[PaulKn]

TORRO CONVECTIVE DISCUSSION 2012/008

A TORRO CONVECTIVE DISCUSSION has been issued at 2340GMT on Monday April 30 2012

Valid from/until: 2340GMT-0800GMT on Monday April 30/Tuesday May 1 2012 for the following regions

Parts of (see map)

Portions of central and southern England

Portions of Wales

THREATS

Hail 10-15mm diameter, locally 20mm; wind gusts to 50mph; CG lightning; heavy rain

DISCUSSION

Plume of moisture above a stable boundary layer has destabilised as a result of differential thermal advection and lift from an approaching upper trough. Reasonable cloud-layer shear of 30-35 knots may allow for brief mid-level rotation, enhancing the risk of marginally severe hail/isolated severe hail. Gusty winds are also likely.

Forecaster: RPK.

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[Tony Gilbert]

5pm

Good call on this one Paul. Last nights models looked a bit hit and miss for me but storms are now developing NW of London.

Below is Herstmonceux skew-t diagram 12Z. This is fairly representative of these storms. Cloud tops could reach over 300mb where a moderate jet exists giving ample chance for a fully sheared thunderstorm to develop. In fact the sounding shows that the jet stream is effective much lower down than the GFS had anticipated. Hence the mean average shearing will be apportioned to the middle of the storm and not just the cloud top.

Whilst low level shear remains weak , these storms should nevertheless have the capacity to become strong for a time!

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This post has been edited by Tony Gilbert: 01 May 2012 - 16:10