Slight Risk of Severe Thunderstorms Central Ireland, Wales, and northern England 11Z-21Z Fri 17th Aug. Prime Risk Severe Gusts
Slight Risk of Tornado Development as per red boxed zones below
Quasi stationary low 980mb west of Ireland draws moist unstable air northwards from Azores. Some late surface troughing expected to develop over Ireland as surface temps increase.For UK the cold front expected to develop initially across Wales where UKMO Fax charts exhibit some surface wave motion which could allow for stronger low level veer of winds. Helicity values predicted up to 250 m/s2 though primarily based on speed shear as opposed to directional shear. With such totals it is nevertheless possible for storms to develop supercell characteristics and the chance of a tornado based on the strong 0-3km shear available. Forecast sounding give uncapped cloud top level. So the stronger upper winds are likely to be fully utilised by any isolated stronger storm development. Convective gust are calculated to peak at around 55kt (severe) based on the mean average winds between 800mb and 600mb. Hail will be possible on the taller isolated storms though with the elevated freezing level I doubt that hail will be the primary risk. With the upper trough only having marginal influence on the the regions effected tomorrow the risk would appear to be associated with the stronger low level lapse rates and dynamic forcing along the cold front itself. It is expected that the NW side of the cold front axis will be over shadowed by heavy cloud cover. It is therefore likely that the strongest solar heating will develop to the SE of the initial convection.Whilst some relatively strong CAPE values are forecast, the upper atmosphere looks saturated reducing potential instability somewhat. Hense I do not expect electrical acivity to be widespread.
This post has been edited by Tony Gilbert: 16 August 2012 - 20:40