Storm Forecast
Valid: Tue 08 Dec 2009 06:00 to Wed 09 Dec 2009 06:00 UTC
Issued: Tue 08 Dec 2009 06:33
Forecaster: VAN DER VELDE

A level 1 was issued for northern Italy, western Balkan mainly for a chance of tornadoes.

SYNOPSIS

A trough over the British Isles cuts off and digs into Italy and the Balkan as a major low pressure system. The associated forcing and jet streak are very strong on the south side of the Alps. Other upper level lows on the map are located over Belgium/NE France following in the wake of the Adriatic system, and over the Baltic region. A frontal system passes Ireland and the UK with some signals of conditional instability, but forcing and jets appear not very favorable.

DISCUSSION

...northern Italy, western Balkan...

A mid level PV maximum digs into the region, providing ample forcing. The exit region of the jet rounding the trough seems to be overlapping the CAPE region, and storms can develop in a kinematic environment characterized by 30 m/s DLS and 10-15 m/s LLS, as well as up to 200 m²/s² SREH. Low LCL heights are predicted. Convection may become strongly linear but some mesocyclones may be embedded and helped by good 0-3 km CAPE over the Adriatic. Tornadoes/waterspouts are possible. The Balkan coastal zone may experience sufficient moisture lifting for local excessive precipitation, but the system moves through at sufficient pace, and PW content is relatively low, so this should not be a very significant threat.

...UK...

15Z-21Z the front has some signals of potential and conditional instability and good LLS (>12 m/s) and SREH (300 m²/s²) are available, however, the dynamics seems to be lacking with some ridging and the jet offset to the west and southeast. If local forcing is strong enough, awareness for convective development with tornado chance is warranted.