Storm Forecast
Valid: Thu 18 Nov 2010 06:00 to Fri 19 Nov 2010 06:00 UTC
Issued: Wed 17 Nov 2010 14:34
Forecaster: GATZEN

SYNOPSIS

A long-wave trough over the Atlantic spreads into western Europe and the Mediterranean. This is associated with cold air advection. At the eastern flank of the trough, a negatively tilted short-wave trough crosses the western Black Sea region. Ahead of this short-wave trough, a tongue of warm air extends from the Black Sea to Poland.

DISCUSSION

Eastern Aegean to eastern Bulgaria and southern Romania

The trough axis of a negatively tilted short-wave trough moves northward during the period. The associated surface cold front is forecast to cross the Aegean in the morning hours and moves into the Black Sea during the day. Along this cold front, a strong southerly flow advects moist air into the Black Sea region. Moist adiabatic lapse rates can be assumed along the cold front given rather cool mid-level air. Quite strong forcing is also likely.

Current thinking is that widespread precipitating clouds will be present near the trough axis. Along the cold front, embedded thunderstorms are forecast given some weak CAPE and EL temperatures around -20°C. The storm mode is expected to be clusters of showers and thunderstorms that do move north-eastward rather quickly with the strong flow. The weak organization of the storms is expected to limit the severe potential. Some marginally severe hail is not ruled out locally.

The convective activity will spread north-eastward during the day and will likely weaken gradually due to decreasing low-level moisture and gradually decreasing forcing as the mid-level trough weakens. In the wake of the cold front, low-level dry air is expected to spread eastward and is forecast to limit the chance of thunderstorms.

Bay of Biscay, north Mediterranean Sea

The axis of the intense Atlantic trough spreads into the Mediterranean during the period. Ahead of the trough, a frontal system is expected to move eastward. Cold polar air masses near the trough axis will lead to a large temperature difference that increases the lapse rates especially over the eastern parts of the Bay of Biscay and over the central Mediterranean, where the low-level air will also moisten. Some showers and thunderstorms will likely develop near the trough axis during the period. Along the cold front, models indicate increasing instability especially over the Adriatic Sea, and embedded thunderstorms are forecast.

Severe convection is not expected as only weak instability is forecast and the potential of organized storms is rather weak. Clusters of storms along the cold front and some stronger storms near the mid-level jet axis where about 20 m/s 0-6 km bulk shear are forecast may be capable of producing marginally severe hail.