Storm Forecast
Valid: Thu 30 Dec 2010 06:00 to Fri 31 Dec 2010 06:00 UTC
Issued: Wed 29 Dec 2010 22:19
Forecaster: GATZEN

SYNOPSIS

To the east of a ridge that extends from the west Mediterranean to Iceland a deep polar trough covers most parts of Europe. Low-level moisture is weak except for the southern parts of the Mediterranean, and some showers and thunderstorms may develop to the south of Greece and Turkey, although low-level convergence will be quite weak. South-western Europe is affected by a cut-off low that enters Iberia during the period.

DISCUSSION

Western Iberia

The approach of the cut-off low will be associated with the advection of rather unstable maritime air masses that are present near the cut-off center. Along the western coasts of the Iberian Peninsula, upslope flow will assist showers and thunderstorms through-out the period. Relatively weak instability and boundary-layer moisture as well as weak vertical wind shear over the sea will not support storm organization. Onshore, vertical wind shear will be more supportive and favourably veering profiles are forecast by latest forecasts, but especially low-level instability is forecast to decrease farther inland. Current thinking is that stronger storms may produce marginally severe hail. Additionally, locally excessive rain is not ruled out. However, the overall threat is expected to be too low for a categorical risk.