Storm Forecast
Valid: Sat 23 Sep 2006 09:00 to Sun 24 Sep 2006 06:00 UTC
Issued: Sat 23 Sep 2006 08:28
Forecaster: DAHL

SYNOPSIS

An omega-type upper pattern is in place over Europe ... with vigorous but slightly de-amplifying upper trough located over W Europe/E Atlantic ... and a rather small but intense upper cut-off low over the S Balkan States/Aegean Sea. Plume of warm and partly unstable air is extending from the central Mediterranean northwards into Norway ahead of the W-European long-wave trough.

DISCUSSION

W Mediterranean ... E Spain ... France

It seems that quite moist LL air mass is present over the W Mediterranean and E Spain ... supporting CAPEs in the 1500 to 2000 J/kg range. Instability should rapidly decrease to the north though a few hundred J/kg of CAPE may still exist e.g. over France. Deep-layer shear will remain ample ... with 20 to 25 m/s expected over France ... and about 15 to 20 m/s over the W Mediterranean. LL shear is progged to increase markedly over France in the afternoon and evening hours ... with more than 15 m/s bulk shear over France at 18Z per latest GFS run.

Though CAPE should remain weak over France due mainly to mid/upper cloudiness ... it seems that TSTMS will form upon approach of strong DCVA-related ascent overspreading the region in the late afternoon hours. Chances exist that linear convective system will develop over central and southern France in the evening hours ... which may eventually build southward into the W Mediterranean. Expect severe wind gusts and some hail with the French system ... though quite strong LLS should also be supportive of a couple of tornadoes. Farther south in rich-CAPE environment ... supercells capable of producing very large hail and damaging wind gusts may develop late Saturday night. A tornado cannot be ruled out either ... but rather strong capping and weak LLS may limit the tornado threat somewhat. ATTM evolution of instability over France ... and coverage of severe storms over the W Mediterranean on Saturday night are somewhat uncertain ... and will thus issue only a LVL1 ATTM. An upgrade may be considered later in the day.

Greece ... Aegean Sea

Strong speed max revolving around the Aegean upper low will affect S Greece and the S Aegean Sea providing 20 m/s DLS over S and W Greece ... increasing to 35 m/s DLS by late Saturday night. CAPE is rather weak ... but little low-level capping and rather strong LL buoyancy coupled with low LCL heights points at some tornado potential despite a lack of significant LLS. A few supercellular storms appear to be possible ... though multicellular storms potentially evolving into bowing line segments may also occur. Expect isolated damaging winds ... hail ... and possibly a few tornadoes. Storms should persist through much of the night.

Ireland

It seems that some potential for shallow supercells exists over Ireland ... where strong shear profiles are in place. Given minimal capping and low LCL heights ... a few brief tornadoes may occur ... as well as some hail and strong/severe wind gusts. Though coverage may be somewhat marginal ... a level one appears to be marginally warranted.