CONVECTIVE FORECAST
VALID 06Z SAT 23/08 - 06Z SUN 24/08 2003
ISSUED: 22/08 18:51Z
FORECASTER: DAHL

There is a slight risk of severe thunderstorms forecast across the Iberian Peninsula.

General thunderstorms are forecast across S Europe.

General thunderstorms are forecast across NE-central and NE Europe.

SYNOPSIS

Intense upper low ATTM off the Scandinavian W coast ... will accelerate southeastwards ... cross NE parts of central Europe during Saturday ... and reach the Belarus/W Russia towards the end of the period. Upper ridge over the E Atlantic/the British Isles ... is expected to amplify downstream of digging Atlantic long-wave trough. Weak southern-stream vort maxima will contiue to cross the Mediterranean. At low-levels ... strong CAA will affect the northern parts of central Europe and NE Europe in the wake of the cold front associated with the NE European upper trough. Maritime subtropical airmass is present across much of central and eastern Mediterranean regions ... partly capped by sheets of deep EML that are present across the southern parts of Europe. Locally, the low-level moisture has been mixed out and the steep lapse rates are extending to the SFC.

DISCUSSION

...S Europe...
Available 12 Z soundings from Friday show the same situation as in the past days/weeks ... locally, rich low-level moisture is present ... capped by strong EML ... promoting CAPEs in the 1500 to 2500 J/kg range (ref. Murcia and LIRE ascents) ... and inverted-V type profiles with minimal CAPE elsewhere across the S and central Mediterranean and central Spain. Numerous TSTMS should again develop across Spain in association with the upper trough ... low-level moisture influx from the Mediterranean ... and upslope flow. Potential problem is the large variability in the depth of the SFC-based moisture across the Mediterranean ... and it appears that again both profiles will be realized ... inverted-V as well as Miller-type-I. Shear will be marginal ... vorticity analyses show several small-scale vort maxima ... which appear to cause some variability in shear strength as indicated by today's soundings. Altogether ... fair chances exist that a few updrafts will rotate especially if cells either interact with outflow boundaries laid out by tonight's convection or with the complex orography ... and a few large hail and damaging wind event may occur. Those storms that develop amidst inverted-V environments ... will likely produce strong outflow winds ... possibly exceeding severe levels. Convective debris will likely impede insolation in the first half of the day ... but it is anticipated that the airmass will recover towards early afternoon.

Though stroms farther east across Italy will likely be more isolated owing to weaker forcing for vertical motion ... situation appears to be quite similar. Over the Balkans ... soundings don't suggest either deep low-level moisture or deep dry-adiabatically mixed subcloud layers ... and severe threat should be substantially weaker than across Iberia/Italy.

...NE-central and NE Europe...
In the postfrontal environment beneath the NE European upper trough ... some shallow TSTMS could develop across S Scandinavia ... North Poland and over the Baltic Sea. Given large hodographs ... potential for a few strong wind gusts exists. Convective development along the cold front is uncertain given the weak lapse rates of the prefrontal airmass ... yielding no CAPE ATTM. PRIND that majority of TSTMS will occur in the polar airmass in the wake of the front.

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