Storm Forecast
Valid: Thu 10 Jan 2013 06:00 to Fri 11 Jan 2013 06:00 UTC
Issued: Thu 10 Jan 2013 05:45
Forecaster: GATZEN

SYNOPSIS / DISCUSSION

A blocking high has build to the west of Scandinavia, and the Scandinavian trough spreads into Central Europe. To the south of the blocking high, a westerly jet extends from the Bay of Biscay aross the West Mediterranean into the east Mediterranean. Two short-wave troughs will affect these regions today. At lower levels, a westerly flow has advected moisture into south-western Europe and the Mediterranean.

The eastern short-wave trough will move across the north Mediterranean today. To the south of France, dry and cold low-level air will lead to stable conditions. Further east, low-level moisture slowly increases, especially across the Adriatic Sea. Showers near the center of the trough are expected be become deeper and thunderstorms will become more likely. Weak vertical wind shear will limit storm organization, and severe storms are not expected.

During the night hours, the trough will reach Greece and the Aegean Sea, where low-level warm air advection is expected ahead of the approaching jet streak. Increasing lapse rates are forecast and thunderstorms will be more widespread. Additionally, strong QG forcing and upslope flow will lead to lift. Additionally, deep layer vertical wind shear will increase ahead of the trough and may also affect the storms near the center. Current thinking is that storms can organize and linear multicells can develop. However, weak CAPE and limited shear seem to be not supportive for severe thunderstorms. Main threat will be excessive precipitation along the western coasts of Greece, where upslope flow will be present. A level is not issued because of the limited contribution of deep moist convection to this precipitation event.

Another short-wave trough will cross the Bay of Biscay and France today. A tongue of moist low-level air will spread eastwards ahead of a cold front. A mid-level jet streak curving around the short-wave trough will nose into this warm air leading to rather strong QG forcing. Increasing lapse rates will spread across France reaching the western Alps at the end of the period. Current thinking is that convection can evolve along the cold front and may organize as a convective line. Limiting factor will be the limited CAPE due to weak lapse rates and low-level moisture. Additionally, low-level winds do not support a pronounced high wind threat. Therefore, only a weak chance of severe wind gusts is expected.