Storm Forecast
Valid: Thu 28 Mar 2013 06:00 to Fri 29 Mar 2013 06:00 UTC
Issued: Wed 27 Mar 2013 23:39
Forecaster: GATZEN
SYNOPSIS / DISCUSSION
The location of the polar jet stream remains across southern Europe. To the north, dry air masses will affect most of Europe where thunderstorms are not expected. The Mediterranean will be crossed by two short-wave troughs with associated mid-level jet streaks. The first will move across Greece and Turkey during the day, the second will leave Iberia and moves across the western and central Mediterranean. Although both systems will provide QG forcing, deep moist convection is rather unlikely across most places. Latest soundings indicate that the low-level air mass is rather cold with inversions above 800 hPa across most places. Near the trough centres, these inversions will likely weaken, but given the cool low levels, CAPE is very limited. However, the boundary-layer moisture across the Mediterranean has recovered with 0-1km mixing ratios around 8 g/kg. Together with diurnal heating, thunderstorms are not ruled out locally, especially in the afternoon hours. Given rather weak vertical wind shear near the trough centres together with the weak instability, severe storms are not forecast.
From northern Algeria to Sicily, chances for severe thunderstorms increase. These regions will be affected by another frontal zone and subtropical air that advects into the south Mediterranean ahead of the approaching trough. This air mass is characterized by steep mid-level lapse rates. Low-level moisture is rather limited, but diurnal heating will likely result in weak CAPE around 300 J/kg. Current thinking is that thunderstorms will develop in response to diurnal heating and QG forcing ahead of the approaching trough. Given strong vertical wind shear (bulk shear 0-3 km 15 m/s and 0-6 km 20 m/s) and large hodographs (SRH 0-3 km 150 J/kg), supercells are not ruled out. Main threat seems to be large hail, although local severe wind gusts are not ruled out. Convective activitiy will decay after sunset.
