Mesoscale Discussion
Valid: Fri 18 Jul 2014 17:00 to Fri 18 Jul 2014 20:00 UTC
Issued: Fri 18 Jul 2014 17:12
Forecaster: GROENEMEIJER

NW and central France, extreme SE England, extreme W Belgium...

On the forward flank of an area of elevated convection that moved northward over Western France, convective storms have intensified after 16 UTC and evidently become surface-based.

The environment in which these strorms develop is characterized by ample MLCAPE (2000-3000 J/kg), and strong (20 m/s in the west) to moderate (10 m/s in the east) deep-layer shear. The most intense storms will likely occur in across far NW France in vicinity of a prexisting convergence zone (near a line from just south of Rouen to Lille). Given the strong CAPE, very large hail will be possible. The storms may well develop into a bow-echo capable of producing gusts > 32 m/s. A threat of tornadoes will exist if a storm can interact directly with the sea-breeze front.

The western flank of the convective system may also affect W Belgium and SEern England around 20 UTC.

In central France, deep convective activity will have more difficulty to form, because of some remaining convective inhibition. Any more isolated storm in that region will also have a threat of producing very large hail and isolated severe wind gusts.