Chinook winds, often just called chinooks, commonly refers to foehn winds in the interior West of North America, where the Canadian Prairies and Great Plains meet various mountain ranges, although the original usage is in reference to wet, warm coastal winds in the Pacific Northwest.
Chinook winds are so named because they come from the country of the Chinook Native Americans: the lower Columbia River, west of the Rocky Mountains. The term originated in the local argot of the fur trade, which spread it to the prairies.
A popular (but entirely false) myth is that Chinook means "snow eater", as a strong Chinook can make snow one foot deep almost vanish in one day. The snow partly melts and partly evaporates in the dry wind. Chinook winds have been observed to raise winter temperature, often from below −20°C (−4°F) to as high as 10°C to 20°C (50°F to 68°F) for a few hours or days, then temperatures plummet to their base levels. The greatest recorded temperature change in 24 hours was caused by Chinook winds on January 15, 1972, in Loma, Montana; the temperature rose from -48°C (-56°F) to 9°C (49°F).
The ch digraph in Chinook is pronounced as in the word "church" in some regions of the Pacific Coast, but as in French (i.e., shinook) in other regions of the Pacific Coast (e.g. Seattle) and on the prairies. This is because the French-speaking voyageurs of the fur companies brought the term from the mountains.
Chinooks are most prevalent over southern Alberta in Canada, especially in a belt from Pincher Creek and Crowsnest Pass through Lethbridge, which get 30 to 35 chinook days per year on average. Chinooks become less frequent further south in the United States, and are not as common north of Red Deer, but occur as far north as Grande Prairie in northwestern Alberta and Fort St. John in northeastern British Columbia, and as far south as Albuquerque, New Mexico
In winters since the 1980s, chinooks and warmer weather have all but banished winter to just a few spells of sharp cold of one or two weeks, and some midwinter months have averaged high temperatures over 5°C (41°F), similar to the West Coast of British Columbia, where Canada's warmest winters are found.
In southern Alberta, most of the winter can be spent with little or no snow on the ground. In Calgary, there is snow about 59% of the time on Christmas, compared to 88% for Edmonton.. In Canada, only the West Coast of British Columbia and southern Ontario have fewer white Christmases than southern Alberta.
In Lethbridge, Chinook winds can gust in excess of hurricane force (120 km/h or 75 mph). On November 19, 1962, an especially powerful chinook there gusted to 171 km/h (107 mph).
In Pincher Creek, the temperature rose by 41°C (from -19°C to 22°C) in one hour in 1962. Also, trains have been known to be derailed by chinook winds there. During the winter, driving can be treacherous as the wind blows snow across roadways sometimes causing roads to vanish and snowdrifts to pile up higher than 1 meter. Empty semi trucks driving along Highway 3 and other routes in Southern Alberta have been known to be blown over by the high gusts of wind caused by chinooks.
In mid-winter, the chinook can seem to do battle with the Arctic air mass at times. It is not unheard of for people in Lethbridge to complain of −20°C (−4°F) temperatures while those in Cardston, just 77 kilometers (48 miles) down the road, enjoy +10°C (50°F) temperatures in shorts and T-shirts. This clash of temperatures can remain stationary, or move back and forth, in the latter case causing such fluctuations as a warm morning, a bitterly cold afternoon, and a warm evening. A curtain of fog often accompanies the clash between warm to the west and cold to the east.
It has been reported on a local TV historical program that many years ago Cardston once reported a curtain of fog remaining over Main Street for many hours. The west side of town was balmy with melting snow, while the east side of town was bitterly cold.
In Calgary, recent winters have seen situations where the airport in the northeast part of the city is reporting around −20°C (−4°F) and the southwest part of the city is sitting at +7°C (45°F).
One of the most striking features of the chinook is the chinook arch, which is a band of stationary stratus clouds caused by air rippling over the mountains due to orographic lifting. To those unfamiliar with the chinook, the chinook arch may look like a threatening storm cloud at times. However, they rarely produce rain or snow. They can also create stunning sunrises and sunsets.
The stunning colors seen in the chinook arch are quite common. Typically the colors will change throughout the day, starting with yellow, orange, red and pink shades in the morning as the sun comes up, gray shades in the mid day changing to pink/red colors, and then orange/yellow hues just before the sun sets.
The Chinook is a foehn wind, a rain shadow wind which results from the subsequent adiabatic warming of air which has dropped most of its moisture on windward slopes (orographic lift). As a consequence of the different adiabatic rates of moist and dry air, the air on the leeward slopes becomes warmer than equivalent elevations on the windward slopes.
As moist winds from the Pacific (also called Chinooks) are forced to rise over the mountains, the moisture in the air is condensed and falls out as precipitation, while the air cools at the moist adiabatic rate of about 3.5°F per 1000 feet. The dried air then descends on the leeward side of the mountains, warming at the dry adiatatic rate of about 5.5°F per 1000 feet.
The turbulence of the high winds also can prevent the normal nocturnal temperature inversion from forming on the lee side of the slope, allowing nighttime temperatures to remain elevated.
Quite often, when the West Coast is being hammered by rain, the windward side of the Rockies is being hammered by snow (as the air loses its moisture), and the leeward side of the Rockies in Alberta is basking in a chinook.
Two common cloud patterns seen during this time are:
Often, a chinook is preceded by a "Manyberries chinook" during the end of a cold spell. This southeast wind (named for a small village, now a hamlet, in southeastern Alberta, from where the wind seems to originate) can be fairly strong and cause bitter windchill and blowing snow. The wind will eventually swing around to the southwest and the temperature rises sharply as the real chinook arrives.
Typically a weather forecaster in Vancouver might say "the Chinook is going to last for another five days, so expect heavy rain for the next week. The mountains [i.e. for skiing] will be rainy to the alpine, so expect lots of slush on the slopes." When a Chinook comes in when an Arctic air mass is holding steady over the coast, the tropical dampness brought in suddenly cools, penetrating the frozen air and coming down in volumes of powder, sometimes to sea level. Snowfalls and the cold spells that spawned them only last a few days during a Chinook, as the weather blows in from the southwest. The snow melts quickly and is gone within a week.
The effects on the Interior of the province when a Chinook is in effect are the reverse. In a rainy spell, most of the heavy moisture will be soaked out by the ramparts of mountains before the air mass reaches the Canyon and the Thompson River-Okanagan area. The effects are similar to those of an Alberta Chinook, though not to the same extreme, in part because the Okanagan is relatively warmer than the Prairies, and because of the additional number of precipitation-catching mountain ranges in between Kelowna and Calgary. When the Chinook brings snow on the Coast during a period of coastal cold, bright but chilly weather in the Interior will give way to a slushy melting of snow because of the warm spell more than because of rain.
The word is in common usage among local fishermen and people in communities along the British Columbia Coast. The term is also used in the Puget Sound area of Washington. It is important to note that Chinook is not pronounced as it is east of the Rockies – shinook – but is in the original coastal pronunciation tshinook.
An outflow wind is more or less the opposite of BC/Pacific Northwest Chinook. These are called a squamish in certain areas, rooted in the direction of such winds coming down out of Howe Sound, home to the Skwxwu7mesh people, and in Alaska are called a williwaw. They consist of cold air streams from the continental air mass pouring out of the interior plateau via certain river valleys and canyons penetrating the Coast Mountains towards the coast.
In British Columbia and parts of the Pacific Northwest, the word Chinook is pronounced with a tshi-, as in Salish. In Central Washington, Alberta, and the rest of Canada, it is pronounced with a shi-, as in French. This difference may be because it was the Métis employees of the Hudson's Bay Company, who were familiar with the Chinook people and country, brought the name east of the Cascades and Rockies, along with their own ethnified pronunciation. Early records are clear that tshinook was the original pronunciation, before the word's transmission east of the Rockies.
While on the one hand this tale tells a tribal family-relations story, and family/tribal history as well, it also seems to be a parable of a typical weather pattern of a southwesterly wind at first bringing snow, then rain, and also of the melting of a glacier, perhaps the Place Glacier near Birken Lake or the once-great Birkenhead River glacier 10,000 years ago, when most of this region was icefield. Thus it also tells of a migration of people to the area, (or a war, depending on how the details of the legend might be read, with Chinook-Wind taking the part of Helen in a First Nations parallel to the Trojan War).
The frequent midwinter thaws in Great Plains chinook country are more of a bane than a blessing to gardeners. Plants can be visibly brought out of dormancy by persistent chinook winds, or have their hardiness reduced even if they appear to be remaining dormant. In either case, they become vulnerable to later cold waves. Many plants which do well at Winnipeg (where constant cold maintains dormancy all winter) are difficult in the Alberta chinook belt; examples include basswood, some apple, raspberry and saskatoon varieties, and Amur maple. Trees in the Chinook affected areas of Alberta are known to be small, with much less growth than trees in areas not affected by Chinooks. This is once again caused by the 'off and on' dormancy throughout winter.
It is said that chinook winds can cause a sharp increase in the number of migraine headaches suffered by the locals and are often called "chinook headaches". At least one study conducted by the department of clinical neurosciences at the University of Calgary supports that belief. It is also popularly believed they can increase irritability and sleeplessness. In mid-winter, over major centers such as Calgary, chinooks can often override cold air in the city, trapping the pollutants in the cold air and causing inversion smog. At such times, it is possible for it to be cold at street level and much warmer at the tops of the skyscrapers and in higher terrain.
Loma, Montana boasts as having the most extreme recorded temperature change in a 24-hour period. On January 15, 1972, the temperature rose from −54 °F (-48 °C) to 49 °F (9 °C), a 103 °F (57 °C) change in temperature; a dramatic example of the regional Chinook wind in action.
The Black Hills of South Dakota are home to the world's fastest recorded rise in temperature. On January 22, 1943, at about 7:30am MST, the temperature in Spearfish, South Dakota was -4 °F (-20 °C). The chinook kicked in, and two minutes later the temperature was +45 °F (7 °C). The 49 degree (27 °C) rise in two minutes set a world record that is still on the books. By 9:00am, the temperature had risen to 54 °F (12 °C). Suddenly, the chinook died down and the temperature tumbled back to -4 °F. The 58 degree drop took only 27 minutes.
The aforementioned 107 mph / 171 km/h wind in Alberta and other local wind records west of the 100th meridian on the Great Plains of the United States and Canada, as well as instances of the record high and low temperature for a given day of the year being set on the same date are largely the result of these winds.
On rare occasions chinook winds generated on the eastern slope of the Rocky Mountains have reached or passed the Mississippi River.
Chinooks are more accurately called foehn winds by meteorologists and climatologists, and, regardless of name, can occur in most places on the leeward side of a nearby mountain range. They are called "chinook winds" throughout most of western North America, particularly the Rocky Mountain region. Montana in particular has a significant amount of Chinook winds across much of the state during the winter months, but particularly coming off of the Rocky Mountain Front in the north and west-central areas of the state.
One such wind occurs in the Cook Inlet region in Alaska as air moves over the Chugach Mountains between Prince William Sound and Portage Glacier. Anchorage residents often believe that the warm winds which melt snow and leave their streets slushy and muddy are a midwinter gift from Hawaii, following a common mistake that the warm winds come from the same place as the similar winds in coastal southern British Columbia, Washington, and Oregon.
Chinooks also occur in Colorado, especially near Denver, where winds blowing over the Front Range have raised winter temperatures from below freezing to around 50 °F (10 °C) in just a few hours. There are also Chinook winds in and around other cities in the Rocky Mountain states, including Billings, Salt Lake City and Albuquerque.