In simple terms, Chinook winds refer to the dry and (surprisingly) warm westerly winds that come down the leeward (eastern) side of the Rocky Mountains (Shafak, 2015). This is described as the rain shadow effect, which is a simple way to describe the effects of the adiabatic process over a mountain range (Anderson, 140). 

In the midst of a freezing Canadian winter, Chinook winds bring a welcome reprieve from the bitter arctic chill. Calgarians rejoice. 

However, not all chinook winds are pleasant.  Despite their warmth, chinook winds can be fierce with some reaching hurricane strength and causing serious damage ("Wicked Winds from the West", 2017). 

In western Canada, warm moist air blows inland from over the Pacific Ocean. This lovely warm air mass contributes to the moderate coastal temperatures that British Columbia enjoys year-round ("Alberta Water", 2018) .  However, as the air mass moves inland, it is blocked by the Rocky Mountains which prevents it from moving smoothly eastward.  Unfortunately, this leaves provinces like Alberta subject to the arctic air masses that funnel in from the north and bring their extremely bitter cold weather with them ("Alberta Water", 2018).  The pacific north-west of the United States experiences the same phenomenon; however, it is not as severe or as common. 

Incredibly (or perhaps, thankfully) the warm Pacific winds have a way of bringing their joyful warm temperatures to Alberta (and inland U.S.A) despite the barrier created by the Rocky Mountains.  In fact, the mountains are the reason the warm air reaches inland at all! As the warm moist air is forced up and over the mountain range, the air parcel is subjected to the adiabatic process causing warm and dry Chinook winds to blow into the prairies (Anderson, 140)(Shafak, 2015). 

Chinook winds are not unique to North America; however, the name ‘Chinook’ is used to describe the phenomenon in a North American context (Ross, 2017).  Globally, the European term ‘foehn’ or ‘föhn’ winds are commonly used to describe the process which can be found wherever there are strong directional winds and large mountain ranges (Ross, 2017). Other local names for Chinook winds include ‘Zonda’ in Argentina, ‘Afganet’ in central Asia, and ‘Puelche’ in South America. (Ross, 2017)(Gibson, 2017). 

When warm moist air blows in from over the Pacific Ocean it brings rain and moderate temperatures to the western coast of North America (Ross, 2017). However, when the air mass reaches the Rocky Mountain range it is forced to rise up and over the peaks which begins the process of chinook wind formation (Anderson, 140).

As the parcel of air rises, atmospheric pressure falls allowing the parcel to expand and become less dense (Anderson, 45). This occurs because air molecules are pulled towards the earth’s surface by gravity and then squeezed by the weight of the air above it (Anderson, 45). Therefore, as altitude increases, the air becomes less dense and air molecules have more room to spread out allowing the parcel of air to expand (Anderson, 45). We describe this as ‘thin air’ as fewer oxygen molecules make it difficult to breathe. 

Due to the adiabatic principle, we know that changes in pressure impact the temperature of air even if no other energy is added/removed (Anderson, 131). When a parcel of air begins to rise up the windward side of a mountain, we can observe this phenomenon (Anderson, 140). As it rises, it expands and also cools at the dry adiabatic lapse rate – which is about 10 degrees for every 1000 metres until the air parcel reaches its dewpoint temperature (Anderson, 131).

Once the parcel of air cools to its dewpoint temperature, it begins to condense and form clouds.  At this point, orographic precipitation occurs, which is just the name for rainfall caused by warm air moving over a mountain range (Anderson, 140). The rain causes a release of latent heat which slows the cooling process to the moist adiabatic lapse rate (Anderson, 132). Eventually, the air parcel rises to the top of the mountain peak and the precipitation stops. 

As the parcel of air descends down the Eastern side (leeward) of the Rocky Mountain range, the adiabatic principle comes into play again (Anderson, 140)(Ross, 2017).  This time, as altitude decreases and atmospheric pressure increases the air becomes denser and compresses (Anderson, 140). Compression causes the air to warm quickly essentially causing the clouds (water droplets and ice crystals) to disappear as they evaporate or sublimate directly into vapour (Ross, 2017).

The warming air parcel continues to descend and the temperature increases as it loses altitude.  At this point the parcel of air is much drier than it was when it came off of the Pacific (Ross, 2017). Considering it lost most of its moisture content during the orographic precipitation phase, there is only warm dry air left (Anderson, 140).  This is often referred to as the ‘rain shadow’ as the leeward side of the mountain rarely experiences as much rain as the windward ("National Geographic - Rain Shadow", n.d.).

The warm dry air descending from the mountain moves fast, bringing sudden and sometimes shockingly warm temperatures into the eastern side of the Rocky Mountain Range. Snow appears to vanish at rates up to an inch per hour causing unexpected thawing and flooding (Shafak, 2015).   In some regions the temperature changes so drastically, that it seems like the seasons have changed.  Increases of up to 20 degrees C are quite common (Shafak, 2015).

In North America, Chinooks are most common between the months of December and January (Gibson, 2017). This is the time of the year the jet-stream is at its strongest and can contribute to the formation of strong winds and storms (Sosnowski, n.d.). On average Calgary experiences around 25 chinook days every winter, which can create quite a roller coaster of temperatures throughout a few weeks (Gibson, 2017. 

Aside from the obvious irritation that may be caused by sudden and drastic changes in temperatures, Chinook winds can impact human heath in more subtle ways.
 
 Several studies have indicated that the frequency and severity of migraine attacks may increase with the onset of Chinook Winds (Ross, 2017). However, since people who experience migraines have different triggers, this determination can be difficult to make. Various other studies have disproven this link, but migraine suffers are adamant that chinooks impact their migraine patterns (Gibson, 2017).

Regardless, for people with migraines or other chronic pain disorders that worsen with weather changes – living on the leeward side of a mountain range might not be a good idea.  As a migraine sufferer, I’ve scratched Calgary off my list of places to live! (Better safe than sorry!). 

 

Anderson, B. (2014). Visualizing weather and climate. John Wiley & Sons

CBC News. (2017). Tips for People who get Chinook Migraines [VIDEO LINK]. Retrieved from https://www.cbc.ca/news/canada/calgary/calgary-chinook-valentines-day-record-high-torneby-environment-canada-1.3982463

Encyclopedia Britannica. Orographic precipitation [Image]. Retrieved from https://www.britannica.com/science/orographic-precipitation

Feher, D. Map of North America, Rocky Mountains [Image]. Retrieved from https://www.researchgate.net/figure/Map-of-North-America-showing-the-location-of-the-Rocky-Mountains-Figure-courtesy-of-Feh_fig1_319280545

Gibson, J. (2017). How chinook winds bring warmth to southern Alberta | CBC News. Retrieved from https://www.cbc.ca/news/canada/calgary/calgary-chinook-valentines-day-record-high-torneby-environment-canada-1.3982463

McEwan, S. (2017). Chinook Arch [Image]. Retrieved from https://www.cbc.ca/news/canada/calgary/calgary-chinook-valentines-day-record-high-torneby-environment-canada-1.3982463

National Geographic - Rain Shadow. Retrieved from https://www.nationalgeographic.org/encyclopedia/rain-shadow/

Ross, R. (2017). What Are Chinook Winds?. Retrieved from https://www.livescience.com/58884-chinook-winds.html

Shafak, S. (2015). Chinook Winds - Nature's Gift to Calgary. Retrieved from https://cwf.ca/news/blog/five-facts-about-chinooks-natures-gift-to-calgary/

Sosnowski, A. What are Chinook Winds?. Retrieved from https://www.accuweather.com/en/weather-news/what-are-chinook-winds/70006865

Thomas Higher Education. (2019). Chinook Wind Formation [Image]. Retrieved from https://www.theweathernetwork.com/news/articles/chinook-winds-and-alberta-weather/43265

Wicked Winds from the West. (2017). Retrieved from https://www.ec.gc.ca/meteo-weather/default.asp?lang=En&n=774B5B53-1

Your Morning. (2019). What is a Chinook - Kelley McEwen [VIDEO]. Retrieved from https://www.youtube.com/watch?v=ak3OJZzlo-E