STORM FORECAST
VALID Sun 09 Apr 06:00 - Mon 10 Apr 06:00 2006 (UTC)
ISSUED: 08 Apr 17:35 (UTC)
FORECASTER: DAHL

A threat level 1 is forecast across southern France.

SYNOPSIS

Main feature this period will be digging upper trough over the North Sea as of Saturday afternoon ... which will merge with an upper cut-off low located off the Iberian W coast over the E Atlantic. This will result in strong DCVA-forced ascent over France during the afternoon hours ... increasing towards the night. Ahead of this feature ... low-level WAA will develop over the north-central Mediterranean and S France ... contributing to strong frontogenesis over southern France.

DISCUSSION

...France...
Models converge towards development of weak CAPE over southern France ahead of the main frontal boundary in the afternoon and evening hours. Low-level moisture seems to be somewhat scarce ... and Saturday's 12Z ascents do not unambiguously reveal source of deep moisture over the NW Mediterranean ... where France's BL air mass is expected to originate from on Sunday. However ... latest SFC OBS suggest that at least shallow moisture is present over S France ... which should be advected farther inland as pressure falls over the SW Mediterranean.

Shear profiles will be more than sufficient for severe storms /possibly supercellular in nature/ with deep shear in excess of 20 m/s and 0-3 km SRH in excess of 300 J/kg.

Strong frontogenetic forcing should be in place ... which should suffice to initiate the storms. WAA ahead of the front may result in predominantly elevated TSTMS. As a result ... storms would could not benefit from strong low-level shear. If storms root down into the BL however ... they will have fair chances of becoming supercellular ... with potential for large hail ... damaging winds and maybe a brief tornado or two. Storms may quickly become more linear however given large front-parallel mean wind vectors. ATTM ... quite some uncertainty exists on whether or not storms will become SFC-based ... but confidence in SFC-based evolution is sufficiently high to warrant a level-one threat.

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