Storm Forecast
Valid: Tue 10 Apr 2012 06:00 to Wed 11 Apr 2012 06:00 UTC
Issued: Mon 09 Apr 2012 14:57
Forecaster: KOROSEC

A level 1 was issued for southern France mainly for excessive convective rainfall, large hail, severe winds and lesser extend for a tornado threat.

SYNOPSIS

A large long-wave trough establishing into west-central Europe on Tuesday, where a strong cold front is pushed across France during the forecast period. A secondary low forms over NW Mediterranean and translates towards Liguria by Wednesday morning. Another trough/low slowly ejects SE Europe into Turkey. There, some convective activity will continue along the upper low and will exit our forecast area towards east later on.

DISCUSSION

... southern France ...

A rather rapid moisture recovery will be on going from western Mediterranean into southern France beneath a steepening lapse rates within the EML plume from Iberia NE-wards into France. Some hundreds of instability seem to build up in the afternoon hours, which should support SFC-based convection when surface front approaches from the NW. Strong jet streak will be in place, rounding the base of the trough and providing ample shear at all levels. Expect a few organized severe storms to take place across the southern France with the main threat of large hail and severe winds, while additional threat should be intense rain given the relatively high BL moisture. Minor chances exist also for a tornado threat with more discrete/intense cells, as low LCLs and good LL shear/SREH will be in place. Extended the level 1 also further north across the Rhone valley where BL conditions improve as well and a few storms could be possible along the frontal boundary crossing there as well.

Storms could cluster into a larger convective system trailing eastwards ahead of the front. Activity will continue overnight when approaching SW Alps. There, mostly excessive convective rain should be the primary threat, where convection seem to combine with orographic rainfalls.