CONVECTIVE FORECAST
VALID 06Z SAT 19/07 - 06Z SUN 20/07 2003
ISSUED: 18/07 16:32Z
FORECASTER: DAHL

General thunderstorms are forecast across E Europe.

General thunderstorms are forecast across the British Isles.

General thunderstorms are forecast across SW Mediterranean Regions.

SYNOPSIS

Main feature this period will be the eastern Atlantic upper long-wave trough which is making slow eastward progress ... reaching the British Isles ... W France and W Iberia towards the end of the FCST period. Ahead of this trough ... elevated mixed layer will be advected off the Atlas mountains across the W Mediterranean and E Spain into S France late in the period. Synoptically quiescent conditions prevailing over the rest of Europe.

DISCUSSION

...British Isles...
Problem appears to be the thermodynamic setup ... lapse rates are expected to be quite weak ... with low-level temperatures being rather modest given the Atlantic origin of the air mass. DCVA-related lift ahead of the trough will act to steepen the lapse rates some ... and indications are that weak instability will be present over the E parts of the UK during the afternoon. Deep-layer shear is expected to be on the order of 40+ knots ... and storms may produce strong outflow winds and possibly some hail ... both of which is rather unlikely to exceed severe levels given weak thermodynamic support.

In the postfrontal environment ... a few shallow TSTMS may form as well with diurnal heating. Severe threat is limited given weak CAPE and marginal shear. However ... an isolated marginally severe wind/hail event cannot be excluded if (e.g. orographically induced) flow perturbations cause sufficient SRH in the inflow of the storms ... allowing for rotating updrafts. However ... allover severe threat is quite low.

...N Spain...
Though upper support will be quite weak ... a few high-based TSTMS may develop over N Spain in upslope-flow regime late in the afternoon. These storms will briefly pose the threat of very gusty winds ... which may exceed severe levels.

Otherwise ... chance of severe evolution is minimal.

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