Storm Forecast
Valid: Fri 19 Dec 2014 06:00 to Sat 20 Dec 2014 06:00 UTC
Issued: Thu 18 Dec 2014 21:06
Forecaster: TUSCHY

A level 1 was issued for N-Germany mainly for severe wind gusts and an isolated tornado threat.

A level 1 was issued for Scotland mainly for severe wind gusts.

SYNOPSIS and DISCUSSION

Between a deep and broad cyclonic vortex over N-Europe and high pressure just west of the Iberian Peninsula, a steep pressure gradient continues to affect most parts of N/CNTRL Europe.

A cold front crosses Benelux and NW Germany during the start of the forecast period and approaches the Alps during the end of the forecast. A narrow cold-frontal rain band probably evolves along that front. During its passage, strong rain and gusty winds occur but the severe risk is very low due to limited CAPE. The level 1 was not issued for that event.

Another line occurs during the night (probably 00-06Z) as mid-level forcing (in terms of a short wave) crosses the North Sea , Denmark and N-Germany from NW to SE. Timing is still a bit uncertain, but most of the models keep this wave in this outlook period. There is plenty of forcing to work with and also LLCAPE signals appear a bit more robust compared to the previous event (next to colder mid-levels). Therefore severe wind gusts, marginal hail and an isolated tornado event seem possible (forecast soundings show SRH-2km in excess of 400 m^2/s^2 and LCLs lower than 800 m). The latter risk will be enhanced in case of a LEWP-type event or a broken line of storms and even a strong even can't be excluded. Favorable placement beneath the left exit of a 50 m/s mid-level jet and rapid mid-layer cooling support the idea of more widespread SBCAPE build-up and initiation. This risk continues during the following day over Poland!

A similar event unfolds over Scotland during the night, as another short wave races to the SE. Despite somewhat less BL moisture, strong forcing should support a forced line of convection. As 850 hPa winds increase to 30 m/s and the air mass remains well mixed, severe or damaging wind gusts will be the main risk (especially for more elevated places, where even extreme wind gusts could occur).

Both areas were considered for an upgrade, but rather marginal CAPE magnitude keeps both events in an high-end level 1. However both areas could see gusts in excess of 120 km/h (65 kt) at least on an isolated scale.

Elsewhere, no organized DMC activity is forecast.