Storm Forecast
Valid: Sat 26 Jul 2025 06:00 to Sun 27 Jul 2025 06:00 UTC
Issued: Fri 25 Jul 2025 22:02
Forecaster: PUCIK
A level 2 was issued across NW Switzerland, S Germany and SW Czechia for heavy rainfall.
A level 1 was issued across Corsica, N Italy, Switzerland, Austria , S Czechia and W Slovakia mainly for heavy rainfall.
A level 2 was issued from central Italy through Croatia, S Slovenia, Bosnia, NW Serbia into Hungary and SE Slovakia mainly for large to very large hail, severe wind gusts and heavy rainfall.
A level 2 was issued for NW Romania and W Ukraine mainly for large to very large hail and severe wind gusts.
A level 1 was issued from south-central Italy through Bosnia, Serbia into Romania mainly for large hail and severe wind gusts.
A level 1 was issued from NW Sweden through Finland into Russia mainly for heavy rainfall and marginally large hail.
A level 1 was issued for N Russia mainly for large hail and heavy rainfall.
A level 1 was issued for the Baltics and Belarus mainly for heavy rainfall.
A level 1 was issued for SW Russia mainly for severe wind gusts.
DISCUSSION
... Switzerland, S Germany, Austria, Czechia ...
Forecast profiles reveal low-centroid CAPE profiles with majority of it in the warm part of the cloud, low LCLs, high RH throughout the troposphere and weak mean wind. Conditions will support very heavy rainfall. High-resolution, convection allowing models indicate a high density of the storms from NW Switzerland to SW Czechia, yielding a higher probability of heavy rainfall events, warranting Lvl 2.
... central-N Italy through Slovenia, Croatia, N Bosnia, NW Serbia, Hungary into S Slovakia ...
This is a complex situation with numerous uncertainties and many differences in the models concerning the timing and coverage of storms. Development of storms has to be monitored closely throughout the day to refine the risk levels over different areas.
Two main players are a deep low in the mid to upper troposphere and a wavy cold-front associated with it. The low will move from the Tyrrhenian Sea towards the Adriatic Sea and Croatia/Bosnia/Kosovo. As the low moves east, so does the cold part of the front in the evening to overnight hours.
Within the warm sector, strong shear with 0-6 km bulk values between 20 and 30 m/s will overlap with moderate MLCAPE ranging typically from 1000 to 2000 J/kg. The highest values are anticipated at the Adriatic sea coastlines. CAPE will increase towards south and east, where the airmass with steeper mid-tropospheric lapse rates can be found. Such environment is certainly conducive to severe storms. However, initiation is uncertain. Warm sector initiation will most likely happen over the Apennines in Italy, with storms becoming supercells and spreading over the Adriatic Sea towards Croatia. Large to very large hail and severe wind gusts are likely. This development will start between 12 and 15 UTC. Over Slovakia, Hungary or Bosnia, initiation in this time frame is less certain. Development of storms has to be monitored as any such development will result in a high threat of damaging wind gusts (given 0-3 km bulk shear of 20+ m/s) combined with large hail. Over N Hungary and Slovakia, the storms would form on a warm wave and some of them may already be elevated if they form further into the cooler airmass of the boundary.
A gradual increase in the coverage of storms will start with the approach of the low and with the movement of the front to the east. While surface based storms are likely till the Adriatic coastline, from 18 UTC onwards, between Croatia and S Slovakia, majority of storms will develop in the wake of surging cold front. Very strongly sheared environment with MUCAPE around 1000 J/kg will still yield severe weather risk, both in form of large hail and damaging wind gusts (despite storms being elevated!). As the low passes east, vertical wind shear will start decreasing from west and this will be accompanied by a transition towards heavy rainfall period late in the forecast period.
... central Italy to Bosnia, Albania, Serbia ...
Here, the environment will be also conducive to severe thunderstorms, featuring very strong vertical wind shear, exceeding 20 m/s in the 0-3 and 0-6 km layer and overlapping with moderate MLCAPE values of 1000 to 2000 J/kg, the highest over the Adriatic Sea. Compared to the area further north, coverage of storms is less certain. Thus, the overall probability of severe weather is lower, but the conditional probability of severe weather given the initiation success remains high and any developing storm will be capable of (very) large hail and severe wind gusts. The highest coverage of storms is expected with the approach of the low in the later part of the forecast period, meaning night hours over Serbia.
... Romania to W Ukraine ...
Two rounds of storms are possible here. The first round will begin over the Carpathians in the afternoon hours. Initiation will be isolated. The best conditions for severe weather will be over northern Romania and Ukraine, where curved hodographs and 0-6/0-3 km bulk shear exceeding 18 m/s will support supercells capable of large to very large hail and severe wind gusts. Further south, multicells will be dominant. The second round of storms is expected in the night with the approach of the cold front. Storms will be elevated and pose risks of isolated severe wind gusts and large hail, especially if a supercell develops. This activity will again primarily impact Ukraine and NW Romania, warranting Lvl 2 over this region.
... NE Sweden through Finland to Russia ...
A subtle short-wave will move from Sweden into Finland with a band of storms forming along a stalling frontal boundary. Environment shows rather moist conditions with low LCLs, plentiful of CAPE in the warm part of the cloud, but also above -10 deg C, combining with 0-6 km bulk shear of 10 - 15 m/s. More intense updrafts will be capable of marginally large hail, while locally heavy precipitation may lead to flash flooding.
... Baltics through Belarus into Russia ...
A cut-off low remains centered over eastern Latvia and Belarus, yielding moist conditions with weak mean wind, supportive of locally heavy rainfall. Further southeast, a more uncertain situation is forecast. Some models, such as ICON-EU indicate a short-wave trough moving from Ukraine to Russia, increasing the shear and also supporting development of more widespread storms with threat of severe wind gusts. On the other hand, ECMWF does not show the trough and the coverage of storms remains more limited here.
... Northern Russia ...
Fat CAPE profiles will combine with weak mean wind and overall disorganised storms due to the weak shear. Expect large hail and heavy rainfall within the more intense pulse storms..
