Storm Forecast
Valid: Fri 21 Jul 2006 06:00 to Sat 22 Jul 2006 06:00 UTC
Issued: Thu 20 Jul 2006 18:22
Forecaster: TUSCHY

SYNOPSIS

Disturbed weather pattern continues for Europe, as a strengthening, northeastward shifting trough // placed over the eastern Atlantic // and its attendant warm air advection continues to reinforce the flat ridging over most parts of central Europe....Therefore, extremely hot conditions will continue for parts of central
Europe.
Another intense longwave trough over NE Europe will start a slow eastward motion due to the evolution of an intense low-level depression.

+++ Correction in the first header due to missing countries ! +++

DISCUSSION

...Northern France,Belgium and parts of the Netherlands...

All-over synoptic weather pattern favors the development for a few organized storms, but there are still some uncertainties about the exact evolution / region of the severe weather.

Models basically agree in the synoptic weather pattern and its evolution.... A trough over the eastern Atlantic is forecast to shift in a more negatively tilted position during the next 24 hours.... As a result, a well defined trough axis will approach the region of interest during the evening /early night hours.
The main problem right now will be the degree of the amplification and therefore the final strength of the upper-level jet, entering the trough on its upstream side ( e.g. discrepancies between GFS and GEM, which aren't negligible. )
A comparison between model calculation and reality was not possible due to temporarily missing data reports over the Atlantic Ocean....
For the moment, I will lean on GFS due to its not too bad handling with the latest convective event.
GFS and NMM both indicate the development of a weak low-level pressure area somewhere over central France.
Position under an ill-defined coupled upper-level jet structure will be conducive for broad area with weak-modest pressure fall over northern France.
Yesterday's dewpoint forecast of GFS was a little bit too bullish ( 1-2°C ) and hence I am not that optimistic with instability release, but locally up to 1000 J/kg looks realistic.
Strong WAA downstream of the east-Atlantic trough and diurnal driven sea-breeze front ( moving southward from the English Channel ) should enhance / develop a baroclinic zone in the level-1 area , which should give enough forcing for storms to penetrate the cap .
This area, north of the surface low and along the English Channel, will be the focus for scattered TSTM initiation.
The final strength of the surface depression will point at how strong the shear finally will be, but indications are, that a broad sector with enhanced 0-3km SRH will develop north of the system.
A well mixed boundary layer, possible backed wind field and low LCLs would favor the risk for a few tornadoes, if indeed all the parameters develop like expected.
Steep mid-level lapse rates and DLS of 15-20m/s would also favor a risk for large hail and severe wind gusts.... mainly with southward displaced cells, where inverted-V profilers are forecast.
A cluster of storms could indeed develop, if enough storms can penetrate the cap and still strong background flow would be able to bring a line of storms far towards the east.

Due to all the uncertainties, significant adjustments ( like including parts of CNTRL United Kingdom or any probability assimilations ) could become necessary later-on !

... NE Germany, Denmark and parts of Sweden...

A short-wave trough continues to circle around the ridge over central Europe.... Attendant forcing in a weakly capped environment should be enough for scattered TSTM development.
The best chance for storms to produce severe weather will be over Sweden, where locally up to 500 J/kg instability and 15-20m/s DLS overlap.... Isolated large hail will be possible but main threat will be strong - severe wind gusts.
A level-1 does not seem necessary ATM due to the degree of the expected storm coverage and the small area of best thermodynamic / kinematic parameters

...S-Germany and mainly mountainous areas of Switzerland and Austria...

Current thinking is that expected instability values ( e.g. GFS ) are not realistic due to wrong dewpoint assumptions. However...steep mid-level lapse rates will be stil present and a few hundred Joule could easily be realized.... Isolated , pulsating storms
should develop and combination of humid mid-levels and dry boundary layers would be conducive for strong downdrafts / marginal hail, locally reaching severe criteria.