Storm Forecast
Valid: Sun 26 Aug 2007 06:00 to Mon 27 Aug 2007 06:00 UTC
Issued: Sat 25 Aug 2007 18:40
Forecaster: DAHL

SYNOPSIS

Upper low over the Iberian Peninsula will retrogate off the Iberian Atlantic coast while undergoing some weakening. Vigorous upper fronal zone it stretching across the North Atlantic and and northern Europe, which will slowly shift southwards during the priod. A weak vort max will also affect the eastern Balkan States. Quasi-stationary low-level baroclinic zone is expected to curve northeastwards from central France across central Germany into northwestern Russia on Sunday 12Z.

DISCUSSION

... western Iberian Peninsula ...

Air mass over western Spain should remain moderately unstable with CAPEs of up to 1500 J/kg. Low-level warm advection during Saturday night will remain in place, maintaining partly well organized, severe convection. This activity will likely persist into the first half of the period on Sunday, before storms redevelop in sustained warm-advection regime. Low-level shear should be somewhat waker than on Saturday, but deep-layer shear will remain in the 20 to 25 m/s range, more than sufficient for severe evolution. Expect supercells and bow echoes, main threats being very large hail and damaging wind gusts. Strong capping and limited low-level shear should limit the tornado threat, though a brief tornado or two cannot completely be ruled out.

... Balkan States ...

It seems that CAPE and shear will remain rather weak across the Balkans. However, relatively dry environment may favor strong downdrafts. Also, rather strong QG upward forcing will likely promote quite widespread thunderstorm development, which may result in strong cold-pool formation and locally/briefly, mainly linearly organized thunderstorms. These may be capable of severe wind gusts. Also, some hail which may briefly attain severe limits may occur. Risk appears to be too low for a categorical risk, however. Intense rainfall with a threat for local flash flooding may occur over estern Romania in the evening hours.