Valid: Tue 06 Feb 2018 06:00 to Wed 07 Feb 2018 06:00 UTC
Issued: Mon 05 Feb 2018 22:40
A level 1 was issued for Central Mediterranean mainly for excessive precipitation large amounts of small hail and/or large hail, severe wind gusts and to a lesser extent for tornadoes/waterspouts.
The previously positively-tilted long wave trough extending from NW Russia down to the NW coasts of Africa has now several vorticity maxima, but mainly 3 well-defined vortices over the Iberian Peninsula, over France (the smallest one) and another one in E Europe. Rather stable conditions over continental areas exclude convective phenomena but the opposite is noticed over the waters of the Mediterranean Sea and E Atlantic. The cold air masses create steep low/mid-level lapse rates and along with adequate moisture, they create some hundreds of CAPE. Several low-topped convective cells will emerge over the sea on Tuesday and early morning of Wednesday, but special consideration must be given to South Italy and NW Balkans, where DMC events are expected. Another trough is approaching from the Atlantic in the afternoon of Tuesday, but rather dry low-levels suggest only a few cells will manage to build-up able to produce charge, thus lightning.
As the cut-off low from the Iberian Peninsula drifts slowly on the north section of the sub-tropical jet stream, steep lapse rates are building-up in Central Mediterranean. Near the surface, a cyclonic vortex is about to form, with its warm front reaching the west coasts of Italy before noon tomorrow. The main threat will be excessive precipitation, but as far as the cold front behind is concerned, storms will be able to produce hail up to 2cm and large amounts of small hail/graupel and severe wind gusts, probably causing disturbances. Severe wind gusts are mostly expected offshore where the downdrafts of the storms can bring the 20-25 m/s 850 hPa jet-streak down to the surface. NWP models show a pronounced tongue of high low-level moisture migrating from S Ionian Sea towards S Italy, increasing the PWAT up to 30 mm. The threat of excessive precipitation will remain throughout the night in SE Italy.
Later during the night, as the fronts progressively move to the east, the threat will increase over the Adriatic Sea and finally at the coasts of S Croatia, Bosnia, and Herzegovina, Montenegro, and Albania. The main threats will be excessive precipitation and large hail from training convection and fast-moving storms respectively. DMC will continue to affect the aforementioned areas during Wednesday as synoptic large-scale lift will continue.
Moreover, several waterspouts are expected in the Mediterranean Sea, from the coasts of Spain and France to Italy and the Adriatic Sea coasts. The low-level steep lapse rates in conjunction with weak wind fields near the surface, create a favorable environment for waterspouts, some them may come ashore causing damage. The strongest cells in West Italy and W Balkans may also produce tornadic events, but meager CAPE and 0-3km shear are not so pronounced to increase significantly this threat.