Storm Forecast
Valid: Tue 23 Jan 2007 06:00 to Wed 24 Jan 2007 06:00 UTC
Issued: Tue 23 Jan 2007 02:42
Forecaster: VAN DER VELDE

SYNOPSIS

A northeast-southwest oriented upper trough/low is present over western Europe and is moving into the Mediterranean. A highly baroclinic situation with warm air advecting northward ahead of the low causes the low to deepen and produce a lot of precipitation (wintery, in elevated areas) as it moves across northern Italy to Hungary with a remaining Genua trough with strong pressure gradients causing high winds in the area.

The warm sector features also rather steep lapse rates, along with Mediterranean moisture, so that instability is present (already at time of writing) in relatively high shear environment. The strongest lift occurs near the cold front, ahead of a mid level vorticity maximum and the left exit of a strong jet. The cold front would affect southern France, Corsica and Sardegna around 12Z, Italy mostly after 18Z, and the east Adriatic coasts during the late evening and night.

Unstable air remains after the cold front, and a new disturbance may affect Corsica and Sardegna during the night, especially, with the jetstream over the latter and newly enhanced SREH by GFS18Z.

Steep lapse rates and a slight mixing ratio swirl associated with a small trough approach Denmark in the morning hours from the northwest and may lead to some thundery showers.


DISCUSSION

...Corsica, Sardegna, Italy, Adriatic coasts...

Throughout the whole area, deep layer shear is forecast to be greater than 20 m/s, while 0-3 km storm-relative helicities (in the warm sector) can exceed 100-250 m2/s2 and low level shear more than 10-15 m/s. MLCAPE by GFS reaches a few hundred J/kg. It is likely that a few tornadoes, over land as well as water, can result from these conditions. Strong updrafts may also bring marginally large hail. Isolated severe convective gusts are possible.

...coasts of northern Spain and Portugal...

An isolated waterspout is not excluded, given very steep low-level lapse rates as cold unstable air advects over relatively warm waters, along with weakening winds.