CONVECTIVE FORECAST
VALID Sat 04 Jun 06:00 - Sun 05 Jun 06:00 2005 (UTC)
ISSUED: 03 Jun 22:29 (UTC)
FORECASTER: DAHL

There is a slight risk of severe thunderstorms forecast across W Poland and the S Baltic States.

SYNOPSIS

Vigorous vort max approaching W-central Europe on Friday evening ... is progged to move into the WRN Baltic Sea/E Sweden during the period. Ahead of this feature ... SFC low is developing over NW Germany on Friday evening ... deepening and tracking to the SE Norwegian/W Swedish border until Sunday 06Z per MM5 ... which seems to handle current position/development of this feature best based on subjective 18Z analysis. Trailing cold front should curve across NERN Germany ... SRN Germany ... SRN France into N Spain ... with the northern portions of the front making fast eastward progress ... reaching the E Baltic States ... the central Belarus and the W Ukraine towards the end of the FCST period. Another vort max pivoting around the mean central European trough is expected to overspread the Alpine regions late in the period ... promoting weak cyclogenesis along the main frontal boundary over the NRN Balkan States ... weak lee-cyclogenesis expected over the Ligurian Sea/N Italy late in the period.

DISCUSSION

...SLGT area...
Main convective activity will likely be tied to the pre-frontal windshift again which should stretch from central Poland across the central Baltic Sea into S Sweden by Saturday 12Z. It seems that SFC dewpoints will be on the order of 12 to 14°C ... though increasingly dry air should be advected into the prefrontal environment with SELY trajectories.

Current thinking is that CAPE will be quite weak ... but sufficient for deep convection. Depending on extent of convective debris ... deep boundary layer mixing may occur ... resulting in rather high LCLs. 850 hPa flow of 10 to 15 m/s and 500 hPa flow of 20 m/s should result in sufficient shear for a few severe TSTM events ... primary threat being damaging winds with bowing line segments. Isolated supercells may also occur ... posing threat for large hail. Though an isolated/brief tornado cannot be ruled out ... modest low-level moisture and rather high LCL/LFC heights should limit tornado threat.

...S Baltic Sea ... W Poland ... Chech Republic...
TSTMs should also re-develop along the cold front ... where shear should be more unidirectional ... and CAPE somewhat weaker and possibly slightly elevated as downstream convection may produce extensive cold pool W of the prefrontal convergence zone. Severe threat should thus be limited ... though an isolated marginally severe hail/wind event cannot be excluded.

...Benelux ... NW Germany ... N British Isles...
In the wake of the cold front ... moderately deep polar air will overspread central Europe. Models agree that top of mixed layer will be on the order of 500 hPa ... sufficient for scattered rain showers and possibly an isolated CG or two ... but insufficient for a large TSTM area. Convection should be deepest ahead of vort maxima affecting Benelux and N Germany as well as the N British isles in the early evening hours ... where TSTM coverage may be maximized. 0-1 km shear over Benelux and N Germany should exceed 10 m/s ... and if long-lived updrafts manage to form ... an isolated severe TSTM event including a brief tornado cannot be ruled out. Allover threat is too low for a categorical risk ATTM.

...N Italy ... NRN Balkans...
Moisture and lapse rates should be quite meager ... and profiles will likely not exhibit much CAPE. Strengthening wind fields ahead of approaching vort max may support a few hail/wind events approaching severe levels ... but severe threat looks to be rather low ATTM. Low-level shear is expected to increase late in the night over the NRN Balkans as frontal wave develops ... but meager instability/bad timing of upper vort max precluding categorical risk ATTM.

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