Storm Forecast
Valid: Thu 05 Jul 2012 06:00 to Fri 06 Jul 2012 06:00 UTC
Issued: Thu 05 Jul 2012 06:25
Forecaster: GATZEN

A level 2 was issued for north-eastern Spain mainly for large hail.

A level 2 was issued for eastern Germany into south-western Poland mainly for large hail.

A level 1 was issued for eastern central Europe and the Balkans mainly for large hail and severe wind gusts.

A level 1 was issued for western central Europe mainly for excessive precipitation.

A level 1 was issued for the Alpine region and the northern Mediterranean mainly for large hail.

SYNOPSIS

The west European cut-off low is centred across north-western France. A vort-max will rotate around the base of this trough today, affecting Spain and France. The associated trough axis will spread north-eastward into Germany on Friday morning, while the strong mid-level jet remains across Spain and southern France. Ahead of the trough, warm air masses continue to spread north-westwards into Central Europe. Latest soundings indicate an EML to the south-east of Germany and western Poland, but rather steep lapse rates are also present across Germany and France. Rich low-level moisture is present in the warm air advection regime.

DISCUSSION

North-eastern Spain

A vort-max will travel across Spain during the day, providing quite strong QG forcing across northern Spain. A cold front has entered the Iberian Peninsula during the night from the west and leads to convection across north-eastern Spain in the morning hours. However, low-level winds will turn to east across north-eastern Spain in response to a thermal low during the day. Moisture advection is therefore expected across eastern Spain today, and diurnal heating and steep lapse rates will result in 1000-1500 J/kg CAPE in the afternoon hours. The unstable air mass will be capped in the southern regions, but the strong QG forcing over northern Spain is expected to limit CIN significantly. Initiation becomes quite likely in the noon hours and and storms are forecast to continue during the afternoon. Although the best vertical shear will be placed to the south of the expected convection, around 20 m/s 0-6 km und 10 m/s 0-3 km bulk shear will be adequate for organized convection even further north. Veering profiles will support supercells. Very large hail is the main threat, but supercells may also produce a tornado or severe wind gusts. In the evening hours, stoms are forecast to decay quickly as cold air advection sets in from the north-west.

Central Europe

The large warm air advection regime is expected to support intense thunderstorms today. Highest coverage is expected along a cold front across eastern France, the Benelux countries, and western Germany. Additionally, a more intense frontal boundary is expected to build ahead of a plume of warm air spreading north-westward into eastern Germany, where cyclogenesis is forecast.

Across eastern France, an increasing southerly flow is expected, and some training stoms are forecast along the frontal boundary that slowly moves eastward into the Benelux countries and western Germany. Locally, excessive precipitation is forecast, although the low-level moisture is not exceptionally high. Additionally, moderate vertical wind shear of 15 m/s bulk shear in the afternoon may support more intense multicells capable of producing isolated large hail. The convection may grow upscale into an MCS capable of producing excessive rain during the night hours.

Further east, steep lapse rates and rich low-level moisture will be associated with high CAPE values around 1000-2000 J/kg from southern Germany and the Baltic States to the northern Balkans and Italy. Highest coverage is expected along the frontal boundary from the Baltic States to eastern and central Germany and further to north-western Italy. Additional storms will develop further south-east over the mountains and along outflow boundaries. Given the high CAPE and at least 10 m/s 0-6 km bulk shear, storms may organize, and large or very large hail is possible. Main focus of very large hail is the region from Austria to south-eastern Germany and western Poland, where 0-3 km bulk shear increases to 10 m/s along the intensifying frontal boundary. Severe wind gusts are most likely in the south-eastern parts from Poland to the northern Balkans given steepest lapse rates there. An additional threat will be excessive precipitation due to high precipitable water content and slow, back-building storms. Storms will likely go on through-out the night across eastern Germany and northern Poland as well as over the Benelux countries and central Germany given weak cyclongenesis along the frontal boundaries.