Storm Forecast
Valid: Sun 08 Jul 2007 09:00 to Mon 09 Jul 2007 06:00 UTC
Issued: Sun 08 Jul 2007 08:56
Forecaster: DAHL
SYNOPSIS
Atlantic long-wave trough is approaching Europe from the west, with its DCVA-forced upward motion regime overspreading France in the afternoon and early evening, and Germany in the evening/night hours.
The associated SFC cold front is currently stretching from SW France northeastward across the N Alpine regions into the Black Sea region, and will make some north- and eastward progress during the period. A frontal wave is anticipated to develop over France in the afternoon and then move northeastwards into Germany towards the end of the period. The strength and position of this feature are somewhat inconsistently progged by the models, but the development of the feature itself seems quite likely.
DISCUSSION
... N Spain ... France ... S Germany ...
The main issue today will be the build-up of sufficient CAPE. Thinking is that some moistening will occur as a result of evapotranspiration, with the depth of the moisture probably increasing near the developing SFC low by moisture convergence. This, and upper-level cooling ahead of the large-scale trough should result in at least a few hundred J/kg of CAPE. Extensive mid/high-level warm-sector cloudiness will likely limit the degree of SFC heating. Still, it is thought that the thermodynamic environment will be sufficiently unstable to allow for deep convection.
The shear profiles are quite strong ... with deep-layer shear in the 20 to 25 m/s range over France and Germany. SRH is simulated to exceed 150 mē/sē already and increase as the LLS increases with the development of the SFC low late in the day. LLS in excess of 12 m/s is advertised by GFS to exist over SW Germany and NE France in the late evening hours. However, GFS is among the models with the most aggressive solution with respect to the developing SFC low, so these values would be somewhat lower with other model solutions.
Thunderstorm coverage should greatly increase during the afternoon hours over France, with storms rapidly evolving into well-organized multicells and supercells, capable of large hail and damaging wind gusts. As the system spreads northeastwards, an additional tornado threat will develop, if the SFC low indeed strengthens as predicted e.g. by the GFS. Only negative is the weak CAPE, which may rather quickly disappear when the LLS is maximized after sundown. However, strong large- and mesoscale ascent should maintain the storms through much of the evening/night.
... extreme NW Russia ...
Steep low-level lapse rates and a nearly saturated boundary layer, as well as partly strong low-level shear may support a few brief tornadoes over extreme NW Russia.
