CONVECTIVE FORECAST
VALID 06Z SAT 18/12 - 06Z SUN 19/12 2004
ISSUED: 17/12 20:34Z
FORECASTER: DAHL
General thunderstorms are forecast across the North Sea and coastal regions of Holland and Germany as well as over Denmark.
General thunderstorms are forecast across the central Mediterranean regions.
SYNOPSIS
Intense cyclone analyzed over SW Germany on Friday evening ... is expected to weaken by Saturday morning while moving into W Poland/Chech Republic. Accompanying upper trough is digging southeastwards ... promoting fairly intense cyclogenesis in the lee of the Alps over the Adriatic Sea. This low is progged to move into the Aegean Sea towards early Sunday morning.
DISCUSSION
...central Mediterranean...
Based on Friday's 12Z ascent it looks that instability will remain fairly weak within 850 hPa theta-e plume over the central Mediterranean. Though deep-layer shear does not appear to increase too much ... 20+ m/s 850 hPa flow will be in place over much of the central and N Mediterranean. However ... fairly strong SFC flow is limiting shear magnitude so that kinematic parameters should be fairly weak. Also ... lapse rates in the lowest kilometers should remain rather meager ... altogether yielding not particularly impressive setup. But ... shear may be sufficient for an isolated mesocyclone or two ... which may produce a tornado given low LCL heights. Also ... strong convective wind gusts are likely with any TSTM.
...North Sea ... N Holland ... N Germany...
Low-topped convection with isolated TSTMS may develop over the North Sea and spread into N Germany and Holland in upper thermal trough region. Though shear magnitude is expected to remain relatively weak ... gradient flow should be fairly strong ... with showers and TSTMS likely augmenting the SFC winds locally. Given rather weak shear magnitude tornado threat seems to be limited ... though especially in the coastal regions 0-1 km shear could be marginally sufficient for a brief tornado. Allover severe convective weather threat should be rather low though.
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