Storm Forecast
Valid: Wed 10 Jan 2007 06:00 to Thu 11 Jan 2007 06:00 UTC
Issued: Tue 09 Jan 2007 19:32
Forecaster: GATZEN

SYNOPSIS

European weather pattern changes during the period: A very strong jet streak forms E of North America and moves into north-western Europe during the period. Latest model output indicates 100 m/s winds at the 300 hPa level. To the east, rather sharp trough W of Europe cuts of into Canary Isles region, while European subtropic ridge tilts and moves eastward. At the surface, two strong cyclones travel rapidely eastward underneath the accelerating European trough and north of the strong Atlantic jet streak. Warm maritime air mass is advected into most of Europe, while colder and well-mixed maritime air mass spreads into North Sea region and Scandinavia between both lows. This air mass may become instable underneath the propagating trough due to strong DCVA and relatively weak CAA. Additionally, warm water surface over the North Sea will lead to rather moist low level air mass. Unfavorable vertical wind shear behind the cold front and even only 10 m/s LLS near the coasts is forecast, and current thinking is that severe thunderstorms are not supported by this set-up. To the south, cold front of the low crosses southern British Isles, northern France, Germany, and Poland during the period. At least over France and Germany models indicate some potential instability, while CAPE is forecast to be below 50 J/kg and restricted to low levels. Although it is not ruled out that forcing may lead to deep instability, chance seems to be low as mid-level inversion is rather strong. Thunderstorms that form will have a potential to organize given strong veering winds and resulting high low-level helicity. An update will be warranted due to possible tornadoes when storms will really form. Later in the period, another region of instable air reaches northern British Isles in the range of the dry intrusion of developing Atlantic storm system. This air mass is forecast to be characterized by neutral lapse rates and rather deep instability due to moist low-level air mass. Showers and thunderstorms are expected. Given strong vertical wind shear and favorable veering, showers and thunderstorms will likely organize, and shallow mesocyclones and/or small bowing lines are forecast, capable of producing severe wind gusts and possible a few tornadoes. Soft hail seems to be likely, either. Current thinking is that a level 1 may verify due to severe wind gusts. However, later observations/model data have to proove the development of the dry intrusion and convection during the period, and an update may be warranted in the evening hours. In the Mediterranean, upper low moves eastward, and associated thunderstorms will also move into eastern Mediterranean. Weak vertical wind shear/forcing and weak instability are forecast, and severe storms seem to be not likely.