Storm Forecast
Valid: Tue 18 Aug 2020 06:00 to Wed 19 Aug 2020 06:00 UTC
Issued: Mon 17 Aug 2020 21:07
Forecaster: DAFIS

A level 1 was issued for a large part of Western, Central, and Eastern Europe mainly for excessive precipitation and large hail.

A level 2 was issued for parts of Italy, S Austria, Slovenia, Croatia, Hungary, Bosnia and Herzegovina,W Romania, Montenegro, Serbia and N Albania for large hail, severe wind gusts and excessive precipitation.

SYNOPSIS

The main synoptic barometric systems on Tue 18/08 will be a strongly negatively tilted trough over Northwestern Europe and a ridge with an axis extending from the Middle East towards the North Sea. Several short-wave troughs can be found in the forecast maps with vorticity maxima, and some of them are associated with dissipating cut-off lows. The most ominous PVA will cross North Italy and the Adriatic Sea and will provide synoptic lift to very unstable air masses inside the Level-2 threat area.
A large level-1 covers the largest part of the continent since several diurnally-driven storms are expected, most of them slow-moving and able to produce excessive rainfall and large hail. In Eastern France and SW Germany some overlap of CAPE and DLS increases the risk of organized convection, but not all the models agree on the development of significant CAPE and CI. A few landspouts in Central Europe are also expected where LCLs are below 800m and waterspouts can form in the North Sea.

DISCUSSION

.... Italy, S Austria, Slovenia, Croatia, Hungary, Bosnia and Herzegovina,W Romania, Montenegro, Serbia and N Albania ....

A pool of very moist low-level air masses is found around the Adriatic Sea, as well as in the Balkans. As a short-wave trough is approaching this area before 12z on Tue 18/08, together with maximum diurnal solar heating they will provide lift to these weakly-capped unstable air masses. Moreover, local convergence zones close to the coasts during sea breeze will be an additional lifting mechanism. Despite the ongoing convection in the area on Monday 17/08, NWP models still show steep lapse rates that will locally build more than 1500 J/kg MLCAPE. Kinematics does not look very impressive, with a lack of veering profiles and modest wind shear, but local signals of 150-200 m2/s2 SREH0-3km and more than 15 m/s DLS suggest that a few supercells are possible. The main threats will be excessive precipitation in the Balkans due to the saturated profiles and the strong westerly flow from Adriatic Sea, and large hail mainly in Italy and NW Balkans where NCAPE and CAPESHEAR are maximized. Close to the coasts waterspouts cannot be ruled out, but also in the mainland, a few landspouts may form. Forecast data do not show very favorable environments for significant tornadic events.