CONVECTIVE FORECAST
VALID 13Z THU 17/07 - 06Z FRI 18/07 2003
ISSUED: 17/07 13:05Z
FORECASTER: DAHL

There is a slight risk of severe thunderstorms forecast across N Italy into NW Balkan.

General thunderstorms are forecast across central and northern portions of Europe.

SYNOPSIS

Upper high is persisting over northern Europe ... as is an intense upper low over the E Atlantic. Short-wave trough ATTM entering W Germany and Switzerland ... will progress east and stretch from NE Germany into Romania Friday morning. Weakening plume of rather high 850 hPa theta-e is present ahead of this trough ... extending from the UK across the North Sea across E Germany into the Balkan states ... as well as into Scandinavia.

DISCUSSION

...North Italy ... NW Balkan....
Soundings across N Italy indicate ample low-level moisture ... and steep mid-level lapse rates ... resulting in afternoon MLCAPEs on the order of 1500 to 2000 J/kg. Deep-layer shear is on the order of 50 knots ... and with ELY SFC winds across NE Italy ... storms will have fair chances of becoming supercellular ... if the cap can be broken. Vort max is grazing N Italy during the next few hours ... and latest IR image shows that first Cb's have initiated.

Threat exists for large hail ... damaging wind gusts and especially towards the evening a few tornadoes given the ELY SFC flow and low dewpoint depressions in the BL. Farther west and east ... low-level veering appears to be weaker ... generally limiting the supercell threat. However ... regions of high SRH are suspected to be present locally over the complex terrain ... and given favorable deep shear along with ample instability ... threat of severe TSTMS also exists W and E of the Po valley.

...Chech Republic ... Germany ... Poland...
Uncertainties exist with respect to the thermodynamic setup. Indications are that high dewpoints across NE Germany are very shallow ... and despite unimpeded insolation ... afternoon MLCAPEs should only be on the order of 1000 J/kg. Rather low dewpoints across Poland ... Chech Republic ... N Austria and adjacent states towards the east should keep MLCAPE's within the 800 to maybe 1500 J/kg range. General problem with this setup appears to be very weak wind shear.

Numerous TSTMS are currently developing primarily in response to DCVA ahead of the trough across Germany and the Chech Republic. TSTMS will likely become more widespread during the afternoon ... but individual cells are expected to be quite short lived. Interactions with gustfronts of neighboring storms may briefly support rotating updrafts ... which would pose the threat of large hail ... damaging winds and even a brief tornado. However ... chances of this to happen are quite low ... and a categorical risk is not necessary. Majority of the storms should be capable though of producing gusty winds and small hail.

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