CONVECTIVE FORECAST
VALID 06Z THU 11/12 - 06Z FRI 12/12 2003
ISSUED: 10/12 22:36Z
FORECASTER: DAHL

General thunderstorms are forecast across central Mediterranean regions.

SYNOPSIS

Elongated upper low ATTM centered over the W Mediterranean ... will close off into a cut-off low by Thursday afternoon over the Algerian/Tunesian border ... and move into the S-central Mediterranean Sea late in the period. Broad meandering upper frontal zone will stretch across northern and central Europe. Embedded trough is progged to cross Scandinavia and N-central Europe during Thursday. At low levels ... strong cyclogenesis is ongoing ahead of negatively-tilted upper trough off the N-Scandinavian W coast ... this feature is expected to continue to strengthen and move into extreme N Scandinavia late in the period. Weak cyclogenesis is assumed to occur ahead of the Mediterranean cut-off low over Tunesia/S-central Mediterranean.

DISCUSSION

...Central Mediterranean Regions...
Low-level SLY flow is establishing ahead of the Mediterranean upper low ... and air mass from as far S as central/S Libya will be advected atop the PBL across the south-central Mediterranean Sea. It appears that the Saharan steep lapse rates have weakened some as revealed by soundings across central Algeria and other parts of the northern Sahara desert ... and lapse rates are believed to remain rather weak over the S-central Mediterranean. NE of the developing SFC low ... ELY flow will advect low-level air from the ESE Mediterranean Sea into the central Meditarrenean regions. Although this airmass is poorly sampled by radiosonde data ... indications are that low-level moisture is rather meager ... with dewpoints on the order of 10°C at low levels. All this seems to be represented fairly well in GFS' 12Z solution which simulates only a few hundred J/kg of CAPE over the central Mediterranean.

Scattered elevated convection with isolated TSTMS should be ongoing at the beginning of the day within broad WAA regime over much of the central Mediterranean ... and will likely persist throughout the period. At the nose of the Libyan theta-e plume ... TSTM activity should be somewhat more concentrated. Strongest focus should be along the W edge of the plume near the low center/triple point late in the day as strong DCVA overspreads the region. Developing/strengthening SFC cold front /located near the W edge of the plume/ could promote SFC-based storms over the S-central Mediterranean Sea which may affect Sicily late in the evening/night. Low-level ESELY winds beneath increasing mid-level southerly winds will create marginally supportive kinematic setup for rotating thunderstorms ... and a few hail events and possibly a tornado or two could occur. However ... this activity appars to be concentrated just S of Italy. Setup is expected to be quite marginal especially due to the weak thermodynamic profiles ... and a SLGT is not necessary ATTM. Slight northward shift of the SFC low/triple point and slight improvement of the thermodynamic fields could necessitate an upgrade to SLGT with later outlooks.

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