Storm Forecast
Valid: Tue 29 Nov 2011 06:00 to Wed 30 Nov 2011 06:00 UTC
Issued: Mon 28 Nov 2011 21:48
Forecaster: KOROSEC
A level 1 was issued for parts of UK mainly for strong to severe wind gusts and tornadoes.
A level 1 was issued for southern Mediterranean sea mainly for strong wind gusts and excessive convective rainfall.
SYNOPSIS
A ridge/high pressure area dominates Europe while very intense confluent trough remains in place over NE Atlantic. At surface, a deep SFC cyclone slowly translating across the Norwegian sea with a strong cold front extending southwards towards the UK. Another focus for Tuesday's convective activity will be a decaying upper low, moving from Tunisia into southern Mediterranean.
DISCUSSION
... parts of UK ...
As the deep cyclone near Iceland moves further NE across the Norwegian sea, an associated strong cold front will be pushed across the British Isles. This setup is characterized by very strong jet streak, providing impressive vertical wind shear at all levels. Despite very limited instability signals on numerical models, strongly forced convection is becoming likely along the trailing cold front. The front will cross the level 1 area during the afternoon and early evening hours. As said, very strong shear will be in place, with above 30 m/s of deep layer shear and 20-25 m/s of LL shear, combined with strong 300-500 m^2/s^2 SR helicity. Expect a likelihood of a well-organized convective line with embedded mesocyclones along the cold front itself. Those storms should support severe wind gusts and possibly tornadoes as well, given the robust shear in place. A polar maritime airmass will overspread the area further north and support widespread low-topped convection.
Persisting strong SW flow will result in excessive amount of rainfall over coastal SW Norway.
... southern Mediterranean sea ...
An upper low continues to move from N Africa into S Mediterranean, where rather cold mid-levels result in moderate instability over warm SSTs. Shear remains rather limited, but looks like around 10-15 m/s of deep layer shear seem enough to support organized storms and especially favorable for maintaining the existing convection (clusters) if they manage to form. Slow moving nature should support some local excessive rain or strong wind gusts threat.
