Storm Forecast
Valid: Thu 03 May 2012 06:00 to Fri 04 May 2012 06:00 UTC
Issued: Thu 03 May 2012 07:25
Forecaster: GATZEN

A level 1 was issued for east central Europe mainly for large hail.

A level 1 was issued for northern Spain and south-eastern France mainly for large hail.

A level 1 was issued for Turkey mainly for large hail and severe wind gusts.

A level 1 was issued for northern Africa mainly for large hail.

SYNOPSIS

Low geopotential persists over western Europe and extends from west of the Iberian Peninsula to the Bay of Biscay and into the Alpine region. With the south-westerly flow ahead of the south-west-European trough, a short-wave trough slowly moves eastward across the Balkans. Cool maritime air masses have spread further east across central Europe and the west Mediterranean during the last 24 hours. A tongue of warm air persists from the Balkans and Poland into north-eastern Germany and Denmark.

DISCUSSION

Eastern Europe

Well developed EMLs are present over eastern Europe and are indicated by latest soundings as far north-east as northern Poland and Denmark. The surface cold front at 6 UTC was located from eastern Germany to eastern Austria and the Adriatic Sea. To the north-east of this frontal boundary, rather rich low-level moisture is observed over the Balkans and southern Poland. A tongue of rich low-level moisture is also present below the warm mid-level air from Poland into northern Germany and the Netherlands. Showers and thunderstorms have developed from the Netherlands to western Poland and over southern-eastern Germany as well as along the cold front from western Hungary to eastern Czech Republic.

Today, moisture is rather limited over most places, but is expected to be sufficient to allow for CAPE especially across the central Balkans and western Romania. To the north-east, the surface frontal boundary is expected to be the focus for instability release. Low-level moisture may increase to the west of this frontal boundary from western Hungary to the Czech Republic and north-eastern Germany. CAPE will be weak to moderate (500-1500 J/kg) from western Poland into the Balkans and to the Black Sea region in the afternoon hours.

Initiation is forecast over the mountainous regions of south-eastern Europe (especially Romania and the Balkans) due to upslope flow and low-level moisture pooling. Additional storms will re-organize along the convergence zone ahead of the frontal boundary from the northern Balkans to Poland. While the mid-level flow has decreases and is rather weak over most places (up to about 10 m/s bulk shear in the lowest 3 km), storms will mostly be rather unorganized. Best potential of isolated supercells is expected over the northern Balkan region where around 100 J/kg 0-3 km SRH is likely ahead of the trough axis and slightly stronger winds at 700 hPa.

Most storms are forecast to organize in clusters with isolated pulse storms capable of producing large hail. Excessive precipitation will be also possible at local places. Severe wind gusts due to intense downdrafts may be likely in the eastern parts where low-level lapse rates and evaporative cooling will be rather large. A rather broad marginal level 1 is issued due to these threats. Storm clusters will likely weaken during the night but may survive along the frontal boundary until the morning.

Iberia

A cool maritime air mass affects Iberia. A cold front has entered the western parts leading to showers and thunderstorms. Rather humid air is advected during the day from the south-west ahead of this front. Diurnal heating may result in weak CAPE and initiation of new storms is not ruled out over northern Iberia. These storms will have the potential to organize given rather strong south-westerly mid-level winds. Locally large hail is forecast. The storms may also spread into western France where low-level easterly winds will contribute to locally favourably veering profiles. Isolated supercells are not ruled out capable of producing large hail. These storms will decay during the night hours.

Turkey, northern Africa

Upslope flow during the day together with increasing low-level moisture and steep mid-level lapse rates will likely result in isolated thunderstorms. Over northern Africa, moderate vertical wind shear (15 m/s bulk shear in the lowest 6 km) may assist for some supercells capable of producing large hail or severe wind gusts. Over Turkey, weak vertical wind shear is expected, but well-mixed low-level may enhance the potential of severe wind gusts. Additionally, pulse storms may be capable of producing large hail. Storms will likely decay during the night hours.