Storm Forecast
Valid: Tue 22 Sep 2009 06:00 to Wed 23 Sep 2009 06:00 UTC
Issued: Tue 22 Sep 2009 05:41
Forecaster: VAN DER VELDE

A level 1 was issued for the east coast of Spain and Balearic Islands mainly for a chance of locally excessive rain and waterspouts.

A level 1 was issued for the west coast of Italy mainly for a chance of locally excessive rain and waterspouts.

SYNOPSIS

Europe is zonally divided into three regimes today: a steady west-circulation above 55°N, an extensive high pressure area between 42°N-55°N and Balkan, and shallow low pressure with easterly winds over the western half of the Mediterranean Sea, associated with unstable air. A small low is also present over the eastern Black Sea.

DISCUSSION

...western Mediterranean Sea area...

Under a weakening upper low, an airmass with MLCAPE values between 200 and 1200 J/kg resides over the warm sea surface. 0-500m lapse rates are >11°/km and 0-3 km CAPE is predicted by GFS to be over 100 J/kg around the Balearic Islands and eastern Spain, and along western and southern Italy, where also large-scale synoptic scale ascending motions are to be expected. In these areas low-level convergence provides the main focus of convective development. LCL heights are around 1000m and capping is weak. Predicted storm motion is slow over a large area and is parallel to the orientation of the forcing convergence line at/between the east coast of Spain and the Balearic islands, which can yield training storms with locally excessive rain sums. Effective precipitable water content (PW - Sat. Deficit SFC-300 hPa) is rather large at 25-35 kg/m². The weak winds and shear conditions combined with significant low-level instability and convergence lines suggest that several waterspouts will occur. The areas with the most convergence are marked with high thunder probability and a level 1 for above-mentioned reasons.