Storm Forecast
Valid: Tue 27 Feb 2018 06:00 to Wed 28 Feb 2018 06:00 UTC
Issued: Mon 26 Feb 2018 23:30
Forecaster: DAFIS

Levels 1 and 2 were issued for Portugal and Spain mainly for excessive precipitation, large hail, and severe wind gusts.

A level 1 was issued for Greece and Turkey mainly for excessive precipitation, large hail, and severe wind gusts.

SYNOPSIS

A high-pressure system over Scandinavia and several low-pressure areas in the Mediterranean compose the weather pattern in Europe. The arctic air mass has now reached the Atlantic Ocean and even though the specific humidity inside this air mass is extremely low, some snow showers are reported in a large part of the continent, mostly in the UK where on Tuesday, baroclinic instability along with steep lapse rates over the North Sea will result in heavy snow showers, as well as in Denmark and North Germany due to “lake effect” snowfall from the Baltic Sea.
Interesting weather set-up is placed in Central – East Mediterranean, where several disturbances at the southern flank of the arctic air mass continue to affect Italy, the Balkans, and Turkey. The jet-stream is intensifying during Tuesday as the ridge from the SW tries to prevail.

DISCUSSION

.... Portugal and Spain ....

The approach of a strongly negatively-tilted trough from the Atlantic and the collision of two very different air masses over Portugal will result in severe weather conditions. The trough brings steep lapse rates and strong positive vorticity over the area, whereas the low-pressure system near the surface creates a prolonged moist tongue from the Azores towards the Iberian Peninsula. During the night of Tuesday, DLS is expected to exceed 35 m/s, overlapping with 400 – 800 J/kg. Apart from excessive rainfall, DLS and 15 m/s 0-3 km shear may create a favorable environment for large hail, exceeding 2 cm in diameter and severe wind gusts. Straight-line forecast hodographs reduce the suspicion for tornadoes and only waterspouts are expected near the coasts of South Portugal, Spain, and Morocco in the morning hours of Tuesday when a short-wave trough moves quickly east. Conditions in Portugal will deteriorate after the end of this outlook.

.... Greece and Turkey ....

As substantial positive vorticity is found over the Adriatic Sea and the Balkans, two low-pressure systems at the surface will move from Central Mediterranean towards Greece and Turkey, bringing unstable air masses from the south. The steep lapse rates and moist low-level air masses in the Aegean will result in several hundreds of CAPE, even 1000 J/kg according to GFS, and in conjunction with the pronounced upper-level wind field we expect organized convection to produce severe weather events. The main threat will be excessive precipitation within the multiple convergence zones which high-resolution models forecast (BOLAM, WRF, ICON, etc) in the Aegean Sea, in the islands of Greece and west coasts of Turkey. Severe wind gusts and locally large hail may as well verify.