Storm Forecast
Valid: Sun 07 Oct 2007 06:00 to Mon 08 Oct 2007 06:00 UTC
Issued: Sat 06 Oct 2007 16:44
Forecaster: TUSCHY

SYNOPSIS:

The 100-hPa height analysis continue to show a part of the polar vortex over Europe and parts of Asia, which is not as compact as over the extreme northern Pacific and results in a quite turbulent upper-air streamline pattern over Europe although the messy-like appearance should become somewhat better defined during the forecast period / next few days.
Major changes will occur over the northern Atlantic Ocean, where a southward advancing intense Canadian jet forces a broad cyclonic vortex in an east-west aligned position wich results in a more zonal appearance of the North-Atlantic streamline pattern.
Two troughs in the subtropical regions are forecast to slowly translate eastwards, one entering the forecast area from the SW while another one crosses Italy from the NW.
An intense trough just west of Norway will absorb an opening low pressure area somewhere north of Belarus.
The eastern Mediterranen will continue to see dry and hot conditions.

As a personal side - note:
The depression north of the Azores, already mentioned during the outlook issued on the 5th Oct., acquired more convection next to a well defined low-level circulation center (LLCC), which is also visible in latest QuikSCAT overpasses, showing 20-30kt in its southern / eastern quadrant. A band of persistent and quite deep convection wrapped nearly 3/4 around the vortex ( although not exactly next to the LLCC) and a new band formed just north of the center yesterday around 12Z. An intense 120kt jet, entering the area from the west caused quite diffluent conditions atop of the system and should have supported latest increase in organisation / convection. This scenario could have partially offset the constantly cooling SSTs.
The National Hurricane Center did not mention the system and I certainly won't arrogate to be able / be in the position to declare anything, but I would at least see some hints on a potential subtropical system northeast of the Azores.
Anyway... the system should be involved in the broad, extratropical vortex to its NW during the forecast period and should constantly loose any subtropical characteristics ... if this ever was the case.
***A short update (23:20UTC) as the National Hurricane Center now has issued a comment about this feature.The system has acquired some subtropical characteristics but further development is not anticipated. The more detailed description can be seen in the Atlantic Tropical Weather Outlook, issued at 530 PM EDT SAT OCT 6 2007. It now is INVEST 95L and has a central pressure of estimated 994hPa and winds of 45kt.***

DISCUSSION

Included missing level-1 area over the Black Sea

... Sicily and southern Italy...

A weakening upper-level trough will cross the area from the NW and is forecast to slow down and become stationary over S-Italy during the latter part of the forecast period.
This will be a moderate - high instability but weakly sheared set-up with multicells being the main storm mode.

An enhanced severe wind gust risk will be present during the morning hours west of / over SW Greece, as 20m/s DLS and robust instability signals overlap. Threat should diminish further towards the east as instability values decrease rapidly.

No question...mesoscale environment could locally support an ambience, sheared enough for an isolated tornado threat and we reflect this possibility in issuing such a broad level-1 area next to the augmented chance to get large hail / severe wind gust reports.

A significant flash flood threat could evolve over southern Italy during the day, as the core of the decaying upper-level vortex settles over the area, providing weakly sheared conditions with strong instability signals. Dewpoints in the upper tens / lower twenties and a persistent influx of a very moist airmass from the south should support intense, convectively induced rainfall especially if storms cluster . Please note that this risk is not reflected in our level-criterion !

...The Black Sea....

A slowly eastward moving frontal boundary will serve as a focus for enhanced convective activity. Instability should be on the lower-end side but a concentrated band of 15-20m/s 0-3km shear will be present and could support an isolated severe wind gust report. We therefore arised the probabilities and issued a marginal level-1.

...Coastal areas of western Norway...

A negatively titled trough will start to affect the area already during the morning hours.The favorable tilt of this system should be supportive for a broad area of low-end instability release. Confidence is low that coverage of SFLOC reports well inland will be high enough for justifying a thunderstorm line and hence we decided to include only the coastal areas. Environment will be favorable for a few tornadic cells but also for an enhanced strong - severe wind gust threat along the coast but also well inland.