Storm Forecast
Valid: Thu 17 Jan 2008 03:00 to Fri 18 Jan 2008 06:00 UTC
Issued: Wed 16 Jan 2008 19:53
Forecaster: GATZEN

SYNOPSIS

Delta of strong westerly flow over the Atlantic is present over western Europe. A very strong jet streak will reach the southern British Isles at around 03:00 UTC and is forecast to spread into west Mediterranean later on. Moist maritime air mass is advected into western Europe in the range of associated low pressure systems. Over Mediterranean, low geopotential is centered over the central regions, where air mass is at least slightly unstable.

DISCUSSION

British Isles

A strong upper jet streak reaches the British Isles early in the morning. In the range of the delta flow regime over western Europe, the jet streak is expected to turn south-eastward, while an amplifying short-wave trough is expected to cross the British Isles, Benelux, and Germany during the period. At lower levels, a tongue of very moist air mass is expected in the range of the warm sector of intensifying surface low pressure system. Current thinking is that strong QG forcing will be present, and warm air mass may become slightly unstable. It will reach Ireland late in the night, where surface-based CAPE is likely due to rather warm water surface. Along the following cold front, a convective line is possible, capable of producing some thunder. Given very strong vertical wind shear and favorably veering profiles, bowing lines and shallow mesocyclones are not ruled out, capable of producing severe wind gusts, small hail, and tornadoes. Some tornadoes may be strong. West of the cold front, Irleand is affected by the trough axis of the following short-wave trough. Models indicate some instability, and showers are forecast, thunderstorms are also not ruled out. Given persisting favorably wind shear, severe wind gusts and a few tornadoes are not ruled out.

Further east, low-level air mass seems to be rather stable initially, and CAPE is expected to be elevated in the range of the occluding frontal system over most of England. However, will not rule out some embedded convective cells that may produce isolated thunder. Although the chance seems to be rather weak, it is not excluded that (strong) tornadoes may occur, given favorably veering winds. Chance seems to be too low for a categorical risk, though.

Later in the period, northern France, and Benelux will be affected by the occlusion of the low pressure system. Elevated instability may still be present as indicated by latest model output, but deep convection seems to be questionable. However, a few thunderstorms are not excluded to occur, with a very weak chance that tornadoes and severe wind gusts will occur.