Storm Forecast
Valid: Thu 07 Aug 2014 06:00 to Fri 08 Aug 2014 06:00 UTC
Issued: Wed 06 Aug 2014 23:00
Forecaster: GATZEN

A level 1 was issued for the Balkan Peninsula mainly for excessive precipitation.

A level 1 was issued for western Turkey mainly for excessive precipitation.

A level 1 was issued for northern Sweden mainly for excessive precipitation.

A level 1 was issued for north-eastern Spain mainly for large hail.

SYNOPSIS

Due to an intense Atlantic polar trough, the westerly jet accelerates and short-wave troughs move across western into central Europe, where they run into a blocking pattern that is still dominated by high geopotential across north-eastern Europe and troughs over eastern and south-eastern Europe. The main low-level convergence zone will remain from northern Sweden across the Baltic States into Poland and the northern Balkans, where rich boundary-layer moisture and diurnally driven CAPE will allow for thunderstorms. A following short-wave trough and low-level frontal boundary will move across Germany. Across the south-eastern parts of Europe, another short-wave trough will increase the potential of storms over Turkey.

DISCUSSION

Western Turkey

A well-developed trough axis will move across western into central Turkey on Thursday. Diurnal heating will allow for steep lapse rates that overlap with rich Mediterranean moisture that advects upslope with westerly low-level winds. CAPE may be as high as 1000 J/kg as indicated by latest GFS model run. Therefore, thunderstorms are forecast that form in the morning hours and will likely go on until the evening, when convection will rapidly decay in the wake of the trough axis and due to low-level cooling. Storms will be rather unorganized due to the weak flow near the trough centre, and main threat will be large hail and locally excessive precipitation due to slow-moving pulse storms or thunderstorm clusters.

Balkans to eastern Poland

Along a broad convergence zone from Greece to eastern Poland, numerous thunderstorms are expected due to rather cool mid-level air, diurnal heating, and rich low-level moisture. Slow storm motion and clustering of storms will increase the potential of excessive precipitation, especially over mountains with upslope flow. Additionally, locally large hail and severe wind gusts are not ruled out.

Northern Sweden

A convergence zone will be quasi-stationary across central and northern Sweden. On Thursday, a short-wave trough will move across northern Sweden and widespread thunderstorms are expected to build clusters. These will be capable of producing excessive precipitation due to slow storm movement and backward building. Additionally, local hail is not ruled out.

Eastern and southern Germany into Alps

A weak short-wave trough and low-level convergence zone slowly moves eastward over Germany. Rather widespread thunderstorms may evolve with a threat of excessive precipitation due to the slow storm movement and storm clusters. Locally large hail and severe wind gusts are not ruled out with the stronger storms, especially over southern Germany and the Alps where vertical wind shear is slightly stronger.

North-eastern Spain

Upslope flow of moist Mediterranean air, overlapping with diurnally driven steep lapse rates will likely allow for some storms in the afternoon hours. With westerly mid-level flow, vertical wind shear may be favourable for storm organization, and supercells are not ruled out with the main threat of producing large hail.