Storm Forecast
Valid: Mon 11 May 2020 06:00 to Tue 12 May 2020 06:00 UTC
Issued: Mon 11 May 2020 03:17
Forecaster: VAN DER VELDE

A level 1 was issued for N Italy and NW Balkan mainly for large hail and tornado chances.
A level 1 was issued for E Lithuania and N Belarus mainly for tornado chances.

SYNOPSIS / DISCUSSION

Warm air over central Europe brought in by an active low over France is being replaced by an invasion of much colder air from the Norwegian Sea. The unusually tight cold front drops temperature by 10 degrees across 100-200 km and lies at the start of the forecast period in northern France and northwest Poland. As it advances faster into central/eastern Europe, gradients tighten by warm air advecting northward over SE Poland and Ukraine. The front stagnates halfway into France and the Alps, and pushes through Hungary at the surface. A cold front that belonged to the French low passes eastward across Italy, but with convection only during the early morning.

The warm zone just ahead of the cold front accumulates enough moisture to allow deep convection, although CAPE remains quite marginal, a few hundred J/kg at most, in a narrow zone. Deep layer shear vectors run parallel to the cold front and barely overlap the CAPE zone with 15 m/s 0-6 km shear, mainly from SW Poland to Lithuania. Along with poor lapse rates and low LCL, chances for large hail seem not that good. Tornado chances appear best over eastern Lithuania/N Belarus where the most solid CAPE signal overlaps some >10 m/s LLS.
Strong 0-1 km shear develops during the evening across central Europe, but south of the unstable air. Over Italy and NW Balkan some spots with decent DLS and a LLS over 10-15 m/s are found, which can support large hail and tornado chances.