Storm Forecast
Valid: Sat 03 Oct 2009 06:00 to Sun 04 Oct 2009 06:00 UTC
Issued: Fri 02 Oct 2009 21:17
Forecaster: KOROSEC

A level 1 was issued for North and Baltic sea, Denmark, southern Sweden and coastal areas of N Germany, Poland and Baltic states mainly for strong winds and tornadoes/waterspouts.

A level 1 was issued for parts of Ionian sea, most of Greece, Aegean sea and extreme W Turkey mainly for excessive rainfall and tornadoes/waterspouts.

SYNOPSIS

A deep and intense trough with developing cyclogenesis ejects into North Sea in the morning and moves across northern Europe during the forecast period. A strong cold front accompanied by this trough rapidly moves ESE-wards and convective activity is expected along it. A weakening trough moves across southern Balkan peninsula during the day and brings another day of active storms with flash floods and tornado threat. Cool weather with stable conditions persist over the rest of Europe.

DISCUSSION

... North and Baltic sea, Denmark, southern Sweden and coastal areas of N Germany, Poland and Baltic states ...

During the morning hours, a deep and intense trough arrives into Northern Europe and rapidly moves across southern Norway and Sweden during the day. Accompanied by this trough, a deep surface low first intensifies over North Sea in the morning hours, central pressure likely down to near 970 hPa, and is then expected to approach Baltic sea by Sunday morning.

A very strong mid-level jet streak with 50-60 m/s wind speeds at 300 hPa digs in and create highly sheared environment. 20-30 m/s of deep layer shear should easily be available, as well as near 15m/s in the lowest 1 km layer shear. Locally, near 200-300 m^2/s^2 of helicity is simulated along the leading cold front. Steepening mid-level lapse rates should result in marginal instability. And especially along the cold front a few hundreds of MLCAPE should result, more likely over still above normal sea temperatures.

High shear, marginal instability and strong frontal forcing suggest that organized storms are possible, capable of producing strong winds as well as a couple of organized mesocyclones. Tornado threat will exist especially along/ahead of the rapidly moving cold front where shear/helicity and instability will be maximized. Behind the cold front, high 0-3 km MLCAPE and steep LL lapse rates in rapidly decreasing shear will favour formation of funnel clouds/waterspouts. For this reason, level 1 was extended a bit more to the west towards North Sea and Denmark.

... parts of Ionian sea, most of Greece and extreme W Turkey ...

An active short wave trough and surface cyclone, which was in effect during the last couple of days over southern and central Mediterranean, continues to weaken as it moves NE-wards onto the southern Balkan peninsula. A cold front is approaching from the north across the Balkans. Moderate instability is forecasted over warm waters, overlaping with 0-6 km bulk shear of near 10-15 m/s across the level 1 area. Numerous storms including organized storm clusters will be on going. High PWAT values suggest that the main threat will be excessive rainfalls expecially over Ionian sea and western Greece. Slow moving storms and steep LL lapse rates in the wake of trough also rise threat for waterspouts.

A level 1 was extended also towards the western Turkey where a threat for tornadoes exists mostly along the coast and Aegean sea. Strong low-level SSE-erly winds will create favorable backing flow, while 0-3 km and 0-6 km shear will be near 15-20 m/s. Models also simulate 0-3 km SR helicity of near 200 m^2/s^2, overlaping with MLCAPE near 1000 J/kg. Therefore a couple of supercells with threat for tornadoes and locally marginal hail will be possible. More to the north, along the slowly southwards pushing cold front, models simulate higher moisture content over NW Turkey and SE Bulgaria and therefore a threat for an excessive rainfalls will also exist.