CONVECTIVE FORECAST
VALID 06Z THU 29/07 - 06Z FRI 30/07 2004
ISSUED: 28/07 22:01Z
FORECASTER: DAHL

General thunderstorms are forecast across E Europe ... Spain and the W Mediterranean.

SYNOPSIS

Fairly intense upper cut-off low has settled over the Balkans ... and a broad meandering upper frontal zone is covering the N Atlantic and portions of NW Europe ... with the imbedded trough currently over the Baltic States progged to close off into an upper cut-off low as well during the period ... becoming anchored over the Baltic States/S Finland. Upstream short-wave trough is expected to cross the British Isles and parts of W Europe on Thursday. At low levels ... weakly to moderately unstable air mass is present over E Europe east of the two upper lows.

DISCUSSION

...E Europe ... W Russia...
Wednesday's soundings revealed maximum MLCAPEs of about 1500 J/kg over E Europe and W Russia ... which is reasonably well simulated by NMM. GFS is offering CAPEs in excess of 2500 J/kg ... but currently there are no indications that this solution is realistic.

So ... expecting mean CAPEs on the order of 500 to 1000 J/kg over E Europe on Thursday ... possibly exceeding 1500 J/kg locally. However ... shear within this air mass is expected to remain fairly weak as the mid level bands of 15 to 20 m/s wind speeds are merely grazing the unstable air mass.

Nonetheless ... the strong thermodynamic profiles may support an isolated severe TSTM event or two ... mainly tied to local augmentations of low-level SRH by outflow boundaries ... orography etc. But allover severe threat should be quite limited ... will place a SEE TEXT area where CAPEs are expected to be highest ... including those regions where wind fields are slightly enhanced in the vicinity of the upper lows.

...Spain ... W Mediterranean...
Scattered ... mainly dirurnally driven high-based TSTMS are expected over Spain again. Deep shear in the 10 to 15 m/s range plus deep/dry CBLs will likely support an isolated severe-wind event or two and possibly some hail. Coverage of severe should be too low for a SLGT. Chances for convective development also exists downstream over the W Mediterranean Isles as weak trough overspreads the area.

...British Isles ... France...
Uncertainty exists with respect to the thermodynamic properties of the air mass ahead of the Atlantic upper trough. Climatologically this air mass has quite weak lapse rates and does not allow for positive CAPE values ... and have little trust in the GFS which does produce weak CAPE. Current thinking is that precip will be mainly stratiform with weak embedded convective cells ... capable of producing a few lightning strikes. Activity should be too isolated for a TSTM outlook.

Weak CAPE is supposed to develop over southern France towards Thursday afternoon ... but there are no indications that substantial destabilization will occur.

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