Storm Forecast
Valid: Fri 01 Dec 2006 06:00 to Sat 02 Dec 2006 06:00 UTC
Issued: Thu 30 Nov 2006 22:35
Forecaster: DAHL

SYNOPSIS

Vigorous large-scale Atlantic upper trough will continue digging southeastwards and reach the British Isles and western continental Europe late in the period before the trough evolves into a cut-off low on Saturday morning. Associated low-level cold front is progged to cross the northern British isles on Friday and to reach extreme NW Iberia by Saturday 06Z. Moderately strong SWLY flow ahead of this feature will maintain unseasonable high temperatures across W Europe. Otherwise ... deep upper ridge and associated SFC high pressure area persist over the E Europen countries.

DISCUSSION

... SW Mediterranean ...

Depth of convection over the W Mediterranean is somewhat uncertain. GFS assumes elongated/narrow region of rather strong DAVA over the W Mediterranean, which will likely suppress deep convection. Weak DCVA will be present E and W of this feature per GFS, though, and some convective precip is advertised. MM5 and NMM are reluctant to produce as clear precip signals. Best chance for isolated thunder seems to exist south of the Balearic Isles, though allover lightning amount may remain quite sparse. Severe threat should be minimal given meager thermodynamic/kinematic setup, though an isolated waterspout or two cannot be discounted. TSTM threat should continue to decrease during the period.

... British Isles ...

Cellular post-frontal convection may affect the British Isles late Friday night. Shear profiles should be supportive of isolated marginally severe storms, and strong DCVA-forced ascent may help sustain the storms as they move inland. Despite the adverse timing ... an isolated tornado or two are not excluded with this activity, and a Level 1 is marginally warranted.

... NW Iberian Peninsula ...

Models hint at presence of weak CAPE in warm-conveyor belt over W Europe ahead of the cold front. Weak cyclogenesis is expected in response to strong DCVA overspreading the W Iberian Peninsula late in the period ... and scattered TSTMS may develop. GFS suggests that strong shear will remain slightly offset from region of positive CAPE and severe threat should be rather limited.