Valid: Wed 23 May 2018 06:00 to Thu 24 May 2018 06:00 UTC
Issued: Wed 23 May 2018 06:01
A level 1 was issued across much of Central Europe, Italy and western Balkans mainly for excessive precipitation and large hail.
A level 1 was issued for Belarus mainly for large hail and severe wind gusts.
A level 1 was issued for northern Caucasus and parts of the Middle East for excessive precipitation and large hail.
As of Wednesday morning, satellite imagery reveals several short-wave troughs / small-scale lows at mid to upper troposphere over Europe. The first one is located west of Iberian coastline moving slowly SE-wards during the day. Another one will reside over NW France, slowly moving W-ward during the forecast period. A short-wave is also crossing Belarus and to the south, a short-wave will move NE-wards from S Italy towards Balkans, already associated with thunderstorm activity in the morning hours.
Generally speaking, much of W / Central / SE Europe is under the pool of lower geopotentials, in rather weak prevailing flow. Combined with warm and modestly moist airmass in the lower troposphere, and lapse rates of around 6 to 6.5 K/km in the lower to mid-troposphere, scattered to widespread convection is forecast across a large part of the continent.
... E France to W Balkans ...
12 UTC soundings from the previous day show weakly sheared environment with skinny CAPE profiles and relatively high RH throughout the low and mid troposphere. Model output shows no significant change in conditions for today. Local boundaries, topography and differential heating of surface will act as triggers in the uncapped airmass. Poorly organized convection is forecast, with multicell clusters being the prevalent convective type. Due to the slow storm movement and moist profiles, heavy precipitation will be the dominant threat. Isolated large hail may occur with stronger cells. While the threat of heavy rainfall is elevated over the whole broad area, the highest threat will be confined to W Balkans coastline, Croatia, W Hungary and E Austria, where the most abundant lower level moisture is forecast. Convergent winds also suggest increased heavy rainfall threat over N France / S Belgium.
... Greece ...
In contrast to the rest of Balkans, stronger flow is forecast at mid-troposphere at the base of the passing short-wave. Thus, environment will be more strongly sheared with DLS values between 15 and 20 m/s. Organized multi and/or supercells are forecast with threats of large hail. Severe wind gust threat will also be elevated due to the drier boundary layer over this area.
... Belarus ...
Near the base of the short-wave trough, 15 to 20 m/s of 500 hPa flow and unidirectional hodographs will result in well organized convection, in the form of multicells and splitting supercells. Large hail will be the main threat particularly with supercells. Severe wind gustss are not ruled out, but the threat is diminished by the lack of deep, dry boundary layer and/or stronger flow at the lower troposphere.
... Northern Caucasus, the Middle East ...
Similarly to Central and SE Europe, weakly sheared, uncapped and unstable airmass will give rise to numerous multicell clusters over the area capable primarily of very heavy precipitation. Given steep lapse rates, large hail will also occur with stronger cells, despite rather weak organisation.