CONVECTIVE FORECAST
VALID 06Z TUE 02/12 - 06Z WED 03/12 2003
ISSUED: 01/12 18:05Z
FORECASTER: DAHL

General thunderstorms are forecast across SW Europe.

SYNOPSIS

Primary feature will be extensive quasi-stationary upper low covering the SW portions of Europe and parts of extreme NW Africa ... weak vort maxima will affect the SE Mediterranean and Turkey. Meandering band of upper westerlies are extending across the northern portions of Europe. SFC low ATTM located over NW France ... is progged to maintain its strength and track southwestwards into the S Biscay by Wednesday 06Z.

DISCUSSION

...Western Mediterranean ... Biscay...
Main challange this period appear to be the possible convective development at the E periphery of the large/intense SW European upper low. Cold front has stalled over the W Mediterranean ... and pre-frontal airmass is poorly sampled by radiosonde data. It appears that bulk of the pre-frontal airmass is rather stable ATTM ... and that small-scale regions of weak CAPE are present as indicated by current TSTM activity over S France. GFS CAPE fields indicate patches of instability ahead of the cold front over the W Mediterranean today ... but the signals improve towards Tuesday afternoon ... possibly in response to sustained low-level WAA with the low-level SLY flow E of the upper low. However ... models assume these signals to be present well E of the cold front/maximum UVM's ... also ... substantial amount of uncertainty remains with respect to the degree/existence of instability. If SFC-based convection can form ... chance for a few severe TSTMS exists as 0-6 km shear will be on the order of 70 knots ... with 0-3 km SRH values progged to exceed 200 J/kg late in the day. However ... considerable uncertainty exists and later OBS have to be awaited to specify severe threat.

In the postfrontal environment ... widespread callular convection is present over the E Atlantic W of the French and Iberian W coast. A few Cb's have also developed during the afternoon over the Iberian Peninsula beneath the upper cold pool ... but per SFLOC data have not produced significant lightning. Cellular convection will likely be present again off the Iberian W coast on Tuesday ... and develop also over the W Mediterranean Sea. However ... it appears that this activity will be quite shallow owing to large-scale subsidence. With diurnal heating ... a few Cb's will likely develop over Spain/Portugal ... but indications are that TSTMS will be very isolated.

Will include those regions in a GEN THUNDER area where chances for deep convection are best ... but allover confidence in large TSTM coverage remains rather low.

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