Storm Forecast
Valid: Sat 15 Mar 2014 06:00 to Sun 16 Mar 2014 06:00 UTC
Issued: Sat 15 Mar 2014 00:43
Forecaster: PISTOTNIK

A level 1 was issued for E Germany, Poland, the Russian exclave of Kaliningrad, and parts of Lithuania and Belarus for severe convective wind gusts and to a lesser extent for tornadoes.

SYNOPSIS

Long waves dominate the European weather. A strong Northwesterly flow pushes into Central and Eastern Europe between low geopotential over Scandinavia and a pronounced Atlantic high pressure system. In the wake of a mature storm cyclone centered over Estonia, a surge of polar air interrupts the early spring in the Northeastern quadrant of Europe.
Otherwise, conditions stay very mild and mostly calm. The only exception is the Central Mediterranean, where a shallow but extensive upper-level low slowly drifts Eastward.

DISCUSSION

... Central and Eastern Europe ...

A pronounced jet streak arrives from the Northwest, and rising motions in its left exit overspread the postfrontal cold air. Together with some diurnal heating, this will result in neutral to slightly unstable profiles. Scattered showers and isolated, low-topped thunderstorms are expected to develop in a strongly sheared and helical flow regime. An organization into multicells or short bowing lines is possible with an enhanced threat of severe wind gusts. Brief mesocyclones may also spawn an isolated tornado.
A level 1 was drawn for the cyclonic side of the jet streak, where convection is expected to grow deep enough to precipitate and to notably enhance the background wind field. Peak activity is expected in inland regions in response to daytime heating. On the other hand, over the Baltic Sea and coastal areas convection may go on overnight, when the coldest upper levels and small tropopause anomalies continue to travel over this region - however, by then the wind field relaxes enough to keep the severe wind threat lower.
Near the jet axis and on its anticyclonic side, the wind profiles would be even better but strong synoptic subsidence will likely keep the convection increasingly shallow. However, the 850 hPa winds equal or exceed 25 m/s over a large region well into Germany and the Eastern Alps, so isolated severe gusts will be possible even the absence of convection.

Likewise, another robust wind event can be expected at the cold front itself during peak daytime heating hours, as it enters a warm and very dry, well-mixed continental boundary layer over Slovakia, Hungary, the Western Ukraine and Romania. The forecast models show uniform signals that evaporative cooling will create a strong cold pool at the leading edge of the (stratiform) precipitation. Resulting wind gusts may easily exceed 25 m/s and could create dust storm conditions after the recent long mild and dry spell. No deep convection is expected and hence no threat level was issued for this phenomenon.

... Southern Mediterranean ...

Large-scale lift will overspread the Southern Mediterranean and Ionian Sea ahead of the upper-level low. Limited CAPE will develop but will be strongly capped beneath the fringes of a Saharan elevated mixed layer. Scattered showers and thunderstorms will form over Eastern Algeria and Tunisia, while it gets more doubtful if the cap will be broken over Sicily and the open sea. With rather weak vertical wind shear, severe weather is unlikely.