CONVECTIVE FORECAST
VALID 06Z SUN 29/08 - 06Z MON 30/08 2004
ISSUED: 28/08 19:47Z
FORECASTER: DAHL

General thunderstorms are forecast across the N UK ... SW into central Europe ... SE Europe.

SYNOPSIS

Vigorous N-Atlantic upper trough is expected to continue digging SE ... reaching the central North Sea towards Monday morning ... thereby ingesting upper short-wave trough FCST over central Europe at the beginning of the period. SE European upper low is progged to fill and leave the FCST area early in the period. At low levels ... SFC low accompanying the Atlantic trough will likewise move into the central North Sea ... with the rest of Europe remaining under rather quiescent conditions. Main frontal boundary ... extending from N France across central Germany into NE Europe by the beginning of the period will commence southward acceleration in response to the approaching upper trough during the day.

DISCUSSION

...central Europe ... including Polish SEE TEXT area...
Air mass in the prefrontal environment over central Europe is largely saturated with neutral lapse rates ... as revealed by Saturday's 12Z launches. Mid/upper level dry air overspreading the SFC front has allowed for clearing skies and sufficient destabilization to allow for TSTM development over W France on Saturday. Evolution of this dry intrusion is quite uncertain ATTM ... but NMM as well as GFS advertise weak CAPE ahead of the front ... hinting at likely TSTM development given increasing large-scale ascent. LCL heights will likely be fairly low ... and with 7.5 to 10 m/s 0-1 km shear across much of the prefrontal regions ... yielding 150+ m2/s2 0-3 km SRH over Poland ... supercell/tornado threat should be limited given allover weak CAPE densities and only about 15 m/s deep-layer shear. Also ... TSTM coverage will likely depend on cloudiness/precip ahead of the cold front which is somewhat uncertain ATTM. Best kinematic setup should evolve over Poland late in the day ... and a marginally severe wind/hail event may be possible if a mesocyclone happens to form.

...E Spain ...
Low-level moisture is underrunning the steep lapse rates/deep CBL's farther inland across the ERN portions of the peninsula - yielding rather strongly capped profiles with CAPE in the 500 to 1000 J/kg range (ref. Saturday's 12Z ascent from Murcia). Farther W ... profiles are attaining increasing increasing inverted-V characteristics. Shear profiles are progged to be too weak for organized severe TSTM threat ... though a few downbursts may occur with any of the storms given dry/isentropic mid-levels.

...SE Europe...
Shape of the thermodynamic profiles is quite uncertain as some of Saturday's ascents are disturbed by convection ... However ... over the E Ukraine ... 1500 J/kg have been present on Saturday 12Z ... which may be advected eastwards as proposed by model guidance. Large-scale ascent will generally decrease in the wake of the upper low ... but ... residual outflow boundaries etc. may cause sufficient mesoscale ascent to initiate TSTMS. Weak shear and weak CAPE suggest that organized severe TSTM threat will be rather limited ... though strong outflow winds ... some hail and large amounts of precip should be possible.

...Italy...
Latest soundings reveal quite shallow low-level moisture over the central Mediterranean regions ... and uncertainty exists with respect to Sunday's moisture depth/mixed-parcel CAPEs. Indications are that moisture will be insufficient ... and will not outlook TSTMS for Italy ATTM.

...N UK...
TSTMS will likely develop beneath the upper thermal low over the N UK. 0-1 km shear should be supportive to a few brief/shallow mesocyclones ... mainly posing the threat for isolated marginally severe hail/wind events ... though a weak tornado cannot be excluded.

#