Storm Forecast
Valid: Tue 05 Sep 2006 06:00 to Wed 06 Sep 2006 06:00 UTC
Issued: Tue 05 Sep 2006 00:36
Forecaster: VAN DER VELDE

SYNOPSIS

While ridging occurs over western and southern Europe, a large low and upper longwave trough affect eastern Europe with cool showery/thundery weather. Some CAPE builds up over France and Spain, but lack of trigger other than a few orographic features will keep storms isolated. Have honoured GFS/NMM precip signals for TSTM areas here.
Off the map to the east, a cold front at the nose of a negatively tilted upper wave is going to cause most organized severe weather. Within the forecast area, some areas of isolated severe weather potential can be defined:

DISCUSSION

...from Lithuania into the northern Ukraine...

Marginal instability in the cool airmass with relatively low LCL heights and no capping will yield thunderstorms with cloud tops into temperature levels below -20 C. Due to the fairly strong flow, moderate deep layer shear (10-15 m/s) and 0-3 km SREH (100-200 m2/s2) occupy mostly the southern parts, while low level shear of 9-12 m/s is present throughout most of this area. Expect a few severe weather events such as an isolated tornado, severe wind gust or marginally large hail event.

...Black Sea...

Especially as the cooler air surges southeastward into the area, a cold front is re-invigorated in the evening. Positioned under the jet, strong deep layer shear (25-30 m/s) will be present, and although cloud top heights are not forecast to be very high in GFS (-10 to -15C), low-level buoyancy and lapse rates will assume high values over the warm Black Sea water surface. The area should see forcing from midlevel vorticity advection and convergence along the frontal zone.
Expect a MCS to form, possibly with supercells embedded, which may succeed very well in producing a few tornadoes (waterspouts) given low LCL and very steep 0-500m lapse rates (>20K/km), as well as large hail and severe gusts.

In the morning hours of Wednesday, the eastern half of the Black Sea (off map) and Turkish coast are probably affected by a more powerful MCS/supercells, with higher EL heights, at the left exit region of the northwesterly jet, with probably higher coverage of severe weather as described above.

...Russia...
at the edge of the map, instability seems to be present with moderate to strong values of deep layer shear and storm-relative helicity. This could yield some severe storms (supercells), when these parameters overlap.
Large hail, severe gusts are possible.

...Baltic states...
Although convective depth is decreasing, GFS model suggests convective precipitation training for hours over the same area. Large precip quantities may occur, especially over western Latvia. Waterspouts may also occur, though winds may be too strong.