CONVECTIVE FORECAST
VALID 06Z SUN 15/08 - 06Z MON 16/08 2004
ISSUED: 14/08 16:25Z
FORECASTER: DAHL
There is a slight risk of severe thunderstorms forecast across N France and Benelux.
There is a slight risk of severe thunderstorms forecast across N Turkey.
General thunderstorms are forecast across E Spain ... France ... Benelux ... S UK.
General thunderstorms are forecast across S Ukraine ... Turkey ... Aegean Sea.
SYNOPSIS
High-amplitude upper flow pattern is progged to re-establish over Europe ... with large-scale upper trough deepening over the E Atlantic ... resulting in intense SSWLY upper flow extending from N Iberia along the continental-European NW coast into NW Russia by Monday morning. Upper ridge will persist across central Europe and the central Mediterranean ... with weak upper low developing over the central Balkans. Ahead of the Atlantic trough ... WAA regime is expected to overspread Iberia ... France ... the S UK ... and towards Monday morning W Germany and Benelux.
DISCUSSION
...France...
Saturday's 12Z launches as well as latest SFC OBS indicate that rich moisture has been able to persist across the SW Mediterranean Sea ... with SFC dewpoints exceeding 20°C. With increasing SLY low-level flow ... this moisture will be advected into NE Spain and S France during Sunday. It appears that deep/dry CBL will develop over Spain during the day ... which should be advected atop the low-level Mediterranean moisture over France ... contributing to MLCAPEs in excess of 1000 J/kg. However ... the presence of the EML will likely result in a fairly strong cap. Farther north ... CAPE as well as CINH should be somewhat weaker in the Atlantic air mass.
15 to 20 m/s 0-6 km shear will likely spread across the S UK ... Iberia and France during the day ... reaching Benelux and W Germany early Monday morning.
Models favor W/NW France for convective development in WAA regime ahead of vort max at the E periphery of the Atlantic long-wave trough late in the day. Development of an MCS may be possible given degree of large-scale forcing for UVVs and sufficient shear.
Main severe threat will likely be a few severe straight-line wind gusts as well as large hail ... Low-level wind fields are expected to increase late in the evening/night ... and any SFC-based storm will likely pose some threat of a brief tornado. However ... anticipated tendency for the MCS to become slightly elevated towards early Monday morning may limit allover severe threat.
... French/Spanish SEE TEXT area ...
More isolated activity may develop during the afternoon and evening hours over S France and NE Spain. Main threats should be large hail and damaging wind gusts. Especially towards the evening and over central portions of France ... some tornado threat should exist given decreasing LCL heights and strengthening low-level shear profiles. Confidence in widespread convection remains rather low ATTM ... and a SLGT does not appear to be warranted.
...UK...
Degree of instability remains uncertain ATTM as no radiosonde data are available from the air mass that is expected to reach the UK tomorrow. Will go with a blend of NMM and GFS CAPE forecasts. Shear profiles should be marginally supportive to a few severe TSTM events ... which could be associated with NRN extension of French MCS ... or with separate convective development. Peak convective activity should occur after about 18Z when vort max will apporach.
...N Turkey...
Quite moist and weakly unstable air is expected to advect into N Turkey during Saturday night. TSTMS will likely exist along NRN edge of the unstable air mass ... which will be overspread by large-scale UVVs per model guidance. Shear profiles should be sufficient for a few severe TSTMS ... main threats being severe winds and large hail ... though low-level shear looks to increase somewhat towards late evening ... which may support an isolated tornado or two.
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