Storm Forecast
Valid: Wed 27 Jun 2007 06:00 to Thu 28 Jun 2007 06:00 UTC
Issued: Wed 27 Jun 2007 06:46
Forecaster: GATZEN

SYNOPSIS

Trough centered over southern Scandinavia/North Sea, and cool air mass has spread across most of Europe W of a cold front from central Italy to central Balkans, and central Ukraine/western Russia. Hot African air mass is expected to reach from Greece to Bulgaria, eastern Romania, and western Black Sea today. In the mid-troposphere, a jet stream is present ahead of the European trough from western Mediterranean to central Balkans, Romania, and central Ukraine. Several embedded short-wave troughs will also influence western Russia, and eastern Scandinavia. Another jet streak is expected to cross Ireland at the western flank of the trough.

DISCUSSION

Central Romania into central/eastern Ukraine

A well-developed frontal boundary is present at the northwestern flank of the hot African air mass. This air mass is characterized by well-mixed low, and mid levels up to the 500 hPa level. This air mass advects northward in the range of approaching strong upper level jet. Thunderstorms have formed during the night hours over northern Black Sea in the WAA regime. More thunderstorms are present over central Romania in the range of the cold front that is expected to remain quasi-stationary today as low pressure center develops over western Black Sea. Thunderstorms are forecast to spread north-eastward during the morning hours as upper level QG forcing will also move into southern/central Ukraine in the range of upper-level short-wave trough. In the wake of the trough, mid-level winds are expected to decrease, but latest GFS indicates at least 20 m/s DLS in the range of the frontal boundary. Expect that thunderstorms will go on moving to the north-east into southern, central, and eastern Ukraine during the period. Given strong vertical wind shear and favorable veering profiles, supercells are expected. Limiting factor is rather shallow moisture over most places and strong CIN/capping inversion. However, along the frontal boundary, low-level convergence/moisture pooling as well as QG forcing in the range of the trough will be sufficient for persisting deep convection. Latest surface obs indicate low-level dewpoints up to 21°C over western Black Sea region, and expect that low-level moisture may still improve during the morning hours below strong inversion. Thunderstorms that form will likely have a high LFC around 3000-4000 m above ground level, and chance for tornadoes seems to be low given relatively weak LLS, LCL heights, and low-level veering. Large hail as well as severe wind gusts seem to be rather likely given well-mixed/dry air mass below the cloud-base, and reports of very large hail are not excluded. Thunderstorms may merge into a MCS over central/northern Ukraine later in the period.

Southeastern Scandinavia region

Intense upper vort-max moves northward over northern Baltic States, northwestern Russia, and southeastern Scandinavia today. In the range of the trough axis, steep mid-level lapse rates are forecast, while low-level air mass will likely remain relatively moist as indicated by latest surface observations. Although stratiform rain will be likely during the period in the range of the trough, slight chance exists that more convective mode becomes dominant during the day. When sunshine warms up low levels during the day, chance for instability and deep convection rapidly increases in the range of the trough axis. Given low LCL heights as well as relatively strong LLS and veering, chance for tornadoes is forecast.

Adriatic, Balkans

Strong upper jet streak will affect this region during the period. Latest soundings indiacte steep low-level lapse rates and some low-level moisture south of the Alps. Expect that a few thunderstorms will form in the range of a short-wave trough moving eastwards in the afternoon/evening hours across Aegean, and Balkans. Given strong vertical wind shear, multicells and maybe supercells are forecast, with a slight chance for large hail or severe wind gusts. Threat seems to be quite low, though, as low-level convergence will be relatively weak along the cold front.