CONVECTIVE FORECAST
VALID 06Z TUE 28/12 - 06Z WED 29/12 2004
ISSUED: 28/12 01:10Z
FORECASTER: DAHL

There is a slight risk of severe thunderstorms forecast across the Ionian Sea and the Aegean Regions.

General thunderstorms are forecast across the central Mediterranean.

General thunderstorms are forecast across the North Sea.

SYNOPSIS

Vigorous Atlantic upper trough reaching the British Isles by Tuesday 00Z is progged to dig southeastwards and merge with Mediterranean upper long-wave trough on Tuesday. As a result ... main vort max associated with the Mediterranean trough will accelerate northeastward and cross the Ionian Sea and Greece late Tuesday night. Upstream vort max associated with the Atlantic trough is expected to cross France and reach the Tyrrhenian Sea by Wednesday morning. At low levels ... plume of relatively high 850 hPa theta-e's should persist across the E Ionian Sea and Greece while more or less deeply mixed polar air masses are dominating the rest of the continent.

DISCUSSION

...Ionian Sea and Aegean regions...
Focus for potentially severe convection will be the vigorous vort max crossing the Ionian Sea and Greece late in the period. Monday's 12Z soundings indicate steep lapse rates withing 850 hPa theta-e tongue ... and MLCAPE on the order of a few 100 J/kg should develop during the afternoon/evening hours within strong UVV regime ahead of the vort max. Low-level shear seems to be somewhat limited per model data ... but about 10 m/s 0-1 km shear should be realized locally. Deep shear should be on the order of 35 m/s which will be more than adequate for a few severe TSTMS. Expect isolated severe wind gusts and large hail ... shape of low-level temperature and moisture profiles is uncertain ATTM ... but if steep low-level lapse rates and sufficient BL moisture a la LGTS Monday 12Z can be realized ... tornado threat will also exist. Despite the weak CAPE ... degree of large-scale forcing for upward vertical motion and strong kinematic fields are marginally warranting a SLGT.

...SEE TEXT region...
Beneath the upper cold pool of the trough digging into the Tyrrhenian-Sea region late Tuesday night ... convective mixing will likely occur. Depending on how fast the boundary layer will moisten ... convection could be deep enough for scattered TSTMS. Shear magnitude looks to be rather low despite strong 850 hPa and 500 hPa flow ... but a few waterspouts could occur. Allover organized severe TSTM threat should be rather low however.

...North Sea...
Cellular convection is accompanying Atlantic upper trough ATTM ... and should spread into the North Sea during the period. Though areal extent of deep mixing should decrease during the day as thermal trough becomes increasingly narrow ... expect a few lightning strikes with this activity. Strong wind gusts may occur ... but severe threat looks to be rather low.

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