Storm Forecast
Valid: Sun 30 Nov 2008 06:00 to Mon 01 Dec 2008 06:00 UTC
Issued: Sat 29 Nov 2008 23:40
Forecaster: SCHLENCZEK

SYNOPSIS

A huge upper trough is present over Scandinavia and western / central Europe with its southern tip over Gibraltar. An associated surface low over France is forecast to weaken during the period while shifting northeastward. Over the Gulf of Lion, cyclogenesis is expected ahead of the trough with a small but relatively intense 995 hPa surface low moving towards the Gulf of Genua / northern Italy on early Monday morning. The eastern / southeastern parts of Europe will see quiescent conditions under an upper ridge.

DISCUSSION

...W-central Mediterranean...

As the upper trough overspreads the region, some hundred J/kg of CAPE should be released. Even though the thermodynamic conditions are not too favourable for severe thunderstorms, strong QG forcing and intense shear should be expected ahead of the developing surface low. 0-3 km shear in order of 20 m/s, 850hPa winds in order of 30 m/s and SRH3 in order of 200 J/kg will allow organized multicells and maybe a few mesocyclones. Given about 15 m/s LLS near the coastlines, a few tornadoes may occur. Downward momentum transport as well as evaporative cooling will provide a distinct possibility of severe gusts. At the moment it is rather uncertain whether isolated storms or shallow convective lines are more likely. Recent GFS runs show very high (> 600 J/kg) SRH3 and intense shear ahead of the surface low over the Gulf of Genua. This region has to be monitored as widespread severe gusts and / or strong tornadoes may become likely if organized convection develops there.

From Gibraltar to the Bay of Biscay, deep layer shear is in order of 10 m/s and both SRH and forcing are much weaker than in the other region. An isolated waterspout is not ruled out but severe weather appears to be unlikely.


...East Atlantic, Irish Sea...

In the wake of the trough, some low-end instability will lead to isolated showers and thunderstorms. Lightning should be very sporadic and a thunderstorm area is not warranted. Severe weather is rather unlikely as vertical shear and forcing are weak.

Isolated thunder is also possible in parts of Austria and SE Germany.