There may be several reasons for the high amount of rainfall on Børtveit, but the topography in the area can explain most of it. The steep cliff that divides the mountainous area from the lowland on Stord gives a natural deflection to the wind that comes from the south. Moist wind masses get thereby pressed together. This increases the precipitation in the area farthest to the south in Langenuen.
West of Børtveit lies Mehamarsåto at 749 metres elevation. When wind and rain come from the west, the moist air is pressed up, and the rainfall increases with elevation. There is usually most rainfall on the west side, but when the wind is strong, much of the precipitation will blow over the mountaintops before it falls on the lee side where the landscape drops sharply down toward the fjord. There are many areas in the county where the topography results in an unusually large amount of rainfall. Børtveit is one of few such places having its own weather station.
