Storm Forecast
Valid: Sat 19 Dec 2015 06:00 to Sun 20 Dec 2015 06:00 UTC
Issued: Fri 18 Dec 2015 22:34
Forecaster: DAFIS

A level 1 was issued for Portugal mainly for excessive rainfall and severe wind gusts.

SYNOPSIS

The weather pattern in Europe is divided into 3 main parts. The Balkan States are under the influence of a dissipating cold pool, but also a shortwave trough will be found over the Adriatic Sea on Saturday with extremely low potential for any convective event. The West Mediterranean and Central Europe experience very high temperatures at 850hPa, with high geopotentials and mostly foggy conditions on the surface. Tomorrow the most western parts, thus Portugal, NW Spain, Ireland and the UK, will see some thunderstorms as a longwave trough is approaching, associated with a cold front on the surface. Better chances for DMC are forecast in Portugal.

DISCUSSION

As the longwave trough is approaching from the Atlantic Sea, wind shear is increasing and temperatures at 500hPa of about -30°C trigger the formation of enough CAPE to feed some thunderstorms. Best overlap of wind shear and CAPE is found off the shore of Portugal, where MLCAPE is expected to reach values up to 1000 J/kg, left from the cold front but on shore the effective CAPE should be much less. Nevertheless, the presence of strong DLS in this unstable air mass with PW up to 30 mm, suggest an environment able to organize thunderstorms into clusters with the threat of excessive rainfall. Another supporting factor is that the level 1 area will be at the left exit of a mid-level jet streak. The winds at 850hPa are forecast to reach the 30 m/s, so we also expect some strong cells to mix some severe wind gusts down to the surface.