Storm Forecast
Valid: Sun 15 Oct 2006 06:00 to Mon 16 Oct 2006 06:00 UTC
Issued: Sun 15 Oct 2006 03:42
Forecaster: VAN DER VELDE

SYNOPSIS

A slowly changing weather pattern with a blocking high pressure area over southern Scandinavia. Low pressure is present over the central Mediterranean Sea where warm air advection deepens the surface low.
The occlusion front belonging to a large Atlantic low approaches Portugal in the second half of the period.
Yet another low develops over the Ukraine, moving into the Black Sea.

DISCUSSION

...Portugal...

Marginal instability is forecast in association with the frontal zone passing during evening and night. Deep layer shear may reach values over 20 m/s, while low level shear will be enhanced to over 10 m/s over land. Storms embedded in the frontal zone could develop brief mesocyclones, with a chance of large hail and possibly an isolated tornado given also low LCL heights.... though some uncertainty is present that the frontal zone remains little convective.

...Ionian Sea...

Deepening of the low pressure area due to warm air advection creates stronger, easterly surface level flow. These backed winds along with southwesterly midlevel winds provide a favourable wind shear environment with DLS over 15-20 m/s and 0-3 km SREH of 100-250 m2/s2. Severe is therefore more likely to occur with today's convection than the past few days.
A well-organised MCS and/or supercells may develop, with values of MLCAPE between 500 and 1000 J/kg. Large hail and possibly also tornadoes could occur - especially near Sicily and southern Italy where LFC heights are forecasted to be the lowest (around 1000 m)

In addition, very weak low level winds and steep lapse rates support the occurrence of a few waterspouts, mostly near the upper level low over Thyrrhenian, Ionian and Adriatic Seas (see e.g. Brindisi 00Z sounding with large low leve CAPE and weak winds)