Storm Forecast
Valid: Thu 04 Jul 2013 06:00 to Fri 05 Jul 2013 06:00 UTC
Issued: Wed 03 Jul 2013 22:44
Forecaster: GATZEN

SYNOPSIS

A weak trough cuts off across central Europe and diggs southeastward crossing Italy on Thursday. In the wake of the cut-off, the south-west European high ridges into central Europe, so that an approaching trough across the British Isles will move into northern Europe. Mostly weak mid-level flow is expected through-out the period across Europe. Due to westerly to northerly winds, deep mixed layers are only present over Spain and Turkey. However, at least low-level lapse rates are quite steep from the Balkans to Poland, the Baltic States, and western Russia, where potential for a few hail events is forecast.

DISCUSSION

Northern Poland to Baltic States

Along the northern flank of warm air across Poland, warm air advection is forecast across the Baltic Sea. QG forcing is expected given weak differential cyclonic vorticity advection due to an approaching short-wave trough from the west. At low-levels, best moisture can be expected from Estonia to northern Poland. Further south, daytime heating will lead to a rather well-mixed boundary-layer is expected in the noon and afternoon hours.

Current thinking is that thunderstorms will initiate near the Baltic Sea due to the sea-breeze convergence, but also further south along outflow-boundaries and the cold front that approaches from the west. Storms near the Baltic Sea will have the best potential to become intense given the better moisture and some low-level vertical wind shear due to the sea breeze. Storms may become weakly organized there with a weak threat of large hail. Additionally, severe wind gusts are not completely ruled out when storms will evolve further south due to the well-mixed boundary-layer. Overall threat is limited given the weak vertical wind shear, low-level convergence and QG forcing.

Western Balkans

The centre of cold mid-level air will move to the Balkans on Thursday. Given rising geopotential further north, winds will turn to easterly direction, advecting rather well-mixed air masses into the Adriatic region. Northerly low-level winds in the wake of the Dinaric Alps will be associated with better low-level moisture, and latest models indicate at least weak CAPE.

Main question is if the capping inversion will be strong enough to suppress initiation. Current thinking is that a few storms will form over the mountains and spread into the Adriatic Sea. Surface-based convection may become better organized due to the better low-level vertical wind shear. Locally, large hail is not ruled out, but the threat is too marginal for a level 1.