Valid: Sun 31 Dec 2017 06:00 to Mon 01 Jan 2018 06:00 UTC
Issued: Sat 30 Dec 2017 21:53
No threat levels have been issued.
A very deep cyclone -962 mb MSLP is forecast at the centre by IFS- passes over north of the British Isles, and reaches Norwegian coasts during the forecast period while filling rapidly. The very cold air mass behind the cyclone, flowing over the Atlantic, makes up a few hundred J/kg of MLCAPE, following the polar jet above. Up to 45 m/s 0-6 km shear and 200-400 J/kg MLCAPE overlap in a narrow band around the cold front passage over S England and NW France. It is possible that this very high shear-low CAPE environment in this limited area result in no DMC, but in case it does, supercells would be likely. Tornadoes are not ruled out with high low level shear and curved hodographs, but no threat levels are issued due to the low confidence. High PWs and kinematics favouring backbuilding storms may introduce flash flood probability over coastal areas facing west. However, storm motion is expected to be very fast. With very high pressure gradients around whole NW Europe, and even a possible sting jet near the heart of the aforementioned cyclone, severe wind affects Scotland, France, Germany, low countries and north of the Iberian Peninsula. These winds are -maybe not entirely, but mostly- nonconvective.
One other cyclone forms over E Mediterranean. Latent instability is weak in this area, but enough for clusters of DMC. Shear is very weak except around the Syrian coasts.