Storm Forecast
Valid: Thu 17 Apr 2008 06:00 to Fri 18 Apr 2008 06:00 UTC
Issued: Wed 16 Apr 2008 21:53
Forecaster: GATZEN

SYNOPSIS

Very cold weather situation goes on over Europe, with a blocking high over Iceland and low geopotential over most of Europe. Cold/dry air mass is present over a widespread area. Warm subtropical air mass is present to the south of the polar jet that extends from Iberian Peninsula to northern Tunisia and further to south-east Mediterranean. During the period, another amplified trough spreads eastward into Iberian Peninsula. Downstream, warm air from northern Africa spreads into east Mediterranean.

DISCUSSION

West Iberian Peninsula

Rather strong cyclogenesis is expected in the range of a strong upper jet streak that spreads eastward over Iberian Peninsula. In the warm sector of the low pressure system, warm and moist low-level air mass is forecast to spread into Portugal. This air mass will likely be characterized by neutral lapse rates. Stratiform precipitation and embedded convection is forecast along the cold front that will cross Portugal during the night. Given the possibility of deep convection and strong veering profiles in the range of the warm sector, a few tornadoes along the leading edge of the front are not ruled out. Threat seems to be quite low, though. In the cold sector of the following low, latest model output suggests neutral to unstable lapse rates and quite rich boundary-layer moisture. Given CAPE and some low-level convergence in the range of the upper trough axis, thunderstorms will likely develop, but given rather weak vertical wind shear, chance for severe convection seems to be low.

West Mediterranean

At the eastern flank of expanding Atlantic trough, a strong upper jet streak extends into west Mediterranean, providing strong QG forcing. Affected air mass is characterized by steep low-level lapse rates, while warm mid-levels are forecast to cool in the range of the propagating trough. While boundary-layer moisture is not well-developed, amount of CAPE is questionable at this time. However, weak CAPE seems to be reasonable, and showers and thunderstorms will likely develop. Given strong DLS of 25 m/s in the range of the upper jet streak, storms may become well organized and may merge into MCSs, capable of producing bowing lines. Chance for severe weather is limited by rather cool boundary layer air mass and convection may be embedded in stratiform rain.