Storm Forecast
Valid: Sun 27 Jul 2008 06:00 to Mon 28 Jul 2008 06:00 UTC
Issued: Sat 26 Jul 2008 21:49
Forecaster: SCHLENCZEK

SYNOPSIS

A stout upper high over southern Scandinavia is surrounded by two upper troughs, leading to an Omega-like upper flow pattern. Widespread convection in a weakly sheared environment is expected over large parts of western-central Europe. At the southern tip of the Atlantic trough, a cut-off low will develop during the period, moving southeastward towards the Bay of Biscay. Another upper low will remain over northwestern Russia.

DISCUSSION

...Benelux countries, western Germany...

In the vicinity of a LL convergence line over the Netherlands, Belgium and western Germany, dewpoints in the upper tens are still present. In the morning hours, insolation and evapotranspiration will lead to T / Td around 30°C / 20°C which creates 2 - 3 kJ/kg MUCAPE during the day. Weak large-scale forcing is expected but mesoscale features like the convergence line will probably create enough lift for convective initiation. Even though vertical shear is rather low, some storms may profit from about 10 m/s shear in the 0-3 km level and SRH3 around 150 J/kg. Isolated mesocyclones may evolve and storms should be capable of producing large hail and severe gusts. During the afternoon, storms will tend to merge into one or two large systems that move northwestward into western Belgium and northeastern France. Storms are expected to move slowly which will lead to heavy precipitation and an enhanced flash flood threat. Thunderstorm activity should gradually decrease after sunset.

...Northern Iberia, southwestern France...

Ahead of the approaching upper trough, low-end instability is expected to form in an environment with about 15 m/s deep layer shear. SRH3 is forecast to increase to about 150 J/kg during the afternoon when convective initiation should take place. A few organized multicells could produce isolated large hail and strong gusts but a threat level is not warranted at the moment.

...Central and eastern Mediterranean...

Kinematic conditions are relatively weak over parts of Italy, Greece and the Balkans. Diurnally driven thunderstorms will evolve in an environment with about 1 kJ/kg MUCAPE. Large-scale forcing is quite weak but low CIN should allow convective initiation due to mesoscale features, e.g. orographic lift. Storms may be accompanied by isolated large hail and a severe gust is not ruled out. Overall threat seems to be too low for a level-one, though. Flash floods may occur where storms persist.