Voor de oostelijke helft van België.
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DISCUSSION
... France to Germany ...
Stalling stationary front from the 18th/19th cold front event continues to retreat northwards during the day and seems to be placed somewhere over central France and central Germany as an active warm front boundary. Air mass over far S-France/W-Mediterranean features a rich BL moisture content with surface dewpoint readings in the upper tens/lower twenties. As an upper low moves towards the Bay of Biscay, WAA strengthens over France and helps to sharpen the boundary during the day with EZMWF/GFS indicating a quite intense moisture gradient along this boundary....with moisture pooling bringing surface dewpoints well above 20°C on a local scale. Steep mid-level lapse rates atop this air mass feature a confined area with high CAPE build-up....probably in the order of 1-2 kJ/kg. However major uncertainties exist in the exact placement of this front due to numerous weak short waves crossing that boundary during the severe weather outlook day-1 period, each of them being able to generate strong to severe thunderstorms, which may modulate final boundary position.
Despite that, overall conditions favor rapid to explosive thunderstorm development on an isolated to scattered scale regarding thunderstorm coverage. Shear in order of 20-25 m/s (6 km bulk shear) will be more than adequate for intense multicell/supercell evolution with the main risk being large to very large hail and severe downbursts. Near parallel alignement of the deep layer shear vector to the frontal boundary also favors the development of numerous smaller scale and progressive clusters with a more widespread severe to damaging wind gust risk. However, major uncertainties in the meso-alpha/beta scale preclude any higher probabilities for now. Also, latest QPF outputs hint on more isolated thunderstorm coverage especially over central France, which also neglects a level 2 for now.
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Bericht laatst bijgewerkt: 20-08-2011 13:23
