1) Pressure difference (general low- and high pressure area's)
2) Warmth radiation of the Sun
3) Local termical differences
4) Obstacles, houses/bushes/etc
The height is intresting, the wind speed at waterlevel is 0 kn. from there the wind increases and at 30m it is 100%. There are a lot of factors that make an difference in height vs windspeed, chop height/strenght gusts/average windspeed. This is quite intresting and makes clear why a spot like Strand Horst is so bloody fast.
In Diagram 1 you can see that when the wind get stronger you need to go higher from surface to get the actual higher windspeed.
In Diagram 2 you can see 3 situations, all are at surface 0% windspeed and at 30m 100% of the windspeed.
-Situation A, Very low windspeed / no waves / with clouds
-Situation B, Average conditions / most days it will look like this
-Situation C, Gusty conditions / no clouds / like Strand Horst
Situation C look very good, this the main reason why it is possible to go fast at Strand Horst, there is less wind but the wind sticks more to the surface. But if the wind increases this effect will disappear, this simply explains why there is no 80kmh average sailed.