Mesoscale Discussion #008 (valid 21/05/2014 15-21 UTC)
*** Environmetal conditions across the discussion area are becoming increasingly supportive of a dangerous severe weather outbreak in the next 3-12 hours. ***
Satellite imagery revealing an extensive clearing area during the last few hours which resulted in strong insolation where temperature has already risen into the range between 22 and 26°C, coupled with gradual moisture recovery with dewpoints in 14-16°C range. Around 5-15 knots of SFC winds are present across the area, expected to increase once a SFC low deepens over W France. SFC T/Td conditions should easily result in very strong instability between 1500 and 2500 J/kg of MLCAPE, providing an explosive environment. Besides this, a strenghtening wind field within the 60-80 kt jet streak across the western Europe has resulted in very strong deep layer shear in range of 50-60 knots and also very impressive LL shear / helicity. 0-1km shear in range between 25-40 knots and SR 3km helicity between 200-400 m^2/s^2 becoming favorable for rapid storm organization into supercells as a primary mode. The most concerned area is from CNTRL France across Belgium into SW Netherlands where LL shear and helicity significantly increases in the late afternoon. Given the simulated SR 1km helicity in excess of 250-300 m^2/s^2 across the broad area, discrete supercells with tornadoes (including strong ones) are becoming likely. As well as very large hail, damaging winds and torrential rainfall. Once the trough kicks in from the N Iberia, a large cluster of storms is likely to form from WSW France, translating further NNW-wards during the evening / early night hours. Damaging winds along the possible bowing segments will remain the main threat with this cluster.
According to the aforementioned conditions above, an upgrade into HIGH risk remains possible by mid afternoon.
