Storm Forecast
Valid: Mon 20 Apr 2009 06:00 to Tue 21 Apr 2009 06:00 UTC
Issued: Sun 19 Apr 2009 19:27
Forecaster: GROENEMEIJER

SYNOPSIS

A large, but not very intense, cold upper-level low is centered over the western Mediterranean Sea. Several shortwave troughs rotate around the low's centre. On its southern flank, a rather strong cyclonically-curved jet is present across the Sahara Desert.

DISCUSSION

Alps, Southern Germany, NE France...

Monday at 06 UTC, a shortwave trough is oriented roughly from the centre of the upper-level vortex west of Corsica across NE Italy and along the Alpine range. As this trough moves northwestward, it should enhance lift across southern Germany and eastern France. GFS is more agressive both in the development of CAPE and in the development of convection across Swabia and Bavaria than is ECMWF, which appears due to a likely overestimation of low-level moisture by the GFS. Therefore the forecast follows ECWMF more closely here.

Balkans...

Another shortwave trough is initially (Mo/06) located from the Tyrrhenean Sea cia the bootheel of Italy to the Peloponnesos. As the trough mvoes eastward during the day, it will enhance lift across the Balkans. Stratiform precipiation should develop across the Dinaric Alps and isolated to scattered convective storms across the southern Pannonian Plain, Transsylvanian, the Serbian and Bulgarian ranges and the northern Pindus.

S Albania, W Greece...

A jet streak that initially stretches from central Algeria and southern Tunisia moves onto the Mediterranean Sea. Both GFS and ECMWF simulate it as a small 40 m/s jet streak across the Ionean Sea early on Tuesday. In its left exit region thunderstorms are expected to develop Tuesday in the 00 - 06 UTC time frame across the Ionean Sea. deep-layer shear should be in excess of 20 m/s, but low-level shear is relatively weak, the convection clustered and instability weak, which mitigates the severe threat.