Storm Forecast
Valid: Sat 20 Oct 2007 06:00 to Sun 21 Oct 2007 06:00 UTC
Issued: Fri 19 Oct 2007 17:04
Forecaster: DAHL

SYNOPSIS

Deep and intense upper long-wave trough is slowly spreading into the central Mediterranean regions, exhibiting several perturbations at its western periphery. As one such perturbation overspreads the low-level frontal zone associated with the large-scale trough, intense cyclogenesis is simulated to result over the Tyrrhenian-Sea region on Saturday afternoon/evening. West of the upper trough ... a large SFC high has developed over central and northern portions of Europe, maintaining a cold-advection regime over the easten portions of central Europe.

DISCUSSION

... south-central Mediterranean ...

It seems that most of the convection developing in the warm sector of the developing Mediterranean SFC low will exist N of the low's center in strong warm-advection regime, and hence will tend to be elevated. Surface-based SRH in this regime will be quite substantial, but storms will likely not benefit from it given their elevated nature. SFC-based storms should also develop, however, mainly along and ahead of the developing cold front. Deep shear should be more than adequate for severe evolution with more than 30 m/s. Limiting factor should be the weak lapse rates, resulting in somewhat meager CAPE, but some storms should nonetheless be able to organize and become severe. Main threat should be severe wind gusts and marginally severe hail, though a few tornadoes could also occur, especially late in the evening/night when low-level shear increases.

Farther downstream over the eastern Aegean, CAPE should be somewhat stronger, and given ample shear, some severe thunderstorms will likely occur. Main threats should be severe wind gusts and hail.

... N Adriatic Sea ... N Tyrrhenian Sea ...

Further north on the cold side of the front ... quite steep low-level lapse rates are anticipated. Although convection may be rather shallow, any misovortex could be stretched into a water spout rather quickly. So it appears that a level-one threat is warranted, assuming that soures of vertical vorticity will be present along mesoscale boundaries especially near the coast lines.

... Baltic Sea ...

Some waterspout threat also exists over the Baltic Sea, but it currently seems that convection will be quite shallow, so that deep/intense sub-cloud upward acceleration may fail to develop ... and a categorical threat does not seem to be warranted at the moment.