Storm Forecast
Valid: Fri 23 Sep 2011 06:00 to Sat 24 Sep 2011 06:00 UTC
Issued: Thu 22 Sep 2011 17:49
Forecaster: TUSCHY

SYNOPSIS

A strong cyclonic vortex is present over Norway/Finland, which steers more disturbances to the east. Numerous upper lows cross the Mediterranean area and keep thunderstorm activity alive during the forecast period. Cool and dry air with increasing pressure over central Europe precludes thunderstorm development.

DISCUSSION

... Iberian Peninsula and central Mediterranean ...

One 'cyclonic' upper wave over the NE Iberian Peninsula and an upper low over Italy gradually move to the SE. Accompanied cool down at mid-levels and regionally enhanced lift assist in isolated to scattered thunderstorms.... next to orographically bound initiation. Marginal to isolated large hail may be the main hazard. Otherwise, weak shear precludes an organized severe risk.

During the evening/night hours, the thunderstorm activity north/west of the Balearic Islands increases as mid-levels cool down. Abundant CAPE and weak shear may allow a cluster of storms to form, which remains loosely organized. Despite heavy rainfall, no severe risk is expected. It remains a bit unclear if isolated storms also develop south of the Baleric Islands due to somewhat stronger cap/weak lift. We expanded the 15% TSTM region well to the south to account for that uncertainty.

... Estonia, parts of Finland and extreme W-Russia ...

A well mixed post frontal air mass and some diabatic heating assist in some low-end to modest CAPE build up (~ 500 J/kg SBCAPE). Strong gradient flow is forecast with 20 m/s at 850 hPa, so strong to isolated severe wind gusts will be the main hazard. Showers/thunderstorms gradually decay after sunset.