Storm Forecast
Valid: Wed 30 Apr 2008 06:00 to Thu 01 May 2008 06:00 UTC
Issued: Tue 29 Apr 2008 21:28
Forecaster: GATZEN

SYNOPSIS

An intense low is present over western Europe. Over eastern Europe, another trough slowly accelerates northward during the period. To the south of both troughs, a rather strong westerly flow builds over the Mediterranean, while strong southerly jet from France to the North Sea weakens gradually. At lower levels, subtropical air masses are present over south Mediterranean, while cool/dry air masses are present over most of Europe. In the eastern portions, diurnal heating has lead to inverted-v profiles and dry low-level air, while the western portions are dominated by maritime polar air mass that is also characterized by quite steep/neutral lapse rates, but rich boundary-layer moisture. During the period, deep convection seems to form in the range of the upper troughs only.

DISCUSSION

France, Benelux, England

In the range of the trough, polar air mass will likely destabilize in response of diurnal heating. Weak CIN will be present, and showers and thunderstorms are expected to form. In the range of convergence zones especially over England, weak tornadoes are not ruled out. To the south-east, deep layer vertical wind shear will be moderate over southern and eastern France as well as over Benelux, and a few thunderstorms may organize, posing a threat of isolated marginally large hail. Although convective mode will likely be single cells and multicells, mesocyclones may develop over Benelux given around 10 m/s low-level vertical wind shear during the afternoon hours, but given rather weak low-level buoyancy, tornadoes are not expected to be likely.

Ukraine to Poland

Thunderstorms are forecast to develop due to diurnal heating and weak CIN in the range of the upper trough. Locally inverted-v profiles and rather high cloud-base may support isolated severe wind gusts. Given rather widespread convective activity over a broad region, a few marginally large hail and flash flood reports are not excluded, as well as a weak tornado. Overall threat for severe convection is low.

South-eastern Germany

Weak upper trough is forecast to move across the Alps during the afternoon. A cold front that propagates eastward during the day may be sufficient to initiate convection, and thunderstorms are forecast to develop. However, although daytime heating is expected, low-level instability may be quite low given dry boundary-layer. Latest GFS model run seems to be optimistic showing around 11°C dewpoint north of the Alps, and current thinking I that storms will be mostly elevated due to dry low-level air mass. Storms will move north-eastward and chance for severe convection will be rather low.

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