Storm Forecast
Valid: Thu 25 Oct 2007 06:00 to Fri 26 Oct 2007 06:00 UTC
Issued: Wed 24 Oct 2007 17:35
Forecaster: GATZEN

SYNOPSIS

To the south of a broad high over northern Europe, a trough affects southern Europe. The main axis of this trough is present from southern France to Morocco and will turn counterclockwise during the period. It is expected from southern France to northern Tunisia at the end of the period. Ahead of this trough axis, a strong mid-level jet points from Algeria to Tunisia and central Mediterranean. Further east, another trough will move eastwards over Turkey.

DISCUSSION

Tyrrhenian Sea

QG forcing is expected over central Mediterranean underneath the cyclonic flank of propagating mid-level jet streak. A surface low will move north-eastward from southern Balearic Islands to Sardinia during the period. At its eastern flank, warm air advection is forecast, and favorable veering profiles are likely along the northern nose of the low-level warm air mass. Latest (00Z) 07761 Ajaccio sounding indicates that low-level moisture has started to increase, while low- and mid-level lapse rates are rather steep. This will likely result in instability in the range of the WAA regime where low-level convergence/ moisture pooling is forecast, while mid-levels will remain quite cool in the range of the upper low. Expect convection in the WAA regime that may root to the boundary-layer given increasing low-level moisture, and that storms will profit from favorable vertical wind shear and will organize. Bowing lines and some mesocyclones are forecast to form. Severe wind gusts and isolated large hail are forecast, as well as a few tornadoes given low LCL heights, and strong (10 m/s) low-level vertical wind shear. Low-level buoyancy will be not too high, but strong vertical shear is expected to compensate this limiting factor. Thunderstorms will likely spread northward, where instability and forcing will gradually decrease, and chance for severe storms will weaken during the night hours.

Southern Adriatic

Comparable to the Tyrrhenian Sea, QG forcing and WAA will also be present over southern Adriatic. However, boundary-layer moisture is much weaker of this region, while mid-level are warmer, resulting in weaker instability and low-level buoyancy. However, latest models do indicate that CAPE will be positive and convection will likely develop underneath the cyclonic flank of the upper jet. Strong vertical wind shear and favorable veering profiles will likely result in some organized storms. A few tornadoes are not ruled out, but chance seems to be lower than for the Tyrrhenian.