Storm Forecast
Valid: Thu 25 Sep 2008 06:00 to Fri 26 Sep 2008 06:00 UTC
Issued: Thu 25 Sep 2008 05:13
Forecaster: GATZEN

SYNOPSIS

Broad high is located over British Isles and North Sea. To the south, an upper cut-off low will slowly move southward over the Adriatic during the period. Low geopotential stretches into Iberian Peninsula and most of the Mediterranean. A strong mid-level jet is present to the south of the low geopotential from northern Africa to southern Mediterranean. Intense upper short-wave troughs affect northern Europe. While cool air mass spreads south-westward over eastern, central, and southern Europe, maritime air mass is advected into the north-western regions.

DISCUSSION

Aegean to southern Turkey

To the south-east of the upper trough centre, warm air mass is pushed eastward over the Aegean during the period. Latest ascend over Crete indicates mid-level steep lapse rates and rich low-level moisture. This air mass spreads into southern Turkey ahead of the trough and associated cold front. During the day, broad mid-level jet over southern Mediterranean spreads eastward, and deep layer vertical wind shear will likely increase reaching more than 20 m/s in the lowest 6 km. In the range of the cold front, low-level forcing will likely be strong enough for ongoing convection, and storms that form will likely organize given strong vertical wind shear. Supercells are forecast that will move eastward over the Sea and may also affect the coasts, capable of producing large or very large hail, strong to severe wind gusts and tornadoes. Although strong tornadoes seem to be not likely as low-level vertical wind shear is weak over southern Turkey, a level 2 seems to be warranted given rather widespread thunderstorms during the period and associated widespread severe convection. Thunderstorms will spread eastward into Cyprus during the period, where severe threat will likely continue during the next couple of hours.

To the west, an airmass characterized by neutral lapse rates is forecast to spread into Greece, and given rather rich low-level moisture, thunderstorms are quite likely near the trough axis. Given increasing vertical wind shear to the south, organized convection capable of producing tornadoes and strong wind gusts is expected.

Mediterranean

In the range of the trough axis, thunderstorms are expected in the range of rather high low-level buoyancy and weak vertical wind shear. Waterspouts may develop. Best potential seems to exist east of Spain near the Balearic Islands and over parts of the Tyrrhenian and Adriatic Sea.

South-eastern Spain

In the range of the trough over south-eastern Spain, quite warm and unstable air mass will spread into south-eastern Spain. Models indicate intense convection due to some WAA and upslope flow. Thunderstorms may organize given moderate to strong vertical wind shear, and mesoscale convective systems may develop. Although severe hail, and wind I not expected, high precipitation and isolated tornadoes are not ruled out.