Storm Forecast
Valid: Fri 03 Nov 2006 06:00 to Sat 04 Nov 2006 06:00 UTC
Issued: Thu 02 Nov 2006 17:57
Forecaster: TUSCHY

SYNOPSIS

Bitterly cold air ( locally as low as -25°C at 700hPa and -40°C at 500 hPa ) continues to flood areas east of Germany - Italy.... This airmass is characterized by low dewpoints and very steep mid-level lapse rates.... Upslope flow along the Carpathian Mountains and aforementioned very steep lapse rates should be enough for a very isolated ,short lived and weakly electrified storm to develop, but expected coverage will be too low for highlighting any specific area.
A well developed LL depression is forecast to evolve north of the Black Sea, moving rapidly towards the North, while a broad upper-level low should continue to affect parts of Portugal and Spain.

DISCUSSION

...Portugal and SW Spain...

Broad upper-level trough will continue to stall between the Azores and Portugal.... Same procedure at lower levels with an SW-NE elongated LL depression west of Portugal....
An interesting note is that GFS and UKMET both see a shallow warm core evolution with this system, which would support an increase in convection around the center, but latest IR images and model outputs do not look excessively supportive for any significant ( possible subtropical )development.
Main concern for scattered TSTM activity continues to be along the belt of rich subtropical moisture, stretching all the way up to Portugal and SW Spain.... 12Z sounding of Lisboa ( 02.11.) already showed nice veering at low levels and some slight cooling during the next 12 hours at the mid-levels should support slightly steeper mid-level lapse rates and hence more robust instability values.
A slightly enhanced tornado risk exists mainly in the level-1 area due to low LCLs and some veering, but main threat should be an excessive rain risk due to very high PWAT values and slow storm motion.

...Extreme E-Ukraine....

Conditions for a well developed LL depression north of the Black Sea will come together during the next 12-18h.... Broad area of intense upper-level divergence in the right entrance region ( partially a coupled jet structure due to an approaching streak from the SSW ) and strong baroclinity should support the rapid development of this depression, which is forecast to move towards the north.... Kinematic parameters seem more than adequate for organized storms to form, but main issue will be the quality of airmass and hence instability release.... Dewpoints along the eastern Black Sea region currently are in the range of 7-11°C and this airmass should continue to advect towards the north.... Current indications are that the best airmass will be east of our forecast area, but slight instability could develop as far west as E-Ukraine..... Any developing storm would pose a severe wind gust and isolated large hail risk.... GFS also indicates broad area of backing LL wind field and therefore strongly veering profilers, so won't exclude one or two tornadoes... Expected storm coverage in our forecast area should be too low for issuing any higher probabilities.


...Coastal areas of Latvia, Lithuania and NE Poland...

Strong temperature gradient between SSTs of about 10-11°C and very cold mid-levels will still be present , although gradient should start to relax during the latter part of the forecast period.... Increasing moisture at mid-levels and long fetch over the Baltic Sea should support enhanced convection development and a few embedded, weakly electrified storms will be possible mainly in the highlighted area.... Threat should ease during the evening hours, when pool of coldest air continues to shift towards the east .

....Norwegian Sea...

Latest sounding report of Keflavikurflugvollur ( Iceland ) already indicates the presence of a modified subtropical airmass, advected rapidly towards the north...This air should cover most parts between Iceland and the west coast of Norway.... Meanwhile, an intense depression is forecast to evolve somewhere NE of Greenland and very cold air should be advected rapidly towards the east.... Airmass modification should be slow ( due to ice coverage east of Greenland and very cold SSTs north of Iceland )....Therefore, a rapidly eastward racing cold front should cross the area of interest during the late afternoon/ early evening hours (onwards).... Don't want to exclude a few isolated storms with a severe wind gust risk , but coverage will be too low for highlighting a special area.