Valid: Tue 22 Aug 2017 06:00 to Wed 23 Aug 2017 06:00 UTC
Issued: Mon 21 Aug 2017 21:32
A level 1 was issued for NW Russia mainly for large hail, severe wind gusts and tornadoes.
A long-wave trough is stretching from Scandinavia towards the Balkans and its axis will become negatively tilted during Tuesday, with several embedded waves, destabilizing the air masses over the Baltic States and NW Russia. The best conditions for severe weather events will be found inside the level 1 area. Most of the western and central parts of Europe are covered by a wide ridge with dry and stable conditions, while a cut-off low with strong PV signals from the Atlantic will reach the British Isles by the early morning of Wednesday. We expect several diurnally driven thunderstorms over this area, but the absence of significant wind shear and mild lapse rates will keep the threat level low. On the other hand, better thermodynamic conditions for an isolated severe storm are found in NW France, but enhanced inhibition limits the probability of CI early in the afternoon. Finally, storms are not ruled out in northern, mountainous parts of Spain where small hail may form as MLCAPE will reach 1 kJ/kg according to GFS.
.... NW Russia ....
A quasi-stationary low-level convergence zone is placed under the eastern flank of the long-wave trough, providing lift to unstable air masses. DLS is fluctuating between 15-20 m/s but 0-3 km of 15-20 m/s or more suggests that storms may become quickly supercells, producing large hail and severe wind gusts. Moreover, directional and speed low-level shear increase the probability of tornadoes mostly in the afternoon. Severe risk will be significantly reduced after the sunset but convective activity will continue during the night.