Storm Forecast
Valid: Sat 23 Feb 2008 06:00 to Sun 24 Feb 2008 06:00 UTC
Issued: Fri 22 Feb 2008 21:57
Forecaster: SCHLENCZEK

SYNOPSIS

Ahead of a large upper trough over the North Atlantic, an intense surface low that is initially located southwest of Iceland will move northeastward. Its cold front will approach parts of Norway in the latter part of the forecast period. Between this upper trough and a high pressure area over central Mediterranean, strong WAA towards central and northwestern Europe is forecast to continue. A strong polar jet over central Europe with wind speeds near 80 m/s at 300hPa will continue southeastward. Unstable conditions are expected over extreme southwestern Europe and eastern Mediterranean where two weak upper lows are present. Subtropical jet over Morocco will spread northeastward and affect southern Spain and Portugal with its left exit region.

DISCUSSION

Morocco, southern Spain and Portugal

Ahead of the upper low, an unstable airmass with a few hundred J/kg of CAPE is advected to southern Spain and Portugal. 0-6 km deep layer shear below 15 m/s and rather weak forcing should limit the severe threat but a low level jet with more than 15 m/s at 850hPa and rich LL moisture will support low level moisture inflow. Storms may persist over some regions for a long period and torrential rainfall will lead to an enhanced flash flood threat.

Aegean Sea

Showers and isolated thunderstorms will likely develop in a weakly sheared environment with a few hundred J/kg of CAPE southwest of Crete. As geopotential heights are forecast to rise, lightning should occur too sporadic to draw a thunderstorm area.

Central Norway

The cold front of the strong surface low near Iceland should arrive at central Norway on Sunday between 00:00 UTC and 06:00 UTC. An intense jet streak with more than 80 m/s forecast at 300hPa on Sunday 00:00 UTC will provide strong upper level divergence beneath the cold front. Very strong QG forcing should create one or two convective lines in the slightly unstable airmass near the cold front that may produce isolated severe wind gusts. As 850hPa wind speeds will likely stay below 30 m/s, severe threat should not exceed the level-one threshold.