Storm Forecast
Valid: Thu 02 Nov 2006 08:00 to Fri 03 Nov 2006 06:00 UTC
Issued: Thu 02 Nov 2006 07:57
Forecaster: GATZEN

SYNOPSIS

Extensive upper trough has built over Europe, reaching into Mediterranean Sea. Cold arctic air has flooded into most of central and eastern Europe ... and weak instability is expected to form over the rather warm North and Baltic Sea. Over Mediterranean ... dry and cool air mass advected southward ... and spreads into eastern Mediterranean. Ahead of the trough's base ... cyclogenesis is forecast along the cold front ... and deepening low should move into Aegean late in the day. Over south-western Europe ... warm Atlantic air mass affects parts of Iberian ahead of a weak cut-off low.

DISCUSSION

Frontal wave has begun to form along the cold front over southern Italy. Given QG forcing ahead of approaching vort-max curving around the long-wave trough's base ... this low is forecast to deepen while moving south-eastward. In the warm sector ... unstable air mass is present. Latest Trapani sounding shows rather deep moisture below steep lapse rates ... and latest observations indicate dewpoints of 12..17°C over Aegean. Given westerly winds in the warm sector initially ... chance for severe thunderstorms will be limited during the next hours south-east of Italy. Increasing veering is expected later on as the low moves into Greece. During the evening/night ... southerly winds will become likely over Aegean Sea. As strong upper westerly jet is expected to spread across Greece ... favorable veering and vertical wind shear will be likely to develop. Along the cold front ... a couple of thunderstorms are expected to merge into an MCS ... moving eastward and capable of producing severe wind gusts along the leading LEWP. Ahead of the front ... some storms are expected to form due to increasing QG forcing and LL WAA. Given favorable veering profiles ... supercells should be possible ... capable of producing large hail, severe wind gusts and tornadoes. At least a level 1 seems to be warranted. Limiting factor is relatively weak instability and rather cool low-level air mass. However ... synoptic situation seems to have the potential for widespread severe wind gusts as well as for a couple of mesocyclones ahead of the main system ... and evolution of pre-frontal instability has to be monitored during the day.

South-western Iberia

Ahead of weak cut-off low ... rather warm and unstable air mass characterized by steep mid-level lapse rates and rather poor low-level moisture is present over south-western Iberian Peninsula. Latest observations show at least knee-deep dewpoint about 16°C ... and GFS seems to be right showing a few 100's J/kg CAPE spreading into southern Portugal region. As relatively weak upper vort-max/jet spreads into southern Iberia ... and given WAA ... QG forcing should be present. GFS shows convective precipitiation that spreads over most of southern Iberia ... and given dry low levels ... most convection should be elevated. Over southern Portugal region ... chance for surface-based convection increases due to moist low levels ... and given south-easterly winds below the westerly jet ... veering profiles should be favorable for mesocyclones ... capable of producing large hail and probably a tornado. Limiting factors will be weak forcing, rather dry boundary layer, and only moderate vertical wind shear. However ... given the fact that thunderstorms have already formed off-shore ... is seems that a (marginal) level 1 is warranted today.