CONVECTIVE FORECAST
VALID 06Z SAT 20/11 - 06Z SUN 21/11 2004
ISSUED: 19/11 21:29Z
FORECASTER: DAHL

General thunderstorms are forecast across E and SE Europe.

General thunderstorms are forecast across central Europe.

SYNOPSIS

Quite stationary high-amplitude upper flow pattern has established over Europe ... with fairly intense and extensive upper long-wave trough covering northern ... central ... southern and eastern Europe. Imbedded vort max ... expected over the W Ukraine early in the period ... is sustaining intense SFC low which is progged to move northwards roughly along the European-Russian border. In its wake ... deep polar air mass is advected into central ... southern and eastern Europe. Upper ridge with associated SFC high is FCST to persist over SW Europe.

DISCUSSION

...E Ukraine ... E Belarus...
Main challange this period will be possible convection along the cold front of E European SFC low. Origin of TSTMS along the cold front on Friday is somewhat uncertain ... lack of instability in the pre-frontal soundings might hint at forced nature of the convection ... or soundings may not be representative of the immediate pre-frontal environment.

GFS 12Z does not suggest any CAPE in the warm-sector air mass ... in contrast to NMM which simulates patches of weak CAPE ahead of the front. Current data do not allow falsification of either scenario ... complicating the forecast for Saturday.

Chance exists that line of shallow convection will be present along portions of the cold front ... especially near the low center where forcing for upward motion should be strongest. This convection would be capable of augmenting already intense large-scale SFC flow. Severe threat is too uncertain for a SLGT ATTM.

...Aegean Regions...
Thermodynamic profiles should improve somewhat farther S ... and weak CAPE may exist over the central Mediterranean. 25+ m/s 500 hPa flow and about 15 m/s 850 hPa flow should provide sufficient shear for a few rotating updrafts ... capable of producing large hail ... severe wind gusts and a tornado or two. Allover setup appears to be rather marginal ... and will thus not go with a SLGT ATTM ... though an upgrade may be necessary on Saturday.

...central Europe...
Another focus for scattered low-topped TSTMS will exist in the deeply mixed polar air over central Europe. MM5 advertises 500 hPa flow on the order of 20 m/s ... yielding quite marginal deep shear given minimal CAPE ... shallow nature of convection and lack of strong mesoscale forcing for ascent. Expect an isolated wind/hail event approaching severe levels ... but allover severe threat looks to be rather low.

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