Storm Forecast
Valid: Tue 02 Dec 2008 06:00 to Wed 03 Dec 2008 06:00 UTC
Issued: Mon 01 Dec 2008 19:54
Forecaster: VAN DER VELDE

SYNOPSIS

An upper trough enters the Mediterranean Sea and destabilizes this region. Meanwhile, a low pressure area develops under the southwesterly jet east of the trough, affecting the central Mediterranean. Warm air advection inforces the cold front, which will drag over southern Italy and the south Adriatic coast. Low pressure and a cold pool move southeast towards the Netherlands during the evening. EL temperatures are cold and QG forcing strong, coastal convergence may lead to a line of storms with thunder along the coast. During Wednesday morning hours, a new disturbance destabilizes the Bay of Biscay region.

DISCUSSION


...Southern Italy, southeastern Adriatic coast...

The cold front is predicted (GFS) to pass slowly, causing storms that can be quasi-steady along a line and produce locally large amounts of precipitation. Storms in the warm sector moving eastward can affect Albania. The strongest convergence is predicted for southern parts of the FYR. The whole region is under significant deep layer (30-40 m/s) and moderate low level shear (>10 m/s). Storm-relative helicity should reach values over 300 m2/s2, invoking storm rotation and associated severe weather threats, mainly large hail and severe gusts. There is a chance of tornadoes, in particular in the level 2 area where low level shear is frictionally enhanced to 15-20 m/s and SREH3 to higher than 400 m2/s2 during evening and night. An isolated strong tornado is not ruled out. The cold front shift slowly to the south and the threat appears to last well into the next forecast day.


...Thyrrenean Sea...

For the morning, GFS simulates an MCS tracking over Sardegna, however the region is within a local minimum of deep layer shear. To the east, the jet creates DLS of 20-30 m/s. Storms may organize well and develop rotating updrafts, and hence a chance of large hail.