Storm Forecast
Valid: Sat 04 Aug 2012 06:00 to Sun 05 Aug 2012 06:00 UTC
Issued: Fri 03 Aug 2012 20:35
Forecaster: GROENEMEIJER

A level 1 was issued for parts of Ireland for marginally severe hail and for tornadoes.

A level 1 was issued for parts of the UK for marginally severe hail and for tornadoes.

A level 1 was issued for northern Spain and southern France for large hail.

A level 1 was issued for the Alps and their surroundings for large hail and for northwestern Italy also for excessive precipitation.

A level 1 was issued for eastern Belarus and extreme western Parts of Russia for large hail.

A level 1 was issued for southeastern and central parts of Finland for heavy rain, large hail and isolated tornadoes.

SYNOPSIS

A broad WSW-ly mid-level flow over Europe is associated with a broad zone of lower-tropospheric temperature gradient stretching from northern Spain across France, southern Germany and Poland to the eastern Baltic States.On either side of this zone, convective storms are expected to develop. The WSW-ly jet is located ahead of a trough with an axis from a cold upper-level low over the British Isles towards the southwest, which slowly approaches western Europe.

Ireland and the UK....

Within unstable air that surrounds the upper-level low, widespread storms are expected to develop in response to diurnal heating. Updraughts may become strong enough to produce some hail exceeding severe levels locally. Vertical vorticity may be stretched in the stronger updraughts of storms that develop in convergence lines circulating around the low, creating a modest risk of a few weak tornadoes.

Spain and far southern France...

Despite very little CAPE being present in NWP guidance, some isolated storms are expected to develop within the level 1 region, enhanced by slight synoptic scale lift indicated by slight advection of PV. Given the 20-30 m/s deep-layer shear any storm that manages to develop may become a strong supercell with a primary threat of large hail.

Alps...

Upslope winds developing as a result of the diurnally returning mesoscale circulation around the Alps in relatively unstable air guarantees storm initiation across large parts of the mountains. With 1000-1500 J/kg CAPE forecast to develop along the plains surrounding the mountains in combination with 15 - 20 m/s of deep-layer shear, the potential for a number of well-organized storms with a threat primarily of large hail is given. GFS and ECMWF models suggest that NW Italy is at risk of seeing persistent storms along the Alpine slopes with an attendant heavy rain threat.

Eastern Belarus and far western Russia...

Along a frontal zone at 06 UTC near the eastern boarder of the Baltic States, a line of storms is expected to develop. Ahead of the front, the air-mass is also sufficiently weakly capped to allow for scattered storm initiation. Since CAPE is expected to be around 1500 J/kg per GFS and ECMWF and moderate (10-15 m/s) shear is expected, some well-organized multicells with a threat of large hail are expected.

Finland...

Pronounced low-level convergence is expected along a SW-NE oriented zone across central Finland, that will be the focus for storm initiation. Given the presence of ample low-level moisture and storm motion vectors at small angles to the orientation of the convergence zone, some threat of training storms with excessive rainfall will exist. In addition, the combination with low LCL height may suffice to for the development of a weak tornado or two.