Storm Forecast
Valid: Wed 04 Dec 2013 06:00 to Thu 05 Dec 2013 06:00 UTC
Issued: Tue 03 Dec 2013 22:58
Forecaster: PUCIK

A level 2 was issued for Northern Scotland mainly for severe wind gusts and to the lesser extent for tornadoes.

A level 1 was issued for the region surrounding Level 2 mainly for severe wind gusts and to the lesser extent for tornadoes.

SYNOPSIS

An active period of weather will slowly diminish over the Mediterranean as the mid-level low slowly shifts towards the east, with expected center over SW Turkey by 12 UTC. Marginal instability in the tongue of moist airmass flowing onshore might still support scattered thunderstorms. A ridge of high pressure will stretch from the Atlantic towards France and southern Germany while much more active pattern will evolve to the north. In the brisk zonal flow, two major disturbances are forecast - the first one influencing Norwegian coast by Wednesday noon, another one in the form of a rapidly deepening low that will affect Great Britain during the night hours.

DISCUSSION

... Northern Ireland, Scotland ...

In the exit region of a cyclonically curved jet-stream, reaching over 80 m/s at 300 hPa level, rapid cyclogenesis is forecast over the Atlantic and the center of the low is forecast to be centered just north of Scotland by Thursday 06 UTC. Intense pressure / geopotential gradient will support windspeeds of 40 to 50 m/s in 925 to 850 hPa level. Both GFS and ECMWF simulate marginal CAPE values just behind the main stratiform rain shield, suggesting split-front character. CAPE should be connected to a tongue of moister airmass just ahead of the surface cold front, so that strong forcing might support a compact, linearly oriented, low-topped convective system. With intense vertical wind field, such system could contribute to the "downward mixing" of momentum and extremely severe wind gusts will be well possible, especially over Scotland around 06 UTC. Tornadoes should be possible too given extreme low level wind shear and low cloud bases, but will likely be limited by the lack of isolated supercell mode. For the region with the highest threat, Level 2 seems to be warranted.