Storm Forecast
Valid: Tue 07 Nov 2017 06:00 to Wed 08 Nov 2017 06:00 UTC
Issued: Mon 06 Nov 2017 21:00
Forecaster: DAFIS

A level 1 was issued for West Balkans and Italy mainly for excessive rainfall, large hail or large amounts of small hail, severe wind gusts and tornadoes.

A level 2 was issued for Greece, Albania and Montenegro mainly for excessive rainfall, large hail, severe wind gusts and tornadoes.

SYNOPSIS

A cold drop has formed in West Mediterranean, tearing off the main airstream, destabilizing a large area. A plume of very moist air masses with steep lapse rates is pushed towards W-SW Balkans, where severe DMC is expected. A mid-level jet streak is forecast at the eastern parts of the low-pressure system, increasing the DLS, enhancing storm activity. For the rest parts of the continent, two more troughs exist in the north, one approaching the British Isles and another one over Scandinavia. Storms may form over the Atlantic, in the cold sector of low-pressure system with its center in Iceland.

DISCUSSION

Unstable air masses from the south are moving north towards SE Italy and SW Balkans. NWP models predict about 1000-1200 J/kg of MLCAPE in Adriatic and Ionian Seas, overlapping with strong DLS and veering 0-3km winds. MCS and supercells are expected in addition to the ongoing linear MCS in Ionian Sea affecting Greece with gusting winds tonight (at 21z). On Tuesday and early morning of Wednesday the main threat will be excessive precipitation at the east coasts of Adriatic Sea, especially in Albania and NW Greece. ECMWF predicts more than 100 mm of rainfall over this area due to training convections, thanks to long-lasting low-level convergence zones and orographic lifting. Better chances for large hail exist in West Greece, where steep lapse rates (7.5-8 K/km) are forecast, with 12K delta theta-e, which also increase the potential for local severe wind gusts.

Colder air masses over Sardinia, Corsica and West Italy will keep storms low-topped but able to produce locally large amounts of small hail and numerous of waterspouts. Actually, we expect a waterspout outbreak tonight and tomorrow under the cold drop, where difference between T850 and SST is maximized. Tornadic waterspouts are also forecast at the coasts of SW Balkans within the strongest storm cells, as LLS and SREH0-1 are enhanced. Tornadoes may also form near the coasts and islands of Ionian Sea as GFS expects a jet streak at 850 hPa, above the unstable air mass, and veering profiles.