Forecast Update
Valid: Sun 21 Aug 2011 09:00 to Mon 22 Aug 2011 06:00 UTC
Issued: Sun 21 Aug 2011 09:42
Forecaster: GROENEMEIJER

A level 2 was issued for parts of E Portugal and W Spain mainly for excessive rainfall, large hail and perhaps a tornado.

A level 2 was issued for parts of the Benelux countries and parts of Nrn and central Germany mainly for severe wind gusts and large hail, and perhaps a tornado.

DISCUSSION

...Benelux and Germany...

Have enlarged the level 2 as confidence in storm initiation has increased.

Current thinking is that convective initiation may occur farther to the west than in yesterday's forecast. ECMWF model appears a bit too quick with the influx of cooler and drier air from the W.

Surface observations at 09 UTC indicate strong northward advection of high dew points into the Benelux countries with values of about 20 C widespread across northern France in the wake of an elevated MCS that is moving into central Germany. A convergence zone stretching from the coast of East-Anglia to near Paris will move Eward and serve as the focus of convective initiation during the early to mid-afternoon as it progresses into the Benelux.

1000 J/kg of MLCAPE should be available across the northern part of the level 2 and up to 2000-2500 J/kg across the southern Benelux. In combination with 25-30 m/s of deep-layer shear this consitutes an environment that will easily sustain severe storms. Storms will likely include a few intense supercells with large hail and bow echoes producing damaging winds. One or two tornadoes cannot be ruled out either where cells interact with backed surface winds.