CONVECTIVE FORECAST
VALID 06Z THU 25/12 - 06Z FRI 26/12 2003
ISSUED: 24/12 13:37Z
FORECASTER: DAHL

General thunderstorms are forecast across the Ionian Sea ... Greece ... the Aegean Sea ... SW Turkey.

SYNOPSIS

Fast upper jet is stretching across the N Atlantic and northern portions of Europe and Russia. As embedded upper trough digs southeastwards across the Atlantic on Thursday ... upper flow over Europe will back somewhat ... promoting upper ridging across central and SW portions of Europe. Mediterranean upper low is progged to weaken somewhat as it slowly migrates eastwards into the east Mediterranean States towards the end of the FCST period. At the SFC ... extensive low-pressure system is present over N Europe and the N Atlantic ... progged to expand into NW portions of Europe in response to the digging Atlantic upper trough ... altogether resulting in deep WSWLY flow from the NRN Biscay across N-central Europe deep into Russia late in the period. Extensive SFC low over the central Mediterranean is expected make only very slow eastward progress ... and is coherently progged to be centered over the S Aegean Sea by Friday 06 Z ... without appreciable loss in intensity over the FCST period.

DISCUSSION

...Mediterranean...


The Mediterranean upper low will likely be the only focus for convective development on the first Christmas day ... posing a rather complicated scenario though.

Tongue of slightly unstable airmass is wrapping around the center of the SFC cyclone ... with LGIR, Crete, Wednesday 00Z ascent being one sample of this airmass. Modifying this sounding with 10°C SFC dewpoint yields a few hundred J/kg of SBCAPE which is also assumed by GFS CAPE fields. This air mass will spread across the Aegean into Greece ... the Ionian Sea ... and the eastern Mediterranean Sea during the period. Current thinking is that elevated convection with a few TSTMS will develop at the nose of the theta-e tongue across Greece late Wednesday night and spread into the Ionian Sea during the period ... where TSTMS may root down into the relatively warm/moist maritime boundary layer. Scattered SFC-based TSTMS should also develop over the Aegean ... however ... bulk activity should be present east of the forecast area ahead of the main vort max.

Given that majority of the convection should be slightly elevated ... and given weak thermodynamic and kinematic fields ... severe thunderstorm threat is fairly low.

Over the S Ionian Sea ... the theta-e plume appears to become quite diffuse per GFS and BOLAM model fields ... and transition to cellular SFC-based convection in the deep polar air mass ATTM covering the central Mediterranean is anticipated. Steep low-level lapse rates ... and relatively cool temperatures will maintain a slight waterspout and small-hail threat ... but organized-severe thunderstorm potential is fairly low owing to weak CAPE and shear parameters.

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