Storm Forecast
Valid: Sat 06 Oct 2007 06:00 to Sun 07 Oct 2007 06:00 UTC
Issued: Fri 05 Oct 2007 17:14
Forecaster: DAHL

SYNOPSIS

Feature of main interest this period will be the upper low which was centered over NE Spain on early Friday evening ... and which will continue moving eastward while phasing with a quasi-stationary large-scale upper low centered over NE Europe.
At low levels ... a quasi-stationary frontal boundary extends from northern France across southern Germany eastward into northern Romania. Moist low-level air underneath an EML, which has been present over the SW Mediterranean on Friday, is resulting in a pocket of moderately unstable air which will affect the western and south-central parts of the Mediterranean on Saturday.

DISCUSSION

... Tyrrhenian Sea ... southern Italy ... western Ionian Sea ...

It seems that strong thermodynamic profiles will remain in place E of the advancing upper low over the western Mediterranean, the Tyrrhenian Sea and the western Ionian Sea. Only concern is the limited depth of the moisture as revealed by Friday's 12Z ascents from LIEE and LFKJ. However, it seems likely that the moisture is deeper elsewhere, so that MLCAPEs in excess of 1500 J/kg should be possible.

Shear profiles should remain supportive of severe evolution with about 20 m/s deep-layer shear and, at least over the Tyrrhenian Sea late on Saturday, 10 m/s 0-1 km shear.

It seems that the best kinemato-thermodynamic setup will evolve over the Tyrrhenian Sea late in the day/night. This is also where GFS develops most precip, with the bulk of it simulated to occur in the 00 to 06 UTC time frame. Expect the entire facet of severe weather, including large hail, damaging winds, as well as tornadoes. Storms may evolve into one or more large MCSs late in the night.

... northern Adriatic Sea ...

Given anticipated strong low-level buoyancy over the northern Adriatic Sea, a threat for water spouts seems to exist, assuming the presence/evolution of mesoscale boundaries that provide the vertical vorticity. This convection is likely to be rather shallow and may even fail to become electrified. Nonetheless, a level-one threat seems to be warranted.

... northeastern Romania ... Moldova ... south-central Ukraine ...

A strong vort max is expected to overspread Romania, Moldova, and the southern Ukraine during the day ... supporting low-level warm/moist advection and vertical stretching of the air column, so that weak CAPE is expected to result. Deep-layer shear is expected to exceed 25 m/s, so that linear segments/bow echoes may develop. Main threat should be severe straight-line wind gusts, though isolated large hail and maybe a brief tornado or two cannot be discounted either.