CONVECTIVE FORECAST
VALID 06Z WED 25/02 - 06Z THU 26/02 2004
ISSUED: 25/02 02:15Z
FORECASTER: GROENEMEIJER

General thunderstorms are forecast across North Sea, north- and northwestern Low countries, northern Germany, Denmark

General thunderstorms are forecast across Southern Iberia, parts of the western Mediterranean

General thunderstorms are forecast across Sicily

SYNOPSIS

Wednesday at 06Z.. a trough/low pressure area at both low and upper levels located over western Scandinavia, dominates the north European weather. On its western flank, a northerly flow advects cold, unstable air southward. Another trough, extending from northern France to Iberia, is moving eastward, while merging with the former trough which digs southsouthwestward. To the southeast of these troughs a west to southwesterly flow is present over the Mediterranean basin, in which a small vort max is embedded that is located over the northern Balkans and is rapidly moving eastward.

DISCUSSION

...North Sea, north- and northwestern Low countries, northern Germany, Denmark...
Within th polar air-mass, the unstable layer is expected to deepen as upper temperatures drop a little further to around or below -40C at 500 hPa. Deep moist convection will likely produce thunder in places, especially where organised near shortwave troughs.

...Southern Iberia, parts of the western Mediterranean...
Wednesday at 06Z... a frontal zone is expected from near Madrid to near Firenze to Sofia. South of this zone, slight warm advection and resulting rising motions are forecast, that will probably have the effect of destabilising the nearly neutral air-mass in places. This will likely lead to the formation of scattered storms over the east of the indicated area. To the west...instability is already present due to lower upper-level temepratures and thunderstorms are expected to continue here. Over Spain and the western Mediterranean, the frontal zone is expected to begin a southward motion in response to weak surface cyclogenesis in the Gulf of Genua. Over the entire area deep-layer shear will be moderate at best and CAPE will remain small. So that chances of severe convective activity will likely be small.

...Sicily...
At the end of the forecast period, a realtively shallow elevated mixed layer from the Sahara desert is expected to move northward over the central Mediterranean. The GFS model produces a few 100's of J/kg CAPE during the last hours of this forecast period as well as some convective precipitation. Forecast soundings indicate the instability will likely be slightly elevated. The AFWA MM5 model agrees with the formation of some latent instability, but is slower, leaving it an issue for the next forecast period. Concluding, a few thunderstorms may affect Sicily in the last hours of this forcast period. The activity will likely not be severe given that CAPE will be very limited at best and the storms, will likely be slightly elevated, if they occur at all in this forecast period.

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