Forecast Update
Valid: Fri 20 Jul 2007 12:00 to Sat 21 Jul 2007 06:00 UTC
Issued: Fri 20 Jul 2007 12:02
Forecaster: GROENEMEIJER

SYNOPSIS

Refer to convective forecast...

DISCUSSION

W Germany, E Benelux...

A large MCS has developed over France and is currently moving northward over the E Benelux and W Germany while causing strong gusts, generally remaining below 25 m/s. In its wake, a rather strong SSWly flow is expected.

Surface winds appear to back to the southeast in response to forcing ahead of the the main mid/upper-level trough that should be over Belgium at around 18 UTC. As a result, the flow will likely be rather helical in a location where insolation and upward vertical motion should be able to create significant CAPE.

Some of the storms initiating over N-central France will therefore likely manage to deveop into supercells with a relatively high tornadic threat. Clustering into a second linear convective system is however, possible as well given the strong forcing, which should reduce the threat of tornadoes. Nevertheless, conditions do look favourable enough to warrant a level 2, as tornadoes exceeding F1 intensity cannot be excluded. Otherwise, the supercells will likely produce some large hail and severe gusts in places.

S and central Germany...

Despite deep-layer shear being relatively meager for supercells with 15-20 m/s deep-layer shear, abundant CAPE is present and a convergence line, orgiinating as an outflow boundary of the aforementioned MCS appears to be a strong focus for well-organized storms, possibly including supercells. Large, possibly very large hail is therefore possible with the storms that should track E or ENEward during the period. Damaging gusts are possible, too.

UK...

The partly convective system currently over the S Uk is expected to move northward slightly slower than forecast earlier, so that the window of opportunity for surface-based convection to develop within its wake and the attendent spout threat appears to be lower, not warranting a level 1 anymore.