Storm Forecast
Valid: Thu 07 Apr 2016 06:00 to Fri 08 Apr 2016 06:00 UTC
Issued: Thu 07 Apr 2016 05:05
Forecaster: GATZEN

A level 1 was issued for the Western Ukraine, south-eastern Poland, Slovakia, Hungary, western Romania, northern Serbia, Bosnia, Croatia, Slovenia, and northern Italy mainly for large hail and to a lesser extent excessive rain and severe wind gusts.

A level 1 was isued for southern Italy and Sicily mainly for large hail and to a lesser extent excessive rain.

SYNOPSIS

Low geopotential is located across north-west Europe. At its western flank, an intense short-wave trough has ejected into the UK and northern France. While the southern portions of this vort-max will further dig into southern France today, the main remaining will lift across NW Germany and the Baltic Sea today. Ahead of the NW European trough, a cut-off low currently over Tunisia will travel north-east and is expected over southern Italy on Friday morning, yielding increasing south-westerly flow over the east Mediterranean and backing winds across eastern Europe.

Lapse rates have improved in the last days especially over south-eastern Europe. These lapse rates overlap with rich low-level moisture along a frontal boundary stretching from the northern Ukraine to Hungary, the northern Balkans and northern and central Italy. Increasing low-level moisture is also expected ahead of the cut-off low over the east Mediterranean.

DISCUSSION

Western Ukraine, south-eastern Poland, Slovakia, Hungary, western Romania, northern Serbia, Bosnia, Croatia, Slovenia, northern Italy

A frontal boundary stretches across this region, marked by low-level convergent flow and dewpoints between 8 and 10°C. This frontal boundary is expected to remain stationary today or may even move north-westwards as the flow turns to southerly directions ahead of the W-European trough. This will be associated with warm air advection over a broad region. Latest soundings indicate mid-level steep lapse rates and some isolated storms are already present like over northern Serbia.

Today, diurnal heating can be expected according to latest satellite data, and CAPE in the order of 500 J/kg can build. Ongoing warm air advection will lead to some QG forcing combined with frontogenetical forcing and topographic forcing. Thunderstorms are expected in the late morning hours that will gradually spread northward during the day. Although the flow is pretty weak, low-level veering profiles are forecast in the warm air advection regime, with longer hodographs at the north-western edge of the affected region. Supercells are therefore possible to form, along with multicells. These storms will be capable of producing large hail. Stronger cells may be also accompanied by severe wind gusts and excessive precipitation. Overall severe potential is expected to justify a robust level 1 threat. Convective activity will decrease in the evening and night hours due to low-level stabilization.

Southern Italy

Ahead of the approaching cut-off low, a tongue of rich low-level moisture spreads into the central and east Mediterranean. Within the base of the cut-off low, steep lapse rates and QG forcing are expected to cause thunderstorms across Sicily today, spreading north-east during the night hours. Although vertical wind shear is weak, stronger storms may form along sea-breeze convergences with enhanced low-level shear. Main threat will be large hail and excessive rain.