Storm Forecast
Valid: Sat 18 Oct 2014 06:00 to Sun 19 Oct 2014 06:00 UTC
Issued: Fri 17 Oct 2014 14:26
Forecaster: PISTOTNIK

A level 1 was issued for Ireland, Ulster and W Scotland for tornadoes and severe wind gusts.

SYNOPSIS

A pronounced long-wave ridge builds over Central Europe with an axis from Algeria to Sweden. It is flanked by two long-wave troughs which sit over the eastern Atlantic Ocean and amplify over far-eastern Europe into Turkey, respectively. At the surface, a filling sub-970-hPa cyclone to the northwest of Ireland and a building 1025 hPa anticyclone centered over Belarus are the corresponding pressure features.
Strong warm air advection spreads into southwestern and central Europe, while polar air rushes southward over far-eastern Europe. Cooler, drier air from the north also pushes the reservoir of plentiful CAPE over the eastern Mediterranean Sea out of our forecast domain.

DISCUSSION

... British Isles ...

Behind a long cold front that becomes stationary across England, a still moist and not too cool southwesterly flow is present. The postfrontal air mass features a few hundred J/kg of CAPE and fairly strong 0-3 km shear (15-20 m/s) and helicity (100-250 m^2/s^2, even more onshore due to stronger surface friction).
Postfrontal convection may organize into shallow multi- or even supercells over Ireland, Ulster and western Scotland. The strong background wind field and enhanced 0-1 km shear and helicity may support isolated severe wind gusts or tornadoes, especially along windward coasts.
Highest coverage of showers and thunderstorms is expected in the evening, when the approach of the main trough supplies some large-scale lift.

... N Turkey ...

Cold air advection over the warm Black Sea will create "lake effect" showers that move onshore in northern Turkey. They may locally grow deep enough to produce a little lightning in the first half of the day, when the passing main trough axis provides additional lift. Localized heavy rainfall and strong wind gusts are possible, but should stay below our level 1 thresholds.
After 12 UTC, increasing large-scale subsidence will gradually dampen the convective activity.

... W Mediterranean Sea ...

Forecast models simulate patches of CAPE where low-level moisture accumulates beneath the warm air advection regime. However, convective initiation is not expected due to a strong cap.

... Portugal ...

Within a stationary axis of enhanced moisture, left over by the remnants of an old occlusion, a band of rain and weakly electrified storms may move onshore. Despite some 15 m/s vertical wind shear over the lowest 3 km, the small amount of CAPE and the embedded nature of convection should preclude any severe weather.