CONVECTIVE FORECAST
VALID 06Z WED 23/06 - 06Z THU 24/06 2004
ISSUED: 22/06 23:54Z
FORECASTER: GROENEMEIJER

There is a slight risk of severe thunderstorms forecast across northern France, extreme southeastern Britain, the Benelux countries and a large part of Germany

General thunderstorms are forecast across much of western and central Europe, the Balkans, Turkey, much of Scandinavia, much of European Russia and the central and eastern Ukraine

SYNOPSIS

Wednesday at 06z... a strong westerly jet at mid and upper levels is expected to move into west-central continental Europe. An unseasonably strong surface cyclone is expected to be located over central England, moving onto the North Sea during the day. Downstream a shortwave trough over the Baltic Sea is expected to move northeastward during the day. A mid/upper low over the southern Ukraine and a trough over the Black Sea and Turkey are expected to remain stationary during the forecast period.

DISCUSSION

...slight risk area...
At 06Z....a cold front is expected near a line from Amsterdam to Luxembourg to Biarritz. A convective line is expected at the cold front that may contain a few embedded mesocyclones. Strong 0-1 SREH (~200 m2/s2) ahead of the front, the presence of some low-level CAPE and low LFC heights suggest a chance of a few tornadoes will exist at the front. A few strong gusts will also be possible.

Current thinking is that postfrontal convection will pose the main severe threat on Wednesday as the low level wind field is expected to strengthen. GFS, MM5 and other numerical models seem to agree quite well that a 30-33 m/s speed maximum at 850 hPa will move from the Channel region over the Benelux countries during afternoon. Most convective activity is expected just ahead of the speed max, and should affect the Benelux and northern France during the early afternoon and move into western Germany. Main convective modes are expected to be convective lines and mini-supercells. The latter will pose a threat of tornadoes given that the low level wind field should become favourable of updraft rotation as 0-1 SREH is forecast to climb to 200 m2/s2 some distance behind the cold front. The strong low-level wind field in general should be capable of producing severe (>25 m/s) gusts with any deep convection that forms and during the evening an night hours in the Benelux perhaps even in absence of deep convection. A few marginally severe hail events should be possible as well. Highest threat of severe seems to be over Belgium, the Netherlands and northwestern and west-central Germany. And upgrade to moderate risk for these areas may be issued later on.

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