Storm Forecast
Valid: Thu 01 Nov 2007 06:00 to Fri 02 Nov 2007 06:00 UTC
Issued: Wed 31 Oct 2007 20:03
Forecaster: GATZEN

SYNOPSIS

High pressure over west Europe ridges into the polar Atlantic, and intense upper long-wave trough moves into Scandinavia. Another broad trough weakens over the Mediterranean Sea while slowly spreading eastward into Aegean. A small cut-off low propagates southward over central Europe.

DISCUSSION

Northern Tunisia, Sicily, southern Italy and Adriatic, Greece, Aegean

At the eastern flank of the Mediterranean trough, a strong upper jet streak moves north-eastward over central Mediterranean pointing towards Aegean. At the end of the period, it is expected over western Turkey. Strong DCVA is expected at the cyclonic flank of the jet maximum, and latest model output suggests cyclogenesis along the frontal boundary over southern Adriatic spreading into Aegean during the period.

Affected air mass is characterized by rather steep mid-level lapse rates over the eastern parts and rich boundary-layer moisture to the west. Overlap of both ingredients is rather questionable at this time. Given rather cool low-levels, unstable air mass is also capped especially over the eastern regions. However, strong QG forcing and low-level convergence/moisture pooling may be sufficient to overcome the cap during the period.

Expect that thunderstorms initially will go on along the frontal boundary from northern Tunisia to Sicily and southern Adriatic region, where weak CIN and nice low-level moisture will be present. Strong vertical wind shear will be favorable for mesoscale convective systems, and isolated severe wind gusts may occur. Isolated convection may also produce tornadoes given locally favorable low-level buoyancy and shear profiles. Later in the period, convective activity may spread eastward into Greece and Aegean region, where increasing CAPE and forcing is expected in the range of the developing frontal wave. If instability will indeed increase significantly, thunderstorms that form may merge into MCSs capable of producing severe wind gusts especially in the range of LEWP. More isolated cells may also pose a threat of severe hail given locally high SRH values. However, given rather poor low-level moisture indicated by latest soundings, GFS may overestimate instability, and convective development may be significantly weaker. Convective activity is forecast to spread into W Black Sea late in the period, where cool boundary is present and elevated, non-severe storms are forecast.

Tyrrhenian Sea

In the range of the trough center, weak vertical wind shear and rather high low-level buoyancy is present, and some waterspouts are forecast.

South Finland, northern Baltic States

Intense frontal system moves eastward over the Baltic Sea. Along the occlusion, moist and rather warm low-level air mass becomes unstable in the range of the propagating upper trough. Instability will be limited to low levels, and thunder is not that likely along the front even with strong QG and low-level forcing. However, severe wind gusts and tornadoes are not ruled out completely given strongly veering profiles and rich boundary-layer moisture. Convective activity will spread eastward during the day, while low-level moisture and severe potential will gradually decrease.