Storm Forecast
Valid: Tue 12 Jan 2016 06:00 to Wed 13 Jan 2016 06:00 UTC
Issued: Mon 11 Jan 2016 21:36
Forecaster: DAFIS

A level 1 was issued for Italy, Croatia, Bosnia and Herzegovina, Montenegro and Albania mainly for severe wind gusts, tornadoes and to a lesser extent for excessive rain and large amounts of small hail.
A level 1 was issued for France mainly for severe convective wind gusts.


SYNOPSIS

Low geopotentials dominate over the continent and several shortwave troughs result in marginal convective and non-convective events. On the surface, two deep cyclones will be the steering mechanisms of weather conditions over Europe this Tuesday, one of them over the North Sea and the center of the other one quickly crossing Poland, Belarus and eventually Russia. The second one is responsible for a extensive cold front that stretches from Russia all the way down to Morocco and it will force air masses, rich in moisture, to move way too south, towards the south Mediterranean basin. But while doing that, it will also feed some DMC events in Tyrrhenian and Adriatic Seas where we expect numerous rounds of convective cells.

DISCUSSION

.... Italy, Croatia, Bosnia and Herzegovina, Montenegro and Albania .....

During the early morning of Tuesday, the aforementioned cold front will cross central Italy and west Balkans, where strong directional and wind speed vertical shear will be present. In addition, the advection of cold air masses above the mild sea will create quite steep vertical lapse rates and CAPE up to 600 J/kg. The main threat will be over Albania, where DLS will be in the range of 25 - 30 m/s with both GFS and ECMWF forecasting MLCAPE of more than 400 J/kg over the same area. Low level convergence zones and SREH0-3km are also promising for the formation of a prefrontal MSC in the morning of Tuesday. PW of 25-30 mm cannot exclude an excessive rainfall event and due to strong vertical wind shear and low freezing levels, large hail or large amounts of small hail are also possible. The presence of LLS and curved forecasting hodographs in low levels cannot rule out some waterspouts, especially at the coasts of Croatia (Dalmatia) in the unstable air mass behind the cold front.

..... France .....

A shortwave trough over France is forecast by both GFS and ECMWF models, but there are some differences about the amount of CAPE that will be effective for DMC. GFS spreads about 200 J/kg of MLCAPE from the Gulf of Biscay up to West Germany but on the contrary ECMWF produces only some patches of up to 200 J/kg over continental France. High resolution models have initial conditions of previous model runs and have not been taken into consideration. Nevertheless, DLS will exceed the 25 m/s, 0-3 km bulk shear will be in the range of 15-17 m/s and SREH0-3km up to 200 m²/s² in Aquitaine (France). Moreover the level 1 area will be under the left exit of a mid level jet streak and the advection of absolute vorticity that is forecast are ingredients that cannot rule out the development of DMC even if CAPE is not promising. Severe wind gusts are the main threats within the most active cells but also there are chances of an isolated tornado event.

During the night of Tuesday, another shortwave trough is approaching Benelux with strong advection of vorticity but only GFS produces some CAPE of less than 150 J/kg. Non-convective severe wind gusts will be the main threat.