Storm Forecast
Valid: Thu 23 Feb 2017 06:00 to Fri 24 Feb 2017 06:00 UTC
Issued: Thu 23 Feb 2017 00:12
Forecaster: GATZEN

A level 1 was issued for south-eastern Spain mainly for large hail.

A level 1 was issued for the Benelux countries and central Germany mainly for severe wind gusts.

SYNOPSIS

A Scandinavian long-wave trough amplifies into central Europe on Thursday. The strong mid-level flow at its southern periphery forms two main short-wave troughs that travel rapidly east. Intense surface lows have already formed and will be situated across southern Finland and southern Scotland in the morning hours. Coupled mid-level jet leads to favourable conditions for the western system that will further intensify during the period according to latest model forecasts, posing a thread for potions of western and central Europe. The Mediterranean is affected by mid-level ridging except for the south-west, where a cut-off low is situated. This cut-off will start to migrate north-east on Friday morning.

DISCUSSION

An impressive EML sampled by latest Lisboa sounding has been advected across south-western Europe at the eastern flank of the cut-off that is centred over Morocco. Thunderstorms have formed on Wednesday across eastern Morocco and western Algeria. This activity is expected to spread into the Iberian Peninsula as the cut-off moves north and a short-wave trough enters south-eastern Spain. Daytime heating is expected to be sufficient to reduce the cap although low-level moisture is limited with around 8-9°C surface dewpoint. Initiation over the mountains of south-eastern Spain is forecast in the course of the day. Single cells and multicells are the most likely convective mode given limited vertical wind shear. Main threat is large hail with the stronger storms. After sunset, most activity will decay. Across the west Mediterranean Sea, further storms are forecast also during the night hours. Activity will be elevated given the cool sea surface, and severe storms are not expected.

British Isles, The Channel and neighbouring North Sea, Benelux countries and northern France into Germany

In association with the coupled jet at mid levels, Shapiro-Keyser cyclogenesis is likely. The cold front moves quite rapidly east. Stretching and lapse rate increase in the pre-frontal air will be limited as the main tropopause fault is located behind the cold front. Some weak CAPE and equilibrium temperatures around -15°C are expected. A frontal rain band with embedded convective storms seems to be the most probable scenario. Limited cold pool development will limit the potential of mesovortices and only some severe wind gusts are expected. In the wake of the cold front, the sting jet will likely produce severe winds that are not included in the threat levels as the contribution of thunderstorms is low.

East Europe

Another PV intrusion spreads across Belarus and Ukraine on Thursday. Lapse rates will increase but low-level moisture is pretty weak and CAPE will be very limited. A few thunderstorms are not ruled out but severe threat is too limited to issue a categorical level.