CONVECTIVE FORECAST
VALID 06Z TUE 15/07 - 06Z WED 16/07 2003
ISSUED: 14/07 20:55Z
FORECASTER: DAHL

There is a slight risk of severe thunderstorms forecast across SW France...NE Spain...W Mediterranean Sea.

General thunderstorms are forecast across SW portiona of Europe.

General thunderstorms are forecast across NE and E Europe.

SYNOPSIS

Quasi-stationary north European upper high will persist throughout the period ... as will extensive upper low which is covering southeastern parts of Europe. Strong vort max at the moment off the Iberian Peninsula over the E Atlantic ... will cross Iberia and S France during the forecast period ... providing focus for potential severe evolution. At low levels ... Cyclogenesis is expected ahead of the Iberian vort max on Tuesday over N Spain and S France. SLY flow ahead of this feature is advecting rich moisture from the W Mediterranean into France ... capped by strong elevated mixed layer.

DISCUSSION

...SLGT RISK area...
Today's soundings indicate that deep moisture is confined to the portions of the western Mediterranean Sea ... while mixed-layer moisture across the central and east Meiterranean is quite meager. Ahead of Spanish heat low/cylogenesis associated with the approaching upper trough ... deep moisture is advected into France ... already supporting dewpoints at and above 20°C over E Spain and S France. Steep lapse-rates associated with an elevated mixed layer are revealed atop this airmass by Today's 12 Z soundings ... yielding MLCAPEs on the order of 1000 to 1500 J/kg. Given sustained moist advection ... moistening by currently ongoing precipitating convection ... evapotranspiration and possibly an increasing EML embedded in the southerly flow ... thermodynamic profiles may strengthen somewhat ... and afternoon CAPEs locally in excess of 1500 J/kg are expected over France. However ... BL airmass will likely be quite strongly capped ... with CINs in excess of 200 J/kg.

Deep-layer shear will be marginal across France ... but is progged to improve drastically to the south closer to the vort max towards late evening ... and 0-6 km shear is expected to exceed 60 knots over the W Mediterranean Sea and E Spain late in the afternoon into the night.

Main question will be where/when convection will initiate. Present indications are that rather weak elevated TSTMS will be possible throughout the day in theta-e advection regime over N and central France ... spreading as far east as into Switzerland and SW Germany. Potential exists that a few cells root down into the boundary layer ... but background low-level SRH is expected to be insufficient for a significant severe-weather threat. However ... strong thermodynamic profiles may support a few strong wind gusts along with some hail ... possibly approaching severe levels.

More significant severe threat appears to evolve over E Spain ... W Mediterranean Sea and W France ... where deep-layer shear will likely be adequate for organized thunderstorms. GFS is assuming 0-3 km SRH of more than 250 J/kg over the W Mediterranean and W France on Tuesday evening and towards the end of the period also over S France ... associated with backed SFC winds ahead of the developing low. Models coherently assume the DCVA maximum across this region at this time ... and confidence is rather high that stroms will develop. PRIND that TSTMS will become rather numerous towards late evening and into the night over western and southern portions of France ... E Spain and the W Mediterranean. Given the favorable kinemtic setup ... supercells are quite likely. Though large hail and severe wind gusts will be the primary threats ... potential for a few tornadoes appears to be enhanced in the face of substantial SRH and low LCL heights during the evening/night. Formation of a linear MCS is anticipated late in the night ... possibly with embedded supercells ... which should gradually weaken until Wednesday morning. Potential problem could be lee effects of the Pyrenees though ... and TSTMS may struggle to initiate close to the mountains over S France. Uncertainties with respect to TSTM coverage preclude a MDT risk ATTM but an upgrade may be needed tomorrow.

...Central Spain...
Initial TSTMS along and ahead of the cold front over central Spain will have the potential to produce severe wind gusts ... Environment appears to be only weakly capped ... and quite numerous TSTMS could develop given strong QG forcing for upward motion. Deep-shear of about 60 knots and the high-based nature of the storms suggest that severe wind gusts may be rather widespread. This region also needs to be monitored for a possible upgrade.

...SE Europe...

Scattered ... primarily diurnally driven TSTMS are expected to develop ... CAPE is expected to be fairly weak ... but around 30 knots deep-layer shear may promote a few multicellular storms. An isolated marginally severe-weather event or two may occur ... but allover severe threat is rather low.

Other regions ... Organized severe TSTMS are quite unlikely.

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