What causes the wind to vary in direction.
 

I fly a flexwing microlight, the wind yesterday (Saturday 24th) was ranging between 150-210 10knts in my neck of the woods making for some interesting landings,

My lightly loaded wing is very susceptible to gusts and crosswinds ect and it got me thinking as I was flying along about the air hitting me from differing directions and as to why the wind should swing about so much on some days like it was today and it stayed like that all day.

I feel I should know the answer already but don't so I sure somebody can tell me.

Nick.

Could I suggest you purchase a copy of Pilot's Weather by Brian Cosgrove which is an excellent Met book written by a microlight pilot for microlight pilots. At the advertised price its an excellent investment.

I do have that edition, obviously I must have missed or forgotten the it,

I will dig it out and see if I can find the info.

Nick.

With the sort of weather we had yesterday, towards the end of the day, I suspect there were a lot of gusts around the thermals which were kicking off. Overlay that on a light and variable southerly (at least in my neck of the woods) and you might easily get 90 degrees variation.

When I got back to the strip, which has an east-west orientation, I didn't expect there to be much between the runways. However I didn't like the feel on 09 so went round, changed circuit direction (with radio calls! - you can do that on a farmstrip if you're careful) and landed fine on 27.

After I landed I noticed the sock doing almost every direction except north.

You don't mention how high these variations were. From say ground level - 500' my understanding is that if you are in the lee of trees, buildings or undulating land, all kinds of whirpools or eddies can be set up; departing thermals can also have an effect.

Multiple reasons.
As already mentioned, local terrain & building characteristics, relative position of the low/high pressure system to your location and its speed of travel, wind gradient due in part to the Coriolis effect, etc