CONVECTIVE FORECAST
VALID 06Z FRI 24/12 - 06Z SAT 25/12 2004
ISSUED: 23/12 23:52Z
FORECASTER: DAHL
General thunderstorms are forecast across the E Atlantic and W Ireland.
General thunderstorms are forecast across the eastern Mediterranean Sea.
SYNOPSIS
Rapidly amplifying Atlantic upper trough is progged to reach the western portions of Europe early Saturday morning. Falling SFC pressure/developing frontal wave ahead of main vort max associated with the trough will lead to southward expansion of already impressively extensive SFC low pressure system covering the northern half of Europe and much of the N Atlantic on Thursday evening. The frontal wave is expected to deepen late in the day and move into the North Sea by Saturday morning. Otherwise ... weaker downstream wave cyclone is FCST to cross N-central Europe during the day ... and SE-European upper long-wave trough is expected to move off into the E Mediterranean.
DISCUSSION
...eastern Mediterranean...
It looks that low-level CAA will stabilize air mass beneath the W periphery of SE-European upper trough ... and thus limit chances of deep convection there. However ... BOLAM 850 hPa theta-e fields indocate residual warm/moist air mass SW of Turkey ... which may still be sufficient for relatively deep convection during the first few hours of the period when band of reasonably strong DCVA crosses the region. MM5 18Z advertises up to 15 m/s 850 hPa flow ... which could be associated with sufficient shear for briefly rotating updrafts. However ... uncertainty on convective development and deteriorating thermodynamic fields preclude severe TSTM outlook ATTM.
...E Atlantic ... W Ireland...
Fields of enhanced cellular convection will likely develop over the E Atlantic especially during the late evening hours. This activity may affect parts of the British Isles ... but weak thermodynamic setup and marginal shear should limit organized severe TSTM threat.
...N France ... Benelux ... W Germany...
Challange of the day will be the potential evolution of shallow but vigorous convection along the cold front of the frontal wave which is expected to reach Denmark late in the period. NMM shows hints of CAPE ahead of the cold front over NW France ... but confidence is quite low that widespread convection will form. Possible scenario appears to be the evolution of short and narrow lines of strongly forced convection along the cold front in the evening hours ... capable of producing severe wind gusts. Tornadoes have occurred in such situations in the past but will not venture into forecasting them in such an uncertain situation ... Situation should be monitored for possible severe but current thinking is that likelihood for severe TSTMS will be quite small ... and a categorical severe outlook is not necessary ATTM.
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