Storm Forecast
Valid: Mon 22 Jul 2019 06:00 to Tue 23 Jul 2019 06:00 UTC
Issued: Sun 21 Jul 2019 12:50
Forecaster: PISTOTNIK

A level is issued for parts of Belarus and the Ukraine mainly for excessive convective precipitation.

A level 1 is issued for parts of Bosnia-Herzegovina and Serbia mainly for large hail and excessive convective precipitation.

A level 1 is issued for parts of Spain for severe convective wind gusts.

A level 1 is issued for the Georgian and Russian Caucasus region for large hail, excessive convective precipitation and to a lesser degree severe convective wind gusts.

SYNOPSIS

A subtropic ridge over SW Europe extends towards the North Sea. A mid-level jet curves around this ridge from the British Isles to S Scandinavia and east-central Europe before it fans out. "Downstream development" ahead of the ridge makes a couple of weak upper-level lows from Russia to Finland and the Baltic States consolidate into a long-wave trough that amplifies to Romania. Another long-wave trough flanks the subtropic ridge to the west over the North Atlantic, yielding a stable streamflow pattern that will persist for a few days.
Very warm to hot air covers the greater Mediterranean region and spreads into increasing parts of W Europe. In contrast, cooler maritime air has entered much of N and E Europe.

DISCUSSION

... E-central Europe, Baltic States, Belarus, W Ukraine, Moldova, Romania ...

A diffuse cold front continues to track SE-ward. It is overspread by several vorticity maxima, but their lift will largely be compensated by cold air advection over the W half of this area, keeping thunderstorm coverage low. Further east, synoptic lift will dominate and will support at least scattered thunderstorms in an environment of low to moderate CAPE (up to 1000 J/kg) and weak vertical wind shear (<10 m/s), though model agreement on their placement and timing is low.
The highest coverage is anticipated over E Belarus and at the sea breeze front around the SW Ukraine. Excessive precipitation is the main risk. Stronger pulse storms might bring marginally large hail and one or two downbursts in addition. Activity will peak in the afternoon and will gradually turn elevated and weaken overnight, while its remnants move E- to SE-ward.

... N Balkans into S Alpine region ...

Similar CAPE up to 1000 J/kg is present in the warm and moist airmass before the tail of the diffuse cold front pushes south. The fringes of the mid-level jet enhance 0-6 km shear to 10-15 m/s, supportive of multicells with a risk of large hail and locally heavy rain. A level 1 is introduced for parts of Bosnia-Herzegovina and Serbia, where at least scattered afternoon storms are expected. Further west towards Croatia and the southern Alpine region, strong synoptic and orographic subsidence will likely mix out the low-level moisture early in the day, and only a few short-lived storms, if any, are anticipated.

... Spain ...

Confidence increases that isolated high-based evening storms will form in the hot and dry inland air. Most of the precipitation will evaporate before it reaches the ground, but this process may well produce a few severe downbursts spreading erratically outward. In addition, lightning strike could cause wildfires (though this risk is not covered in our threat level scheme). A few storms may survive into the night (as in particular GFS suggests), but nocturnal cooling will decouple them from the surface and will limit the downburst risk then.
More robust CAPE and enhanced vertical wind shear are present in the sea breezes that push inland in the afternoon, but the strong cap will likely suppress any convective initiation there.

... Georgia and around ...

CAPE up to 1000 J/kg and 0-6 km shear around 20 m/s overlap in the SW-erly flow ahead of the deepening east-European trough. Weak synoptic lift and upvalley/upslope circulations will cause some daytime-driven storms that can at least locally produce large hail, heavy rain and perhaps a few downbursts. Forecast soundings show a massive warm layer between 700 and 600 hPa, originating from the Turkish plateau, hence surface-based convection will probably be confined to the mountains, while the better CAPE-and shear overlap over the lowlands will rather be untouched.