CONVECTIVE FORECAST
VALID 06Z FRI 19/12 - 06Z SAT 20/12 2003
ISSUED: 18/12 19:22Z
FORECASTER: DAHL

General thunderstorms are forecast across weatern and central Mediterranean Sea.

SYNOPSIS

Two upper frontal zones are present over Europe ... the northern one is extending across the NRN British Isles and Scandinavia into Russia. The southern E-W oriented frontal zone is stretching across the Mediterranean ... SRN stream short-wave trough ATTM over the Iberian Peninsula is expected to close off into a cut-off low towards Friday morning and move into the S-central Mediterranean Sea by the end of the forecast period. At low levels ... Extensive SFC low is covering the NE Atlantic and Scandinavia ... and will slowly weaken while moving NE into NW Russia. Weak pressure falls are FCST ahead of the Mediterranean vort max ... while high pressure will dominate the most of the rest of Europe.

DISCUSSION

...Western and Central Mediterranean...
Only focus for convective development appears to be the Mediterranean upper low ... Weak plume of subtropical/Atlantic air mass will advect northwards ahead of the developing weak SFC cyclone in advance of the vort max. Modifying the soundings of this plume (ref. Mallorca and Murcia, Spain, soundings) suggests that minimal CAPE could develop ... strongly capped beneath steep mid-level lapse rates. Given increasing UVM ahead of the vort max ... the cap could be reduced somewhat ... and a few TSTMS could develop over the western Mediterranean. However .. TSTM coverage should be rather small given meager thermodynamic support. Vertical shear is expected to remain quite weak as well ... and severe threat is minimal.

Somewhat farther NW underneath the thermal trough associated with the vort max ... cellular convection will likely be present. 12Z Madrid ascent reveals nearly netral lapse rates in the cool air beneath the vort max ... and as this airmass advects across the relatively warm sea waters ... deep enough convective mixing should ensue to allow for a few lightning strikes. Thermodynamic and kinematic setup will be very weak and severe TSTMS are quite unlikely.

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