Forecast Update
Valid: Sun 29 Aug 2010 14:00 to Mon 30 Aug 2010 06:00 UTC
Issued: Sun 29 Aug 2010 15:04
Forecaster: VAN DER VELDE
A level 1 was issued for Benelux and NW Germany mainly for severe convective wind gusts and a chance of tornadoes and locally excessive convective precipitation.
SYNOPSIS / DISCUSSION
An intensifying surface low pressure area over the southeRN North Sea, backed by a very strong mid level vorticity maximum, is entering the Benelux area and NW Germany. A band of rain with embedded convection is observed at time of writing entering the NW of the Netherlands. 12Z De Bilt sounding has showed that hodographs are long with potential for enhancing mesocyclone formation, and are more favorable than in the GFS 06Z model run. The GFS model does show an intensification of hodograph size during late afternoon and evening for the Netherlands, and a very circular shape with large S-R mid level winds. However, MLCAPE and ICAPE (shallow parcel layer depth) are on the low side and clearly supplied by the warmer sea. Strong convergence can nevertheless concentrate instability in smaller areas.
Radar still shows mostly isolated cells embedded in the band, which given strong low-mid level shear (>200 mē/sē SREH) can develop into mini-supercells or bow segments. This may lead to an isolated tornado and isolated severe convective wind gusts, unless the forcing manages to create a strongly forced convective line. Hail is possible but will likely remain under 2 cm size.
As the surface low enters Germany later in the evening, the flow becomes more northerly, and convective cells may drag in bands during most of the night over the northern Netherlands and northern Germany. As a result, there is some chance that precipitation amounts could reach excessive levels very locally.
Over southern Scandinavia and along the Baltic Sea, the pressure distribution is more flat with weaker winds and strong low-level buoyancy, which enhances potential for spout-type tornadoes.
