Storm Forecast
Valid: Sun 26 Nov 2006 06:00 to Mon 27 Nov 2006 06:00 UTC
Issued: Sat 25 Nov 2006 23:48
Forecaster: DAHL

SYNOPSIS

Deep Atlantic upper trough is expected to close off into a cut-off low over the N-central Maghreb States during the period. Remaining upper trough will accelerate northeastward towards the Norwegian Sea and Scandinavia. Next Atlantic upper trough is rapidly approaching the British Isles, and it is accompanied by a major surface low which will reach the British Isles late in the period. Upper ridge and quiescent SFC conditions prevail over the Mediterranean and SE Europe.

DISCUSSION

... S British Isles ... extreme N France ...

Weakly organized polar-air MCS tied to strong DCVA-forced ascent should affect the British Isles and possibly extreme N Grance early in the period. Low-level shear will be in place, and chance of the development of rotating updrafts exists, which may result in a tornado or two and severe straight-line winds.

... S France ... NW Mediterranean Sea ...

Saturday's 12Z ascents from the W Mediterranean indicate quite shallow low-level moisture and it is somewhat questionable whether it will become deep enough to sustain deep convective updrafts. However ... surface convergence associated with a mesoscale low progged to persist over the western Mediterranean may aid in deepening the moisture and allow for deep convection. QPF fields of the GFS do not suggest much activity however. If storms form, deep shear of about 15 m/s may be marginally supportive of severe, possible multicellular evolution, main threats probably being marginally severe hail and wind gusts. However, minimal low-level capping and low LCL heights may also be supportive of a brief tornado or two. Convective potential extends towards southern France where shear profiles will be somewhat increased compared to the W Mediterranean. Threat should be too low to warrant a categorical risk, owing to anticipated low coverage. Best chances for convective development are advertised by GFS to exist over southern France.

... south-central Mediterranean including the Aegean Sea ...

South-Balkan vort max is expected to advance westward at the southern flank of the E European upper high. Though instability should be quite meager, scattered thunderstorms should develop in the DCVA-related lift regime. Shear profiles should be too weak to support severe thunderstorm development though a few water spouts are not discounted given favorable low-level thermodynamic parameters.