Storm Forecast
Valid: Fri 20 Oct 2006 06:00 to Sat 21 Oct 2006 06:00 UTC
Issued: Thu 19 Oct 2006 18:12
Forecaster: DAHL

SYNOPSIS

As upper low over the central North Atlantic deepens ... W European upper trough is progged to lift northeastwards ... resulting in a rather broad WSWLY upper flow over Europe. Large low-pressure complex will persist over much of Europe and the E Atlantic ... maintaining advection of unseasonably warm/moist air masses into central portions of Europe.

DISCUSSION

.. Central Mediterranean ...

It seems that locally rich moisture will be present which may result in MLCAPEs in excess of 1000 J/kg ... but nearly neutral/weak-CAPE environments should prevail on Friday. LLS and DLS are both expected to be quite weak as well ... and severe threat should be limited. However ... WAA over the Ionian and S Adriatic Sea is expected to boost the 0-3 km SRH ... especially over N Greece in the late evening hours. The storms in the WAA regime may tend to be elevated however ... and severe threat may be limited as the SFC-based helicity may not be ingested into the updraft. Nonetheless ... isolated SFC-based convection may occur ... having the potential for becoming mesocyclonic. Some hail ... damaging winds and maybe a tornado may result ... however ... weak DLS should limit allover severe threat and a categorical risk will not be introduced over the Ionian/S Adriatic Sea as well as N Greece ATTM.

... Iberian Peninsula ... France ...

Main issue will be the lack of CAPE in the presence of strong LLS (up to 18 m/s) and moderate DLS (15 to 20 m/s). About neutral (mostly weakly stable) profiles are expected with GFS simulating only small/weak patches of positive CAPE. This situation is too conditional for a large categorical risk ... but mesoscale regions where positive CAPE may develop should be watched. If convection initiates ... it will likely become supercellular with a substantial threat for tornadoes ... along with damaging straight-line winds and large hail. Will include the area that should be watched in a TSTM forecast ... with the possibility of an upgrade once foci for convective evolution become apparent.