Storm Forecast
Valid: Thu 13 Jul 2023 06:00 to Fri 14 Jul 2023 06:00 UTC
Issued: Wed 12 Jul 2023 23:17
Forecaster: PUCIK
A level 3 is issued for NE Croatia, S Hungary, N Serbia and central/N Romania mainly for damaging wind gusts and large to very large hail. Over Romania, tornado threat will be present as well.
A level 2 is issued across N Italy and Slovenia mainly for large to very large hail and severe wind gusts.
A level 2 is issued across N Hungary, E Slovakia and Romania mainly for severe wind gusts, excessive precipitation and large hail.
SYNOPSIS
A de-amplified short-wave trough is forecast to move across central Europe. Behind it, a ridge will build ahead of a deepening cyclone over the Atlantic. A frontal system will cross from central Europe to Serbia and Romania and Ukraine, wrapping around the eastern flank of the Alpine range. Along and ahead of the front, very moist airmass will allow for a large area of 1000+ J/kg of MLCAPE.
DISCUSSION
!!! An outbreak of severe to extremely severe storms is expected in a belt from N Italy to Romania and Ukraine !!!
... N Italy ...
The storms will be most intense between 06 and 12 UTC, when a low-level forcing overspreads the area and moistens the profiles. Especially along the Apenines, models predict up to 30 m/s of 0-6 km shear with very high CAPE values. Models agree on initiation in the area. Expect supercells with very large, possibly even giant hail and damaging wind gusts. It's possible that one or more linear segments will form and quickly move across the Adriatic Sea towards Croatia. After 12 UTC, synoptic-scale descent and drying of the mid-troposphere will gradually weaken the storm activity.
... Slovenia, Croatia, N Serbia, S Hungary, Romania ...
The overall progress of the situation will depend on how strong the morning storms are and how far east they move. Nevertheless, models agree on a significant increase in the activity after 12 UTC, with storms spreading from Alps further E and SE. Models simulate a belt of 1500 - 3000 J/kg of MLCAPE overlapping with 25 - 35 m/s of 0-6 km bulk shear and over 20 m/s of 0-3 km shear from N Croatia towards Romania. As the frontal lift aids in scatered to widespread storm initiation, initial supercells with very large hail will cluster into one or more bow-echoes which will rapidly move E or ESE. The parallel orientation of 0-3 km shear vectors to the zone of abundant CAPE give further confidence in storms moving for a long time in zone of very favorable environment for extremely severe wind gusts. Lvl 3 is issued for this belt. The storms may eventually reach Moldova and Ukraine overnight.
Possible limitation, besides the morning convection and associated cloudiness, may be the southward movement of the cold-front, undercutting the storms moving E. Nevertheless, due to the very fast storm motion towards E and warmer airmass, this factor may not limit the storm intensity too much.
Some models simulate curved hodographs with over 10 m/s of 0-1 km shear and 100 m2/s2 SRH in the 0-500m layer over the western flank of the Carpathians over central-N Romania around 18 UTC. In such environment, both supercells and linear segments may be capable of tornadoes. A supercell may even produce a strong tornado in such environment. The degree of low-level shear and convective mode thus needs to be monitored here.
... Slovakia, N Hungary, Ukraine ...
The situation is more uncertain over Slovakia, where models agree on abundant overnight convection. Will maintain a Lvl 2 over E part of Slovakia as models persist CAPE even after the first rounds of storms. The storms will have less shear than further S, but still 15 - 20 m/s of 0-6 km bulk shear will be available. Current scenario is that an existing MCS will either strengthen or a new one will develop, with threats of primarily severe wind gusts or very heavy rainfall. The system will progress towards NE Hungary, Ukraine and N Romania, likely strengthening further as it encounters more abundant CAPE.
