Storm Forecast
Valid: Mon 22 Oct 2007 06:00 to Tue 23 Oct 2007 06:00 UTC
Issued: Sun 21 Oct 2007 15:07
Forecaster: TUSCHY

SYNOPSIS

Well developed upper-level cyclonic vortex over Italy gets more vertically stacked and starts to weaken and so does the depression at the surface.
Most parts of western / northern Europe stay under high pressure and will see stable conditions throughout the forecast period.
Portugal and Spain will stay warm and dry.

DISCUSSION

... Northern Aegean Sea ...

The highest threat for organized storms exists between 06 and 12Z over the Aegean Sea and until 15-18Z over SW Turkey.

Forward propagation of the northeastward moving cold front should be slow as frontal boundary is located nearly parallel to the background flow. Shear at lower levels is still impressive with LL shear of about 15m/s, SRH1 values of 400/kg and 0-3km shear of 25-30m/s. The wind field at 850hPa indicates a broad jet of 25m/s and this should support an augmented severe wind gust threat, especially as 0-3km CAPE release is forecast to be quite strong and atmosphere is nearly uncapped. The risk for severe weather should ease gradually as storms move onshore, but intense forcing could support more elevated storms.

It is somewhat unclear how significant the tornado threat will be because we expect a cluster of storms to go on and environment is not favorable for more discrete storms. Anyway, any more isolated cell and even embedded supercells pose a risk for tornadoes but main risk will be a severe wind gust / isolated large hail threat.

...W / SW Turkey...

Indications are present that a more robust tornado threat evolves over the coastal areas of SW / W Turkey reaching well inland. Moderate instability release and strong influx of moist air from the south should help for scattered to widespread thunderstorms to move towards the east/northeast. A broad belt of 15 m/s LL shear and 200-300J/kg SRH1 will support numerous tornadic cells and even a strong tornado will be possible.
Instability values decrease towards the north but steep-mid-level lapse rates and impressive SRH3 values of 400-700 J/kg hint on an enhanced large hail risk.... we did not expand the level-2 area that far to the north as strong and persistent convection and attendant latent heat release could support weaker lapse rates over west-central Turkey than currently expected.

...Parts of Bulgaria and Romania...

PBL continues to moisten as tongue of higher Theta-E values advects towards the west ( 0-1km mixing ratio increases to about 8g/kg ). As atmosphere cools down, some low-end instability release is forecast. Winds at 850hPa of 30m/s and intense shear at all levels indicate an augmented tornado / severe wind gust risk especially over NW Bulgaria / SW Romania. We will stick with a level-1 as instability looks to be too marginal right now.

...Ionian Sea...

Nice instability release at lowest 3km and weak shear point to an enhanced risk for a few waterspouts, mainly along windshift zones / convergence lines and along the coast.