Mesoscale Discussion
Valid: Fri 24 Jul 2020 16:00 to Fri 24 Jul 2020 20:00 UTC
Issued: Fri 24 Jul 2020 16:08
Forecaster: PISTOTNIK

... Bosnia-Herzegovina, Croatia, SW Hungary ...

Latest satellite imagery shows a large storm cluster over the N parts of Croatia and exploding storms over Bosnia-Herzegovina, which probably initiated along a dryline downstream of the Dinaric Mountains. These storms tap into very warm and moist air along their ENE-ward tracks with 2m temperatures in the upper 20ies and 2m dewpoints between 17 and 20C. As the 12 UTC soundings from Zagreb, Zadar, Belgrade and Szeged indicate, this airmass features CAPE around 1000 J/kg under increasing 0-6 km shear up to 20 m/s as the mid-level trough approaches.
It appears likely that the storms will merge and continue to grow into a very large cluster, which could even meet the criteria of a Mesoscale Convective Complex (MCC) in the course of the evening. The risk of severe wind gusts at the leading edge and excessive rain with flooding increases if this development materializes. In addition, embedded discrete updrafts can be supercellular and can still produce large to isolated very large hail, especially towards the south.
These risks will probably persist after 20 UTC to the east of the highlighted area, following the expected storm track(s).

... NW to central Italy, Corsica ...

Several large and severe storm clusters have propagated as far southeast as the Tuscany and Marche regions in north-central Italy. These storms are now encountering a stronger cap over the Adriatic Sea and outrunning the areas of synoptic and/or orographic lift, hence they are expected to weaken.
Satellite and station data indicate pronounced outflow boundaries running southward across the Ligurian Sea, central Italy and the central Adriatic Sea. 12 UTC soundings from Cuneo and Pratica di Mare indicate that CAPE up to 2500 J/kg is available in this airmass, though capping is considerable and will further increase as synoptic subsidence sets in in the wake of the mid-level trough. The arc-shaped drawn area highlights the belt which should still be monitored for secondary convective initiation for a couple of hours. If isolated to scattered storms can at least temporarily form, they pose a risk of large hail and severe downbursts due to high CAPE under at least moderate vertical wind shear.