Storm Forecast
Valid: Sun 07 May 2006 06:00 to Mon 08 May 2006 06:00 UTC
Issued: Sat 06 May 2006 18:38
Forecaster: DAHL

SYNOPSIS

Vort max at periphery of E Atlantic large-scale upper low is expected to dig into W France late in the forecast period ... thereby promoting rather strong SFC cyclogenesis over W France late in the afternoon/evening which should be the main focus for potentially severe convective development late this forecast period. SE European upper low remains in place ... exhibiting several small-scale vort maxima at its periphery.

DISCUSSION

France...
Rather widespread TSTMS should develop over France in the early afternoon hours in nearly uncapped/neutral thermodynamic environment ... and should become increasingly organized in the late evening hours ahead of approaching upper trough. Negative factors will be i) widespread daytime convection which may contaminate the environment for subsequent SFC-based convection ii) generally weak back-ground thermodynamic fields and iii) late arrival of the upper vort max/favorable kinematic fields. However ... thinking is that large-scale forcing for UVVs will be sufficiently strong to maintain convection through the late evening and early night hours.Main threat should be severe wind gusts and hail with linear MCS which should develop along or ahead of the main cold front over W France in the late afternoon/evening hours. Any isolated cells ahead of or within the line may become supercellular given increasing LL shear ... posing an additional threat for large hail and possibly a tornado or two.

N Germany ... Denmark...
Saturday's 12Z launches from N Germany and Poland reveal unusually deep/dry CBLs ... and sufficiently steep mid-level lapse rates for a couple of Joules CAPE despite the meager LL moisture. GFS indicates that weak large-scale forcing for ascent should persist across N Germany ... and a few isolated high-based afternoon showers and TSTMS may occur. Given deep/dry CBLs ... storms may be accompanied by very gusty winds. Organized severe threat should be too low for a categorical risk however.

SE Europe...
Scattered TSTMS should develop in the vicinity of the SE European upper low ... possibly being augmented ahead of small perturbations revolving about the main cyclone. Shear near these perturbations may be sufficient to support an isolated severe TSTM or two ... main threats being marginally severe wind/hail ... but allover severe threat should be too low for a categorical threat level.