Storm Forecast
Valid: Wed 15 Oct 2008 06:00 to Thu 16 Oct 2008 06:00 UTC
Issued: Tue 14 Oct 2008 23:42
Forecaster: PUCIK

SYNOPSIS

A deep low pressure system is forecast to affect the region of NW Europe, from Britain to Scandinavia. Its movement will slow down with center being over the Norwegian sea by the end of the forecast period. Low should be promiment both at the surface and mid-levels, where a very cold air mass is observed in its center. Windspeeds up to 35 m/s should occur in the strong mid level flow, which is surrounding the low and its attendant trough. Cold front, associated with the low, is anticipated to pass over Germany/France during late evening / night hours. A weakening ridge should be stretching from the Central Mediterranean to E Scandinavia. Mid-level cut off lows will slowly fill over Morocco and Turkey.

DISCUSSION


...Norwegian and North seas...

Cold mid-level airmass with warm SSTs underneath should result in steep mid-level lapse rates, exceeding 7K/1000m. GFS simulates conditionally unstable conditions around the center of the low, with MLCAPEs around 500 J/kg. Satellite images support this, as widespread convection is already taking place around the low ( as of 23Z 14th October). Predicted low-level convergence and synoptic-scale support will guarantee widespread convective initiation. However, climatological studies have shown that lightning is very scarce in this area, so it is better to refrain from issuing a large TSTM area. On the other hand, ELs below -40°C, mixing ratios over 5g/kg and favourable synoptic setup are suggestive that TSTMs will occur after all, especially by the coast of Norway and a TSTM area is necessary. It is issued for the region, where the best conditions for convection will exist. Some ltg strikes might occur out of the area, both over the Norwegian and North sea. Also, few waterspout reports are possible as abundant low level buoyancy, steep lapse rates in 0 -500 m and convergence will overlap. This will especially be true for the Norwegian coastal area. Generally unfavourable conditions for organised convection ( DLS under 10 m/s) preclude issuance of a risk level.

Otherwise, most of the continent will be under stable conditions. Few loci of TSTM development are anticipated, especially over the Algeria and Turkey, where moderately unstable conditions with lift provided by mid-level lows will combine. Lack of wind shear or more significant instability release suggest that no severe weather will accompany thunderstorms.