Storm Forecast
Valid: Sat 21 Jul 2007 08:00 to Sun 22 Jul 2007 06:00 UTC
Issued: Sat 21 Jul 2007 08:30
Forecaster: DAHL

SYNOPSIS

Deep upper longwave trough is located over western Europe ... imbedded vorticity maximum is expected to move NEWD along the eastern periphery of this trough and induce a frontal wave semewhere between southern Germany and the N Balkans in the afternoon hours, which will move towards western Poland through the night. The point of initiation of the cyclogenesis is not quite agreed upon by the models, but this feature does appear in all solutions with rather coherently progged strength. Otherwise ... synoptically quiescent SFC conditions will prevail.


DISCUSSION

... E Germany ... Czech Republic ... W Poland ... N Austria ...

The main SFC cold frontal boundary seems to have stretched from extreme southern France across N Italy and Austria towards E Europe. However, much LL moisture has accumulated on the cool side of the boundary in the shallow and somewhat cool air over over E Germany and farther east, so that with diurnal heating appreciable CAPE should develop, possibly as high as 1500 J/kg. With backing LL winds afead of the developing SFC low, steep lapse rates may be advected atop the boundary layer in the evening hours over SE Germany, the Czech Republic and S Poland.

Storms may initiate elevated upon the approach of the upper vort max/LL warm advection across SW Germany (or they may already have developed over France in the early afternoon) and spread northeastward, rooting down into the boundary layer rather quickly.

Deep shear will initially be quite favorable for organized convection, but is to decrease to about 15 m/s during the evening, which will be somewhat marginal for long-lived updrafts. LL shear will likely increase with the developing SFC low over E Germany towards the late evening hours. This kinematic setup should suffice for multicell storms capable of marginally severe hail and strong wind gusts. Isolated mesocyclones are also possible, also posing a threat mainly for large hail. Storms that develop in the strong LLS at the periphery of the SFC low will have some potential for producing a tornado in the late evening. However, this tendency may be offset by the storms conglomerating into a big MCS which may primarily produce large amounts of rain, with only limited storm-scale organization.

... NE Spain ... S France ...

Another focus for organized severe storms appears to develop over N Spain, where very rich LL moisture from the W Mediterranean is underruninng the deep Spanish CBL, resulting in strong CAPE. DLS in excess of 35 m/s should be supportive of supercells and well-organized multicells which may evolve into line segments or bow echoes. Main threats will be (very) large hail and damaging wind gusts. However, air mass will likely be capped rather strongly, which may limit the coverage of the storms. At the moment, a level one threat seems to suffice. It seems that isolated storms in weaker thermodynamic, but equally strong kinematic environment may also form over France, but the coverage should be rather low.