Storm Forecast
Valid: Sat 28 Aug 2010 06:00 to Sun 29 Aug 2010 06:00 UTC
Issued: Sat 28 Aug 2010 04:40
Forecaster: VAN DER VELDE
A level 1 was issued for NE Italy, Slovenia, Istria, Croatia mainly for isolated large hail and flash floods.
A level 1 was issued for W Russia mainly for severe convective wind gusts.
SYNOPSIS
At 500 hPa, low geopotential heights and a cyclonic flow pattern covers almost all of Europe, except the southern Mediterranean. Cool air from around Iceland is transported into southern Scandinavia and north-central Europe and destabilizes over the eastern North Sea and southern Baltic Sea, and as a result convection can develop in a large area.
The most active surface low is found over western Russia, other lows over the northern Adriatic, Romania, and southern Scandinavia.
Conditions of strong vertical wind shear occur from France to the northern Balkan, Ukraine and around the Russian low.
DISCUSSION
...W Russia region...
Moderately unstable air combined with a cold front and strong winds in the lower levels, large shear in the 0-1 km layer (15 m/s), but small shear in middle levels are favorable for a linear MCS with a primary threat of severe wind gusts. A tornado cannot be ruled out.
Very large curved hodographs with >500 mē/sē appear to be in stable air around the warm front and should pose no threat.
...NE Italy, NW Balkan region...
MLCAPE (1000 m mixed parcel) values are only around 500 J/kg in GFS, although 00Z soundings show larger values up to 1500 J/kg (500 m mixed parcel) and very dry mid levels over moist lower levels. Much of that is consumed during the nocturnal MCSses and moves out of the region, but it would not be surprising if 1000 J/kg can be attained today. Significant forcing and strong deep layer shear (30 m/s) and SREH (100-300 mē/sē in a band over northern Slovenia and Croatia) are favorable for supercells, while predicted storm motion vectors are only <8 m/s. This makes for a flash flood threat, as well as large hail. Severe storm coverage may be low, though. Tornado threat should be low, given weak shear and absence of veering in the lowest kilometer, in GFS output.
...Romania, Ukraine...
Large wind shear and curved hodographs are favorable for supercells with large hail, but it is unlikely that with such low instability as indicated (<200 J/kg) something can develop.
...southern Scandinavia, Netherlands, N Germany, N Poland...
0-3 km low level CAPE is predicted to be strong over a large area, in combination with steep near-surface lapse rates. Although boundary layer winds will likely not be very weak, the conditions seem favorable for a spout-type tornado here and there. Coastal convergence can cause enhanced clustering in the southeastern North Sea area and can provide a focus for these events.
