Storm Forecast
Valid: Mon 04 Oct 2010 06:00 to Tue 05 Oct 2010 06:00 UTC
Issued: Sun 03 Oct 2010 23:22
Forecaster: DAHL

A level 1 was issued across central France mainly for severe wind gusts and tornadoes.

A level 1 was issued across the W/NW Mediterranean mainly for severe wind gusts, large hail, and tornadoes.

SYNOPSIS

A deep upper-level trough over western Europe has been in the process of closing off into a cut-off cyclone on Sunday evening ... with the remaining short-wave trough lifting into the Norwegian Sea on Monday ... and the cut-off low moving across the western Mediterranean. A SFC low will be maintained ahead of this feature, supporting WAA over western and parts of central Europe on Monday. The next Atlantic system(s) will evolve into an impressively large and intense trough, being accompanied by an equally extensive SFC low, which will cover large parts of the northern North Atlantic by Monday evening.

DISCUSSION

... western/northwestern Mediterranean ...

MLCAPE on the order of 1000 J/kg is anticipated ahead of the Mediterranean upper low, which will provide large-scale forcing for ascent as well as rather decent shear profiles. However, the maximum shear seems to lag the unstable air somewhat. Still, GFS suggests that 15 - 20 m/s DLS will be exist across most of the western and central Mediterranean on Monday.
A few line segments and also supercells may occur, capable of marginally severe wind and hail. Low-level shear is advertised to exceed 12 m/s over central Italy and parts of the central Mediterranean Sea, suggesting that an additional tornado threat exists. Over the western Mediterranean, the LLS will be weak, but strong low-level lapse rates / buoyancy may still support an isolated (non-mesocyclonic) tornado there.

... central and southern France ...

Weak instability is forecasted over France where GFS simulates bands of strong LLS (> 15 m/s) and DLS (20 m/s), but these seem to be rather localized and displaced from the regions of unstable air. However, there are small spatio-temporal windows where the shear and instability could overlap ... the biggest chances of this to happen being over central France early in the period. Expect at least briefly rotating thunderstorms, capable of damaging wind gusts and tornadoes.

... N Black Sea ...

It seems that a few waterspouts could occur over the N Black sea with shallow, and probably non-electrified convection. The overall severe probabilities are too low for a LVL1 threat, however.