CONVECTIVE FORECAST
VALID 06Z SAT 31/07 - 06Z SUN 01/08 2004
ISSUED: 31/07 00:10Z
FORECASTER: DAHL

General thunderstorms are forecast across SW ... S ... central ... SE and E Europe.

SYNOPSIS

Upper cut-off low present over the Balkans ... is exhibiting several vort maxima at its periphery ... and is expected to remain in place throughout the period. Upper low over the Baltic States is progged to merge with short-wave troughs/small upper cut-off lows ejecting from large-scale upper low centered over the central N Atlantic. SW European upper ridge will move into the W Mediterranean by Sunday 06Z ... with quiescent conditions persisting at low levels ... SLP charts featuring only quite a weak but extensive SFC low over Europe. Allover weak kinematic and thermodynamic setup across Europe will limit severe TSTM threat on Saturday.

DISCUSSION

...Belarus ... Ukraine...
Strongest thermodynamic profiles will likely be present over E Europe again ... with mixed-layer CAPEs in excess of 1500 J/kg. Given weak deep-layer shear ... storms will likely struggle to organize ... and severe TSTM threat should be rather limited. However ... inhomogeneities in the BL wind field ... e.g. caused by outflow boundaries and orographic features ... may create locally enhanced low-level shear ... and slight chances for a briefly rotating updraft or two exists ... capable of producing large hail and damaging winds. Allover severe threat is too low for a SLGT though.

...Central Europe...
Best large-scale signals in the UVM and deep-layer shear fields are present over Benelux and N Germany ahead of weak disturbances which will likely support scattered TSTMS in weakly unstable and weakly capped environment. 0-6 km shear magnitudes are expected to be in the 15 to 20 m/s range. Expect weakly organized multicellular storms to be the dominant convective mode ... capable of producing small hail and strong wind gusts. However ... despite expected weak shear in the inflow layer ... an isolated mesocyclone or two may form resultant from interaction with small-scale boundary-layer features that may alter the low-level wind field ... posing primarily a threat for large hail and severe wind gusts. However ... chance for mesocyclones and allover TSTM coverage should be too slim for a SLGT. Though weak CAPE is also expected to develop farther SW over France ... TSTM threat will be substantially lower given weak mid-level ridging.

...southern Italy...
Weak vort max grazing Italy may support a few TSTMS towards late afternoon. MM5 and GFS hint at enhanced low-level shear over S Italy late in the day ... and stroms in this kinematic environment will have some potential for developing a rotating updraft with a concomitant threat for large hail. Threat appears to be too conditional for a SLGT though.

...Portugal ... W Spain...
Scattered high-based TSTMS are expected over Portugal and Spain late in the afternoon as weak vort maxima overspread the area. Besides strong evaporative downdraft cooling owing to the dry environment ... 10 to 15 m/s 500 hPa flow may additionally enhance the vigor of outflow winds ... and a few severe wind gusts may occur. Severe TSTM events will likely be too isolated for a SLGT. Late in the period ... TSTMS may spread across the Gulf of Biscay and maybe into France by early Sunday morning.

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