Storm Forecast
Valid: Mon 24 Sep 2018 06:00 to Tue 25 Sep 2018 06:00 UTC
Issued: Mon 24 Sep 2018 01:17
Forecaster: VAN DER VELDE

A level 1 was issued across Slovenia and N Adriatic Sea mainly for chance of tornadoes and large hail.

A level 1 was issued across S Moldova and SW Ukraine mainly for chance of tornadoes and large hail.

A level 1 was issued across Corsica and W Italy coast mainly for waterspout type tornadoes.

DISCUSSION

High pressure over the British Isles and low pressure over Belarus has set up a significant northwesterly flow across a large part of Europe. A very tight cold front for European standards is making its way into the northern Mediterranean Sea area as well as eastern and southeastern Europe. The influence of the upper trough touches upon the Adriatic Sea after which it moves eastward into the Balkan where no CAPE is able to form, according to various models, until the front reaches the Black Sea.

While CAPE is predicted to be rather modest, the modification of lapse rates by the Alps may be more significant than predicted and the GFS model includes strong local convergence signals suggestive of large scale convective development over Slovenia, to happen under the right entrance of a jet streak at Monday 03-06Z over the Slovenia, Croatia and Hungary region. Strong vertical wind shear in upper levels will increase large hail chances, while tornado (waterspout) chances are enhanced over sea where strong low-level lapse rates form upon arrival of cold air, with an extreme horizontal thermal gradient and convergence signal. The line would move southward, where the Italy coastline seems the limit of its reach.

A similar but a lot more marginal and short-lived setup seems to occur in the afternoon in the NW corner of the Black Sea, where shear will be good, but CAPE minimal.

The cold front may also trigger isolated convection where it wraps around the Pyrenees and cause a narrow strip of CAPE and convergence from central Catalonia to the coast.
Also, vortical areas with CAPE near the Genua low forming and moving to Corsica could spawn waterspouts.