Storm Forecast
Valid: Sun 25 Dec 2011 10:00 to Mon 26 Dec 2011 06:00 UTC
Issued: Sun 25 Dec 2011 10:30
Forecaster: SCHLENCZEK
A level 2 was issued for parts of S Norway and Sweden mainly for damaging convectively enhanced wind gusts and the possibility of a strong tornado.
A level 1 surrounds the level 2 for the same type of events but a lower expected coverage of storms.
SYNOPSIS / DISCUSSION
A deepening low pressure system over the British Isles translates northeastwards towards Scandinavia. South of the core of this system, a strong pressure gradient leads to intense wind gusts in parts of N England and Scotland, the North Sea, and S Norway / Sweden that could easily exceed 33 m/s in most places. When the cyclone approaches Norway in the late afternoon / early evening, GFS and HIRLAM show some hints for low-end instability and convective initiation along the cold front where the LL flow is strongest. Some wind gusts should be convectively enhanced and therefore a level 2 is issued. GFS and HIRLAM also indicate very high SRH1 and SRH3 (> 600 mē/sē) ahead of the cold front in combination with 25 - 30 m/s of LL shear. There is a possibility of an isolated strong tornado (F2 - F3 intensity) as well.
Please note that the majority of the wind gusts is expected to be non-convective, otherwise a level 3 would be required.
Some instability is present over the central Mediterranean and will lead to showers and thunderstorms in a rather weakly sheared environment. Due to the absence of a strong background flow, some waterspouts are not ruled out.
