Storm Forecast
Valid: Sat 01 Feb 2020 06:00 to Sun 02 Feb 2020 06:00 UTC
Issued: Fri 31 Jan 2020 20:55
Forecaster: PISTOTNIK

A level 1 is issued for SE Germany, parts of the Czech Republic and Austria for severe convective wind gusts.

SYNOPSIS

The weather pattern stays very active with a quick progression of short-wave troughs and ridges embedded in a strong zonal flow. An amplified mid-level trough exits our forecast area to the east. Another one moves from the British Isles (Sat 06 UTC) to the Baltic Sea, Poland and Romania (Sun 06 UTC) while it undergoes moderate deepening. It is associated with a mature storm cyclone with a center near central Norway, whose occluding frontal system crosses central Europe. The pronounced warm front of the next Atlantic storm cyclone approaches the British Isles towards the end of the forecast period.
High pressure brings calm weather to the Mediterranean region.

DISCUSSION

... central Europe ...

Strong synoptic lift overspreads the occluding warm sector and creates neutral to marginally unstable vertical profiles thanks to the unseasonably rich boundary layer moisture, originating from the subtropic Atlantic region. In a wide region from E France to Poland, the precipitation will gradually break up into showers and probably isolated low-topped thunderstorms in the afternoon and evening. Most of the storms should stay non-severe due to marginal CAPE and not too strong vertical wind shear yet.
After ca. 21 UTC, however, a pronounced mid-level jet streak will approach from the west, and increasing vertical wind shear and lift in its left exit region enhance the potential for still active storms to organize. Forecast models differ widely both on the track and the intensity of this mesoscale feature. The most aggressive runs of convection-resolving models showed storms with several swaths of severe to extreme wind gusts, but were not confirmed by later model runs. Due to these ongoing uncertainties, only a limited level 1 is drawn for a belt from SE Germany into Austria and adjacent Bohemia where agreement on deep convection overnight is highest.
In the improving kinematic environment (0-1 km shear ~15 m/s, 0-3 km shear ~20 m/s), multicells and short bowing line segments will be the dominant storm mode. Isolated to scattered severe wind gusts are expected. In case discrete updrafts can be dominant for a while, at least temporary updraft rotation and an isolated tornado are not ruled out.

... British Isles to Denmark ...

A surface trough in the wake of the Norwegian cyclone will be accompanied by a confined area of widespread wind gusts around 25 m/s. In deeply mixed maritime polar air, showers may be involved but are not expected to grow deep enough to produce thunder. Therefore, these gusts are not reflected by our threat levels.