A SEVERE THUNDERSTORM WATCH has been issued at 09:50GMT on Tuesday 28th June 2011
Valid from/until: 09:50 - 23:00GMT on Tuesday 28th June 2011, for the following regions of the United Kingdom & Eire:
Cent S England
Hail to 3-4cms diameter; wind gusts to 60mph; cloud-ground lightning; isolated tornadoes
Fairly steep mid-level lapse rates atop a moist lower atmosphere, along with the the approach of an upper trough is allowing thunderstorms to develop. These are currently elevated, but within a region of increasing shear. This shear /35-40 knots of 850-500hPa shear/ suggests that elevated mesocyclones are possible, capable of producing fairly large hail. In addition, some surface based instability is expected to develop, especially across the eastern part of the WATCH area. Any such activity will have the potential to become supercellular, but there are question marks over how long any cell might remain over land. Again, large hail is the prime threat, but strong winds are possible too.
Local convergence zones may develop along the east coast and close to the Thames Estuary. Such a development would increase low-level shear locally, and bring a low risk of a tornado. As this threat appears to be conditional on the development of sea breezes, the a SEVERE THUNDERSTORM WATCH is deemed more appropriate.
Image Credit: Malvern Wells Weather