Storm Forecast
Valid: Mon 21 Jun 2021 06:00 to Tue 22 Jun 2021 06:00 UTC
Issued: Mon 21 Jun 2021 04:07
Forecaster: VAN DER VELDE

A level 2 was issued across NE France, N Switzerland, S Germany, N Austria, Czechia, W Poland, N Hungary for large hail, excessive precipitation, and severe wind gusts.

A level 2 was issued for N Finland for severe wind gusts, tornadoes and large hail.

A level 2 was issued for the W Balkan for large hail and severe wind gusts.

A level 1 was issued for adjacent areas for precipitation, hail and severe wind gusts.

SYNOPSIS

A mid level trough across western Europe with a surface low in the Bay of Biscay pushes cool mid level air into France and Germany, while unstable low level warm air still resides over E France and central Europe. A southwesterly jet generates 15-20 m/s DLS across E France, Switzerland, S Germany, as well as over the Balkan with NW-ly upper winds.

Over N Germany, an older convective system will track into E Denmark and S Sweden, and can remain active with mostly elevated CAPE, with models predicting large SREH and 0-1 km shear but in the stable layer near ground, making it ineffective.

Another low over N Norway with a high over Russia push warm air into Finland, under a jet, where WAA creates strong SREH.


DISCUSSION

...France, Switzerland, S Germany, N Austria...

Models indicate quite humid profiles with weakly capped MLCAPE mostly in the 800-1500 J/kg range, overlapped by 15-20 m/s 0-6 km shear. Cloud base heights should be mostly in the 1000-1500m range. In lack of clear frontal/through forcing, storms form as isolated and clustered multi- and supercells, with large hail and severe wind gusts as the main threat. The hodographs lack the curvature and low-level shear required for tornadoes. During the evening an MCS may form, as seems indicated by several models, traversing S Germany into Czechia.

...E Austria, N Hungary, Czechia, W Poland, Slovakia...

Weakly capped 2000 J/kg MLCAPE and 1500-2000 m LCL easily support large hail and severe wind gusts even though DLS is on the weaker side with 7-13 m/s.

...W Balkan...

Similar conditions as above, but with higher shear (14-17 m/s 0-3 km and 0-6 km) supercells are more likely. There is no organized lift, so cells will be more isolated.

...N Finland...

Curved hodographs with 20 m/s DLS, 250-400 m2/s2 SREH, 13 m/s 0-1 km shear and 1000-1800 J/kg MLCAPE make for an environment supportive of supercells with tornadoes. Large hail and severe wind gusts also can occur.