Storm Forecast

Storm Forecast
Valid: Wed 31 May 2017 07:00 to Thu 01 Jun 2017 06:00 UTC
Issued: Wed 31 May 2017 06:54
Forecaster: PUCIK

A level 1 was issued for C France and the Alpine range with adjancent lowlands mainly for excessive precipitation and to the lesser degree for large hail and severe wind gusts.

A level 1 was issued for E Hungary, W Romania, E Slovakia and W Ukraine mainly for excessive precipitation, large hail and severe wind gusts.

A level 1 was issued for Belarus, E Latvia, E Lithuania and W Russia mainly for severe wind gusts.

A level 2 was issued for NE Belarus and W Russia mainly for severe wind gusts and to the lesser degree for tornadoes.

SYNOPSIS

At mid to upper troposphere, a sharp short-wave will quickly translate from S Scandinavia and the Baltic Sea towards Russia with a jet-streak embedded at the base of the trough. At the same time, cyclogenesis is simulated over NW Russia with attendant frontal system crossing the region. Cold front is expected to stretch from NW Russia through Belarus, SE Poland, N Czech Republic, S Germany into Central France at 12 UTC. Cold front will move quickly across Belarus towards W Russia during the day and rather stall over the other regions. A cut-off low at mid-troposphere is centred over S France with virtually no motion. Scattered DMC activity is forecast especially along and south of the cold front, where dew points around 15 and are commonly observed.

DISCUSSION

... C France towards Austria and Slovenia ...

Scattered initiation is forecast especially along the mountain chains with development spreading towards the adjacent lowlands during the later afternoon and evening. Rather weak DLS is forecast for the region, around 10 m/s, with values up to 15 m/s over C France. Shear may also be enhanced on the lee side of the Alps with respect to prevailing flow - i.e. SE Austria. Primary threat will be excessive precipitation from slow moving, or perhaps even quasistationary multicell clusters, followed by some chance of marginally large hail and severe wind gusts from the stronger "pulse" storms.

... E Hungary, E Slovakia, W Romania, W Ukraine ...

Along and ahead of the advancing cold front, 10 to 15 m/s of DLS is simulated by models with around 15 m/s over SE Slovakia as the lee cyclogenesis occurs behind the Carpathian range. Dewpoint readings above 15 C in the area confirm the presence of moist airmass, which in conjunction with surface heating may be sufficient for several hundreds to around 1000 J/kg of MLCAPE. Isolated to scattered multi, or perhaps even brief supercells, will initiate especially along the mountain chains or the frontal system. Storms may be capable of large hail (limiting factor being rather weak lapse rates), severe wind gusts or excessive precipitation from slower moving or quasi-stationary multicells.

... Belarus to W Russia ...

At the forward flank of the sharp short-wave, strong cold front will progress across the region to E. Observed 00 UTC soundings, as well as model soundings suggest strong unidirectional flow with 0-6 km shear around 20 m/s near the trough, decreasing towards S. 850 hPa winds will reach 15 - 20 m/s, increasing towards the evening hours as the low pressure system over NW Russia deepens. Several hundreds J/kg of CAPE are simulated over Belarus as moist airmass is advected from W, decreasing towards E, where moisture is scarce. It is likely that a strongly forced squall line forms at the cold front with primary threat of severe wind gusts. A lvl 2 is issued for the belt with the best forcing and the strongest lower tropospheric flow. Here, more widespread nature of severe convective wind gusts will be possible. Given strong LLS, tornadoes will be possible if isolated supercells manage to form, which is questionable atm.


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