Storm Forecast
Valid: Mon 12 Aug 2019 06:00 to Tue 13 Aug 2019 06:00 UTC
Issued: Sun 11 Aug 2019 21:08
Forecaster: GROENEMEIJER/PUCIK

A level 2 was issued across Northwest Italy and extreme South Switzerland for large hail, severe wind gusts and to a lesser extent for heavy rain.

A level 2 was issued across Northeast Austria, South and East Czechia for severe wind gusts, tornadoes and to a lesser extent for heavy rain and hail.

A level 2 was issued across parts of South and East Poland, Southwest Belarus and extreme Northwest Ukraine mainly for large hail, and to a lesser extent for wind gusts and heavy rainfall.

A level 1 surrounding these areas, stretching from southeast France across the Alps to Belarus, also including parts of Germany and Hungary was issued for large hail, severe wind gusts and heavy rainfall.


A level 1 was issued across parts of Estonia, Latvia, and Russia's northern Pskov Oblast for large hail and tornadoes.

SYNOPSIS

A trough with an axis between the British Isles and Iberia moves eastward. Within a strong southwesterly flow ahead of the trough, a cold front stretching from Southeast France acroos the Alps to North Poland moves eastward as well. Despite somewhat modest lapse rates overlap of strong shear and weak to moderate instability east of the front, gives rise to the development of severe storms. A second area of possible severe weather exists where strong shear and weak CAPE overlaps acrosss the northern Baltic states.

Northwest Italy and South Switzerland...

Rather deep moisture with dew point temperatures around 20 C exist across the western Po Valley yielding 1000-2000 J/kg of MLCAPE in response to diurnal heating. Convective initiation is expected across the Alpine flanks during the afternoon. Given the (very) strong, 30 m/s, deep-layer shear, a few supercells with large hail and isolated severe winds will likely develop and move across the southern Alpine flanks and/or across the western Po Valley. More isolated storms including a few supercells are expected across the higher Alps.

Northeast Austria, Czech Republic, extreme Northwest Slovakia, southern Poland...

In response to lee cyclogenesis north of the Alps, upslope flow is expected to ultimately lead to convective intiation during the late afternoon or early evening. In addition, elevated convection in vicinity of the warm side of the cold front is expected to intensify during the evening. Promoted by the strong, 25-30 m/s, deep-layer shear and increasing low-level hodographs over eastern Austria and Czechia, linearly organized storms and supercells are expected to develop possibly embedded in larger systems. They will bear a risk of severe winds, while a few tornadoes will also be possible, in particular if the strong CAPE/low-level shear overlap that the ECMWF model is consistently predicting develops during the evening. The storms will probably affect south-central Poland, while weakening somewhat overnight.

Poland, Southwest Belarus, extreme Northwest Ukraine...

Ahead of the cold front, scattered thunderstorm development is expected during the afternoon within an environment characterized by modest lapse rates and 1000-1500 J/kg of CAPE. The strong deep-layer shear will likely lead to a few supercells that locally cause large hail (2-5 cm) and scattered severe wind gusts.

Estonia, Latvia, northern Pskov oblast...

Rather steep low-level lapse rates and seasonably high low-level humidity are expected to lead to 500-1000 J/kg of CAPE. In a strongly sheared western flow, with 25-30 m/s of DLS, some storms may develop into low-topped supercells with a risk of large hail. Given that LCL heights should be fairly low and low-level hodographs are curved with around 10 m/s of 0-1 low level shear, a tornado or two may develop.