CONVECTIVE FORECAST
VALID Thu 15 Sep 06:00 - Fri 16 Sep 06:00 2005 (UTC)
ISSUED: 14 Sep 18:38 (UTC)
FORECASTER: GATZEN

There is a slight risk of severe thunderstorms forecast across Greece and Aegean Sea, SWern Turkey

There is a slight risk of severe thunderstorms forecast across SWern Iberian Peninsula

SYNOPSIS

Broad polar trough builds over northern Europe. At its southern flank ... intense frontal boundary affects northern and central Europe. Associated maritime airmasses are characterized by quite rich low-level moisture and neutral to slightly unstable lapse rates. To the south ... Mediterranean is affected by two short-wave troughs SW of Iberian Peninsula and W of Greece.

DISCUSSION

...Greece and Aegean Sea, SWern Turkey ...
Warm and unstable airmass characterized by rich boundary-layer moisture reaching 14 g/kg mixing ratio at Trapani (12UTC) is advected eastward into Greece and southern Aegean Sea as indicated by latest model output. Strong QG forcing at the cyclonic flank of upper jet streak curving around the upper trough is expected ... and nocturnal convection/MCS is forecast in the morning hours. Strong DLS should be present ... and bow echoes/LEWP may form ... capable of producing severe wind gusts and intense precip. Isolated large hail and one or two tornadoes are not ruled out, but chance seems to be quite low. As the upper cut-off moves eastward ... northerly low-level winds and CAA is expected to increase during the day ... and convective activity should spread eastward into SWern Turkey. Decreasing QG forcing should limit severe potential. A couple of events are expected, though. Chance for tornadoes may increase in the late evening as LLS should increase along the coast of SWern Turkey ... and one or two tornaodes are not completely ruled out.

...SWern Iberian Peninsula ...
Models suggest that convective activity will go on in the range of low-level convergence north of surface low pressure system over northern Morocco. Given low level easterly winds and relatively strong upper level SWerly jet ... supercells and multicells are forecast. Large hail, severe wind gusts and intense precip are expected with any supercell that forms. One or two tornadoes are not ruled out along the Iberian coast as LLS may be enhanced near the coast.

...Eastern central Mediterranean ...
Underneath the cut-off trough ... low-level instability and weak vertical wind shear are expected. Showers and thunderstorms are forecast ... and chance for waterspouts should be enhanced.

...Southern Scandinavia ...
Strong upper vort-max is expected to travel eastwards over Scandinavia ... affecting convectively mixed maritime airmass charcterized by steep low-level lapse rates and low-level CAPE as indicated by latest Goteborg sounding. Showers and thunderstorms are forecast ... that should organize into multicells and mesoclyclones due to strong DLS. As LLS will be strong ... tornadoes may form. Severe wind gusts and isolated large hail should be the main severe threat, though. However ... as CAA is expected and amount of low-level moisture is unclear ATTM ... overall threat seems to be too low for a SLGT.

...Southern British Isles, channel region ...
Warm and moist airmass characterized by neutral lapse rates is expected in the range of a warm sector that will be present underneath the strong westerly upper jet. Although amount of instability should be limited ... showers and thunderstorms may form along intense frontal boundary slowly propagating southward. Strong vertical wind shear is forecast ... and severe wind gusts and probably non-supercell tornadoes may be possible.

#