Storm Forecast
Valid: Fri 28 Jun 2019 06:00 to Sat 29 Jun 2019 06:00 UTC
Issued: Thu 27 Jun 2019 22:58
Forecaster: PISTOTNIK

Level 1 areas are issued for parts of SW Russia, Georgia, N Turkey, Bulgaria and S Romania for excessive convective precipitation, large hail and severe convective wind gusts.

SYNOPSIS

An amplified flow pattern covers Europe. A stationary long-wave trough is in place over the Atlantic Ocean, another one amplifies over European Russia and the Ukraine towards Turkey. In-between, a subtropic long-wave ridge stretches from Algeria to the North Sea.
Cooler and drier air floods eastern Europe in the wake of the eastern trough. In contrast, extremely hot air remains in place over Spain, Italy, Switzerland, France and England ahead of the western trough.

DISCUSSION

... SW Russia, Black Sea region, Georgia, N Turkey, Bulgaria and S Romania ...

The cold front of a 990 hPa surface cyclone between Moscow and Nishny Nowgorod moves SE-ward and crosses SW Russia, the Asow and Black Sea. Its tail becomes nearly stationary along the Turkish north coast and over Bulgaria and Romania. A belt of enhanced low-level moisture ahead of the cold front provides CAPE on the order of some hundred J/kg, possibly up to 1000 J/kg, though the model forecast will likely overestimate low-level moisture to some degree (2m dewpoints in the warm sector were several degrees lower than predicted on Thursday).
Scattered thunderstorms will likely be active throughout the forecast period, most of them in the afternoon. Strong lift ahead of the upper-level trough and moist, only slightly unstable vertical wind profiles point to a primary risk of excessive precipitation, especially near the cyclone's center, where the storm motion is slow. 0-3 km shear between 10 and 15 m/s can support multicellular convection. Moderately large hail and severe wind gusts are therefore also possible with the strongest storms, the former mostly in case of discrete convection and the latter mostly in case a convective line forms at the cold front.

A similar environment of low to moderate CAPE and moderate vertical wind shear exists also ahead of the cold front over NE Turkey, Georgia and the Russian Caucasus region, where the increasing westerly flow pumps Black Sea moisture onshore. Scattered, mostly diurnally driven thunderstorms over the mountains or at the sea breeze front pose a risk of a few flash flood, large hail and downburst events.

... N Italy, Switzerland, France, Celtic Sea, SW England, Ireland towards Faroe Islands ...

A belt of huge CAPE, possibly up to 4000 J/kg (see the Thursday 12z Milan and Cuneo soundings) remains in place where abundant low-level moisture has accumulated under a pronounced elevated mixed layer of Saharan origin. Isolated, short-lived afternoon storms are possible over the Italian mountains, but are not expected to tap into the CAPE reservoir over the adjacent lowlands. Otherwise, the massive capping inversion will still hold.
Robust CAPE of probably more than 1000 J/kg is also advected NW-ward over the Celtic Sea, Ireland and towards the Faroe Island. Strong vertical wind shear and synoptic lift overspread it and would create a favorable environment for severe storms. However, forecast soundings show an impenetrable cap due to the cool sea surface. A rather large low probability lightning area is drawn to account for the possibility of an elevated MCS, which could form in the strong warm air advection regime but is difficult to locate. If it forms, heavy precipitation and large hail are not ruled out.