Storm Forecast
Valid: Sat 08 Mar 2008 06:00 to Sun 09 Mar 2008 06:00 UTC
Issued: Fri 07 Mar 2008 22:14
Forecaster: DAHL

SYNOPSIS

Main feature this period will be a rather intense quasi-stationary upper long-wave trough/cut-off cyclone over the central Mediterranean. East of this trough, warm but quite dry air is present over Turkey and the Black Sea. The northern branch of the upper frontal zone is extending across the northern portions of Europe. An imbedded Atlantic trough will continue digging eastwards, reaching western continental Europe towards the end of the period. Attendant to this feature is quite an extensive SFC low, covering much of the northern Atlantic and the western portions of Europe early on Sunday.

DISCUSSION

... western Turkey ...

GFS is reluctant to come up with any CAPE in the warm air mass ahead of the central Mediterranean upper trough owing to quite feeble low-level moisture. Friday's 12Z ascents from Turkey indicate environments conducive to elevated convective activity, however, and there does not seem to be a compelling reason not to expect similar thermodynamic environments also on Saturday. Main negative will be the lack of large-scale forcing for ascent, though a cross-frontal mesoscale circulation will likely persist, maintaining a weak threat for some elevated convection over western Turkey. After 18Z, DCVA-related ascent should overspread the frontal boundary, which may result in an increased threat for isolated elevated storms. However, convective threat should be too low for a thunderstorm area.

... central Mediterranean ...

More widespread convective threat will exist in the modified polar air beneath the upper themal trough region over the central Mediterranean. Deepest convection should occur in nearly barotropic - and hence minimally sheared - environment, but some severe threat exists as nearly saturated surface-based air mass and slightly superadiabatic lapse rates should supprt strong LL buoyancy. This may result in a few waterspouts. However, lapse rates appear to be slightly too weak to necessitate a large categorical severe thunderstorm risk. Over the southern Ionian Sea, strong DCVA-forced ascent should enable deep convection in the evening hours. This activity will benefit from 20 m/s DLS, and moderately well-organized multicellular storms and isolated mesocyclones may occur. These will have the potential for marginally severe wind gusts, in addition to the slightly enhanced tornado risk owing to the favorable LL thermodynamic environment.