Storm Forecast
Valid: Mon 02 Oct 2006 06:00 to Tue 03 Oct 2006 06:00 UTC
Issued: Sun 01 Oct 2006 23:23
Forecaster: GROENEMEIJER

SYNOPSIS

Monday at 06:00 UTC... a strong WSWly flow in the mid-troposphere is expected to be centered along an axis from NWrn Spain to SWrn Poland. The flow is located between a vertically-stacked low over the western North Sea and a broad ridge over NW Africa. In the range of the low-pressure system the air-mass possesses weak latent instability over and nearby water surfaces. During the forecast period, a frontal system is expected to develop along a line stretching from the upper Rhine valley via the Gironde to northwestern Galicia.

DISCUSSION

Eastern France, low Switzerland, SWrn Germany

South of the aforementioned frontal boundary, moisture is expected to be advected northward through the Rhône valley into the level 1 area. In concert with some insolation south of the increasing frontal cloudiness, this will likely increase the low-level theta-e sufficiently for the formation of weak CAPE. Although models do not agree that convective storms will form, GFS consistently does so, and we assess that is has a reasonable chance. Given that 25 m/s deep-layer shear and over 200 m2/s2 SREH are expected across the area, supercell storms appear likely whenever convection manages to form. Low-level (0-1 km) shear around 15 m/s should create an attendant threat of tornadoes. The threat will likely persist into the evening until the boundary layer has cooled sufficiently for the convection to be become fully elevated. The overall threat strongly depends on whether convection forms at all, but this conditional probability is judged to be of sufficient magnitude to warrant a threat level 1.