK, Wales, E.Anglia and South Midlands 06-18Z

Probably the most serious forecast that I have posted to the UKWW so far this year;

Deep break away upper trough moves east through Monday increasing lift with steep lapse rates at all levels. Moderate divergent upper jet stream further increases lift with primary focus to the front left exit region. Increasing low level jet at 850mb establishes strong low level shear. Models currently develop high CAPE values as heavy surface moisture advects east mixing with mild air from the south. Potential instability is utilised as dry incursion pushes through inline with the predicted surface trough. Strong vertically stacked PVA max builds over Wales and moves east  adding to stronger convective potential.

Quite a day in store with potential for non severe convective gusts of around 30kts based on mean average values from 800mb to 600mb. Threat of large hail and defined risk of one or more strong tornado events are possible.

Particular attention is given to south Midlands  late in the day where the low level jet is shown to increase and overrun lighter winds at surface. Whilst winds would seem to be straight lined the speed shear should compensate to increase low level field vorticity. Upper winds are strong but show only slight increase with height hense a SLIGHT risk of Severe Thunderstorms is expected ATM.


As per earlier forecast with enhanced tornado risk zone (blue box) 15Z-18Z

Additional risk box added Scotland for enhanced risk of Convergence Zone Tornadoes.

Based on the most recent model update there would appear to be an enhanced risk for tornadoes this afternoon from north Dorset arcing through to E.Anglia where surface vector is reduced increasing LL shear. Upper dry air incursion times in nicely and pushes in from the west creating an arcing line of isolated strong convective cells. It is within this line that severe weather potential today will peak.

It is however noted that due to lack of any considerable veer at surface the risk for meso derived tornadoes today remains SLIGHT. A reminder that the broad coverage box does not mean that everyone in that box will see a storm today, but just that there is a defined risk. In fact I do not expect the thundery activity to be widespread in nature!
« Last Edit: July 06, 2009, 10:27:51 am by martinastro » Report Spam   Logged

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