Storm Forecast
Valid: Thu 12 Jul 2007 06:00 to Fri 13 Jul 2007 06:00 UTC
Issued: Wed 11 Jul 2007 20:41
Forecaster: GATZEN

SYNOPSIS

European trough axis turns northward around the center of low geopotential over southern Scandinavia. The southern edge of the trough moves across the Black Sea region and Ukraine during the period. While cold air advects into Bulgaria and Romania, warm air mass characterized by steep lapse rates will remain over eastern Ukraine and southwest Russia. Over western, and central Europe, upper ridge begins to amplify due to strong warm air advection ahead of propagating Atlantic low.

DISCUSSION

Central Ukraine, eastern Belarus, western Russia

Again, focus of expected severe convection is the frontal boundary over east Europe. On Thursday, surface low pressure center is expected over central Ukraine and will slowly propagate northward into western Russia during the period. While cold air advection and stabilization is forecast in the wake of the low, warm air mass remains in the range and northeast of the low pressure center. Warm air mass is quite dry as indicated by latest soundings, but latest model output shows a narrow moisture axis ahead of the cold front that was already observed on Wednesday. During the period, a strong upper jet streak is forecast to spread across western Black Sea, pointing towards the central Ukraine. DCVA can be expected underneath the cyclonic exit region over central Ukraine, where initiation of thunderstorms seems to be most likely. Convection may become mesocyclones given strong southerly mid-level winds and easterly surface winds, creating strong DLS. Supercells that form will be capable of producing large hail and severe wind gusts, given quite steep lapse rates. A limiting factor will be the small region with substantial moisture, and thunderstorms will likely weaken when they encounter dry low-level air mass present east of the convergence. West of the convergence line, low-level cool air mass will also limit severe potential. Best chances seem to exist near the low-pressure center, where boundary-layer moisture is forecast to be highest.

Finland

Strong southerly jet will enter the region during the period. Strong DCVA is expected underneath the cyclonic flank of this jet over most of Finland. At lower levels, warm air mass present over eastern Finland will spread into central, and northern Finland ahead of the vort-max. Associated cold font will propagate northward into southern Finland during the morning hours, reaching northern Finland late in the period. This air mass is forecast to be slightly unstable due to cooling mid levels and some boundary-layer moisture. Thunderstorms are expected along the cold front and will likely merge into a convective line given linear forcing ahead of the vort-max and dry layers above the boundary layer, leading to cold pool formation. Moderate to strong DLS and expected organization of the system may be favorable for a few severe wind gusts along the cold front. Overall threat seems to be low at this time, but an update may be needed when a well-developed convective line will develop indeed. South of the cold front, rapidly stabilization is forecast by latest model guidance, and chance for severe convection is rather low.