Storm Forecast
Valid: Wed 26 Nov 2008 06:00 to Thu 27 Nov 2008 06:00 UTC
Issued: Tue 25 Nov 2008 23:25
Forecaster: PUCIK

SYNOPSIS

At midlevels, deep trough is expected to slowly lose its significance. A ridge will move eastwards from E Atlantic, with its axis stretching from France to Slovakia. Trough has attained a well-developed positive tilt with strong mid-level flow surrounding it. Looking at the surface charts, northern Europe should be under the influence of several low pressure systems, whereas central and western parts will be dominated by a large high. Main frontal zone will stretch from Tunisia to Ukraine, moving slowly eastwards. A wave cyclone has developed with this baroclinic zone and its center is forecast to move over the Black Sea during the period. Cool and stable airmass is advected behind the cold front.

DISCUSSION


Most of Europe should be under stable conditions, too hostile for thunderstorm development. There are few areas, especially over the Mediterranean, where few storms are expected to form. Overall degree of instability should be limiting and no overlap with sufficient lift and wind shear should exist, therefore no threat level is introduced at the moment.

... The Mediterranean...

Cold air advection regime will bring marginally unstable conditions to the area. The unstable layer should be only shallow and MLCAPE values mostly under 400 J/kg. Synoptic lift from the above mentioned trough is expected to initiate convection and thunderstorms will form in the environment with strong DLS. Especially by the western coast of Italy, mid level flow will increase DLS values to approximately 30 m/s. Shear should however stay confined to higher levels and if we take 0-3 km layer only, it will decrease to a mere 10 m/s. As thunderstorms will be low-topped, they will probably not be able to use up the strong upper level flow and should stay only in the form of weakly organizes multicells. No severe threat is anticipated due to the unfavourable environment. Few waterspout reports are not ruled out, however, as strong low level buoyancy will develop in response to cold airmass passage over the warm SSTs.

...Black Sea...

As the cold front will pass over the sea, its influence along with the strong lift provided by the approaching through should result in a slight destabilization. Strong wind profiles should result in more than 20 m/s shear in the lowest 3 kms and more than 10 m/s in 1 km. SREH values are expected to rise significantly, but only after the passage of the front, so out of the unstable area. Problem is, that models are simulating only elevated instability, therefore storms will not be rooted in the boundary layer and due to this, overall threat of wind gusts and tornadoes will be too low to warrant a threat level. If a surface-based instability will manage to develop ahead of the frontal zone, Lvl 1 and the update might become necessary.