Quite often when the Pacific Northwest coast is being drenched by rain, the windward side of the Rockies is being hammered by snow, and the leeward side of the Rockies in Alberta is basking in a chinook. The three different weather conditions are all caused by the same flow of air, hence the confusion over the use of the name “Chinook wind”. Such winds are extremely wet and warm and come from the southwest, and are also known as the Pineapple Express since they are of tropical origin, roughly from the area of Hawaii.
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 the air mass being forced to a higher elevation. 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 colours seen in the chinook arch are quite common. Typically the colours will change throughout the day, starting with yellow, orange, red and pink shades in the morning as the sun comes up, grey shades in the mid day changing to pink/red colours, and then orange/yellow hues just before the sun sets.
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 10–20 °C (50–68 °F) for a few hours or days, then temperatures plummet to their base levels.
In southwestern Alberta, Chinook winds can gust in excess of hurricane force 120 or 75 km/h (75 or 47 mph). On November 19, 1962, an especially powerful chinook in Lethbridge gusted to 171 km/h (106 mph).
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 to 49 °F , a 103 °F change in temperature; a dramatic example of the regional Chinook wind in action.
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.
The Bow Valley in the Canadian Rockies west of the Calgary acts as a natural wind tunnel funneling the chinook winds to the city.