It is generally thought that south winds bring warm temperatures, particularly in the fall and winter. However, our recent record warm days have occurred with a predominately west wind. The difference: With south winds, we are tapping into warm, relatively moist tropical air – thus the warmer temperatures. With a west wind, the driving force is compression. As the air moves down slope, it is compressed which produces heat – again creating warmer air. A significant difference is that these downslope winds tend to be MUCH drier. Although uncommon, the west winds do occur regularly. The most famous examples are the Chinook winds, well known for rapid temperature increases during the Plains winters. The colder the temperatures at the onset, the more dramatic the change.
Mary Knapp, Weather Data Library