Storm Forecast
Valid: Tue 24 Nov 2020 06:00 to Wed 25 Nov 2020 06:00 UTC
Issued: Mon 23 Nov 2020 17:26
Forecaster: DAFIS

A level 1 has been issued for parts of Portugal and NW Spain mainly for severe convective wind gusts.

A level 1 has been issued for S Italy and Malta mainly for excessive convective precipitation.

SYNOPSIS

A blocking high affects the largest part of the continent with strong subsidence, lack of precipitation, and unseasonably high temperatures. Lower geopotentials are found in the southern and eastern parts of the Mediterranean where storms are expected, but mostly offshore. Over the N Atlantic a long-wave trough is forming and moves fast east towards the western coasts of Europe where DMC events may develop.

DISCUSSION

.... Portugal and Spain ....

As the trough approaches the Iberian Peninsula from the west during the night on Tue 24/11, a well-defined surface cold front will be the main triggering mechanism for thunderstorm development. CAPE is rather low in most NWP model outputs, lower than 500 J/kg and mostly confined below the freezing level, but storms that will succeed to reach the coasts will be able to produce severe wind guts. The 850 hPa wind field is strong and locally will exceed 15 m/s, increasing the threat for winds to be translated to the surface during storms. The level-1 threat area will be in the cold sector of the front by the early morning on Wed 25/11 when the conditions will be favorable for waterspouts close to the coasts.

.... South Italy and Malta ....

A cut-off low above the coasts of North Africa is surrounded by several short-wave troughs. Near the surface, an air mass with high theta-e values lies over the Central Mediterranean where slow-moving storms produce locally high amounts of precipitation. Even though most of the storms will be active offshore, there is a threat of flash floods near the coasts of S Italy and the surrounded islands. Finally, many of these storms will be able to produce waterspouts.