Storm Forecast
Valid: Sat 22 Nov 2014 06:00 to Sun 23 Nov 2014 06:00 UTC
Issued: Sat 22 Nov 2014 00:57
Forecaster: PISTOTNIK

No threat levels were issued.

SYNOPSIS

The eastern half of Europe is dominated by rather low 500 hPa geopotential, high surface pressure and cool to cold, dry air.
An upper-level ridge amplifies from Algeria towards southern Norway. To its west, SSW-erly flow ahead of an Atlantic cyclone advects very warm air from northwestern Africa into western Europe. With a seasonable lack of diurnal heating and a strong capping inversion in place, the lift support ahead of travelling short-wave troughs becomes crucial to release limited CAPE (over sea) or to create it at all (over land).

DISCUSSION

... Morocco across Portugal and Spain into central France ...

A compact short-wave trough will move from central Spain (06 UTC) into central France (21 UTC). During peak daytime heating hours, its lift may help to create a few hundred J/kg of CAPE in the wake of the Pyrenees over southern France. Isolated afternoon storms are not ruled out, probably starting as elevated convection and then rooting down to the surface.

A second short-wave trough will move from Morocco towards southern Portugal and Spain, entering our forecast domain after 15 UTC. GFS predicts CAPE >1000 J/kg over the open sea and smaller values over coastal areas, as well as pockets of enhanced vertical wind shear and helicity in the warm air advection regime. However, the capping inversion may fully suppress convective initiation (as it did on Friday), at least long enough until the wind field relaxes.
Isolated storms breaking the cap in the afternoon could turn well-organized with a risk of severe wind gusts and large hail in northern Morocco. Storms might merge into an ill-defined cluster overnight , capable of producing heavy rain if it moves onshore in southern Portugal and Spain.

No high probability thunder or level 1 areas were issued in either case due to remaining uncertainties and sparse precipitation signals in the forecast models.

... W Mediterranean into S France ...

In the absence of any lift mechanisms, a few hundred J/kg of CAPE over the open sea between Malta and Catalonia will remain strongly capped.
At the northern fringe of this belt, persistent onshore flow creates a precipitation episode on the upwind side of the Cevennes mountains in southern France, but neither remarkable precipitation totals nor an involvement of thunderstorms are expected.