Storm Forecast
Valid: Thu 28 Apr 2016 06:00 to Fri 29 Apr 2016 06:00 UTC
Issued: Wed 27 Apr 2016 22:48
Forecaster: GATZEN

SYNOPSIS and DISCUSSION

An intense polar trough over Central Europe will lift ahead of a new impulse feeding the long-wave trough across western Europe. At the periphery of the long-wave trough, a strong south-westerly mid-level jet extends across north-western Africa into the southern Mediterranean. Further vort-maxima are present ahead of the long-wave trough over the Black Sea region and south-west Russia. At lower levels, cold polar air masses have spread over large portions of western and central Europe. A tongue of warm and moist air spreads into north and east Scandinavia ahead of the lifting trough. Furthermore, a sharp frontal boundary is present over the south Mediterranean, where an elevated mixed layer starts to spread north-eastward.

The current situation is characterized by weak moisture across most regions of Europe. Some moisture increase is expected over the central Mediterranean within a capped easterly low-level flow and some moisture convergence especially along land-sea-breeze fronts. This increased moisture can allow for some CAPE where it overlaps with steep lapse rates evolving in cold air masses in response to diurnal heating. This can be expected over the eastern Iberian Peninsula and the west Mediterranean, but also across parts of the Balkans. Over southern Italy and the southern Adriatic Sea, increased moisture will also overlap with the African elevated mixed layer, but the weak CAPE will be capped. Forcing will be quite strong over portions of the Mediterranean as a trough axis moves east from the Iberian Peninsula, and strong differential cyclonic shear vorticity advection can be expected at the left exit of the strong Mediterranean mid-level jet.

Embedded storms are expected over around Italy and the southern Adriatic, but weak low-level buoyancy is expected to limit well-organized storms. Some large hail may be possible from elevated storms from Tunisia to Sicily as deep layer vertical wind shear is strong. Over the west Mediterranean and the Balkans, diurnal heating and associated steep low-level lapse rates in cold air masses could allow for some storms. Vertical wind shear is rather strong especially over eastern Spain, and stronger storms could produce large hail. Quite warm mid-levels will limit the vertical extend of these storms, though.

More storms are forecast across south-western Russia and portions of Belarus and the Ukraine where moist low-level air masses overlap with steeper lapse rates underneath the vort-maximum. Weak vertical wind shear and rather weak CAPE will limit severe potential, a few hail events are possible with the stronger cells, though.

Central Europe will be affected by steep low-level lapse rates in response to diurnal heating, resulting in low-topped storms during the day. Convective activity will spread north with the trough center. Locally, severe wind gusts are not ruled out in regions with well-mixed low-levels. Weak degree of organization is forecast given weak vertical wind shear, and chance of severe weather is limited.