mercredi 23 avril 2014

European Storm Forecast Experiment

Storm Forecast
Storm Forecast
Valid: Thu 24 Apr 2014 06:00 to Fri 25 Apr 2014 06:00 UTC
Issued: Wed 23 Apr 2014 22:41
Forecaster: GATZEN
A level 2 was issued for north-eastern Spain and southern France mainly for large hail.

A level 1 was issued for northern Turkey mainly for large hail.

A level 1 was issued for the central Balkans, western Poland, eastern and north-western Germany, the Benelux countries, north-eastern and central France mainly for large hail.


A weak cut-off low is present over the Balkans. The strong mid-level flow at its south-eastern flank will affect Greece and Turkey on Thursday. North of the cut-off, weak geopotential gradients are forecast across the forecast area except for the northern British Isles and the Iberian Peninsula, where Atlantic troughs are present.


North-eastern Spain, southern France

An intense digging trough will cross the Iberian Peninsula until Friday, 6 UTC. Ahead of the trough, a strong south-westerly jet will spread east and affects eastern Spain and France in the afternoon and evening hours. Diurnal heating will lead to steep lapse rates especially at low levels, and adequate low-level moisture is expected to overlap with these lapse rates, resulting in CAPE around 400 J/kg.

Initiation may be quite early across northern Spain due to the approaching trough and spreads east in the noon and afternoon hours. DCVA and WAA will assist in numerous storms that may merge into larger clusters. Given favourable vertical wind shear and 150 m²/s² 0-3 km SRH, rapid storm organization is expected, and supercells or multicells capable of producing large hail and severe wind gusts are forecast. Tornadoes are not excluded due to slightly increasing low-level vertical wind shear in the evening hours. Additionally, excessive rain is not ruled out, with the greatest chance in the evening hours when storms start to cluster. Low-level stabilization and advection of drier air from the west will lead to a rapid decay of the activity during the night.

Northern Turkey

Steep lapse rates are forecast ahead of the cut-off trough across Turkey. Although low-level moisture is limited, CAPE will likely exceed 500 J/kg. Due to a capping inversion and rather weak low-level convergence, widespread initiation is not forecast over the southern parts. Better moisture and upslope low-level flow are expected to increase the thunderstorm potential over the northern parts. Given strong deep layer vertical wind shear in excess of 20 m/s, supercells and multicells are forecast, capable of producing large hail as the main threat. Storms are expected to weaken in the evening hours.

Central Balkans, western Poland, eastern and north-western Germany into Benelux and north-eastern and central France

A broad region of rich low-level moisture is expected from the Balkans to northern Germany and further into central France. Rather cool mid-level temperatures and diurnal heating will lead to increasing low-level lapse rates and rather cold EL temperatures. Daytime heating will result in initiation around noon and numerous storms are forecast. Weak vertical wind shear will limit the potential of storm organization. Isolated pulse storms will be capable of producing large hail, strong wind gusts, and excessive precipitation. Storms will weaken in the evening hours.

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