Storm Forecast
Valid: Sun 21 Nov 2010 06:00 to Mon 22 Nov 2010 06:00 UTC
Issued: Sun 21 Nov 2010 06:06
Forecaster: SCHLENCZEK
A level 1 was issued for Corsica, Sardinia and for parts of N-central Italy and the Dinaric Mountains mainly for excessive rainfall and to a lesser extent for severe wind gusts.
SYNOPSIS
Omega blocking is present over the north-central Atlantic with significant CAA starting over the northern parts of Europe. Therefore, good conditions for convective storms can only be expected in the southern / southwestern parts of Europe. Some storms may develop over the Bay of Biscay and parts of Iberia in the wake of an upper trough and there is also some potential over the western Mediterranean and France. The greatest chance for thunderstorms with significant lightning should be expected over the central Mediterranean and S Adriatic during the late evening / night hours as instability and forcing ahead of the upper trough should increase. As often observed in similar situations, intense rainfall affects the Mediterranean region when cold air overspreads the northern and central parts of Europe.
DISCUSSION
...Bay of Biscay, NW Iberia...
Showers and thunderstorms may develop near the upper cold core of the low which is centered over the W Mediterranean / S France. Overall shear and SRH are quite low (10 m/s deep layer shear, no significant signal in SRH) and therefore severe weather is unlikely as CAPE should be only in order of 200 - 400 J/kg.
...W Mediterranean...
Some low-end CAPE and only weak vertical shear are expected over the W Mediterranean and showers / thunderstorms may form during the day, continuing through the night hours. Apart from an isolated funnel / waterspout, severe weather is not expected.
...Corsica, Sardinia, parts of Italy, Adriatic...
Further east, some 20 - 25 m/s deep layer shear will overlap with a few hundred J/kg CAPE. At lower levels, shear is mostly below 10 m/s and only low to moderate forcing is expected. Some multicells may pose a risk of isolated severe wind gusts but the main threat is the intense convective rainfall as shown by some models (GFS has QPF signals around 50mm / 6h for some regions). Most of the rain is expected to fall over the western parts of Italy and over the mountaneous region east of the Adriatic. The sea region in between is not covered by the level 1 as excessive precipitation won't cause damage over the sea.
...Central Mediterranean, S Adriatic, Ionian Sea...
Advection of warm and moist air ahead of the upper trough will lead to an increase in CAPE to moderate values (500 - 1000 J/kg). As the southern parts of this region of moderate CAPE are strongly capped, convective initiation is unlikely. If convection starts to develop, it will be most likely in the southern parts of the central Mediterranean. Severe weather is not expected as shear and forcing are considerably weak.
