Storm Forecast
Valid: Sat 29 Oct 2016 06:00 to Sun 30 Oct 2016 06:00 UTC
Issued: Sat 29 Oct 2016 09:09
Forecaster: PISTOTNIK

A level 1 was issued for the S Ionian Sea, Malta and parts of Sicily for severe convective wind gusts and excessive convective precipitation.

SYNOPSIS

A long-wave trough at 500 hPa filled with polar air amplifies over E Europe. The associated surface cyclone moves from Finland into W Russia.
The W half of Europe enjoys mild and dry conditions under strong anticyclonic influence. Somewhat lower 500 hPa covers the E Mediterranean region and allows deep convection in the range of a warm-core cyclone over the S Ionian Sea.

DISCUSSION

... S Ionian Sea, Sicily and Malta ...

With CAPE on the order of 500 J/kg (or higher towards the south, mostly outside our forecast domain) and almost no shear, clusters of thunderstorms will continue throughout the forecast period near the center of the cyclone. Heavy rain and severe wind gusts must be expected in a confined area around its core (or possibly multiple cores).
At the cyclone's NW flank, strong gradient winds (10-meter mean winds around 20 m/s forecasted by NWP models, gusts up to 30 m/s reported), high waves and heavy precipitation (up to 300 mm measured) have affected the E coasts of Calabria and Sicily over the past 48 hours. Thunderstorms were not involved, though.
Situation will still be similarly rough for these regions and also for Malta today before it starts to ease overnight. Most of these rainfalls and winds will again be non-convective, but a level 1 area was extended over Malta and the SE tip of Sicily in line with the border of the CAPE plume to reflect a low possibility of embedded convection.

... NE Europe ...

Beneath the long-wave trough, showers and scattered thunderstorms are active in the stream of polar air which has turned slightly unstable even far inland in response to the strong lift. Activity will be mostly daytime-driven and will subside in the evening.
Vertical wind shear and storm-relative helicity are enhanced to values around 10 m/s and 150 m^2/s^2, respectively, mostly concentrated in the lowest kilometer and supported by surface friction. A minority of storms may organize into multicells and short bowing lines, and isolated severe wind gusts or even a tornado are not ruled out.
The southern rim of the drawn thunder area (i.e., the bordering regions between Poland, the Ukraine, Romania and Moldova) experience still strong lift of the deepening trough and enhanced vertical wind shear also across deeper layers. Conditional probability for showers to produce severe wind gusts is higher here, but at the same time the depth of the convection is more limited and the risk of thunderstorms quite lower. The almost flow-parallel alignment of the cold front's tail does not favor convective organization, either.