what are leeward and windward sides

The windward side of a mountain is typically the west side of the mountain, receiving the various weather as weather moves west to east. The leeward side of a mountain opposes the windward side, making it the east side of the mountain, receiving little weather, blocking weather (rain) and warming air rapidly as it moves down this side of the mountain. The leeward side of mountains causes deserts, dry places, little rain, etc., for it releases warm air unto these places, and blocks weather (rain) from moistening them (I.E. Las Vegas, etc. on the eastern side of the mountain ranges).

Look at this figure... Hope it helps...=))