Storm Forecast
Valid: Wed 14 Jan 2015 06:00 to Thu 15 Jan 2015 06:00 UTC
Issued: Tue 13 Jan 2015 22:20
Forecaster: PUCIK

A level 1 was issued for NW / E France, Belgium and W Germany mainly for the severe wind gusts and to the lesser extent for tornadoes.

SYNOPSIS

An active weather pattern will continue over much of the western and northern Europe with prevailing westerly to southwesterly flow at mid to upper troposphere. Two main disturbances are forecast during the period. The first one in form of a trough, that is forecast to move from France towards E Germany, the Czech Republic and Poland during the day. The second one will be a deep low pressure system affecting British Isles with heavy rain and severe wind gusts. Wind gusts will be of non-convective origin albeit some instability will be available for offshore low topped convection, especially in the morning and late night hours. Towards southeast, a cut-off low will remain south of Turkey.

DISCUSSION

... NW France, Belgium towards W Germany ...

In conjunction with a mid and upper tropospheric trough, colder airmass will advect over the region, resulting in the steeper lapse rates, reaching over 7 K/km in the 800 to 600 hPa layer. However, with low-level moisture only reaching around 4 g/kg, CAPE values will be marginal at best, very likely not exceeding 200 J/kg. A slight compensation for this should come from the synoptic scale forcing, as suggested by PVA and divergence in the left exit region of the jet-stream feeding into the rear of the trough. A broken band of DMC is forecast, weakly electrified, with some linear segments likely. In the axis of the trough, winds at 850 hPa should reach up to 25 m/s with bulk LLS values above 10 m/s. Furthermore, slight veering of the winds with height will induce SREH 0-1 km values of 100 to 250 m^2/s^2. In such conditions, isolated severe wind gusts are forecast especially along the linear segments of convection. As WRF simulates also some isolated cellular structures, tornado event is not discounted either, given the strong LLS and low LCLs.