Storm Forecast
Valid: Sun 06 Nov 2016 06:00 to Mon 07 Nov 2016 06:00 UTC
Issued: Sun 06 Nov 2016 07:29
Forecaster: KAHRAMAN

A level 1 was issued for W Italian and E Adriatic coasts mainly for excessive precipitation, tornadoes, and severe wind gusts.

SYNOPSIS

With a major SW-NE oriented trough over Europe, a very cold air mass is propagating on a wide part of the continent, except southeastern regions of the forecast domain. 18~23 C SSTs in Western and Central Mediterranean, and steep lapse rates aloft, result in up to 1250 J/kg MLCAPE just E of the frontal zone approaching from northwest. With high amounts of shear, well-organized deep moist convection is forecast along a long segment in Western Mediterranean, moving towards Central Mediterranean during the forecast period. Western coasts of Corsica and Sardinia, Italy, and Eastern Adriatic are the areas where the topography supplies stronger lift and longer exposure to storms. Even warmer SSTs over Ionian Sea, and stronger advection of moisture from SW increase the ML mixing ratio values up to 13 g/kg, enhancing the CAPE further in the night around Albania, Montenegro, and W Greece (up to ~2000 J/kg MUCAPE is forecast by mesoscale models).
One other area which can be marginally favourable for storm formation is the North Sea and Bay of Biscay, with very cold air advection aloft. Patches of a few hundred J/kg MLCAPE will move southwestwards in these locations, forming air mass thunderstorms. Due to weak kinematic environments, the convection will not be well organized in these areas.

DISCUSSION

Southwesterly flow in the Western Mediterranean will advect low level moisture towards the SW-looking coasts in the area. Convective precipitation, enhanced with orography will result in excessive values (up to 150~300 mm locally) in W coasts of Italy, Croatia, and Slovenia as well as Montenegro, Albania, and SW Bosnia Herzegovinia. Given 25-30 m/s 0-6 km shear, some storms should evolve into supercells. 10 m/s 0-1 km shear, and favourable hodographs indicate also a tornado risk in these areas. The severe wind risk in the broader area mainly relies on the background environments, with nonconvective mechanisms, such as strong downslope flow. However, convection will contribute to stronger gusts in part.