CONVECTIVE FORECAST
VALID 06Z SAT 15/11 - 06Z SUN 16/11 2003
ISSUED: 14/11 20:21Z
FORECASTER: DAHL

General thunderstorms are forecast across The Iberian Peninsula ... S France and the W Mediterranean Sea.

General thunderstorms are forecast across The S Adriatic Sea ... the Ionian Sea ... Greece and the Aegean Sea.

SYNOPSIS

Primary feature will be upper long-wave trough ATTM approaching SW Europe ... which will close off into an upper low during the period. Associated SFC low is progged to move across Iberia into the W Mediterranean Sea by Sunday morning ... prompting deep SSWLY flow across Morocco and Algeria into the W Mediterranean. Weak short-wave trough will cross the central Mediterranean regions and the Aegean Sea during Saturday.

DISCUSSION

...Iberia ... W Mediterranean...
A few CGs have been detected over the past hours in the vicinity of the SW European upper trough off the Iberian peninsula over the ocean. The involved warm-sector airmass is not sampled by available rawinsonde data yet ... but climatology suggests that this airmass uses to be only marginally unstable owing to weak temperature lapse rates. Plume of relatively warm 850 hPa theta-e's is coherently progged to reach Iberia ahead of the main vort max associated with the developing upper cut-off low towards the beginning of the period. GFS assumes a few 100 J/kg CAPE amidst this plume which appears to be reasonable.

Indications are that TSTMS will (re-) develop along the cold front at the W edge of the theta-e plume ... and possibly ahead of the front in the WAA regime. It appears that there will be extensive mid/upper cloudiness/stratiform precip in the pre-frontal environ ... and chance of SFC TSTMS should be rather small there. If storms tapped BL air ... helicity in the inflow would be favorable for briefly rotating updrafts ... but this appears to be rather unlikely. Along the cold front ... chances for SFC-based convection is higher and a few mesocyclones could occur despite the marginal deep-layer shear and weak instability given rather favorable low-level shear (MM5 suggests 35+ knots at 850 hPa ... and GFS assumes 0-3 km SRH in excess of 250 J/kg). However ... allover severe TSTM threat looks to be rather low and a SLGT is not necessary ATTM.

As steep lapse rates are advected across the SW Mediterraean Sea late Saturday night/early Sunday morning ... elevated TSTMS should develop ... which may root down into the BL over the relatively warm sea waters.

...Central Mediterranean ...
A few TSTMS will likely develop ahead of weak Mediterranean short-wave trough over the Adriatic ... the Ionian Sea ... the Aegean Sea and possibly across Greece. Weak thermodynamic and kinematic fields suggest that threat of organized severe storms is quite low.

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