CONVECTIVE FORECAST
VALID 06Z MON 01/11 - 06Z TUE 02/11 2004
ISSUED: 01/11 00:16Z
FORECASTER: GROENEMEIJER

General thunderstorms are forecast across Portugal and western Spain, extreme eastern Spain, the western Mediterranean Sea, eastern France, southern Germany, southwestern Czech Republic and the Alpine countries, Italy and Slovenia and across parts of the eastern Mediterranean Sea.

There is a slight risk of severe thunderstorms forecast across central and western Sicily, much of the Tyrrhenean Sea, central Italy and parts of northern Italy.

SYNOPSIS

Monday at 06Z... a strong westerly flow is present over northern Europe while a mid/upper-level low pressure area is forecast across northern Spain.

DISCUSSION

...Italy / slight risk area ...
A north-south oriented frontal zone is expected from northwestern Italy over the Tyrrhenean Sea into Tunisia. On its eastern side, a warm air-mass is advected northward. A northward moving wave in the front is expected over northern Italy at the beginning fo the period and is associated with a 20 m/s low level jet on the warm side of the front. Clustered thunderstorm activity is expected to be ongoing over central and/or northern Italy during the morning, moving northward. In excess of 200 m2/s2 0-3 km Storm Relative Helicity is forecast in the warm sector by NMM and somewhat lower by GFS, implying that rotating updrafts are possible so that one or two tornadoes, strong winds and some severe hail are all possible across the northern half of the slight risk area during the morning.

A second wave is expected over the Tyrrhenean Sea at the end of the evening. Numerical models agree on developing an even stronger low-level jet in excess of 25 m/s at 850 hPa in its warm sector by Tuesday morning. A new round of thunderstorms is expected to affect Sicily from the early evening on and central Italy early on Tuesday morning. These bring a renewed threat of a few tornadoes, severe gusts and perhaps some large hail that will likely persist into the next forecast period.

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