Storm Forecast
Valid: Sun 19 Dec 2010 13:00 to Mon 20 Dec 2010 06:00 UTC
Issued: Sun 19 Dec 2010 13:57
Forecaster: SCHLENCZEK
A level 1 was issued for parts of W France for severe wind gusts and tornadoes.
A level 1 was issued for the S Adriatic including Greece and S Albania for large hail, severe wind gusts and tornadoes.
SYNOPSIS
A large low pressure system stretches from the N Atlantic via the British Isles towards the Baltics, leading to cold conditions over N Europe while mild air with temperatures around 5°C at 850 hPa should make progress towards central Europe during the next 72 hours. On Sunday, the feature of interest is a region of cold air at upper levels underneath a strong westerly upper jet over the S Adriatic. Ahead of an embedded shortwave trough, unstable subtropical air should arrive at the Greek coast until midnight.
DISCUSSION
...N Atlantic and Irish Sea...
Low-end instability is expected close to the center of the upper low where shear is quite weak. Severe weather should be unlikely.
...W France...
GFS suggests a few small regions with approx. 100 J/kg CAPE, EL temperatures around -20°C and some 25 - 40 m/s deep layer shear. Some convection has developed at the southern edge of a cyclonic vortex northwest of Brittany and the linear structure could point at a severe wind gust risk. At the northern edge of the convective system, a mesocyclone may be embedded. The region with marginal instability should be there until late evening and a low-end level 1 is issued for a small tornado chance and some isolated severe wind gusts.
...S Adriatic, Greece, Albania...
A plume of unstable subtropical air is advected northwards towards Greece and Albania. Until now, no convection has formed as the airmass is strongly capped. The cap should weaken during the evening / night hours and some QG forcing from the shortwave trough should initiate some storms in an environment with 500 - 1000 J/kg MLCAPE and some 15 - 20 m/s deep layer shear. GFS shows enhanced SRH3 / SRH1 values along the coastlines (> 200 m²/s²) which may allow a few, possibly tornadic, supercells. The main threat is expected to be isolated severe wind gusts and large hail.
