CONVECTIVE FORECAST
VALID 06Z SAT 25/12 - 06Z SUN 26/12 2004
ISSUED: 24/12 13:25Z
FORECASTER: DAHL

There is a slight risk of severe thunderstorms forecast across S Italy and the S Tyrrhenian Sea.

General thunderstorms are forecast across western Mediterranean Sea.

General thunderstorms are forecast across the E Atlantic ... the Gulf of Biscay and the North Sea.

SYNOPSIS

Upper low over Morocco on Friday afternoon is progged to merge with digging Atlantic long-wave trough ... and travel northwards across the W Mediterranean at the E periphery of the trough as a strong vort max. This will augment the lee cyclogenesis over the NW Mediterranean ... resulting in fairly strong and relatively large SFC low over the western half of the Mediterranean by Sunday 06Z.

DISCUSSION

...S Italy ... S Tyrrhenian Sea...
Focus for potentially severe evolution will be the vort max which will cross the W Mediterranean late on Saturday and Saturday night. Models show patches of weak CAPE towards Sunday early morning over the W Mediterranean within modified subtropical/Atlantic air mass ahead of the vort max. Also ... plume of high Saharan 850 hPa theta-e's ... and possibly steep mid-level lapse rates ... are expected to overspread the central Mediterranean in the strengthening SLY flow. CAPE will likely be rather weak ... but it should allow for scattered deep convection.

Wind field should be quite supportive to severe evolution ... with 15 to 20 m/s low-level shear ... and increasing potential for a few supercells and bow echoes should exist especially towards early Sunday morning when kinematic setup should be best. Though severe straight-line winds should be the main threat ... large hail and a few tornados may also occur.

Given that models are in fair agreement as to the evolution of CAPE ... confidence that TSTMS will occur is rather high ... and a SLGT is marginally warranted.

...E Atlantic ... Gulf of Biscay ... North Sea...
Benard-type convection should persist in deep polar air over the E Atlantic ... the North Sea and the Gulf of Biscay ... and may spread into the coastal areas of the British Isles ... Spain ... France and Benelux. Though strong wind gusts may occur with this activity ... organized-severe TSTM threat seems to be quite low.

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