Storm Forecast
Valid: Tue 22 Oct 2013 06:00 to Wed 23 Oct 2013 06:00 UTC
Issued: Mon 21 Oct 2013 20:01
Forecaster: GROENEMEIJER

A level 1 was issued for W France, S and SW England and Wales mainly for isolated tornadoes.

A level 1 was issued for NE France, southeastern Benelux and extreme W Germany, mainly for isolated severe wind gusts and tornadoes.

A level 1 was issued for SE France, mainly for very heavy rainfall.

A level 1 was issued for Portugal and SW Spain, mainly for very heavy rainfall.

SYNOPSIS

On the eastern flank of a large-scale trough, a strong SW flow is in place over western Europe. In the realm of this trough a humid unstable air-mass is in place and scattered storms are expected. A weak front is expected to move eastward across France, Spain and Portugal.

DISCUSSION

W France, S and SW England and Wales...

Showers and thunderstorms are expected to occur throughout the forecast period. As they are embedded in a strong SW-flow and 0-1 km bulk shear in the range of 10-15 m/s is expected, significant low-level rotation may develop in some storms and a few short-lived tornadoes or waterspouts may occur. Some risk of isolated non-tornadic severe wind gusts will also exist.

NE France, W Germany, SE Benelux...

Within a warm and relatively moist air mass, storms are expected to develop during the evening across N and E France as mid-level temperatures drop slightly. Given the strong shear, these storms may develop rotating updraughts. The strong low-level flow and -shear suggests a threat of severe wind gusts will exist and an isolated tornado will also be possible. Some marginally severe hail is not ruled out either.

SE France...

Convective activity is expected to pick up during the evening hours and may result in some training storms. Some high precipitation amounts may result locally. Given the strong low-level shear a (waterspout) tornado will also be possible.

Portugal and SW Spain...

A zone of heavy precipitation associated with a frontal system will move southeastward across the area. The training convection associated with it, may locally produce very high rainfall amounts. In addition, the strong low-level wind shear and low cloud bases suggest that a small risk of tornadoes will also exist, possibly also with isolated storms in the wake of the rain zone.