Storm Forecast
Valid: Thu 31 Dec 2015 06:00 to Fri 01 Jan 2016 06:00 UTC
Issued: Wed 30 Dec 2015 20:10
Forecaster: GATZEN

SYNOPSIS and DISCUSSION

High amplitude ridge over western Europe will weaken durung the forecast period between a short-wave trough moving into the North Sea and the continental long-wave trough across NE Europe. The vort-max of the short-wave trough will enter western and central Europe during the period. The northern part will cause rapid cyclogenesis west of Norway, the southern will start to travel south-east along the periphery of the east-European trough. Another vort-max will follow, affecting the British Isles.

Very dry air masses cover all of eastern Europe. Rather rich moisture is present in the western portions. Lapse rates are weak over most regions due to pretty warm mid levels except for NW Europe, where mixed maritime air masses are present at the cyclonically sheared flank of a strong mid-level jet and associated stretching.

On Thursday, the short-wave trough will move into the North Sea region. It is accompagnied by steep lapse rates, allowing for weak CAPE. However, synoptic forcing is pretty weak and low-level convergence will be too marginal to allow for a lot of storms. Over the sea, a few showers and thunderstorms are forecast. More storms may form along the coasts of SW Norway in the wake of the strong surface low that moves north. Weak vertical wind shear will limit storm organization.

The following vort maximum will cross the British Isles during the noon. Although synoptic forcing will be limited as well, rather rich low-level moisture and convectively mixed maritime air masses will likely allow for thunderstorms. Strong low-level flow around 20 m/s at 850 hPa indicate a threat of severe wind gusts especially when lines of storms manage to form. Given limited forcing and that severe convective wind gusts are expected to occur only isolated, a level 1 is not issued. Convective activity is expected to weaken later in the period across the British Isles due to weaker moisture, but some thunder is well possible until the end of the period across the North Sea.