Storm Forecast
Valid: Thu 28 Dec 2017 06:00 to Fri 29 Dec 2017 06:00 UTC
Issued: Thu 28 Dec 2017 01:17
Forecaster: GATZEN

A level 1 was issued for the Ionian Sea, southern Adriatic Sea and western coasts of Greece and the Balkans mainly for excessive precipitation.

A level 2 was issued for southern Ireland and the northern Celtic Sea mainly for severe wind gusts and to a lesser extent tornadoes.

SYNOPSIS

Ionian, southern Adriatic and Aegean Sea into Greece and the northern Balkans

A trough is located across Europe. An embedded vorticity maximum moves over Italy into the northern Balkans on Thursday, farther curving north-east towards the Ukraine and Poland late in the period. In its wake, another embedded vort-max enters the trough’s base over the central Mediterranean. Cold and dry air masses spread with Mistral winds into the west Mediterranean. Ahead of the vort-max, warmer and moist air advects across the Ionian Sea into the south Adriatic Sea and farther across the Aegean. Excessive rain can be expected along the cold front especially along the western coasts of Greece and Albania where upslope flow is present. A level one is issued for this activity although the rain is party caused by non-convective processes. Main activity is forecast on Thursday morning. When the vort-max lifts northward weaker low-level moisture over the Balkans limits thunderstorm potential. However, some storms may form onshore and models even indicate some CAPE over eastern Croatia or northern Serbia in the afternoon. Long low-level hodographs indicate a risk of severe wind gusts with any storm that forms. A threat level is not issued as only isolated storms are expected.

Celtic Sea westward into North Atlantic

A powerful 65 m/s mid-level jet streak approaches over western Europe late in the period. A well-developed tropopause fold evolves and crosses the North Atlantic west of Ireland and enters the Celtic Sea. At low levels, a moist maritime air mass advects into the area with a south-westerly low-level jet. This air mass is slightly unstable given steep mid-level lapse rates that overlap with the rich moisture. Therefore, some thunderstorms are forecast along the cold front in the night and morning hours. Further north across southern Ireland and the southern Irish Sea, strong low-level stretching is expected to result in steep low-level lapse rates and weak CIN. Along the cold front, a narrow rain band could develop into a line of thunderstorms. With strong flow at lot to mid levels, severe wind gusts are forecast with this convective line. Additionally, tornadoes are not ruled out given large SRH ahead of the cold front. Severe winds further north are expected to be non-convective.