Storm Forecast
Valid: Wed 18 Oct 2006 07:00 to Thu 19 Oct 2006 06:00 UTC
Issued: Wed 18 Oct 2006 07:13
Forecaster: GATZEN

SYNOPSIS

Central European omega continues ... with two troughs centered W of Biscay and over Crete. Ahead of both troughs ... unstable air mass is present ... and convection is expected to go on. At the surface ... frontal boundary affects western Europe. W of this boundary ... moist convectively mixed Atlantic air mass spreads into Iberian Peninsula ... Bay of Biscay ... and SWrn British Isles. S of continental high centered over eastern Europe ... intense surface low has formed in the range of the cut off over Aegean. Strong frontal system is expected to affect southern Turkey today.

DISCUSSION

Southern Turkey

Large MCS has formed S of Turkey ... affecting the coastal regions. This system is expected to go on during the forecast period and should spread eastward as surface cold front moves into the region. Although we have no actual sounding data that characterizes the warm air mass ... we expect that steep lapse rates are present in mid-levels ... while rather moist air mass is present in the boundary layer as indicated by latest surface observations. Given well-developed MCS ATTM ... and strong vertical wind shear with easterly surface winds and rather strong southerly jet streak aloft at the 500 hPa level ... expect that this convective system will go on during the forecast period until surface cold front spreads eastward in the evening/night hours. Severe wind gusts should be the most significant severe threat ... but given favorable wind shear in the warm sector and quite moist low-level air mass ... embedded mesocyclones may also pose a slight chance of large hail and tornadoes. Despite of this ... intense precipitation may lead to flash flooding over the southern portions of Turkey today.

Western Europe

Very moist maritime air mass spreads northward over western Europe with strong southerly flow. Soundings indicate dewpoints up to 20°C over south-western Iberian Peninsula. In the range of this air mass ... satellite images show much convective activity that spreads into Iberian Peninsula, Bay of Biscay, and southern British Isles. Today ... convective activity is expected to go on in the range of the strong southerly flow E of the surface trough over north-eastern Atlantic. This should be supported by upper vort-max traveling north-eastward into France during the day. Given quite strong vertical wind shear especially in low levels near the coasts ... embedded mesocyclones are not ruled out ... capable of producing severe wind gusts. There is also a slight threat of tornadoes given low LCL heights and strong LLS locally. Chance for severe convection should gradually decreases over land and the northern portions of the risk area ... where low levels tend to be rather cool and stable. Although we do not issue a level 1 over southern British Isles ... an isolated event is not ruled out completely.

Southern France

Latest observations show a strong increase of low-level moisture near the Balearic Islands. Latest soundings indicate that there is a strong capping inversion with steep lapse rates from 800 to 550 hPa. Given surface dewpoints up to 20°C actually ... quite large CAPE should be possible during the next couple of hours. As southerly flow goes on ... unstable air mass is forecast to spread into north-western Mediterranean. As the upper vort-max of Atlantic trough approaches ... models show strong QG forcing along the northern part of the WAA regime ... and it seems that widespread convection is likely over southern France in the evening/night hours. Given strong southerly jet streak moving northward ... and south-easterly low-level winds advecting moist air mass ... convection should likely merge into a MCS. It is not ruled out that this convective system will produve severe wind gusts ... as strong LLJ is forecast to develop over southern France. In the range of this LLJ ... strong low-level vertical wind shear will be favorable for embedded mesocyclones ... capable of producing large hail and tornadoes. Limiting factor is quite stable boundary layer ... and main convection is expected to be elevated. However ... a few events are not ruled out. Intense precip and flash flooding should be also possible during the forecast period.