Storm Forecast

Storm Forecast
Valid: Thu 18 Jan 2018 06:00 to Fri 19 Jan 2018 06:00 UTC
Issued: Thu 18 Jan 2018 00:11
Forecaster: GATZEN

A level 1 was issued across eastern France, northern Switzerland, southern Germany mainly for severe wind gusts.

A level 1 was issued across southern Turkey into Syria mainly for large hail, severe wind gusts, and tornadoes.


Western and central Europe

Deep trough across central Europe is pushed east as a strong mid-level jet approaches over western Europe. Intense surface cyclone will move along the coasts of the Netherlands, Germany and Poland during the period. The cold front is ill-defined close to the low centre with the possibility of a sting jet indicated by some models. Some shallow CAPE over France, the Benelux countries and western Germany is expected and showers are forecast along the cold front. Low-level mixing and reduced dewpoints ahead of the cold front and weak convergence at the cold front limit chances of linear convection, however, intense showers can form, though. Warm EL temperatures are expected and thunderstorms are not too likely.

Farther east, stable low levels and weaker moisture do not allow for surface-based CAPE, but strong stretching below the tropopause fold can result in elevated CAPE as indicated by latest GFS. Here, some thunderstorms are possible ahead and along the cold front.

Over southern Germany, eastern France and over the northern Alpine region, a narrow cold-frontal rain band is forecast as the cold front develops in the afternoon, then with better low-level convergence. Latest GFS even indicates strong lapse rate increase in the evening hours when a strong low-level jet is pushed along the Alpine rim and is affected by the tropopause fold. As a consequence, thunderstorms that move rapidly east can be embedded in the rain band, capable of producing severe wind gusts and marginal hail. Low-level shear is strong (0-1 km shear 30 m/s, SRH 500 m²/s²), and mesovortices could form if storms produce a cold pool. In that case, tornadoes and extreme gusts are not ruled out.

In the wake of the storm, cold mid-level air overspreads the British Isles and the North Sea where thunderstorms are likely. Although low-level vertical wind shear is strong over the British Isles and Benelux and northern France, potential of severe weather are limited given weak CAPE inland and very long linear hodographs.

Southern Turkey

The southern vortex of the European trough spreads into the east Mediterranean. Some low-level moisture can remain along the southern Turkish coast while lapse rates increase below the tropopause fold. Thunderstorms are likely to form that move eastward. Strong vertical wind shear supports multicells and some supercells close to the shore, capable of producing marginally severe hail and severe wind gusts. A tornado is not ruled out. Severe potential gradually decreases from the west during the day as stronger mixing results in decreasing moisture.

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