Storm Forecast
Valid: Thu 03 May 2018 06:00 to Fri 04 May 2018 06:00 UTC
Issued: Thu 03 May 2018 00:09
Forecaster: GATZEN

A level 2 was issued across the northern Balkans mainly for large hail and excessive precipitation and to a lesser extent severe wind gusts and tornadoes.

A level 1 was issued across eastern central Europe into western Russia and central Italy mainly for large hail and severe wind gusts and to a lesser extend tornadoes and excessive precipitation.

DISCUSSION

SYNOPSIS

A cut-off low forms across the central Mediterranean. Ahead of this low, steep lapse rates have spread across eastern central Europe. These lapse rates overlap with rich boundary-layer moisture along a warm front that moves north to the Baltic States and along a cold front that moves east across Poland, the Czech Republic, and Austria. Another cold front enters the Balkans from the west.

DISCUSSION

Austria to Czech Republic, central Poland, southern Baltic States, central Belarus, and western Russia

CAPE in the order of 1500 J/kg is expected to build along the frontal boundaries over eastern Central Europe. Scattered thunderstorms are expected to form due to frontal lift. Given limited vertical wind shear, single cells and some pulse storms are forecast across Poland and the Czech Republic, capable of producing isolated large hail and flash floods. Especially at the eastern flank of the frontal boundary, severe downbursts can evolve due to the deep boundary layer. Overall threat is high enough to issue a level 1. Storms are expected to cluster in the afternoon and decay in the evening.

Farther north, stronger vertical wind shear affects the warm front across the Baltic States and Belarus and western Russia. Curved hodographs are expected with 0-3 km vertical wind shear around 10 m/s. Multicells and supercells are forecast. Main limiting factor for severe wind gusts and tornadoes is the cold boundary layer close to the warm front, and storms may be hardly rooted to the boundary layer. However, large hail and excessive precipitation is forecast. An isolated tornado and a few severe wind gusts are also not ruled out.

Over Austria, increasing low-level vertical wind shear is forecast in the evening hours. In the warm air advection regime, supercells may form capable of producing large hail, severe wind gusts and an isolated tornado or two.

Balkans

A cold front approaches from the Adriatic Sea. Ahead of this front, rich low-level moisture overlaps with steep lapse rates. CAPE builds during the day reaching 1000 J/kg according to latest models. Thunderstorms are forecast to form over the mountains and will likely increase in coverage as the cold front approaches and a mid-level trough passes. Strong mid-level flow results in strong deep layer vertical wind shear so that supercells can form that can produce all kinds of severe weather including very large hail and a few tornadoes. Storms may merge into an MCS in the afternoon and evening with an increased threat of excessive precipitation.

Italy

Close to the cut-off low, thunderstorms are expected to form in an airmass with rather steep lapse rates and some low-level moisture. Stronger vertical wind shear is expected in the noon at the eastern flank of the cut-off core across Italy. Multicells and supercells are not ruled out and may produce large hail and severe wind gusts.