Storm Forecast
Valid: Wed 07 Dec 2011 06:00 to Thu 08 Dec 2011 06:00 UTC
Issued: Wed 07 Dec 2011 01:49
Forecaster: PUCIK

A level 1 was issued for parts of BENELUX and NW Germany mainly for tornadoes and severe wind gusts.

A level 1 was issued for SW Turkey mainly for excessive precipitation.

SYNOPSIS

Very strong northwesterly flow ( induced between the high geopotentials over extreme SW Europe and low geopotentials over N Europe. Northwesterly flow is expected to amplify deep trough over N/Central Europe towards southeast. Several disturbances in terms of short-wave troughs and cyclonic vortices are simulated in this environment. The most important one, forming in the exit region of a strong mid to upper level jet-streak will influence most of Western and Central Europe during the day, including strong wind field at lower levels. Another disturbance with deep low at lower levels will affect the British Isles during the night hours. Further cyclogenesis is forecast over southern slopes of Alpine range and over the Aegean Sea.

Convective weather should be confined mostly to the region of the Aegan Sea and then to the belt of maritime polar airmass characterised by high lapse rates, which will be advected by the northwesterly flow from the Atlantic towards Central Europe.

DISCUSSION

... Parts of BENELUX and NW Germany ...

In the left exit region of a rapidly advancing mid-level jet-streak (over 55 m/s at 500 hPa level), steep PV gradients and considerable values of PVA point to the highly dynamic situation. This should go in hands with very strong wind shear, both at deep and low layers of troposphere. Around 25 m/s flow is predicted at 850 hPa by most of the models, yielding 15 m/s of LLS. Advection of high lapse rates, dry intrusion behind the main stratiform cloud head of the disturbance and a slight increase in the dew point values might aid in the development of marginal latent instability, especially close to the coastline. Nevertheless, CAPE values are not likely to exceed 100-200 J/kg and they will likely not be surfaced based very far inland. A marginal Level 1 is proposed for this region due to the tornado and marginally severe wind gust threat with strongly forced DMC that might develop behind the precipitation rain shield. Threat will be very conditional due to the instability issues and should be most pronounced from 06 to 12 UTC.

... SW Turkey ...

Partly thanks to the mid and upper level forcing from the approaching trough and to the cooler airmass overspreading relatively warm sea, cyclogenesis is forecast over the Aegean Sea. This should factor in the enhancement of a low level flow of humid and warm airmass towards SW Turkey. With steepening lapse rates, CAPE values should gradually increase towards the evening. Thanks to the orographic lifting and flow perpendicular to the coastline (850 hPa speeds over 15 m/s), strong convergence will likely repeatedly initiate several waves of DMC over this region. Sufficiently humid airmass with high RHs at lower levels might promote effective rain producing storms, so with this factor in mind, excessive rainfall threat warranting Level 1 is justified.