CONVECTIVE FORECAST
VALID Sat 13 Aug 06:00 - Sun 14 Aug 06:00 2005 (UTC)
ISSUED: 12 Aug 20:22 (UTC)
FORECASTER: DAHL

SYNOPSIS

Broad meandering WLY mid/upper flow is present across Europe ... with rather intense trough expected to dig across the British Isles and western central Europe during the period ... while numerous weak/small vort maxima are expected to affect the central Mediterranean and eastern portions of Europe. British upper trough is progged to be accompanied by weak SFC low ... E of which plume of moist/subtropical air will be present. Weak SFC low persists across N Scandinavia.

DISCUSSION

...Balkans...
Friday's 12Z launches from SRN Italy revealed strongly capped shallow BL air mass ... with about 1500 J/kg of CAPE. This air mass is expected to be advected eastwards into the Balkan States ... and CAPEs on the order of 1000+ J/kg are expected. Shear profiles should to remain fairly weak ... with about 10 to 15 m/s DLS and less than 5 m/s LLS. Given potential orographic LL flow augmentations ... a few storms may briefly attain supercellular structures ... with an attendant severe wind/hail threat ... but allover severe threat seems to be quite low.

...S Italy...
It seems that steep low/midlevel lapse rates will be advected into the Balkans ... so that only weak lapse rates and weak CAPE will remain across Italy. Shear profiles appear to be strongest across S Italy in the vicinity of base of s/w trough ... but weak CAPE should generally limit organized severe threat. However ... isolated large hail and marginally severe straight-line winds could occur with the strongest cells.

...Finland ... NW Russia...
Friday's soundings exhibited steep LL lapse rates ... moist BLs ... weak shear and partly impressive CAPE densities in the lowest kilometers. This suggests that a few non-mesocyclonic tornadoes may occur once a cell encounters ... and stays positioned above ... misoscale vertical vortices. Threat will be too isolated for categorical risk.

...British Isles...
Models predict weak CAPE in subtropical plume ahead of the digging trough ... and there seems to be little reason to disbelieve that. Uncertainty exists on the convective mode ... as strong forcing due to WAA may promote rather widespread elevated/imbedded ... and rather weak ... convective development. Shear in the cloud-bearing layer would likely be insufficient for a severe TSTM threat in this case. However ... potential for SFC-based development seems to exist along the cold front. LLS along the front should be 12+ m/s ... with deep shear of 15 -20 m/s. This suggests that line segments and short-lived bow echoes may develop along the front ... primarily posing a threat for strong/severe wind gusts ... though an isolated marginally severe hail event and a brief tornado or two may occur as well. Allover threat seems to be too low for a SLGT.

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