Storm Forecast
Valid: Tue 18 Mar 2014 06:00 to Wed 19 Mar 2014 06:00 UTC
Issued: Mon 17 Mar 2014 23:36
Forecaster: PISTOTNIK

A level 1 was issued for Central and E Germany for severe convective wind gusts and to a lesser extent for tornadoes.

A level 1 was issued for S Germany and parts of the Czech Republic for severe convective wind gusts.

SYNOPSIS

A strong segment of the polar jet still stretches from Iceland to the Ukraine. The associated frontal zone separates polar air to the North from maritime subtropical air to the South. A shallow wave travels from Southern Norway to the Baltics, followed by an occluding low which moves from Scotland to Poland. Otherwise, large stretches of the frontal zone turn warm-active again over Eastern Europe as well as later in the forecast period over the Atlantic and the British Isles.
Southwestern Europe and most of the Mediterranean are under the influence of high pressure with above-normal temperatures and clear skies.

DISCUSSION

... England, North Sea, BeNeLux, Germany, Poland, Czech Republic ...

A short-wave trough ejects Southeastward from the frontal zone and overspreads the occluding and disintegrating frontal system, while it moves from the British Isles into Central Europe. The forecast maps show a temporarily very good phasing between the various sources of lift in the 18 to 06 UTC time frame.
Rich low-level moisture and steepening lapse rates will likely create neutral or marginally unstable profiles in the ill-defined warm sector in the course of the day. Scattered convection is expected to initiate over England around noon and to move across the Channel to the Netherlands till 18 UTC. Then it will enter Germany, where its chances to grow deeper and produce some lightning increase.
15-20 m/s shear and 100-200 m^2/s^2 storm-relative helicity between 0 and 3 km (and slightly lower values between 0 and 1 km) seem easily sufficient for the sustainance of multicells or short bowing lines. With unseasonably mild conditions (forecast temperatures around 10°C and dewpoints around 6°C overnight), storm may manage to stay surface-based all night long. A level 1 was issued for a risk of isolated severe wind gusts. Small hail is possible as well. An isolated tornado is not ruled out near the Northern rim of the level 1 area where the cloud bases are lowest and the low-level veering is strongest. Convection will gradually taper off over Poland and the Czech Republic towards the end of the forecast period.

Further South, equally high nighttime temperatures are expected but better mixing will lower the dewpoints to close to 0°C towards the Alpine rim, where a forming barrier jet with 850 hPa winds up to 25 m/s will form overnight. Downward mixing of momentum and evaporative cooling might suffice for isolated severe wind gusts as well when the cold front comes in after midnight. A low-end level 1 was extended Southward for that reason. The lift by the tail of the vorticity lobe in combination with upslope flow may also be strong enough to still produce a few lightning strikes along the frontal rain band.

... Spain ...

First isolated springtime showers can form over the mountains in the afternoon hours. Very deep and dry boundary layers (expected maximum temperatures are around 25°C and dewpoints around 0°C) may create a few dry microbursts. Not much precipitation will reach the ground and the chances for lightning are considered too small to issue a thunder area.