CONVECTIVE FORECAST
VALID 06Z SUN 16/11 - 06Z MON 17/11 2003
ISSUED: 15/11 22:08Z
FORECASTER: DAHL

General thunderstorms are forecast across the eastern Iberian Peninsula and the western Mediterranean Sea.

SYNOPSIS

Primary feature remains developing upper cut-off low ATTM over Iberia ... and remnant NRN stream short-wave trough ATTM approaching the British Isles ... which will cross N France ... BeNeLux and Germany during Sunday. In response ... tongue of subtropical-Atlantic airmass will be advected into E France and S Germany ... promoting development of a thermal boundary from west France into central Germany ... along which weak cyclogenesis is expected. Cold front associated with the Iberian upper low ... is expected to stall over the west Mediterranean Sea and weaken towards the end of the period.

DISCUSSION

...W Mediterranea ... Iberia ...
Convection has predominantly developed in the modified polar air beneath the upper thermal low over Iberia on Saturday as warm-sector airmass has been stabilized by extensive stratiform precip. 20°C warm sea waters ... and advection of moderately steep lapse rates from N Aftica should improve thermodynamic environment in the warm sector over the W Mediterranean ... but DCVA-related lift is progged to weaken some. However ... scattered TSTMS will likely develop along the cold front over the W Mediterranean Sea. A few waterspouts cannot be ruled out with any SFC-based convection given steep low-level lapse rates over the Sea ... low LCL heights and relatively weak low-level shear.

Ahead of the front ... Low/mid-level WAA at the nose of the theta-e plume could support a few weak elevated TSTMS but indications are that any TSTM will be quite isolated over the W Mediterranean.

Shear and thermodynamic profiles across the region appear to be too weak to support significant severe thunderstorm threat.

Over the Iberian Peninsula ... low-level flow will turn to NLY directions ... and advect somewhat cooler/drier air into Iberia. General subsiding motion in the wake of the southward-moving upper low will likely limit depth of convective mixing.

...Germany...
Weak cyclogenesis is progged to occur beneath vigorous DCVA max along the thermal gradient over central/W Germany ... but airmass ahead of the upper trough will likely be too stable for convective development. Strong DAVA and low-level CAA in the polar air will likely suppress deep convection in the postfrontal environment.

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