Storm Forecast
Valid: Sun 11 Jun 2017 06:00 to Mon 12 Jun 2017 06:00 UTC
Issued: Sat 10 Jun 2017 22:49
Forecaster: PISTOTNIK

A level 1 was issued for parts of Romania, Bulgaria, FYROM and Greece for excessive convective precipitation.

SYNOPSIS

The zonal flow features a progressive pattern of positively tilted troughs and ridges. A mid-level trough stretches from the Ukraine towards Greece, where its tip cuts off into a closed low over the Aegean Sea. A mid-level ridge extends from Iberia towards Germany. The third macrosynoptic feature is a strong cyclone north of the British Isles, at whose southern flank a mid-level jet streak stretches from the British Isles to southern Scandinavia.
Near the surface, much of Europe is dominated by weak pressure gradients and covered by warm and moist air. However, weak lapse rates keep the CAPE magnitude low.

DISCUSSION

... Eastern Europe ...

CAPE up to 500 J/kg will form in response to daytime heating in a long belt from S Finland and Russia into Greece and Turkey. Scattered, daytime-driven thunderstorms are expected, especially over mountain ranges and ahead of numerous small, southward moving vorticity maxima.
The deepest instability and the highest storm coverage are expected from Romania to the Greek mainland, where a level 1 is issued for the possibility of some flash floods. Otherwise, weak vertical wind shear will keep storms disorganized and the severe weather risk low.

... from France to the S Baltic Sea ...

Broad warm air advection reinforces from the SW. Evaporation will gradually increase the low-level moisture content beneath the advancing warm air (probably not as strongly as forecasted by GFS, though). A few hundred J/kg of CAPE may form by evening, limited by weak lapse rates aloft as the hot "Spanish plume" won't be picked up by the mid-level flow.
Warm air advection and the approaching British long-wave trough will create persistent lift. Scattered elevated convection is expected to emerge from Altocumulus clouds along the axis of the warmest air and may become weakly electrified by evening and overnight. The following cold front, which will move inland from the Channel and the North Sea in the afternoon and evening, will very likely be too shallow to break the cap and make convection root down to the surface. Current thinking is that convection will stay elevated and hence will not benefit from increasing vertical wind shear.

... N British Isles ...

Scattered daytime showers will form in the well-mixed maritime air behind the cold front. They are unlikely to grow deep enough to produce thunder, but shallow mesocyclones are not ruled out due to strong 0-1 km shear (>10 m/s) and storm-relative helicity (>100 m^2/s^2). They might produce a short-lived tornado along coastal convergence lines and sea breeze fronts.

... N Spain, S France, Italy ...

Isolated, short-lived and non-severe afternoon storms are possible over the Cantabrian Mountains, the Pyrenees, the W Alps and S Italy if enough low-level moisture is fed into upslope flows.