Storm Forecast
Valid: Sat 25 Jun 2022 08:00 to Sun 26 Jun 2022 06:00 UTC
Issued: Sat 25 Jun 2022 08:38
Forecaster: PISTOTNIK

A level 1 and level 2 are issued for parts of France for large hail, excessive convective rainfall and to a lesser degree for severe convective wind gusts.

A level 1 is issued for Denmark, E Germany, the Czech Republic and parts of Hungary for excessive convective rainfall.

A level 1 is issued for the central Balkans for large hail, excessive convective rainfall and to a lesser degree for severe convective wind gusts.

A level 1 is issued for E Turkey, Georgia, Armenia, Azerbaijan and the Russian Caucasus region mainly for excessive convective rainfall and large hail and to a lesser degree for severe convective wind gusts.


SYNOPSIS

A blocking anticyclone remains centered over the Baltic States. It is surrounded by gradually filling cut-off lows over the Black Sea and Hungary and a vigorous cyclone stretching from Ireland to the Bay of Biscay. Almost the entire continent experiences seasonable to warm conditions. A strengthening SW-erly to S-erly flow advects particularly warm air from the W Mediterranean region to west-central Europe and Scandinavia ahead of the western cyclone. Another branch of an enhanced, anticyclonically curved mid-level flow stretches from west to east across the Mediterranean region.

DISCUSSION

... France across BeNeLux and NW Germany into Norway, N Sweden and N Finland ...

Aided by warm air advection, diurnal heating and moisture accumulation, some hundred J/kg CAPE build in a long belt ahead of a slowly eastward shifting cold front. Warm air advection and several travelling vorticity maxima also create synoptic lift, while mesoscale lift is provided by the frontal cross-circulation.
Scattered storms are expected to initiate from the early afternoon onwards mainly across France. Deep-layer shear mostly varies around 15 m/s during daytime, hence multicells are likely to be the primary storm mode and pose a risk of (moderately) large hail, heavy rainfall and isolated severe wind gusts. A level 1 covers the area where these storms are expected to travel while being surface-based. Parts of S France are upgraded to a level 2 due to higher CAPE values up to 1000 J/kg and stronger signals of synoptic lift.
A secondary maximum of scattered afternoon storms may evolve over S Norway, but the overlap of CAPE and shear appears just not convincing enough for a level 1.
Supported by warm air advection, storms can travel quite some distance northward across BeNeLux, NW Germany, the North Sea and Norway in the evening and overnight, but should soon turn elevated and not pose an enhanced severe weather risk anymore despite further increasing vertical wind shear. A similar, narrow belt of possible elevated convection may affect N Scandinavia overnight ahead of another short-wave trough and is also highlighted by a low probability lightning area.

... Denmark, E Germany, Czech Republic, Slovakia, Hungary ...

Moisture is maximized along a convergence zone (formerly Friday's cold front) and allows some hundred J/kg CAPE after some daytime heating. Scattered daytime-driven storms are expected. Under poor lapse rates due to Friday's convective overworking and weak vertical wind shear, excessive rain with localized flooding is the main risk. Large amounts of small hail are not ruled out with the strongest pulse storms, either.

... Balkans ...

Strong daytime heating creates CAPE up to 1000 J/kg, though the CAPE magnitude is difficult to asses due to the complex topography and differing solutions from the forecast model pool. Aided by synoptic lift ahead of a short-wave trough, scattered afternoon storms are likely. Similar to the day before, precipitation signals in ECMWF are stronger and persist more into the night than in ICON-EU and GFS. Deep-layer shear increases from 10 m/s to the north to 20 m/s to the south, hence better storm organization into multicells and possibly some supercells with a risk of large hail (isolated very large hail not ruled out with a supercell) and a few severe downbursts is expected further south. Otherwise, excessive rain is the main risk as soon as storms grow into larger clusters, and in general after sunset when they gradually turn elevated and weaken.

... Black Sea region and around ...

Ahead of the eastern cut-off low, some hundred J/kg CAPE are predicted to build under enhanced deep-layer shear (mostly 15-20 m/s) and at least some signs of synoptic lift from E Turkey into Armenia, Azerbaijan, Georgia and the Russian Caucasus region. In these regions, scattered and mostly daytime-driven storms can organize somewhat better and produce heavy rain, large hail and severe wind events alike.
Closer to the center of the cut-off low that remains over open waters, CAPE is rather marginal (but may be partly compensated by strong lift) and vertical wind shear is weak. Some storms can be embedded in various precipitation bands that circle the low center, but the degree of involved deep convection was already low on Friday and is expected to further decrease on Saturday, hence only a low probability lightning area and no risk level cover this regime. Nonetheless, a few flash floods are not ruled out in coastal areas, whereas non-supercellular tornadoes may spin up near the cyclone's center and along nocturnal land breeze fronts.