Storm Forecast
Valid: Sat 01 Dec 2007 06:00 to Sun 02 Dec 2007 06:00 UTC
Issued: Fri 30 Nov 2007 23:09
Forecaster: DAHL

SYNOPSIS

A large-scale upper low is present south of Iceland and will deamplify as more of a progressive upper flow pattern is establishing over the Atlantic/Europe. Lead vort max will reach western Europe towards Saturday evening, maintaining residual large and intense SFC low complex over the NW quadrant of Europe and the E Atlantic. The lead vort max is currently not simulated to become baroclinically unstable so that no appreciable cyclogenesis is anticipated. However, a weak frontal system will be associated with it.

DISCUSSION

... N France ... Benelux ... NW Germany ...

A weakening cold front will cross central Europe during the day, and it seems that some shallow convection may occur along it. However, weakening mesoscale forcing for ascent is anticipated as the associated upper trough lifts out to the northeast ... and convective activity should not be too impressive. However, the background gradient flow may locally be augmented by downward transport of momentum by the convection.

There are some indications that convection may develop along the weak cold-frontal boundary that should stretch from N France across central Benelux into NW Germany around Sunday 00Z. Shear and deep-layer forcing for upward motion should be abundant along this boundary, the only - and quite significant - uncertainty being the buoyancy. If it should indeed be present, a shallow, strongly forced linear convective system could develop, with a threat for marginally severe wind gusts and possibly a tornado or two.

In the wake of this system, relatively deep polar-air convection should spread from the North Sea into N France, Benelux, and NW Germany late in the evening/night. Though deep shear is expected to be rather weak, ample low-level shear is simulated. The most favorable environment will likely exist in the coastal regions where SFC cooling has not stabilized the air mass yet, and where at the same time low-level shear will be augmented owing to surface friction. This implies that a brief tornado or two could be associated with this activity.

These two potential foci, the linear system, as well as the postfrontal convection, marginally warrant a level one threat.