Extended Forecast
Valid: Wed 27 Feb 2008 06:00 to Thu 28 Feb 2008 06:00 UTC
Issued: Mon 25 Feb 2008 18:18
Forecaster: TUSCHY

SYNOPSIS

A southward displaced frontal zone, running from central France, to the Alpes to Belarus only shifts more towards the south / east during the next 24 hours, separating a more humid and warmer airmass to its south from a much drier and colder airmass to its north / west. Activation of the frontal zone regarding precipitation dispersal depends on local topography and influence of complex upper-level geopotential height distribution, featuring numerous weak troughs.
Our main system of interest is a 975hPa depression over S-Norway / Sweden which drifts towards the ENE-NE while weakening as dynamics / thermodynamics won't be supportive for further intensification. A few stronger showers / short-lived thunderstorms could occur over S-Norway and Sweden, but coverage and intensity will be insufficient for a thunderstorm area.

The weather over the Mediterranean remains mostly dry and stable.

DISCUSSION

... The Netherlands, NW-Germany, parts of central Germany and NW / central Poland...

This area is characterized by a cool and well mixed postfrontal airmass, spreading southeastwards during the morning hours. The first focus for low-topped convection exists over N-central Germany in the morning hours until about 12Z as upper-level trough axis approaches from the NW. Numerous negative points including low surface dewpoints ( 3-4°C ), marginal moisture content in the lowest 1000 m and weak forcing are present and should preclude a higher thunderstorm risk. However, LL lapse rates are steep and main inversion climbs to near 3km so a few more robust updrafts still look possible, not necessarily electrified. The wind field would be supportive for low-level mesocyclones, but currently predicted traces of instability preclude any level areas. If dewpoints behind the cold front recover better than currently anticipated or forcing is stronger, higher probabilities may be needed.

The risk continues for the remainder of the forecast mainly in a swatch of the Netherlands SE-wards, where some 0-3km CAPE and strong helicity overlap. Again, we decided to issue no highlighted / level area as instability is marginal at best and airmass does not seem auxiliary for good updraft support .

The same for central Poland.

Gusty winds and sleet / marginal hail could accompany stronger convective activity in the area of interest.