Storm Forecast
Valid: Mon 20 Jul 2009 06:00 to Tue 21 Jul 2009 06:00 UTC
Issued: Sun 19 Jul 2009 20:37
Forecaster: DAHL
A level 1 was issued across S France and N Spain for large hail and severe wind gusts.
A level 1 was issued across extreme NE Germany and W Poland mainly for marginally severe hail and tornadoes.
A level 1 was issued across N Ukraine and parts of W-central Russia mainly for large hail, excessive rain, and severe wind gusts.
SYNOPSIS
Extensive, zonally-elongated upper low is present over the northern portions of the forecast area, with a broad westerly flow being present at its southern periphery over central and southern portions of Europe. Several vorticity maxima are imbedded in this flow, one of which will travel from Iberia across the NW Mediterranean into N Italy during the period. At low levels, a large cyclonic circulation is accompanying the main upper low over northern portions of Europe. Farther south, rather quiescent SFC conditions prevail. As the westernmost portion of the N-European upper-low complex drops southwards, the deep-layer flow is expected to back, resulting in warm advection over western parts of Europe late in the period.
DISCUSSION
... S France ... NW Spain ...
It seems that some CAPE will develop over N Spain and S France in the afternoon hours as backing low-level flow advects moisture from the western Mediterranean westwards. DCVA-forced ascent ahead of the Iberian short-wave trough and upslope flow south of the Pyrenees should aid in initiating scattered thunderstorms in the afteroon hours. Deep shear is expected to be on the order of 20 m /s, which will be sufficient for well-organized multicells and isolated supercells. Main threats should be large hail and severe wind gusts. There seems to be a small threat for tornadoes in the evening hours, given lowering LCLs and increasing LLS late in the day. However, the time frame is rather small, as convection should slowly diminish after sundown.
... extreme NE Germany ... W Poland ...
A weakly capped, modified polar air mass will be present over the northern parts of central Europe. Deepest convection should occur over N Germany and N Poland. Though depth of convection should still be rather limited, there seems to be a marginally favorable overlap of DLS and LLS over W Poland and extreme NE Germany in the evening hours. Though convection should be decreasing by then, there seems to be a short time window when rotating updrafts are possible in the early evening hours. These would pose some threat for marginally severe hail and possibly an isolated tornado or two.
... N Ukraine ... parts of W-central Russia ...
A plume of warm/moist low-level air is present E of the N-European upper-low system. CAPEs are expected to be rather strong within this plume, probably reaching 1500 J/kg. There will be 15 to 20 m/s DLS over N Ukraine and adjacent regions in Russia per GFS, which will be sufficient for severe evolution. Main threats should be large hail, severe outflow winds, and excessive rainfall.
