CONVECTIVE FORECAST
VALID Thu 28 Jul 09:00 - Fri 29 Jul 06:00 2005 (UTC)
ISSUED: 28 Jul 09:22 (UTC)
FORECASTER: GATZEN

There is a moderate risk of severe thunderstorms forecast across southern and central France

There is a slight risk of severe thunderstorms forecast across northern Iberian Peninsula, Bay of Biscay, France, Benelux, NW Germany, southern North Sea and Baltic Sea region

SYNOPSIS

Axis of well-developed long-wave trough extends from Scotland to Azores. While this trough starts to cut-off over southwestern British Isles ... the mean vort-max starts to turn counterclockwise over Iberian Peninsula, western Mediterranean, and France during the forecast period. Downstream ... European upper level high ridges northwestward into Germany ... and strong upper level jet stream is pushed westward over central Europe ... extending from Iberian Peninsula to western France, southern North Sea, and southern Baltic Sea region on Thursday, 18 UTC. Several vort-maxima are embedded in the upper flow. At lower levels ... warm airmass has spread across southern and central Europe in the range of high pressure system over eastern Europe ... and advects northward into southern North Sea region east of a surface low over southern British Isles. Associated cold front will cross most of Iberian Peninsula, France, and southern British Isles during the forecast period.

DISCUSSION

...Northern Iberian Peninsula, most of France, southern British Isles, Benelux, northwestern Germany ...
Focus of severe weather will be underneath the strong upper jet extending from Iberian Peninsula to western France, southern North Sea, and southern Baltic Sea region on Thursday, 18 UTC ... where models show DLS of 20+ m/s during the period. Several vort-maxima are embedded in the strong upper flow ... leading to QG forcing in the range of the warm front/warm sector over western/central Europe. Affected airmass is characterized by steep low-level lapse rates over most of France, Benelux, Germany, and Alpine region ... and boundary layer moisture has increased during the last 24 hours ... reaching 12-13 g/kg mixing ratio over a widespread region. Models agree that strong instability will realize during the next hours due to insolation ... and CAPE up to more than 1500 J/kg is forecast. Thunderstorms are expected to form in the range and ahead of the trough axis/vort-max that is forecast to move over Iberian Peninsula and Bay of Biscay/western France during the period ... as well as in the range of the upper jet/associated warm front from northern France/ southern British Isles to northern Poland. Over British Isles, the North Sea, and Baltic Sea ... thunderstorms may be elevated ... and chance for organized convection are relatively low. To the south ... thunderstorms will likely organized due to strong DLS ... and multicells and mesocyclones are forecast ... capable of producing large hail and severe wind gusts. A few tornadoes are not ruled out ... best chances seem to exist along the coastal regions of Germany, over Benelux and northwestern Germany, and over France, where low-level wind shear will be most favorable. If surface based convection will form over southeastern British Isles ... chance for a few tornadoes will be also enhanced. On late Thursday/early Friday ... DLS is expected to increase in the range of the main vort-max over Iberian Peninsula, France, western Alpine region, western Germany, and Benelux. Thunderstorms that form along the cold front and further east along prefrontal convergence expected by latest model output in the range of the DCVA regime will likely be well-organized ... and are expected to merge into a few MCS over northern Spain/ southern and central France ... moving ENE-ward. Rather strong low-level jet is expected at the southern edge of the building system ... and large MCS may evolve over central/southern France. Damaging wind gusts and flash flooding should be the main threat. Supercells are also expected ... capable of producing large hail and severe wind gusts. A few tornadoes are not ruled out given relatively strong LLS. Further south .. quite strong capping inversion should inhibit deep convection over western Mediterranean. Convective activity associated with the upper vort-max is expected to reach western Alpine region/western Germany on Friday morning. Intense precip and severe wind gusts should be the most significant threat.

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