Montana Earth Science Picture of the Week

A dubious distinction . . .
The map shows the location of four small towns known for their especially cold winter temperatures. Quite often the nightly news reports that one of these towns has recorded the coldest temperature in the state during the previous 24 hours. But which one earns the distinction of having the coldest winters?

Climate factors . . .
Climate is the "average weather" experienced at a location over a period of years. Of course there is much more to climate than just temperature. Humidity, the type and timing of precipitation, cloud cover, seasonal change, and wind are also important considerations. Each of these "symptoms" of climate is influenced by various combinations of the climate factors listed here.

latitude . . . . . . . . . . . . . . . . elevation
prevailing winds . . . . . . . . . the shape of the land
nearby ocean currents . . . . distance from large bodies of water

Wisdom: 6,100 ft. . . . Westby: 1,900 ft. . . . West Yellowstone: 7,000 ft. . . . Cooke City: 8,000 ft.

Another consideration is latitude. Obviously Westby is the farthest north of the four towns. A third consideration is prevailing winds. In Montana the wind usually blows from the west, southwest, or northwest. Since winds are names by the direction that they are coming from, our wind belt is known as the "westerlies".

And the winner is . . .
Despite the fact that it sits at a much lower elevation than the other three towns, over the past 30 years Westby has experienced the coldest winters in Montana. Although Cooke City edges out West Yellowstone as the coldest town based on year round temperatures, Westby's winter temperatures average about 5 degrees colder than the nearest competitor (see yellow lines on the graphs below).

The Canadians are coming . . .
Westby's distinction is due to a combination of latitude and prevailing winds. Since Westby is farthest north it gets less solar energy in the winter than the other towns. More importantly, its location in the northeastern corner of the state also means that Westby is the town most likely to experience air masses that move in from Canada (see map to right). As this cold air moves southward the westerlies often prevent it from reaching western and southern regions of the state.

Climate graphs (below) . . .
The yellow line on these climate graphs show that Westby has a greater annual temperature range than Cooke City. Locations that are closer to the center of continents tend to have hotter summers and colder winters than places that are closer to large bodies of water. Water warms more slowly than land during the summer and it also cools off more slowly than land during the winter. This is why Bismarck, North Dakota has hotter summers and colder winters than Seattle. Although the ocean is not a huge influence in Cooke City, it is more likely to influenced by air from the Pacific than Westby is. In the winter Maritime Polar air from the Pacific is cool and moist compared to the cold, dry Continental Polar air, and the bitter cold Continental Arctic air that often moves into northeastern Montana.

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Term: annual temperature range