Storm Forecast
Valid: Thu 07 Sep 2017 06:00 to Fri 08 Sep 2017 06:00 UTC
Issued: Wed 06 Sep 2017 22:08
Forecaster: GATZEN

A level 1 was issued for Italy, the Ligurian, Tyrrhenian, and Adriatic Sea, western Balkans, Balearic Islands, Gulf of Valencia and surroundings, mainly for excessive rain and to a lesser extent tornadoes.

A level 1 was issued for northern Algeria and Tunisia mainly for excessive rain and to a lesser extent large hail.

SYNOPSIS

Low geopotential extents from the North Atlantic towards the Baltic States. A westerly flow affects most of Europe. Two intense short-wave troughs, one over eastern Central Europe and another over France moving into the Mediterranean are embedded in this flow. At low levels, cool and dry air masses have spread into western Europe and continue to be advected south-east into eastern Europe and the western Mediterranean. Rich moisture remains ahead of the cold front over the south-west and central and northern Mediterranean where it is affected by the approaching short-wave trough.

DISCUSSION

Italy, Ligurian, Tyrrhenian, and Adriatic Sea, western Balkans, Balearic Islands, Gulf of Valencia and surroundings, northern Algeria and Tunisia

A moist air mass is located over the region as indicated by latest soundings. Cooler air masses will spread into the west Mediterranean during the day behind a cold front. Ahead of the approaching trough, low-level flow will back to the south and east over most of the area, causing warm air advection over the Adriatic and parts of northern Italy and the Ligurian Sea, from the Balearic Islands towards Spain, and later on also over northern Africa. Mid-level temperatures will be low enough to allow for convective storms that will form in a moist air mass with rather weak flow. This will result in a threat of excessive rain and flash flooding. Regions that are most at risk are the mountainous areas that see upslope flow. Furthermore, steeper lapse rates and higher CAPE over the western and southern parts of the area indicate that large hail can occur with the stronger storms. Over the Adriatic and the Gulf of Valencia, tornadoes may be possible as low-level buoyancy overlaps with curved low-level hodographs and 0-1 km SRH around 100-200 m²/s².

North Sea

Late in the period, upper-level cold front will spread across the southern UK. Rather moist air mass over the North Sea will become slightly unstable and showers and thunderstorms are forecast. With very strong low-level flow, severe wind gusts are likely. Main contribution will be the large scale flow, however.