Storm Forecast
Valid: Wed 26 Sep 2012 06:00 to Thu 27 Sep 2012 06:00 UTC
Issued: Tue 25 Sep 2012 20:49
Forecaster: PUCIK

A level 1 was issued for Southeastern France, Northwestern Italy and Northern Adriatics mainly for excessive precipitation, tornadoes and to the lesser degree for severe wind gusts and marginally large hail.

A level 1 was issued for Morocco mainly for excessive precipitation.

SYNOPSIS

A large, mid and upper level trough over the Atlantic is expected to fill during the forecast period with its base amplifying towards Northwestern Africa towards Thursday morning. A belt of strong mid/upper level winds will persist near the base and the forward flank of the trough. Closer to the surface, a well occludded low centered over the British Isles will fill in quite quickly, with its frontal system only slowly translating towards east over Western / Central Europe. Higher geopotentials are expected to build over the eastern part of Europe during the day.

Generally speaking, unfavorable conditions for widespread and severe thunderstorms will be present over Europe, as steep lapse rates will be confined only to the
A/ postfrontal airmass of western Europe cold front system, but in the limited low level moisture
B/ area with EML over Southern and Central Mediterranean with too strong cap to be overcome
Frontal zone itself will manifest only marginal latent instability with perhaps spotty weak thunderstorms, deserving only 15% prob tstm line.


DISCUSSION

... Southeastern France, Northwestern Italy, Northern Adriatics region ...

20 m/s at 500 hPa flow will contribute to the strong DLS (about 25 m/s) over these areas and moderate SREH (locally even over 300 J/kg) due to the vertical veering of the winds in the lower troposphere. Also, LLS will likely be enhanced (especially concerning the Northern Adriatics) with values exceeding 10 m/s, locally even 15 m/s. Speaking of stability point of view, meager mid level lapse rates will limit the instability, which should be most pronounced in the coastal areas. Likely only few hundreds of J/kg of MLCAPE will be available inland. A mid-level impulse in terms of embedded short-wave will arrive over the region in the late evening/night hours. Along with the cold front, these should be two primary factors in terms of the "forcing" factor.

Well organised MCS and/or supercells are well possible given impressive kinematic setup, but instability will likely limit the severe potential to some degree. Marginally large hail, severe wind gusts and/or isolated tornadoes might occur with supercells, while MCS, that will likely form especially along the cold front over SE France should be capable of isolated excessive precipitation. Threat will be the greatest over the both Lvl 1 areas during the evening / night hours.

... Morocco ...

Approach of the mid-level trough will contribute to the destabilisation over the region, with the highest degree over the coastal areas. Especially close to the evening/night hours, coastal convergence will likely trigger numerous rounds of DMC that will travel close to the coastline in the brisk SW-ly flow. Excessive precipitation should be the primary threat in this region.