Storm Forecast
Valid: Fri 30 Mar 2007 06:00 to Sat 31 Mar 2007 06:00 UTC
Issued: Thu 29 Mar 2007 18:10
Forecaster: TUSCHY

SYNOPSIS

A pool of lower geopotential heights can be found over western / central Europe, surrounded by high pressure areas.
A well established cold front will affect parts of Norway and Sweden with adjacent intense CAA during the daytime hours. An isolated SFLOC report can't be excluded, but coverage will be too low for warranting a TSTM line.

DISCUSSION

....Central and eastern Mediterranean....

A pretty strong at or above 160kt jet over N-Egypt will help to push a negatively inclined upper-level trough over southern Italy towards the NE.
This kind of constellation will support capped conditions under and on the anticyclone side of the jet and this is also captured by yesterday's 12Z sounding report of Heraklion, indicating a nice EML layer with pretty steep lapse rates between 900-600hPa ( also observably in model outputs).
Hence the main focus for storm activation will be under the base of the NE-ward shifting trough, characterized by slowly warming mid-levels and a surge of a pretty moist BL airmass on its upstream side towards the north.
Keeping in mind that SSTs will be around 15-16°C, lapse rates at the mid-levels stay pretty steep and dewpoints will be about at or above 10°C, an area of 200-400 J/kg SBCAPE looks reasonable.
The suggestion of GFS with up to 800 J/kg looks somewhat overdone, comparing the atmospheric stratification of yesterday and today.
DLS of 10-20m/s ( increasing southwards ) will be enough for an isolated large hail risk.
Further towards the north, background shear will be weaker and this would enhance an isolated waterspout threat.

The final reason for a level-1 area was the fact that both, thermodynamic and kinematic parameters look fine for a low-end severe TSTM threat over Sicily and S-Italy.

The same for the coastal areas of western Greece and the Aegean Sea, where enhanced DLS would pose a risk for a few severe wind gusts and an isolated large hail report.

...France,S-UK, Germany , the Netherlands and Belgium....

Upper-level low pressure area will continue to spin around over France although a final SW-ward movement will arise during the latter part of my forecast period.
Diffuse upper-level forcing and no real "frontal" boundary signal at lower-levels makes it difficult to define locations of enhanced thunderstorm development that far out.
Re-circulated tongue of higher PBL moisture - stretching from SE / E France NW-wards - attained the main advertence for storm initiation during a 12Z-20Z time frame.
Mixing ration values of 6g/kg, enhanced convergent flow along this Theta-E tongue and steep lapse rates at mid-levels will support 100-200 J/kg SBCAPE mainly over Belgium and the Netherlands, where diabatic heating and moisture advection will be maximized. Again, GFS looks like to be somehwat too aggressive regarding the expected instability values ( although dewpoints were acquired pretty well ). No significant thermodynamic change at 800-700 hPa will occur, which should keep instability values pretty slim.

Expected minimal instability values and weak shear will support weak pulse storms, which should not produce gusts/hail, reaching the severe weather criteria.