Storm Forecast
Valid: Sat 18 Nov 2006 06:00 to Sun 19 Nov 2006 06:00 UTC
Issued: Sat 18 Nov 2006 01:48
Forecaster: DAHL

SYNOPSIS

Intense quasi-stationary large-scale upper trough is centered roughly between Iceland and Greenland, yielding a deep southwesterly flow over western portions of Europe. Associated low-level warm-advection regime is affecting SW and central parts of Europe, with a westward-propagating cold front expected to stretch from the Biscay across central France and Germany into southern Scandinavia by 12Z. Stable frontal wave along this boundary is expected to reach the Gulf of Biscay and western France late in the forecast period.

DISCUSSION

... central Mediterranean ...

Scattered thunderstorms should continue ahead of weak vorticity maximum over the central/northern Mediterranean through the period. GFS advertises minimal low-level and weak (10, locally 15 m/s) deep shear, which is also supported by the latest MM5 solution. Given nearly neutral lapse rates, CAPE will likely remain minimal. Though multicellular storms may develop, it does not seem that severe threat will be significant owing to weak kinematic and thermodynamic fields.

... British Isles ...

Scattered thunderstorms will likely continue in association with cellular convection in the polar air mass in the vicinity of the upper thermal trough axis. GFS suggests that CAPE will be deepest where shear will be minimized, and threat for severe thunderstorms should be rather low. However, it seems that low-level shear will be rather strong over the British Isles due mainly to surface friction. Convection should be weaker over land, however, than over the water, but a brief mesocyclone cannot be ruled out especially over the western coastal regions, maybe producing a brief tornado or two as well as marginally severe hail. Given anticipated weakening of the convection as it makes landfall, a categorical risk is not introduced at this time.