CONVECTIVE FORECAST - UPDATE
VALID 21Z WED 25/06 - 06Z THU 26/06 2003
ISSUED: 25/06 20:51Z
FORECASTER: HUGO

There is a slight risk of severe thunderstorms forecast across N=ern, Central & S=ern France, N=ern Spain & Far SE=ern Counties of England

General thunderstorms are forecast across Southern England & Southern Wales, France (expect SLGT risk region) Spain

General thunderstorms are forecast across Parts of the BENELUX, W=ern Germany, Switzerland, Austria, N=ern Italy, Slovenia, Croatia, Bosnia Hercegovina & parts of Yugoslavia

SYNOPSIS

Minor short wave 500mb trough over parts of N=ern France and into S=ern England will be associated with a significant PV anom will persist throughout the time period this update is valid for...This feature will also be tied in with a weak surface low pressure over N=ern France...Slack pressure gradient dominates across many Central/Southern regions of Europe with a long wave upper trough over E=ern parts of Europe continue to move E=wards and filling...

DISCUSSION

...N=ern, Central & S=ern France, N=ern Spain & Far SE=ern Counties of England...
Convection has initiated during the course of the afternoon and evening within the SLGT risk region, especially over parts of N=ern France, NE=ern Spain and now into the English Channel...Convection is expected to persist into the overnight period especially in the SLGT risk region in assocation with upper forcing from the 500mb short wave trough and its associated PV anom and also the surface low pressure over France and its associated frontal features...Forecast ascents remain unstable within the SLGT risk region throughout the time period this update covers with a persistent risk of some organised severe TSTSM activity...Lowest 30hPa MLCAPE values within the region are expected to remain between 800 and 1300j/kg especially within the thermal WBPT plume through central France and into the Central English Channel...Over Central/Southern France deep layer shear (0-6KM) of between 35 to 40KT coupled with 0-3KM helicity values of >175m2/s2 would allow for more significant organisation if convection persists, however with an expected low STP value and also unfavourable LFC and LCL heights there is only a limited risk of tornadic activity...Some strong surface gusts (>45-50KT) and medium sized hail are all possible however within the SLGT risk region.

...All other GEN risk region except SLGT risk region...
The 500mb trough and associated PV anom affecting Southern parts of England will persist throughout the overnight period bringing a persist risk of imports from France to regions generally South of the M4 corridor and possibly also into the extreme Southern regions of Wales...There will be an E=ward movement to the upper trough during the course of this update and by 06z Thursday any convective activity over England will be reserved for far SE=ern regions before clearing away...With generally limited deep layer shear (0-6KM <10KT) any TSTSM activity is expected to be single celled across Southern England but with some reasonable helicity values (0-3KM s-rh 125 - 150m2/s2) some minimal organisation could occur...With favourable WBZ heights some medium sized hail is possible along with some torrential rainfall in places however numerous cells are expected to be medium level so some of the current intense radar returns may not actually be representative of surface rainfall rates across the Channel/Southern England...Convective activity that has developed during the course of the day in association with diurnal heating across the other regions will gradual decay overnight except for possible NE=ern regions of Spain and also Central/Southern France in association with a greater chance of convective organisation during the course of the night and possible nocturnal cloud top cooling.

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