Storm Forecast
Valid: Sat 22 Jun 2024 08:00 to Sun 23 Jun 2024 06:00 UTC
Issued: Sat 22 Jun 2024 08:12
Forecaster: PUCIK

A level 3 was issued across E Bosnia, N Serbia, SE Hungary and W Romania mainly for very large hail and damaging wind gusts.

A level 2 was issued in a belt from E Bosnia and E Croatia through Serbia, Hungary, Romania into E Slovakia, W Ukraine and SE Poland mainly for large to very large hail, severe wind gusts and heavy rainfall.

A level 1 was issued for NE Poland and W Belarus mainly for severe wind gusts, large hail and heavy rainfall.

A level 2 was issued across parts of N Italy mainly for large to very large hail, heavy rainfall and severe wind gusts.

A level 1 was issued across N Italy mainly for large hail, heavy rainfall and severe wind gusts.

A level 1 was issued across N Alps and S Germany mainly for heavy rainfall.

A level 1 was issued across Caucasus mainly for large hail and severe wind gusts.

DISCUSSION

... E Croatia, Bosnia, Serbia, Romania, Hungary, Slovakia, Poland, W Ukraine ...

An outbreak of severe storms is likely within Lvl 2, with the most likely swath of damaging severe wind gusts highlighted by Lvl 3.

As of 8 UTC, a large number of elevated storms exists in the wake of the frontal boundary, some of them already posing threats of isolated large hail and severe wind gusts. Satellite imagery reveals clear conditions ahead of the boundary with a potential for an abundant heating. The boundary is now established across E Poland, central Slovakia, E Hungary, curving into far S Austria. Surface observations show that the 2m temperature has risen to around 30 deg C with dewpoints around 20 deg C. Therefore, we expect that the model predictions of high CAPE values, ranging from 2 to 3.5 kJ/kg are well on track. The boundary is forecast to become even more established during the day and will separate slightly cooler, moister airmass with a very well mixed airmass to the east, where dewpoints will likely fall slightly during the day due to the mixing.

Vertical wind shear will be strong enough to allow for well-organised storms. The highest values of deep-layer shear are forecast on the western flank of the boundary with N-ly surface wind component. 0-6 km bulk shear will change from 15 m/s to the E of the boundary to 25 m/s to the W of the boundary.

Expect explosive growth of convective storms, initiated by the frontal boundary and the orography over Bosnia/Serbia/Slovakia/Romania/S Poland. Convective mode will consist of a mix of supercells and linear segments. Given fat CAPE profiles with much of CAPE above -10 deg C isotherm, storms will be capable of 5+ cm hail. The strongest supercells may produce hail with diameter close to 10 cm. The highest threat of destructive hail is over E Croatia, Bosnia, N Serbia, E Hungary, extreme W Romania and extreme SE Slovakia. Severe wind gusts are likely as well. Their threat will be the greatest over Serbia, where high-res models most consistently show a development of linear segments. Once the storms reach the well-mixed airmass E of the frontal boundary, rapid cold pool development is forecast with a threat of wind gusts > 32 m/s. The most likely track of these linear segments (likely including bow echoes) is towards W Romania. Numerous rounds of severe storms are possible, especially across Bosnia, Serbia, E Hungary and Romania.

The threat will decrease from SE Poland towards NE Poland, where less CAPE is forecast. Furthermore, the area of NE Poland is already affected by storms now, rendering airmass recovery very questionable even though it is shown by the models.

West of the highlighted Lvl 2 area the storms will be typically elevated and pose mostly heavy rainfall threat, combined with isolated large hail threat. South and east of the highlighted Lvl 2 area, the coverage of severe storms is more questionable. Here, the main threat will be severe wind gusts in well-mixed boundary layer, combined with large hail.

... N Italy ...

Less shear and CAPE is forecast across the area compared to yesterday. An approach of a pronounced low at mid to upper troposphere will provide substantial synoptic-scale lift over the area and coverage of storms will quickly ramp up, likely culminating in late evening and late night hours, especially over the plains. CAPE-shear overlap will still suffice for well-organised storms capable of large hail, severe wind gusts and heavy rainfall. The highest threat of very large hail is forecast over central-N Italy, in the wake of the Appenines. Piemonte looks to be another hotspot in this regard. Heavy rainfall will likely take over as the main threat in the late evening hours as storms cluster and the shear weakens.

... Caucasus region ...

Expect isolated (very) large hail and severe wind gusts with storms that develop in around 20 m/s of 0-6 km bulk shear.