Storm Forecast
Valid: Tue 03 Jul 2007 06:00 to Wed 04 Jul 2007 06:00 UTC
Issued: Tue 03 Jul 2007 00:29
Forecaster: VAN DER VELDE

SYNOPSIS

Large low pressure system over the British Isles, western Europe and into Germany, a frontal wave coming from the Atlantic Ocean over northern France into Germany. Air will mostly be unstable in the cool theta-e sector at middle levels, with a tongue of higher theta-e trailing that of mid levels, so that the air is also potentially unstable, and this in the vicinity of the upper jet. Larger instability will be present over central/eastern Europe, where a plume of warmer airmass is present.

DISCUSSION

...N France, S Belgium, W Germany...

At the rear side of the wave in middle levels, modest instability should develop. This may perhaps only occur at the mesoscale by forced linear ascent where potential instability is converted to conditional instability. Given that low level shear ranges well over 12 m/s and SREH over 200 m2/s2, one should be alert for shallow supercells and bow echoes.... however, instability is progged to be behind these enhanced shear fields... so this likely is less favourable as it looks. Will not exclude some locally overlapping shear and instability though, with chances of severe gusts and an isolated tornado.

...S UK...

Positioning of several hundred J/kg MLCAPE, humid low levels and relatively weak flow under an upper trough is the classic setup for a few to numerous spout-type funnels/tornadoes. Also, beware of local flash flooding due to slow movement of thunderstorms.

...N Russia...

Mostly elevated instability is forecast within the range of good shear and especially SREH conditions. Although most convection will not profit of this, expect that a hail/wind risk is enhanced and that more eastward surface-based convection under moderate shear conditions can develop with the full range of severe weather, including tornadoes, possibly candidate for a level 2.

...Serbia, W Romania, E Poland, Lithuania, Belarus...

500-1000 J/kg MLCAPE is likely to develop in this area, with steep 2-4 km lapse rates, 0-6 km shear generally above 10 m/s and SREH3 locally over 100 m2/s2 (latter especially over northern half of level 1 area), not great, but sufficient to organise multicell clusters and an isolated supercell with an attendant large hail threat and severe gusts (high LCLs). In the north, a squally MCS may produce a higher density of severe gusts. Low level shear will be moderate (up to 10 m/s) and might be just sufficient for a tornado especially in eastern Lithuania where LCLs are forecast to be rather low.

...N Austria, C Czech Republic...

Zone of convergence and a small area of unspectacular instability forecast during the evening hours, but where warm air advection creates a respectable 400 m2/s2 SREH and approaching jet 20 m/s deep layer shear. This may just come together and produce a supercell with large hail and/or a tornado.