Forecast Update
Valid: Fri 05 Sep 2008 18:00 to Sat 06 Sep 2008 06:00 UTC
Issued: Fri 05 Sep 2008 18:03
Forecaster: GROENEMEIJER

SYNOPSIS

Please refer to the outlook issued at Thu 04 Sep 2008 18:13.

DISCUSSION

... E-France and W-Germany ...

Rather more convection has developed than anticipated earlier on. The storms have organized into a prefrontal squall. Between a few 100 to around 1000 J/kg MLCAPE should be available ahead of the line, with relatively high buoyancy at low levels. Especially in the area upgraded to a marginal level 2 should CAPE closer to 1000 J/kg. As the squall line, that is initially oriented from the Rheinland across the Saarland and western Burgundy to the Massif Central, moves eastward, it encounters a quite helical low-level flow. SRH computer with Bunkers storm motion gives values of around 200, to near 300 m2/s2. This, and the fact that both low-level and deep-layer shear are strong, suggest that an tornado or two is possible with the line, with an isolated strong tornado not ruled out. Additionally, some damaging wind gusts are likely. Around midnight, the activity of the storms should gradually diminish as the boundary layer cools.

... S-UK ...

The strongest shear has now left all but the extreme SE of the UK, mitigating the threat of any isolated tornado. The level 1 has therefore been cancelled over this area.