The Santa Ana winds in southern California are Foen winds. Chinook winds are Foen winds. The lee side of the Alps have very strong Foen winds. Foen winds are simply warm dry winds coming off the lee slopes of a mountain range. Warm and dry hardly does justice to foen (pronounced fern winds), however. A foen wind can gain 50 degrees of more (Farenheit) as it rushes down a mountain slope. Considering that most of these winds start out hot and dry on the other side of the mountains, that makes for a very hot, very dry, very strong wind. The Santa Ana's are responsible for fanning the flames of many southern California wildfires. These winds are so hot and so dry that wild land firefighters fear them.

First, some specifics about how Foen winds are formed. Foen winds form when strong warm winds are forced up over a mountain range. These winds are usually forced over the range by an incoming high pressure zone. As the wind, which is already warm, gains altitude, the moisture is lost in the air. Now our wind is warm and very dry. As the wind races down the slope and becomes denser and under more pressure, it heats up tremendously. We now have an extremely hot, dry, strong wind. These winds can blow for days, day and night. For most people, they are just inconvenient and maybe a bit uncomfortable. For firefighters, they are dangerous.

For wild land firefighters, the cooler temperatures and higher humidities that occur after dark are very important. This is when most progress in controlling a fire occurs. If a Foen wind is active at the time, there is little temperature reduction or humidity recovery at night. The strong dry winds also dry out the fuels for the fire, so the fire can spread much faster. A fire driven by Santa Ana winds is almost unstoppable. I remember sitting in fire camp watching a fire spread across a hillside in southern California one year. We were watching fire trucks attempting to outrace the fire. This fire was moving faster than the trucks, and to our horror, we watched the fire overtake and destroy two of the trucks. Luckily the firefighters escaped injury, but it was a powerful demonstration of Foen winds.

Another aspect of the Foen winds that I find interesting is the claim that the winds carry a highly positive charge. Some people claim that positive ions increase aggressiveness and hostility in people, while negative ions do just the opposite. These people claim that during times of Santa Ana activity the crime rate, traffic accidents, and road rage incidents skyrocket. Of course, it could just be the heat.