Storm Forecast
Valid: Fri 16 Nov 2007 06:00 to Sat 17 Nov 2007 06:00 UTC
Issued: Thu 15 Nov 2007 19:01
Forecaster: TUSCHY

SYNOPSIS

A low-index pattern continues over Europe as strong ridging is present west of Europe and as an highly amplified upper-level trough covers most parts of Europe. This combination supports the advection of very cold air over the western and central Mediterranean, while strong WAA affects the extreme eastern parts of our forecast area.
At the surface, numerous small-scale depressions over the Mediterranean will be the main focus for thunderstorm activity and severe weather.
Otherwise weather in western / northern and eastern Europe stays stable.

DISCUSSION

...Ionian Sea and surrounding areas...

Despite the fact that we deal with a developing depression in an area with bad data coverage, probability maps of NCEP show a nice accord regarding placement of this surface depression. This feature will develop somewhere around Malta during the morning hours and should move rapidly towards the northeast. The center enters the Ionian Sea from the SW during the early afternoon hours and slows down west of Albania during the evening and night hours.
Moisture advection and mid-level lapse rates of about 6-7 K / km favor at least low-end to moderate instability release with the highest values offshore and along the coastal areas.

Dependant on the final strength of this system, severe wind gusts and tornadoes will be the main risk. As depression strengthens, winds at 850hPa start to increase to 25-30m/s, covering the Ionian Sea between 14 and 18Z. Intense forcing spreads northeastwards during this time-frame and scattered thunderstorms are expected to evolve. Rapid organisation of those thunderstorms is likely as helicity values are significantly enhanced and severe wind gusts can be expected especially if storms line-up.
Despite the fact that there exists a potential significantly enhanced severe wind gust and tornado risk along the SW coast of Albania and the NW coast of Greece, confidence in this scenario and the final depression's location is not high enough for a level-2 right now. An update may become necessary later on. The time-frame will be between 15 and 21Z.
We extended the level - 1 area well southwards as shear over western Greece could support a few tornadoes, too.

...Coastal areas of the Aegean Sea...

During the morning hours, thunderstorm coverage over NW Turkey should see a weakening trend but LL shear still supports an isolated tornado report. This risk extends far northeastwards into the extreme SW part of the Black Sea.

Surface pressure over this area is forecast to fall during the evening and night hours. As atmosphere cools down and a strengthening jet at lower levels advects better moisture over the area of interest, conditions become good for moderate instability release. Enhanced LL shear and low LCLs favor an augmented risk of an isolated tornado. Instability will diminish further onshore and storms tend to stay more elevated.
Stronger thunderstorms could locally produce hail, matching our criteron.

...Tyrrhenian Sea, coastal areas of Sardinia, Corsica and northern parts of Tunisia and extreme NE Algeria...

As very cold low-/ mid-level airmass overspreads the still warm SSTs, LL CAPE release increases and as DLS relaxes, conditions will be favorable for numerous waterspout reports. We went with a broad level-1 area, as mesoscale forcing mechanism can't be forecast that far out. Regions with an enhanced risk will be coastal areas, convergence zones and stronger updrafts.