Storm Forecast
Valid: Sat 05 Nov 2016 06:00 to Sun 06 Nov 2016 06:00 UTC
Issued: Sat 05 Nov 2016 01:50
Forecaster: TASZAREK

A level 1 was issued for parts of W Mediterranean, Corsica, Sardinia, and parts of W Italy mainly for large hail, severe wind gusts, excessive precipitation and in lesser extent for tornadoes.

A level 1 was issued for SW Spain mainly for severe wind gusts and in lesser extent for large hail.

SYNOPSIS and DISCUSSION

A configuration of a broad high W of British Isles and low centred over North Sea pushes cold polar airmasses into W, SW and CNTRL Europe. Within this advection, emerging frontal boundaries and increasing vertical temperature gradient create a favourable conditions to the development of convection, and thus thunderstorms. An eastwardly moving long-wave trough with axis extending from Iberian Peninsula up to Scandinavia keeps broadening and begins to slow down within the forecast period. A CAPE developing on the SE flank of the wave (W Mediterranean, W Italy) increases up to ~ 1000-1500 J/kg as a result of 10 g/kg MIXR over sea surface and lapse rates exceeding 7 K/km. In Spain where the land is already cooler than the sea surface, CAPE jumps locally only to 300-500 J/kg. Although small instability limits the potential of severe weather, an isolated severe wind or large hail event cannot be ruled out given DLS exceeding 20 m/s. In the cold section of the trough, a marginal CAPE up to 100-200 J/kg develops over the North Sea and Bay of Biscay. A low topped convection with a small potential of lightning is possible over these areas. A strong jet stream stretching from Iceland through Spain, up to Balkan Peninsula increases DLS to 20-30 m/s. Convection developing in such an environment may be capable of evolving into multicell clusters and supercells capable of producing large hail and severe wind gusts. The highest chances for such phenomena exists over W Mediterranean and W Italy where a moderate thermodynamic instability and QG-lift will be available. In addition, thanks to the PW exceeding 30mm, an excessive precipitation event cannot be ruled out, especially when considering southwesterly orographic lift along Apennines. In the late afternoon hours, an increasing LLS (> 10 m/s) along with favourable vertical wind profile (SRH 300-400 m2/s2) and ongoing supercell thunderstorms, may results in an isolated tornado event along W Italian coast or Corsica. However, due to rather limited instability, probability for such an event is low.