Forecast Update
Valid: Sat 09 May 2009 15:00 to Sun 10 May 2009 06:00 UTC
Issued: Sat 09 May 2009 15:48
Forecaster: GROENEMEIJER
A level 1 was issued for extreme NE France and much if SW and central Germany and northern Switzerland, mainly for large hail and severe winds.
A level 1 was issued for SW France and parts of central France mainly for a risk of large hail and severe wind gusts.
SYNOPSIS
Refer to the convective forecast.
DISCUSSION
NE France, Germany, Switzerland...
The closed sfc low associated with a frontal wave was located about 200 km east of Paris around 1500 UTC.
Scattered storms are expected to develop within the warm air ahead of the system's cold front, that stretches southward from the core. Within this air mass, around 1000 J/kg of MLCAPE has formed. Scattered storms are expected to develop across NE France, and are developing over parts of northern Switzerland and SW Germany. Given that relatively strong 15-20 m/s 0-3 km shear is in place, the storms may well include a couple of supercells. These will have a threat of large hail and severe winds. As the storms track northeastward, they may gradually cluster. As this happens during the evening, low-level shear should also gradually increase and the threat of severe winds may increase. The threat of tornadoes is now thought to be relatively small because of a rather low boundary layer moisture, but they cannot be ruled out especially in the NW half of the level 1 area.
SW France...
Observations show that about 1000-1500 J/kg has formed in a strongly sheared environment across SW France, and similar amounts of CAPE are available over N-central Spain. Storms ongoing across the basque country, Rioja and NE Castille could be and/or become supercells and produce some large hail and damaging downdraft winds. Later, storms will also initiate across France. During the late evening, the storms will likely become less intense and gradually die out.
Austria, NW Balkans, W Hungary...
Some weak storms have developed across the area, but CAPE and storm coverage appear to be smaller than what was initially anticipated. Hence, the level 1 has been cancelled across this area.
