Storm Forecast
Valid: Sat 08 Nov 2008 06:00 to Sun 09 Nov 2008 06:00 UTC
Issued: Fri 07 Nov 2008 23:36
Forecaster: DAHL

SYNOPSIS

Dominant feature this period will be an intense upper jet streak moving towards the British Isles/Channel region until early Sunday morning. A fairly intense SFC will develop underneath its left-exit region W of the British Isles at the periphery of a large-scale quasi-stationary SFC low complex over the N Atlantic.
A weak upper trough persists over the central Mediterranean while a deep-layer high pressure area covers the eastern portions of Europe. Quiescent SFC conditions prevail over the Mediterranean regions.

DISCUSSION

... British Isles ...

It seems that some convective potential will materialize along the cold front trailing from the SFC low which is expected to skirt the N British Isles during the second half of the period. Large front-normal upper flow component seems to be indicative of a dry-air intrusion overspreading the SFC front, which could play a role in destabilizing the immediate pre-frontal air mass. GFS indicates weak ICAPE and marginally deep instability for thunderstorms. It seems that narrow and comparatively shallow line segments of convection may occur along the SFC cold front over the British Isles and extreme NW France late on Saturday. Shear profiles will be quite robust, so that the convection will likely be associated with very gusty winds and possibly an isolated tornado or two.

However, substantial uncertainty remains on whether sufficiently deep convection will develop along the front at all, as evolution of instability is simulated somewhat inconsistently. Nonetheless, will place a marginal level-one area where deep-layer ascent appears to be most favorable for sustaining an unstable stratification.

In the wake of the front, deep convective mixing should be present, partly being appreciably sheared. This may aid in the formation of shallow mesocyclones and line segments, capable mainly of severe wind gusts and small hail.

... central Mediterranean ...

It seems that the nearly saturated Mediterranean boundary layer will maintain rather large low-level buoyancy, which suggests that a few waterspouts may occur if a misoscale vorticity source is encountered. However, generally weak low-level lapse rates seem to limit allover waterspout threat somewhat, and a categorical risk area does not seem to be warranted at the moment.