A katabatic is a wind that occurs on steep-sided valleys such as you find across much of the West Country like Cooper's Hill in Gloucestershire. After a fine day during the late autumn and early spring - once the sun sets - the air at the top of a large hill cools down quickly. You see, temperatures decrease with height anyway. So the air near the top of the hill cools quickly, certainly more quickly than at the bottom of the hill. And of course, cold air is denser than warm air - so the air at the top of the hill flows downhill. You can feel a cool draught blowing downhill on cold nights. Wind speeds are generally light, between 5 and 10 miles per hour. In other parts of the world these winds are much stronger. On the Antarctic ice shelf speeds of over 200 miles per hour have been recorded. Of course, by day, as the top of the hill warms, the air becomes less dense and the flow is reversed - that’s an anabatic wind. Paragliders and hang-gliders can take advantage of this breeze on the steepest of hill. There are lots of local winds around our region. On a Points West forecast I can only hope to give a general wind speed and direction. But our winds are funnelled up the Bristol Channel; squeezed between the moors and they develop off the sea. And to that list you can add the katabatic. | 
