Storm Forecast
Valid: Thu 19 Mar 2009 06:00 to Fri 20 Mar 2009 06:00 UTC
Issued: Wed 18 Mar 2009 21:00
Forecaster: GATZEN

SYNOPSIS

A high pressure system is located over western Europe, while an intense long-wave trough amplifies over the eastern portions evading into the Mediterranean. Cold air masses will advect into the north Mediterranean Sea during the period, while warmer air remains over the south. As an upper trough axis approaches over the Mediterranean, cyclogenesis sets in along the frontal boundary during the period. Over the Iberian Peninsula, rather warm but stable air will be present throughout the period, and convection I unlikely.

DISCUSSION

North Mediterranean

The air mass to the south-west of the cold front is stable across the west Mediterranean Sea and the Iberian Peninsula. This will likely be associated with some moisture enhancement during the next couple of hours over the sea surface, especially in the range of the frontal boundary where low-level convergence will lead to moisture pooling. At higher levels, lapse rates are expected to become steeper as a trough axis curving around the European trough moves southward over the central Mediterranean. Latest GFS model output indicates -30 to -34°C at the 500 hPa level late in the day. Instability is questionable at this time, but when deep instability will develop, deep moist convection is likely given forcing along the convective line and QG forcing in the range of the trough. Current thinking is that convection will be embedded in stratiform precipitation and lightning will only be isolated. Best potential seems to exist to the south of the developing surface low, where a few thunderstorms are forecast. Chance for severe convection is expected to be low given weak instability and vertical wind shear.

Turkey

An intense trough axis will also affect northern Turkey. Showers are forecast that may be accompanied by soft hail and isolated thunder. Given rather weal vertical wind shear, organized convection is not expected.

South-eastern Europe

In the range of the cold air mass, steep lapse rates and some low-level moisture my lead to diurnal destabilization, and showers and isolated thunderstorms are not ruled out in the range of the trough center, where weak vertical wind shear will limit severe potential.