Storm Forecast
Valid: Fri 04 Dec 2009 06:00 to Sat 05 Dec 2009 06:00 UTC
Issued: Thu 03 Dec 2009 18:32
Forecaster: TUSCHY

A level 1 was issued for the east coast of the Ionian Sea and the extreme SE Adriatic Sea mainly for isolated waterspouts and to a lesser extent for heavy rainfall.

A level 1 was issued for the SW coast of Turkey mainly for excessive rainfall.

A level 1 was issued over parts of the Tyrrhenian Sea and Sicily mainly for severe wind gusts.

SYNOPSIS

A huge vortex over Europe gradually decays and features various vortices. Ridging builds in from the west over W-/NW-Europe. CAA over NE-Europe causes rising pressure and stable conditions.

DISCUSSION

... Central and east Mediterranean ...

A trough over the central Mediterranean re-enforces as another disturbance comes in from the NW. However, those features are in the wake of the last, potent upper trough, so airmass modification over the Mediterranean is still in progress. Cold airmass again causes another round of scattered showers and thunderstorms. Background shear over the Adriatic Sea, the Ionian Sea and the Aegean Sea is weak to moderate, so waterspouts mainly along the coast and along existing convergence zones can occur, as LL CAPE increases during the forecast. Best conditions seem to evolve over the Ionian Sea and adjacent coastal areas, but also over the S-Adriatic Sea.

LLCAPE over the Tyrrhenian Sea is even better, but a strong vortex crosses the area from the NW with enhanced deep layer shear. An isolated waterspout event can't be ruled out, but conditions for a persistent convergence zone look too hostile. However, a cold front pushes southeastwards during the forecast with strong winds along its back ( 35m/s at 700hPa, 25m/s at 850hPa). A forced line of convection, partially electrified, is forecast with numerous severe wind gusts/isolated tornado reports possible. Right now, we think that strongest convection along this front will be displaced from the best shear, but not much mixing is needed for severe wind gusts at the surface, so we issued a broad level 1 (partially non-thundery).

Strong wind gusts, marginal hail and locally high rain amounts occur with the stronger storms over the rest of the Mediterranean. A level 1 for rain was included for SW-Turkey during the morning hours (5th Dez.), as cooling mid-levels and upper divergence support storm clustering along the coast.

... Extreme SW/W-UK ...

A weakening cold front affects UK during the night hours. Compared to the past events, prefrontal moisture advection is more conditional, so CAPE will be weak at best. Shear increases and any convective element will be able to produce strong to isolated severe wind gusts, but currently forecast conditions don't warrant a TSTM area.

... Coast of the Netherlands...

A cold-core vortex affects the area during the day with showers and isolated thunderstorms. Isolated large hail is possible offshore and along the coast next to strong wind gusts. Some LL CAPE is possible, so an isolated waterspout event can occur. Overall risk is too low for a level area. Showers/thunderstorms spread east/northeastwards with decreasing activity during the night.