Extended Forecast
Valid: Mon 02 Jun 2008 06:00 to Tue 03 Jun 2008 06:00 UTC
Issued: Sat 31 May 2008 18:42
Forecaster: TUSCHY

SYNOPSIS

The upper - level trough over SW Europe, which was decisive for the weather during the past few days for central Europe, starts to take in a more negative tilt as this feature interacts with the strong subtropical jet. This evolution does not mean that a lot will change as ridging over central Europe with very warm conditions prevails. A persistent upper - level trough over eastern Europe will help to sustain the influx of cool and stable air well towards the south.

DISCUSSION

... The Low Countries ...

A new splash of a modified EML approaches from the south during the morning hours, spreading north / northwestwards during the forecast period. This results in steepening mid - level lapse rates. At the moment we see no reason why we should doubt instability forecasts of more than 1 kJ / kg over a broad area. GFS has numerous vorticity maxima crossing the area from the SW during the day but exact timing and strength are not assignable that far out. However, the approaching trough from the south should support scattered to widespread thunderstorms during the afternoon / evening and night hours ( exact initiation depends on convective debris, the strength of the cap and potential outflow boundaries ). DLS in the order of 10 - 15 m/s is not that strong but robust instability release should offset weaker shear parameters and any more discrete thunderstorm will be able to produce large hail and even significant hail larger than 5cm can't be ruled out. Weak background flow and high PWAT values also point to an enhanced flash flood risk especially when thunderstorms cluster betimes.

Due to so many uncertainties we decided to stick with a high - end level - 1 area but an upgrade may become necessary later - on.

... Germany ...

Another round of strong to severe thunderstorms will be possible over most parts of Germany. A combination of rich BL moisture, steepening mid - level lapse rates and the approaching trough from the S will support scattered to widespead thunderstorms. DLS is very weak with values below or just above 10 m/s but strong instability release of 1000 - 1500 J/kg MLCAPE could offset missing shear. In addition GFS develops enough veering with height to support potential storm rotation, also apparent by a slightly enhanced SCP ( supercell composite parameter ). During the initiation, when thunderstorms stay more discrete, there will be a risk for large hail but the whole environment points to a potential torrential rainfall threat as storm motion will be very slow and as storms cluster.

Later model runs have to been revised regarding the risk for thunderstorms over far N and E - Germany and a slight expansion of the level area may be needed later - on.

... Rest of Europe ...

For the rest of Europe it looks like there will be numerous places with thunderstorm activity but weak shear and only modest instability release should preclude a more robust risk for organized thunderstorms. Those thunderstorms will be mainly diurnal driven and should decrease in coverage after sunset.




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