Weather and Geography
November 16-22 is the National Geographic Society’s Geography Awareness Week. This is a great time to remind your viewers about the close links between geography and weather with some well-known examples around the US:
- Pacific Northwest: When winter-time temperature inversions occur in the Puget Sound Region, which sits in a “bowl” between the Olympic and Cascade Mountains, cooler air is trapped near the Earth’s surface and air pollution levels can rise significantly.
- Western US: As prevailing westerly winds carry moist Pacific air up the windward side of mountains, the air cools, condenses, and precipitates, leaving the leeward side warmer and dryer. This effect creates “rain shadow deserts,” areas with less precipitation and cloud cover than the windward side of the mountains. The Colorado Front Range along the Rocky Mountains, the Great Basin of Nevada and Utah, and the Mojave Desert east of the Sierra Nevada Mountains in California are all rain shadow deserts.
- Great Lakes: This Region is known for its lake effect snow. As cold air passes over the Lakes, warmer lake water below evaporates and heats the bottom layer of cold air. Warm, moist air rises and cools, causing condensation and cloud formation. If humidity is high enough and temperatures are cold enough, snow falls. Winds push these clouds over land, where increased friction slows the winds, leading to more snowfall accumulation. As winds move farther inland and encounter hills, rising air cools even more, creating even more snow!
- Great Plains: The broad, flat expanses of the Great Plains are ideal for tornado formation. The flat geography allows dry, cold air from Canada and warm, moist air from the Gulf of Mexico to come together – most tornadoes form along the front between these air masses.
- Eastern US: When a high pressure system stalls over New England during winter and blows cold, dry air southwestward into the mid-Atlantic region, this air “bumps” into the Appalachian Mountains and stops. Warm air flowing over the Mountains from the Midwest overruns the cold air and traps it along the Atlantic coastal plain, creating “cold air damming.” Precipitation from the warm air aloft falls through the cold air and freezes. Some major ice storms in the Northeast and mid-Atlantic regions have occurred during cold air damming episodes.
Learn more about Geography Awareness Week: www.nationalgeographic.com/geography-action/index.html.
Season: Fall
(Sources: Puget Sound Clean Air Agency.”Weather and Topography.” http://www.pscleanair.org/airq/basics/weather/default.aspx; University Corporation for Atmospheric Research. 2008. “Windows to the Universe: Rain Shadow.” http://www.windows.ucar.edu/tour/link=/earth/Atmosphere/precipitation/rain_shadow.html; “Warm water helps create Great Lakes snowstorms.” University Corporation for Atmospheric Research. 2008. “Windows to the Universe: What is Tornado Alley?” http://www.windows.ucar.edu/tour/link=/earth/Atmosphere/tornado/alley.html; USAToday: http://www.usatoday.com/weather/tg/wlakeeff/wlakeeff.htm; “Cold air damming can bring ice to East.” http://www.usatoday.com/weather/tg/wcolddam/wcolddam.htm)
