Storm Forecast
Valid: Sun 07 Sep 2008 06:00 to Mon 08 Sep 2008 06:00 UTC
Issued: Sat 06 Sep 2008 23:17
Forecaster: DAHL

SYNOPSIS

Rather intense quasi-stationary upper long-wave trough is covering central portions of Europe, attaining an increasingly negative tilt as a vort max rounds its base during Sunday. East of this feature, a plume of moist/unstable air mass is adveced northwards with some weak cyclogenesis expected ahead of the associated cold front over Poland and the Baltic states. More pronounced SFC low pressure center should persist over the North Sea. Elsewhere, quiescent synoptic conditions prevail at the surface.

DISCUSSION

... N Italy ... Austria ... W Slovakia ... NW Balkans ...

MLCAPE on the order of 500 to 1000 J/kg should be realized in the warm-sector air mass E of the central European upper trough. DLS exceeding 25 m/s is simulated across the southern parts of the warm sector over Italy, the N Balkans, and the Alpine region. In addition, local LLS maxima in excess of 10 m/s are anticipated.

Currently, the precip along the deep-layer frontal zone at the E periohery of the upper trough has mainly been of stratiform nature, and uncertainty exists whether isolated cells will form on Sunday. If they do, there will exist a threat for severe evolution given favorable shear, possibly resulting in isolated large hail and severe straight-line wind events. Low-level shear profiles suggest that some of the cells may become tornadic.

... N Belarus ... extreme W Russia ...

Over N Belarus and towards western Russia, there seems to develop a small overlap of 10 m/s LLS and positive CAPE, but with weak DLS. This suggests that some of the cells may develop at least brief mesocyclones, posing some threat for an isolated tornado. However, it seems that the environment conducive to tornadoes will be rather confined spatially, in addition to the allover marginal setup. Will thus not introduce a categorical risk at the moment.

... North Sea ...

Near the center of the deep-layer cyclone over the North Sea, EL temperatures below -40°C are expected, implying that convection is sufficiently deep for electrification, although it does seem that flashes will remain somewhat sporadic. A brief funnel/tornado or two could occur at the Benelux coast where some 7 m/s LLS are expected. This threat seems to be too insubstantial to warrant a categorical risk, however.