Storm Forecast
Valid: Wed 30 Jun 2010 06:00 to Thu 01 Jul 2010 06:00 UTC
Issued: Wed 30 Jun 2010 05:42
Forecaster: PUCIK

A level 1 was issued for Serbia, Eastern half of Croatia and Bosnia and Herzegovina, Western Romania mainly for marginally large hail, severe wind gusts or locally excessive precipitation.

SYNOPSIS

Rather inconspicuous synoptic-scale conditions are forecast over most of Europe during the forecast period. At midlevels, a trough will slowly translate eastwards over Scandinavia and a shallow cut-off low will remain almost stationary over the Black Sea. A ridge will stretch over Southwestern Europe and Northwestern Russia. British Isles will be under the influence of a significant disturbance during the second half of the period.

At the surface a shallow surface low will remain over Scandinavia and to the north of the Black Sea. No significant frontal boundaries are forecast, except for a weak cold front which should move eastwards over Poland and Baltic States. Most of Europe will be under a warm, locally modified airmass.


DISCUSSION

Large area over Europe is expected to experience thunderstorms, as instability builds-up with during the daytime heating. Diurnally driven thunderstorms are expected, triggered by the local factors, such as differential heating, anabatic winds and local convergence zones. With very weak flow in the troposphere, DLS values are expected to stay mostly under 10 m/s. Mostly disorganised convection is forecast, probably in the form of pulse storms or multicell clusters.

With lack of concentrated forcing on the synoptic scale and weak shear, chances for severe weather will be rather slim. However, in locally favorable conditions if CAPE values over 2000 J/kg verify, even pulse thunderstorms might be capable of marginally large hail or downbursts. Also, very slow movement of cells might especially in the hilly or mountainous terrain lead to the excessive precipitation and threat of local flooding.

One of the interesting factors regarding this situation is a discrepancy between GFS and ECMWF regarding CAPE values over France and therefore, storm formation is quite questionable. 00 UTC soundings do show some instability over southern half of France, albeit of lower extent than forecast by GFS.


...Serbia, Eastern half of Croatia and Bosnia and Herzegovina, Western Romania...

This area seems to be most favorable for the development of severe pulse-storm convection with MLCAPE values probably exceeding 2000 J/kg, as suggested by both GFS and ECMWF output. Marginally severe hail might occur as well as some highly localised downburst / short period of excessive precipitation. Convection will probably quickly dimnish during the late evening or early night hours.