Storm Forecast
Valid: Fri 23 Nov 2007 06:00 to Sat 24 Nov 2007 06:00 UTC
Issued: Thu 22 Nov 2007 18:49
Forecaster: TUSCHY

SYNOPSIS

There is no significant change compared to the past 24 hours, as strong upper-level trough still covers western Europe with ridging downstream, affecting central and eastern Europe.
The main story happens south of Iceland and Greenland as geopotential height gradients sharpen and the upper-level jet starts to intensify to up to 150kt south of Greenland during the end of the forecast period.
This won't have any affects on the European weather at least for the next 24 hours.

DISCUSSION

...Balearic Islands and surrounding areas ...

Although highest thunderstorm coverage is expected to occur further towards the south, a level-1 was issued for those regions as an enhanced risk for waterspouts exists.

The main question is how warm the temperatures below 850hPa will be and how quick the dry and cold airmass from Spain will get mixed out. Right now, we believe that a significant cool-down especially at 700hPa will occur over the level-1 area with a more modest cool down at 850hPa, still bumping up the 0-3km CAPE values to interesting values.
Although parameters look supportive for waterspouts it is not possible to pinpoint any specific area for an enhanced spout threat that far out but we want to emphasize the chance for a few funnels / waterspouts along the coastlines, along convergence / wind shift zones and below more intense updrafts.
A stronger moisture gradient is forecast to cross the Balearic Islands from the west during the afternoon hours which could be another focus for an augmented threat.

We decided not to inlcude a fetch for mixing just east of SE Spain, because thermodynamic environment becomes increasingly favorable for thunderstorms betimes so we can't exclude a few storms to develop just offshore ( beside the lasting offshore flow of cold, dry and stable air ).

Each stronger thunderstorm could produce gusty winds and marginal hail but there are no hints on any significant thunderstorm organisation.

...Strait of Gibraltar and surrounding areas...

A developing depression southwest of the Strait of Gibraltar should support a quite dense thunderstorm coverage over the area of interest.
We decided not to issue any level area, as best chances for any severe weather threat will be out of the area of responsibility.
Shear will be weak but LL lapse rates pretty steep so an isolated waterspout report can't be excluded.
An area east of the Strait of Gibraltar has to be monitored for any more significant development during the 00-06Z time frame as SRH 3km values increase and shear at lowest 3km reaches 15m/s. An isolated rotating storm could be possible but confidence in a more robust severe thunderstorm risk is too low right now to introduce higher probabilities.

...Tyrrhenian Sea...

Despite a slow cooling trend at mid-levels, atmosphere will stay capped during most of the day. There are two areas which could see a better thunderstorm risk:

a) coastal areas of west-central Italy, where cap is weaker and shear / instability combination more supportive for a low-end severe weather threat ( an isolated tornado as LL shear along the coast is enhanced ). Overall set-up is not that impressive and we decided not to issue any level-1.
It looks like this could be an excessive rainmaker as storms should tend to cluster. This cluster of thunderstorms should tend to rebuild southwards during the evening and night hours.
Stronger thunderstorms could also produce gusty winds and marginal hail.

b) Between 00 and 06Z, more thunderstorms could also develop northeast of Tunisia and west of Sicily. There won't be any severe weather threat.

...Northern Italy...

Numerous short waves cross the area from the S/SW and will be the focus for a few isolated thunderstorms. There won't be any severe weather risk with those storms.

An isolated SFLOC report can't be excluded even over western and central Austria / SW Czech Republic as lapse rates steepen somewhat and EL temperatures cool down, but thunderstorm coverage should be too sparse for extending a thunderstorm area all the way to Austria.