CONVECTIVE FORECAST
VALID 06Z TUE 19/10 - 06Z WED 20/10 2004
ISSUED: 18/10 23:03Z
FORECASTER: DAHL

General thunderstorms are forecast across SW-central Europe ... SW Europe ... central Mediterranean.

SYNOPSIS

Upper low is currently (Monday 22Z) located between the British Isles and Iceland ... with a broad WSWLY upper flow stretching from the Iberian Peninsula into the Ukraine. The upper low is progged to discontinue its SRN motion and expand as perturbation at its NW periphery amplifies. By that time ... another ... weaker upper low currently approaching the Azores is FCST to merge with the N Atlantic feature ... creating a deep ... broad and intense SSWLY flow over the WRN half of Europe by the end of the period. NE European upper low will make little NEWD progress and move into NW Russia. At low levels ... quite moist subtropical-Atlantic air mass is advected NEWD ahead of the Atlantic upper lows. SFC cyclogenesis associated with the upper low over the Azores is expected spread eastwards and affect the French/Iberian west coasts late in the ... though details of this development remain uncertain ATTM.

DISCUSSION

...Iberian Peninsula ... France...
Convective focus will likely be tied to the tongue of moist subtropical-Atlantic air spreading into S France on Tuesday morning. Sounding data are not available from this air mass ... but current convective activity indicates that CAPE is greater than zero. Will not venture estimating how much CAPE will be available on Tuesday ... but confidence exists that sufficiently clear regions will persist within this air mass so that locally SFC-based convection should be possible. During the day ... main negative will be sustained WAA/precip and a concommitant tendency for the convection to be elevated. If surface-based convection does form though ... shear could be sufficient to support isolated severe. Early Wednesday morning ... vigorous large-scale forcing for ascent will overspread W Iberia per GFS 12Z. Timing of this feature is quite unfavorable ... also ... models disagree on its exact position.

Suspected weak thermodynamic fields ... uncertainty about the potential for SFC-based convection and about the position of potent vor max/UVV regime preculding a SLGT ATTM. Weak elevated convection may spread as far N as into SW Germany towards the end of the period.

...Italy...
Short-wave trough imbedded in the WSWLY upper flow is expected to cross the central Mediterranean on Tuesday ... and it looks that low-level lapse rates will steepen as Saharan EML is spreading north ... so that weak CAPE should develop during the day. About 20 m/s deep shear may promote a few marginally severe TSTMS ... but allover threat appears to be rather low.

#