Ridge top winds?
 

Can anyone tell me the meteorological reason for wind on top of a ridge sometimes being about twice the free-air wind speed?

Think Bernoulli's law... :)

Bernoulli principle (ridges force the moving air into a smaller area) is a factor as C* suggests along with boundary layer flow (moving air near the ground will be slower than that aloft).

ZeBedie - forget all that science rubbish!!

If you ran up and over the ridge while your mate ran past it on the flat, who would have to run faster to meet up again?

Very nice, Groucho.

Groucho, who's to say that the chap running over the ridge won't take longer, on account of being slower, and fail to make the rendezvous on time?

A ridge is effectively half a venturi.

It's also effected by inversion.
Got caught out two years ago paragliding post sea breeze front when the wind slowly drops but strong inversion descended following the sun...wind increased from 25 to 40 kph...landed backwards luckily into a bramble bush in front of a pine plantation which snagged the wing saving my @rse!