CONVECTIVE FORECAST
VALID 06Z SAT 10/04 - 06Z SUN 11/04 2004
ISSUED: 09/04 18:20Z
FORECASTER: DAHL

General thunderstorms are forecast across central Mediterranean regions.

General thunderstorms are forecast across NE Spain.

SYNOPSIS

Main feature this period will be the upper cut-off low ATTM over central France ... this feature is progged to make little eastward progress on Saturday ... resulting in deep ... persistent and quite intense SSWLY flow over the central Mediterranean. Weak SFC low is present over N Algeria downstream from the upper low ... pushing plume of Saharan steep lapse rates across the central Mediterranean. Otherwise ... polar air masses are dominating major parts of western ... northern and central Europe.

DISCUSSION

...Central Mediterranean ...

Early Saturday morning

Friday's LIBR 00Z through 12Z launches reveal rapid improvement of the thermodynamic profiles as the EML is advected across the central Med with increasing boundary-layer moisture ... apparently originating from over S-central Mediterranean sea. Current thinking is that at least weak ... strongly capped CAPE will evolve beneath the EML during Friday night. Low-level warm advection will likely maintain high-based storms that are currently advecting northward off the Atlas mountains ... which could congeal into one or more MCSs towards early Saturday morning. These storms may tap boundary-layer air ... and given SELY SFC flow beneath SWLY 850 hPa flow ... SRH may be sufficient to promote updraft rotation ... GFS advertises SRH in the 150 to 450 m2/s2 range across the central Med early Saturday morning. Degree of SFC-based CAPE is somewhat uncertain ATTM ... mainly depending on the depth and adundance of low-level moisture. If SFC-based storms form ... chances for them to become severe are quite high ... posing threats of large hail ... damaging winds and maybe a brief torndo or two. However ... uncertainty regarding likelihood of SFC-based convection precludes a SLGT with this activity ATTM.

During the day ...

Though thermodynamic setup will likely be marginal owing to possibly weak low-level moisture ... kinematic setup will be favorable for sustained rotating updrafts. Model fields suggest maximum low-level WAA along baroclinic zone at the W edge of the theta plume ... also ... several ill-defined 500 hPa CVA maxima are progged to move across the region ... both rendering baroclinic zone a potential focus for convective initiation. This convection may tend to be elevated ... and uncertainty exists whether it will root down into the BL. Farther E over S Italy ... orographic forcing may prove to be intrumental in initiating SFC-based convection. Dry mid levels ... steep lapse rates ... and favorable low-level veering plus deep-layer shear in the 20 to 30 m/s range ... will likely promote severe evolution. Chance exists for widespread convection along the W edge of the EML ... and more isolated convection over S Italy. If low-level moisture turns out to be sufficient for SFC-based storms ... some of them may evolve into supercells and bow echoes ... being accompanied by large hail ... severe straight-line winds and maybe a few tornadoes. Uncertainties with respect to the low-level moisture fields preclude a SLGT ATTM ... but an upgrade may be necessary tomorrow.

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