CONVECTIVE FORECAST
VALID Sat 20 Aug 06:00 - Sun 21 Aug 06:00 2005 (UTC)
ISSUED: 19 Aug 18:45 (UTC)
FORECASTER: DAHL

SYNOPSIS

Intense large-scale upper trough over the channel on Friday evening ... is progged to close off into a cut-off low while dropping southwards into the NW Mediterranean by Sunday 06Z. Upper high over NERN Europe is progged to remain in place ... and slowly weaken through the period ... while SE European upper low slowly moves E ... covering the Black Sea on Sunday morning. At low levels ... NE European SFC low will remain anchored over NE Europe ... with weak pressure falls expected across central Europe within plume of weakly unstable subtropical air E of the developing upper low. Over the Mediterranean ... quiescent conditions/flat pressure distribution will persist.

DISCUSSION

...Western Mediterranean...
Lapse rates over the Mediterranean are rather weak ... and despite BL moisture being rather rich/deep over the W Mediterranean ... only about 500 J/kg MLCAPE have been present on Friday afternoon. Strong large-scale forcing for ascent is expected to overspread the western portions of the Mediterranean on Saturday ... though widespread convective development seems somewhat uncertain ATTM due mainly to two factors:

* somewhat cooler low-level air seems to be entrained into the pre-frontal environment

* SFC convergence / frontal boundary is progged to be quite diffuse

However ... if storms form ... shear should be sufficient for a few severe storms (about 30 m/s DLS and up to 10 m/s 0-1 km shear per GFS) including possibility of a brief tornado. Allover risk seems to be too low for a SLGT ATTM.

#