Storm Forecast
Valid: Wed 21 Sep 2011 06:00 to Thu 22 Sep 2011 06:00 UTC
Issued: Tue 20 Sep 2011 22:21
Forecaster: KOROSEC

A level 2 was issued for parts of Greece and western Turkey mainly for excessive convective rainfall, large hail, strong to severe wind gusts and a tornado threat.

A level 1 was issued for Greece, Ionian sea and Aegean sea mainly for waterspouts and locally excessive rainfalls.

A level 1 was issued for parts of northern UK mainly for strong/severe wind gusts and brief tornado or two.

SYNOPSIS

The main synoptic features today will be two cyclonic vortices, one over SE Mediterranean and another vortex situated over the Northern Atlantic with its short-wave trough progressing over northern UK towards Scandinavia. At surface, a broad surface low with cold front moves across Aegean sea into western Turkey while deep surface low makes only slow progress beneath the vortex near UK. A cold front pushes eastwards across North sea. Elswhere, stable conditions prevail.

DISCUSSION

... parts of Greece and western Turkey ...

The still organized upper low continues across the SE Mediterranean, it moves from eastern Greece into western Turkey during the forecast period. Characterized by the still cold mid levels, a well-defined DCVA, very impressive moist influx and strong WAA on its front side, an excessive convective threat will continue for another day there. A level 2 has been placed where the flash floods threat seem maximized. Parts of NW Turkey were also included into higher risk given the likelihood of strong orographic precipitation partly combined with convection on the back side of the system onshore. Especially the SW Turkish coast will be in pole for numerous severe storms where strong instability and shear/SREH favours well organized convection. Those will be capable of producing large hail, severe winds and also a tornado or two. Persisting southerly flow will maintain orographic lifting, resulting in excessive rainfalls which will be enhanced by the convective storms.

In the wave of the upper level vortex, the coastal areas of Greece including Aegean and Ionian sea will be under weak pressure gradient and wind field. With the current high SSTs there and with a moderate instabilily/lapse rates available, expect a few waterspouts to occur. Slow moving storms will again support excessive convective rain locally.

... parts of northern UK ...

Quite impressive mid-level jet rounds the trough axis moving across the northern UK, providing strong shear at all levels. Models are in an agreement of marginal instability release along the rapidly moving cold front. Some convective activity is expected with a convective line possibly to form along the frontal convergence. With very strong mid/low level wind profiles and shear, some organized storms could take place within the line. The main threat will be strong/severe wind gusts while given the strong LL shear and SR helicity available, a tornado or two could occur as well. Front should rapidly move across the North sea and reach SW Scandinavia in the early night.