Storm Forecast
Valid: Mon 12 Sep 2011 06:00 to Tue 13 Sep 2011 06:00 UTC
Issued: Sun 11 Sep 2011 18:41
Forecaster: TUSCHY

A level 1 was issued for NE Poland, extreme W-Belarus, parts of Lithuania and Latvia mainly for isolated large hail and strong wind gusts.

SYNOPSIS

Ex-hurricane Katia races eastwards and affects parts of NW-Europe during the forecast. 300 hPa temperatures well above -30°C ! and cyclone phase diagrams indicating some type of shallow warm core structure, so Katia will be an high-energetic/increasingly baroclinic depression. Further extratropical transformation expected but right now there are no hints on any enhanced thunderstorm activity with Katia. Very strong wind field is expected to affect Scotland/parts of UK. Please refer to the UK Met Office at www.metoffice.gov.uk/weather for further informations.

Otherwise various upper troughs affect most parts of Europe with unsettled conditions.

DISCUSSION

... Level 1 ...

An eastward moving cold front serves as focus for some thunderstorm activity. Within the level 1, best CAPE/shear overlap exists with marginal/isolated large hail and strong wind gusts. Main time frame for better organized multicells exists between 12Z-18Z. Further east/south, weaker CAPE and shear preclude the development of organized storms. Thunderstorms move to the east during the night with a constant weakening trend.

... Lightning area over the central Mediterranean ...

A flat upper trough affects the highlighted area. Daytime driven thunderstorm activity (onshore and offshore) is forecast with weak shear and locally modest CAPE. Locally heavy rain will be the main risk, but I'd like to see better moisture in the mid levels for a more excessive rainfall event. However, with 700 hPa moisture locally exceeding 60% and rich BL moisture (Td above 20°C), isolated excessive rainfall can't be ruled out completely. No level will be introduced for that risk due to the isolated nature.