Storm Forecast
Valid: Thu 08 Jan 2015 06:00 to Fri 09 Jan 2015 06:00 UTC
Issued: Wed 07 Jan 2015 22:26
Forecaster: GATZEN

SYNOPSIS AND DISCUSSION

In the wake of an amplified trough across eastern Europe, cold and dry air masses have spread into eastern Europe, and thunderstorms are not expected. Upstream, a strong westerly flow evolves between an Atlantic ridge and a trough across Greenland. A sharp short-wave trough will rapidly move into central Europe during the period. In its wake, a northerly jet stream will spread into the British Isles and North Sea region.

Main concern for convective initiation is the strongly-forced situation due to the trough passage from the British Isles into central Europe. Cold and dry air masses at mid-level will rapidly spread eastward. At low levels, a moist maritime air mass will advect into Germany ahead of a cold front that moves into Poland in the evening hours. A well-mixed polar air mass will follow the cold front.

The forecast structure of the short-wave trough is different for latest models. The ECMWF indicates a quite dynamic situation with a well-developed tropopause fold in the wake of the trough, together with a 50 m/s mid-level jet streak. If this scenario comes true, CAPE is expected due to the overlap of moist low levels and increasing lapse rates along the upper level front. Thunderstorms with a potential of severe wind gusts could be expected from the southern British Isles across Belgium in the afternoon hours, spreading into the western Alps and southern Germany in the evening.

However, GFS shows consistent results for the last model runs that indicate weaker upper level frontogenesis along the flanks of the trough. Following this model, lapse rates will be weaker with low equilibrium level heights. Favouring the GFS solution, thunderstorms are not expected to be likely and a thunder line is not warranted, although a few storms are not ruled out.

Some more deep moist convection can be expected near the base of the trough across the North Sea, where the rather warm sea surface leads to an overlap of moist low-level air and neutral to unstable lapse rates. Showers and thunderstorms are expected. Although severe wind gusts are possible, the convective contribution is expected to be weak.