Storm Forecast
Valid: Wed 22 Nov 2006 08:00 to Thu 23 Nov 2006 06:00 UTC
Issued: Wed 22 Nov 2006 07:52
Forecaster: GATZEN

SYNOPSIS

Long-wave trough over north-eastern Atlantic amplifies today, and another trough actually over central Europe and central Mediterranean moves north-eastward during the period. In the range of the European trough, cold mid-level air mass spreads over the North Sea, Germany, Alpine region, and northern Mediterranean today. At lower levels, cold air mass advected from the North Sea into Alpine region and north-western Mediterranean. Ahead of the cold front that is expected to reach from Tunisia to central Italy this evening, unstable air mass remains over most of central Mediterranean, and convective activity is expected to go on, spreading into eastern Mediterranean as the trough propagates eastward.

DISCUSSION

Central and southern Italy, Sicily, Adriatic, Greece, Aegean

Unstable air mass characterized by steep low-level lapse rates, moist low-level air mass and almost no CIN is indicated by latest soundings over central Mediterranean. This air mass advects into southern Italy, Adriatic, Greece, and Aegean during the period ahead of approaching cold front. While the cold front reaches central Greece late in the period, mid-level trough axis is forecast from northern Balkans to southern Italy. Strong upper jet streak curves around the tip of the trough moving across southern Italy and southern Adriatic into Balkans today. Warm air advection and differential cyclonic vorticity advection at the cyclonic flank of the upper jet streak support a surface low moving across Adriatic today ahead of the cold front. While cold air mass spreads eastward into Greece, cold air advection is expected and surface low is forecast to weaken over Adriatic. South and east of the low, chance for organized convection seems to be enhanced compared with surrounding areas due to rather strong (20 m/s) deep layer wind shear caused by southerly low-level winds ahead of the cold front and strong south-westerly jet aloft. Expect that convective activity goes on today, embedded mesocyclones are forecast, capable of producing severe wind gusts. There is also a slight chance for tornadoes given weak CIN and some low-level CAPE. Another focus of convection will be tha warm air advection regime over Greece and Aegean as well as the cold front. Given weak vertical wind shear, severe convection seems to be not likely. Low level instability and increasing low-level shear and storm-relative helicity in the range of the cold front, especially near the coasts, are expected to pose a threat of tornadoes, but limiting factors (weak deep layer shear, rather weak forcing) will reduce the chance or severe convection, and a level 1 is not warranted at this time.