Storm Forecast
Valid: Tue 14 Jul 2020 06:00 to Wed 15 Jul 2020 06:00 UTC
Issued: Mon 13 Jul 2020 20:54
Forecaster: DAFIS

A level 2 was issued for parts of W Russia for large hail, severe wind gusts, excessive precipitation and tornadoes.

A level 1 was issued for parts of W Russia and E Ukraine for large hail, severe wind gusts and excessive precipitation.

A level 1 was issued for Spain for large hail and severe wind gusts.

SYNOPSIS

Two long-wave troughs will be the main synoptic features during this outlook which will affect the largest part of the continent, while a strong ridge is building up in North Atlantic. The easternmost trough is associated with a PV streamer extending from Scandinavia towards the Black Sea, becoming thinner during Tue 14/07 and then gets cut-off from the high-PV reservoir in N Scandinavia. The "treble clef" PV structure in the forecast maps most possibly will lead to an occlusion close to the surface as high vorticity is expected. In the warm sector of the cyclone and on the occlusion we expect widespread and severe DMC activity.
The trough in western Europe is associated with drier and colder, and thus less unstable, air masses. Nevertheless, the leading edge of this trough will provide synoptic lift to unstable air masses in the Iberia Peninsula where we also expect DMC activity. Many more areas will be covered by low CAPE and low wind shear, limiting organized convection, but in some areas thunderstorm activity will be widespread (ex. Scandinavia and E Turkey).

DISCUSSION

.... Russia ....

The trough over eastern Europe during the night of Mon 13/07 has a negative tilt and by Tue morning the NWP models predict the development of a cut-off low with a strong PVA in the mid/upper troposphere. A pre-existing stationary front over the area has already led to numerous thunderstorms and high amounts of moisture are found in the PBL. In addition, the WAA advection from the NW Caspia is creating a very well-mixed PBL but more to the west, close to the borders of Ukraine and Russia, air masses with very different characteristics will meet. Strong baroclinicity will create a strong wind configuration near the surface with veering vertical profiles. A large part of the warm sector of the cyclone will be strongly capped and convection will struggle to initiate, but emerging storms in the afternoon will be able to quickly get organized in MCSs and supercells. The convective mode should be mainly isolated supercells. On the cold front, CI will be achieved much easier and surface-based storms will get the benefit from low-level helicity to also organize into supercells. MLCAPE up to 2500 J/kg will overlap with 20-25 m/s DLS and 15-20 m/s 0-3km shear. All kinds of severe weather are expected within this environment but damaging hail and severe convective wind gusts will be the main threats.

Tornadoes are also expected in the southern parts of the level-2 area. High SBCAPE, curved hodographs, low LCLs and high SREH0-1km suggest that supercells will be able to produce tornadoes.

... Spain ...

The passage of the axis trough over Spain will coincide with the time of maximum diurnal heating of the surface and CI should not be a problem even under high CIN. High delta-theta-e values in the NWP models show an environment conducive for accelerating downdrafts through evaporation cooling. Moreover, locally DLS will exceed 15-20 m/s, overlapping with more than 1000 J/kg MLCAPE. A few large hail events cannot be ruled out.