Mesoscale Discussion
Valid: Sun 25 Jun 2017 08:00 to Sun 25 Jun 2017 21:00 UTC
Issued: Sun 25 Jun 2017 07:58
Forecaster: TASZAREK

This long-term mesoscale discussion was issued to highlight elevated risk for a severe thunderstorms capable of producing large to very large hail, damaging wind gusts and heavy rain over NE Italy, S Austria, Slovenia, N Croatia and W Hungary.

Currently passing shortwave trough over Alps provides a good source of lift and maintain storms over Alps. In the following hours a wave will move eastward and trigger new storms over E Alps. NWP scenarios predicts a healthy instability of 1500-2500 J/kg ML CAPE with steep lapse rates, 10-15 m/s DLS and PW exceeding 40mm. 00 UTC sounding observations from N Italy confirm it and indicate > 7 K/km lapse rates with moderate shear (~ 15 m/s) and high relative humidity along vertical profile. Present surface observations over Austria, Slovenia and W Hungary indicate recovering moisture (after the nighttime MCS) with dew points ranging from 13 to 18.

Currently ongoing MCS in N Italy is electrically very active and move slowly to the east producing high amounts of precipitation and downburst-type severe wind gusts. Confirmed hail reports indicate hailstones up to 5-6cm. In the following hours system will move to S Austria and Slovenia posing enhanced risk for severe weather.

Along with increasing vertical wind shear and helicity over SE Austria / N Slovenia / W Hungary (SE surface winds will increase SRH to 100-200 m2/s2), cells developing along converging winds will likely evolve into multicells and supercells capable of producing large hail, severe wind gusts and heavy rain. In the late afternoon along with increasing LL shear, a chances for a tornado event will increase. Given high relative humidity in the low to mid troposphere (PW > 40mm) and a possibility of slowly moving multicell clusters, a risk for severe flash flooding event within Alpine area will be possible.

Given decent instability, increasing MLS shear, persistent lift and already organized MCS, a scenario with QLCS capable of producing severe wind gusts in the corridor from NE Italy to W Hungary also cannot be ruled out. A large MCS should form in the late afternoon hours over Hungary.