CONVECTIVE FORECAST
VALID 06Z SAT 04/09 - 06Z SUN 05/09 2004
ISSUED: 03/09 21:55Z
FORECASTER: DAHL

There is a moderate risk of severe thunderstorms forecast across E Spain and the SW Mediterranean Sea.

There is a slight risk of severe thunderstorms forecast across the Iberian Peninsula and the SW Mediterranean Sea.

General thunderstorms are forecast across southern ... south-central and portions of eastern Europe.

SYNOPSIS

Upper cut-off low off the Iberian W coast is progged to remain in place ... continuing to support advection of Saharan EML plume across the W Mediterranean Sea into Spain and S France during the period. Rich low-level moisture has been trapped beneath the EML ... with BL mixing ratios ranging from 12 to 15+ g/kg ... yielding MLCAPEs on the order of 1500+ J/kg. As E-European upper cut-off low moves SEWD ... reaching the Black Sea towards Sunday morning ... upstream ridge will build over central and NE Europe. Weak/broad upper trough surrounding the E-European upper low is expected to persist over the central and SE Mediterranean Regions.

DISCUSSION

...Iberian Peninsula...
Extensive convective debris will likely be present over portions of Spain ... the SW Mediterranean Sea and S France at the beginning of the FCST period. However ... much of the air mass should recover during the day ... again allowing for MLCAPEs up to 2000 J/kg ... though sustained WAA may locally support persistent/weak mid-level cloudiness and weak elevated TSTMS. Richest BL moisture and highest CAPEs should be present over the SW Mediterranean Sea ... eastern Spain and over southern France.

Ample deep-layer shear is progged to persist across the SE Mediterranean and over Iberia with 25 to 30 m/s. Towards Saturday evening ... GFS produces 12+ m/s 0-1 km shear over much of Spain and the SW Med... yielding 200 to 400 m2/s2 0-3 km SRH mainly over E Spain ... spreading into central N-Spain late in the evening. 200+ 0-1 km SRH are simulated after 18Z over E Spain.

GFS 12Z indicates maximum of 850 hPA WAA over E Spain during the day ... and fairly strong DCVA over ERN portions of Iberia. This suggests that storms in the best thermodynamic and kinematic environments may tend to be elevated inititally ... but should have fair chances of rooting down into the BL. Also ... outflow boundaries laid out from Friday's convection as well as orographic forcing may promote convective initiation.

TSTMS will likely merge into several large MCS's during the afternoon/evening hours with embedded mesocyclones and bow echoes. Any supercell in the MDT area will likely pose the threat for very large hail ... destructive downbursts as especially towards the evening tornadoes ... some of which may be significant (F3 or stronger). Farther west ... lower dewpoints should limit tornado threat somewhat and main threat appears to be damaging wind gusts and large hail.

...France ...
Confidence in development of SFC-based convection is somewhat limited ATTM given increasing cap strength and weak large-scale forcing for ascent. However ... NRN edge of the theta-e plume as well as mesoscale features and orography may support isolated TSTM development. If SFC-based storms form ... thermodynamic environment should be supportive to intense ... though rather short-lived ... convection capable of producing some hail and strong/damaging wind gusts ... especially if locally sufficient SRH is provided to support briefly rotating updrafts. Minimal large-scale shear should limit organized severe TSTM threat.

...Italy...
Storms should develop during peak heating hours ahead of weak upper trough crossing the central Mediterranean regions. Shear and instability should be rather limited ... and majority iof the storms should be non-severe. However ... an isolated large-hail and/or damaging wind event cannot be excluded.

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