CONVECTIVE FORECAST
VALID 06Z SAT 02/08 - 06Z SUN 03/08 2003
ISSUED: 01/08 19:16Z
FORECASTER: DAHL

General thunderstorms are forecast across Scandinavia ... east-central Europe ... the Balkan States and the central Mediterranean.

General thunderstorms are forecast across SW Iberia.

SYNOPSIS

Strong high-over-low block is present over the eastern portions of Europe and W Russia ... with an amplifying slowly eastward progressing upper ridge ATTM located over SW Europe. Vort max at the periphery of extensive quasistationary upper low over the north Atlantic ... will cross S and central Scandinavia during the forecast period. At low levels ... main baroclinic zone is progged to stretch from N Scandinavia across the Channel into the Biscay at the begininng of the FCST period ... and will make eastward progress only over Scandinavia ahead of the upper trough.

DISCUSSION

...Central Mediterranean ...
Upper low over the S-central Mediterranean Sea will likely be focus for primarily diurnally driven TSTMS ... soundings indicate that instability is quite weak over this region with CAPEs hardly above 500 J/kg. As upper low is in the process of weakening ... vertical shear is also expected to further decrease ... possibly to 10 to 20 knots in the lowest 6 km towards the afternoon. This suggests that organized severe TSTMS are rather unlikely across this region. Given complex orography though ... SRH may locally be sufficient for updraft rotation ... and an isolated severe hail event cannot be excluded ... but allover risk appears to be quite small.

...East-central Europe...
At the periphery of the other closed upper low farther north, covering parts of the Belarus and N Ukraine ... models assume regions of DCVA-related ascent ... which are apt to contribute to TSTM formation in the weakly capped and slightly unstable environment. Large-scale shear will be quite weak. However ... mesoscale wind field associated with the small vort maxima could locally enhance the shear profiles. This suggests that a few marginally severe wind gusts/hail events could occur over N Romania ... Moldavia and S Ukraine ... but allover threat does not warrant a SLGT ATTM.

...S Scandinavia ...
Occluded frontal system ahead of the upper short-wave trough will bring subtropical-Atlantic low-level airmass into the region where strongest UVV's are expected. This airmass has proven to be quite stable owing to very weak lapse rates ... suggesting rather small TSTM threat. Ahead of this feature however ... marginally unstable airmass is present ... and with increasing DCVA and daytime heating ... a few TSTMs may form. Deep shear in excess of 40 knots could promote briefly organized lines of TSTMs which may produce a few marginally severe wind and hail events. Coverage of TSTMS is expected to be too low though for a SLGT risk. If convection does form along the cold front ... coverage of marginally severe wind events may be somewhat greater ... and an upgrade to a SLGT risk may be considered tomorrow.

...Portugal ... W Spain ...
Ahead of weak upper low ... scattered TSTMs are expected to develop within upslope flow regime towards the afternoon and persist into the night. It appears that some Mediterranean moisture will be advected into the region during the night ... but this moisture will likely be mixed out ... yielding LCL heights of about 600 hPa and most of the precip will likely evaporate before reaching the ground. Very deep/dry subcloud layer suggests that TSTMS may be accompanied by very gusty winds ... which may briefly exceed severe levels.

#