Storm Forecast
Valid: Sat 30 Aug 2008 06:00 to Sun 31 Aug 2008 06:00 UTC
Issued: Fri 29 Aug 2008 22:45
Forecaster: DAHL

SYNOPSIS

High-amplitude upper flow pattern exists over Europe ... with an upper ridge covering the central portions of Europe and two quite intense upper troughs/cyclones over the NW Atlantic and E Europe/W Russia, respectively. Weak upper trough is simulated to cross N Iberia and the Biscay on Saturday. Unstable subtropical air will affect the western portions of Europe, the Mediterranean regions, as well as E Europe.

DISCUSSION

... N Iberia ... W France ...

Some potential for severe weather will exist over N Spain and W France in association with the upper trough which is expected over the Gulf of Biscay by Sunday 00Z. Given quite steep mid-level lapse rates as well as ample low-level moisture, strong CAPE should be in place, possibly above 1500 J/kg. Over N Spain and the coast of the Gulf of Biscay, some 20 m/s DLS are expected in the afternoon/evening, decreasing towards central France. Expect large hail and severe wind gusts over N Spain in the afternoon hours. During the night hours, when storms spread across France, severe potential will be somewhat reduced, but rather strong instability and 10 to 15 m/s DLS may still suffice for isolated large hail and damaging wind gusts.

... SW Mediterranean ...

Strong instability, possibly on the order of 2000 J/kg, will persist over the SW Mediterranean. However, models do not suggest that convection will be initiated, except over the Atlas mountains, where profiles should be more of the inverted-V type with little instability. Also, shear profiles should be rather weak over this region. Still, strong evaporative cooling in the downdrafts may result in gusty outflow winds.

... E Europe ...

At the beginning of the period, some CAPE will exist across the Black Sea region and to the northeast ahead of a cold front ... moving eastwards out of the forecast area during the day. It does not seem that CAPE will be particularly strong, but 20 m/s DLS are forecasted immediately ahead and along the cold front. This should suffice for organized storms capable of large hail and damaging winds gusts over the Black Sea region, the E Ukraine and extreme W Russia.