What are Chinook winds & what causes them?

Everything you need to know about Chinook winds

Chinook winds are a weather phenomenon featuring the rapid appearance of dry, warm, high-pressure winds on the sheltered side of mountain ranges. Most common in winter, they produce shocking temperature increases. Here’s everything you need to know about Chinook winds.

How do Chinook winds develop?

The recipe for a Chinook really requires just two things: moist ocean air; and mountains. To understand how Chinooks occur, picture yourself on the western side of the Rocky Mountains, somewhere between the Rockies and the Pacific Ocean.

Moist air coming inland off the Pacific Ocean is forced to climb up and over the Rockies. As that moist air climbs, it expands, cools, and picks up enormous volumes of water vapor. As that water vapor cools as the air climbs, it eventually condenses into precipitation — rain or snow — that falls onto the western slopes of the mountains. By the time the air makes its way across the tops of the Rockies, it’s cold but dry.

On the other side of the mountain, the air that lays along the mountainsides cools and becomes denser at night. The farther inland you get away from the mountainsides, the warmer and less dense the air is.

None can defy gravity… not even air. Gravity pulls the cool dense air laying along the eastern slopes of the mountains in a rush down the mountainside. Dragged along behind that rushing dense and cool air is the dry mountaintop air that had left its rain and snow behind.

The dense and cold mountainside air, seemingly chased by the dry and cold mountain top air, rushes downhill and is compressed as it goes. As it is compressed, it generates a lot of heat. How much? That current of downhill-rushing air warms up at the rate of 5.5 degrees Fahrenheit for every 1,000-foot drop. That may not sound like a lot, but — considering the Rockies stand 14,440 feet above sea level at Mount Elbert in Colorado — it means those downhill-rushing winds might be fifty degrees warmer than the air they push ahead of them.

Turbulent winds

Not only is the wind warmer, it’s boisterous too. National Geographic has described the turbulent air that results from the rapidly descending air as “similar to the action river water makes when it hits a rock. As the air flows down, waves are created.”

The southern part of the province of Alberta in Canada includes the eastern slopes of the Rocky Mountains. They experience 30 to 35 Chinook wind and temperature events ever year that last for hours or days. In 1962, a Canadian-record-setting Chinook in Pincher Creek, Alberta sent the mercury up 41 degrees Celsius in just one hour.

Want an American example of extreme changes related to Chinook wind events? One day at 7:30 a.m. in January 1943 in South Dakota, the temperature was -4 degrees Fahrenheit. Shortly after that, the Chinook winds began to blow and pushed the temperature to +54 degrees Fahrenheit by 9:00 a.m. the same day. Once the Chinook winds stopped blowing, the temperature dropped right back to -4 degrees Fahrenheit within 27 minutes.

Where does the name ‘Chinook’ come from?

The name “Chinook” comes is the name of the indigenous peoples who live near the Pacific ocean and along the lower Columbia River. Chinookan peoples include several indigenous groups who live in present-day Oregon and Washington. “Chinook” is not the only name for the weather phenomenon. The Blackfoot peoples called the wind “Snow Eater.” It’s been said that a Chinook wind can “eat” one foot of snow in a single day.

Chinooks can occur anywhere you find mountain ranges. Chinooks occurring in the European Alps are called föhn or foehn. In central Asia, they’re called afganet. In South America’s Andes, they are called puelche. Even in North America, though, they can be called different things. If you’re in southern California and someone talks about the “Santa Ana winds,” they’re probably talking about a Chinook.

The mythology of the Chinook winds

The mythology connected to the Chinook winds is, by turns, moving and fascinating.

There are many indigenous tellings of the origins and mythology of the Chinook winds. One, reported in “Indian Legends of the Northern Rockies” by Ella E. Clark, goes like this.

The Creative High Mystery gave part of North Crow Creek Canyon of the Mission Range to Thunderbird, who raised her family there. One day, a careless hunter caused a huge fire by not extinguishing his campfire. All life in Thunderbird’s canyon was destroyed. An angry Thunderbird punished the Salish people by sending the cold Northeast Wind to drive the people out of the canyon to Bitterroot Valley.

After many winters, Thunderbird took mercy out of loneliness for her daughters and the animals and people who were driven from the valley. Thunderbird asked the Northeast Wind to leave. The chief of the Salish people who heard the gentle rumbling of weeping Thunderbird asked Coyote if there was a way to warm up their former lands.

Coyote refused to help, but Bluejay — one of Thunderbird’s daughters — loved the Salish people and missed her mother. Bluejay flew west and asked warm and kind Chinook wind to help the Salish return to their former grounds by warming up the valley for new life. “Show me the way my little friend,” Chinook Wind whispered.

Extreme Chinook weather events

Not only is the wind warmer, it’s boisterous too. National Geographic has described the turbulent air that results from the rapidly descending air as “similar to the action river water makes when it hits a rock. As the air flows down, waves are created.”

The Foothills of southeastern Wyoming and Colorado regularly experience Chinook winds. Extreme Chinook-related events occurred there in January 1982. On January 17 and 24, 1982, Chinook winds in Boulder, Colorado caused tornado-scale damage. The National Weather Service rates tornados according to the Enhanced Fujita Damage Intensity Scale. An EF1 is a moderate tornado with winds from 86-110 miles per hour. An EF2 is a significant tornado with winds from 111-135 miles per hour. Boulder’s Chinook winds in January 1982 cause damage like EF1 and EF2 tornados, including uprooted trees, downed powerlines, and damaged roofs.

Before its power failed in the maelstrom, the Earth System Research Laboratory measured a 118 mile per hour wind gust on January 17, 1982. The National Center for Atmospheric Research measured in southwest Boulder measured a 137 mile per hour wind gust on its rooftop 600 feet above the city.

As many as 40% of Boulder’s buildings sustained damage. Fifty homes were rendered uninhabitable. Twenty small planes at Boulder Municipal Airport were destroyed. Thousands were left without power when utility poles snapped. Tens of thousands of acres of farmland in Boulder County suffered erosion damage.

Do Chinooks cause health problems?

A 1992 study found an anecdotal correlation between migraines in 13 patients and Chinooks, but could not prove any statistical correlation.

“Chinook wind barosinusitis: an anatomic evaluation” in the November-December 2009 edition of American Journal of Rhinology and Allergy investigated reports of Chinook-related facial pain. The goal of the study, as reported in the Journal, was to determine if there was any relationship between sinonasal anatomy and chinook headaches.

The study analyzed 38 patients who reported chinook-related headaches and 27 control patients with no reported Chinook-related headaches. CT scans identified variations in the sinus anatomy of patients who reported Chinook-related headaches. The study determined that anatomical variants may predispose patients to facial pain and pressure by blocking the natural sinus ostia. That blockage prevents proper pressure equilibrium.

A 1992 study found an anecdotal correlation between migraines in 13 patients and Chinooks, but could not prove any statistical correlation. A 2002 study of strokes analyzed wind speeds, temperatures, humidity, and barometric pressure over a five-year period compared to the number and type of strokes in the same period. The authors found no correlation between Chinooks and the type or number of strokes experienced.

A New Zealand study published in 1999 considered the connection between SIDS and the Föhn winds. Data relating to 646 cases of SIDS in Christchurch, New Zealand disclosed correlations to some environmental factors, but the Föhn winds did not seem to be one of them.

Environmental effects of Chinook winds

The hot and dry conditions associated with Chinook winds can increase the risk of fires.

Soil can lose moisture and mass as Chinook winds carry away water content and the soil itself. Trees and plants can be awakened from hibernation by the sudden increases in temperature only to suffer dehydration because the soil lacks moisture that was present before the winds began. Melting snows reveal grass that may provide pasture for grazing animals, but eliminates the snow’s insulation effect for other animals that had been hibernating.

The hot and dry conditions associated with Chinook winds can also increase the risk of fires. What might otherwise have been just a small spark can cause a major conflagration when propelled and fuelled by Chinook winds. In Boulder, Colorado — again — two fires 19 years apart were fueled by Chinook winds. The 1990 fire was fuelled by 80-mile per hour winds while burning 3,000 acres of land and destroying 15 buildings. The 2009 fire in the same area burned 3,000 acres while fueled by 60-mile per hour winds.

A deeper dive — Related reading from the 101:

• The most outlandish natural phenomena you’ll every see | Science 101
  Chinooks are fascinating events, but there are many other fascinating natural phenomena.
• As Great Barrier Reef temperatures rises, its ecosystem collapses | Science 101
  Temperature changes — whether fast and enormous or slow and small — wreck havoc on the environment.