Storm Forecast
Valid: Mon 06 Apr 2009 06:00 to Tue 07 Apr 2009 06:00 UTC
Issued: Sun 05 Apr 2009 17:02
Forecaster: TUSCHY

SYNOPSIS

High over low block slowly extenuates as an upper trough approaches from the west. At lower levels, quiescent conditions prevail over most parts of Europe. A weak cold front draws near from the Atlantic during the evening/night hours.

DISCUSSION

...Sicily, Sardinia, Italy, parts of Switzerland and Austria, parts of Germany, the Czech Republic, S-Poland, parts of Romania, Bosnia and Herzegovina and W-Turkey ...

The set-up remains supportive for weakly organized, ordinary thunderstorms, daytime driven and slow moving. Small hail and strong wind gusts are forecast with strongest activity. Yesterday, first reports of local flash flooding were recieved with those slow moving thunderstorms and this hazard persists for this forecast period.

... Spain and France ...

A sharp upper trough approaches western Europe during the evening and night hours. A cold front trails eastward, showing weakening signs in the theta-e gradients but it is placed under the favorable right entrance region of a north-south aligned upper speed maximum. An EML mixes northwards ahead of the front, so in combination with some boundary layer moisture recovery and strengthening divergence at upper levels, isolated to scattered, electrified convective activity is expected along the cold front during the afternoon and evening hours. Strongest moisture advection is forecast to occur over NE-Spain and dewpoints at or above 10°C seem reasonable after checking airmass quality over the western Mediterranean. This region also has the highest chances to see an isolated large hail report, as deep layer shear increases to 15-20m/s in the evening. Conditions assist in the development of a large convective cluster with thunderstorm activity decreasing after sunset. However, embedded thunderstorms are possible well into the night hours with some low-end MUCAPE values and strong divergence all the way up to central France.

The same for SE-Spain during the night hours, as a weak surface depression evolves offshore. Isolated thunderstorms are possible all night long.

A few thunderstorms are also possible under the base of the trough, e.g. Bay of Biscay. Enhanced convection seems likely but there are no foci like convergence zones, so we do not yet introduce a general thunderstorm area.