Storm Forecast

Storm Forecast
Valid: Mon 07 Jul 2008 06:00 to Tue 08 Jul 2008 06:00 UTC
Issued: Sun 06 Jul 2008 20:17


On Monday morning, a strong southwesterly mid-level flow affects western parts of Europe. This flow on the southeastern flank of low geopotential heights over the British Isles contains two jet streaks. A jet streak is located over the western Mediterranean Sea and stretches from eastern Spain to Corsica and gradually strengthens as its moves eastward. A shortwave trough, initially over the Bay of Biscay moves eastward during the day, and crosses the Alps during the second half of the afternoon and early evening. A frontal zone is found from SE Spain via northern Italy to east-central Hungary. It forms the northern boundary of warm and moist air.

Po-Valley, northern Adriatic Sea Region, northern Dinaric Alps...

Rather unstable conditions with near 1500 J/kg MLCAPE are expected to develop across the northern half of Italy as dew points rise to near 18-21 degrees C and 16-18 C further eastward into Slovenia, Hungary and Croatia. Convective inhibition (CIN) increases to the south where the chance of convective initiation diminishes accordingly. During the morning hours, some precipitating convection will likely be ongoing across the Alps. A combination of diurnal heating and the approach of the shortwave trough from the west will likely lead to convective initiation across the Po Valley, NE Italy and Slovenia during the early afternoon. Later, storms will probably develop across parts of Croatia and western Hungary and possibly further south in Italy as well.

Deep-layer (0-6 km) bulk shear is expected to increase to around 30 m/s as the jet streak over the western Mediterranean approaches from the west. As this happens and considerable storm-relative helicity develops (near 200 m2/s2) rapid storm organization is expected. A number of powerful supercells are expected that should be able to produce large, possibly very large, hail and damaging gusts. Additionally, a few tornadoes may occur, that may be strong (F2 ). Especially during the evening, low-level shear is forecast to become stronger and supportive of low-level rotation, which enhances the tornado threat. Naturally, a threat of flash flooding will also be present.

E Austria, Hungary, Slovakia...

Primarily during the late afternoon and evening hours, convection is forecast to develop across these areas. Deep-layer shear of near 20 m/s and MLCAPE of 500-1000 J/kg should suffice for the development of supercells, that gradually cluster into one or two linear systems moving eastward. Most likely severe weather types are large hail and severe gusts. Low-level shear of 10-15 m/s however, suggests that one or two tornadoes will be possible too. A flash flooding threat will exist as well. The convection should become increasingly elevated during the late evening and night and the severe weather threat should diminish.

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