Storm Forecast
Valid: Tue 22 Apr 2014 06:00 to Wed 23 Apr 2014 06:00 UTC
Issued: Mon 21 Apr 2014 21:21
Forecaster: GROENEMEIJER

A level 1 was issued for the central Balkans, mainly for large hail.

A level 1 was issued for NE Algeria and W Tunisia, mainly for large hail and excessive rainfall.

SYNOPSIS

A high over Scandinavia and a trough over Spain, which evolves into a closed low over the central Mediterranean, are the components of a blocking pattern that sets up during the forecast period. In the lower troposhere, there is weak flow over much of the European continent, with the notable exception of northeast Europe, where an outbreak of arctic air takes place. Across northern Africa, a strong southerly flow ahead of a low pressure system over Algeria brings warm air into Tunisia and the central Mediterranean Region. The air over most of central and western Europe becomes marginally unstable in response to insolation, and scattered thunderstorms should develop.

DISCUSSION

Central Balkans...

In the wake of a weak shortwave trough, a westerly mid-tropospheric wind maximum, associated with a weak PV anomaly should travel eastward on Tuesday. In the wake of areas of stratiform rain initially over Hungary and Romania, this system should provide the setting for a slight severe threat across the indicated level 1 area. Most importantly, 0-6 km bulk shear of 15-20 m/s are forecast to overlap with modest CAPE during the day, suggesting that some storms should become well-organized creating some risk for severe hail. After sunset, the storms should subside.

Northeast Algeria, Tunisia...

A slight overlap of strong deep-layer wind shear (25 m/s) and moderate CAPE is expected ahead of the mid-level trough and associated frontal zone as it crosses the Aures Mountains. A few severe thunderstorms are forecast develop across the area with the main threats being large hail and excessive rainfall.

European continent...

In many areas, storms will develop in response to solar heating, modulated by subtle troughs and ridges. MLCAPE values should be around 400-800 J/kg or lower, suggesting that most updraughts will not be strong enough to sustain large hail, although a few exceptions may occur. Low-level moisture is not expected to be high with typical values of 6 - 9 g/kg, so that the flood risk should remain relatively low even though some storms will be slow-moving.

North and Northeast Europe...

A few lightning strikes cannot be ruled out in association with relatively shallow convectivion that will probably develop within the southeastward rushing arctic air-mass. Strong gusts should occur both with, but also outside of moist convection embedded in this air-mass.