Storm Forecast
Valid: Thu 09 Aug 2007 06:00 to Fri 10 Aug 2007 06:00 UTC
Issued: Thu 09 Aug 2007 08:04
Forecaster: GATZEN

SYNOPSIS

Intense cut-off low has moved to northern Italy. It will remain over northern Mediterranean area where cyclogenesis is expected as very strong westerly jet spreads is directed towards the Adriatic. Warm and moist air mass is advected around the low into central Europe, and southern Scandinavia. Cool and rather dry air mass remains in the wake of the cut-off low from western Europe to western Mediterranean as well as in the range of eastern European high over north-eastern Europe.

DISCUSSION

Adriatic and western Balkans

A frontal boundary is expected to be present over Adriatic today moving eastwards into western Balkans. East of this frontal boundary, latest soundings indicate relatively steep lapse rates and locally rich boundary-layer moisture, and latest GFS CAPE calculation seems to be reasonable showing instability over Adriatic and western Balkans today, although amount of CAPE seems to be too high. Today, nose of approaching very strong westerly jet points towards the central Adriatic, where QG forcing is expected in the diffluent delta flow. Thunderstorms will likely go on today. Given weak low-level winds and moderate to strong south-westerly mid-level winds, DLS may be strong locally. Intense multicells are forecast to develop, capable of producing isolated large hail and severe wind gusts. Locally favorable veering profiles may also assist mesocyclones with the chance of an isolated tornado, but given rather weak LLS, potential seems to be quite low. Thunderstorms will likely go on during the night given persisting QG forcing at the cyclonic flank of the jet streak.

Northern Germany

At the northern flank of the cut-off, warm air mass spreads westward over northern Germany. This air mass is characterized by rich low-level moisture as indicated by latest observations. Soundings also indicate rather steep low-level lapse rates over north-eastern Germany. Today, advection of unstable air mass into northern Germany seems to be likely, and positive CAPE is expected. Thunderstorms will likely develop over a widespread region and will likely produce local flash flooding. Best chance for severe convection exist over the eastern portions, where strongest instability and lapse rates are present, and strong updrafts may produce isolated large hail. At the south-western low-level frontal boundary, vertical wind shear is relatively strong with most favorable veering at low levels, resulting in 100 J/kg 0-1 km SRH values, and isolated storms may be capable of producing tornadoes. Best potential seems to exist over central Germany, where strong low-level easterly winds are expected by latest GFS model run (up to 15 m/s 850 hPa winds).

Balkans and Black Sea into Poland, and Scandinavia

Underneath the broad low geopotential, instability and weak CIN will be present, and widespread thunderstorms are expected. Given weak vertical wind shear, chance of organized thunderstorms is weak, but isolated severe weather is not completely ruled out. Best potential for severe convection exists near the cut-off low, where stronger DLS and locally favorable veering profiles are forecast especially north of a weak surface low over eastern Austria, Hungary, and Slovakia/Czech Rep.