This case study describes the evolution of a Water Vapour Dark Stripe associated with a Cold Front over the period October 27 to 28 2002. Initially, an Ana Cold Front can be seen, but by 12.00 UTC, the entire Cold Front has changed into a Kata front. The Dark Stripe develops and the potential vorticity descends to around 600 hPa by October 27th at 12.00 UTC. The atmosphere is potentially unstable up to 800 hPa.

During the period of the case study strong to very strong wind gusts were observed in the transition zones from light to dark in the water vapour images. In these zones high wind speeds were present, not only near the tropopause but also in the lower troposphere. In these areas potential vorticity anomalies penetrated deep down into the atmosphere in a potentially unstable environment. In the lower layers of the atmosphere a strong exchange of vertical momentum took place, resulting in strong, gusty winds at the surface. The strongest gusts were observed in the cold air near the gradient zones of the Cold Front and the Occlusion.