Storm Forecast
Valid: Fri 07 Dec 2007 06:00 to Sat 08 Dec 2007 06:00 UTC
Issued: Thu 06 Dec 2007 22:18
Forecaster: GROENEMEIJER

SYNOPSIS

Friday at 6:00 UTC... a surface low is located under a mid/upper trough over the northern North Sea. Ahead of the trough lies a diffuse NE-SW oriented cold front expected along a line from NW Germany to NW France. The eastward-moving front that is preceded by a relatively moist warm conveyor belt, is closely followed by an instant-occlusion type disturbance.
The surface low over the North Sea moves southeastward as the trough and the NNWly jet upstream of it dig into the central Mediterranean. Cyclogenesis is expected to occur in the lee of the Alps in the afternoon before the surface low moves over the Adriatic Sea during the evening and night.

DISCUSSION

NW and N Germany...

A vorticity maximum currently over Ireland is expected to track to the east during the night and be located over the Benelux/NWrn Germany at the beginning of the forecast period. Interaction of an associated surface trough/low with the frontal zone ahead of it will likely aid in improving low-level directional shear as its moves closer to the diffuse frontal zone ahead of it. Within this entire zone abundant low-level moisture will probably linger on, which is consistent with AFWA MM5 and GFS 18Z simulating some instability reaching up to 500 hPa. The strongly-sheared environment and presence of surface-based instability indicates that a threat of intense convective lines as well as isolated rotating updrafts exist. These may produce severe wind gusts and perhaps one or two tornadoes.This risk should diminish during the day as low-level moisture decreases.

Central Italy, the northern Adriatic and its coasts...

As the left exit region of the strong mid/upper jet moves across the Western Alps into the central Mediterranean, low-level convergence may well lead to scattered thunderstorms within more widespread areas of stratiform rain. The storms wil likely form within the northern parts of the indicated area before moving southeastward. Although the storms are expected within an area of moderate vertical wind shear, very weak CAPE suggests the severe weather threat will be small enough not to warrant a threat level.