The Cascades and the Sierra Nevada, two major mountain ranges in the American West, experienced record-high temperatures in February 2015. In most areas, even in the middle of winter, it was too warm to snow. Freezing levels were as much as 1,051 meters (3,448 feet) higher than normal, based on the average from 1980 to 2010.
This year’s lack of snowpack — which is below 25 percent of normal in both mountain ranges — means less water than usual will be available in the late summer, when snowmelt is important for farm irrigation, fish habitat, and peak demand in cities. The Sierra Nevada is a water tower for more than 25 million Californians and millions of acres of the nation’s most productive farmland. The low snowpack is a main factor in last week’s decision by the Bureau of Reclamation, a federal agency, to deliver no water this summer to Central Valley farmers. In the Cascades snowmelt is an important water source for Seattle, the nation’s fastest growing big city, and for farmers, hydropower dams, and salmon in the Columbia, Klamath, Willamette, Yakima, and other river basins.
In both ranges, this winter is a glimpse of the future. Computer models project that the meager snow levels of today will be commonplace within 50 or 60 years if greenhouse gas emissions continue to rise.
The maps below estimate the area in which temperatures were below 0 degrees C (32 degrees F) during February 2015, and thus conducive to snow. Data from the North American Freezing Level Tracker was used to compare February 2015 freezing levels (in dark red) with the 1980 to 2010 February mean (in pink). Freezing elevation levels were determined using one central data point each for the Northern, Middle, and Southern Cascades, as well as one point for the Sierra Nevada. Though one data point per mountain range can only give an estimate, the difference is still astounding.
Brett Walton contributed to this infographic, which was made to accompany Walton’s article Pacific Northwest’s Winter, Warm and Wet, Is Climate Change Preview. Contact Brett Walton or send a tweet to @WaltonWater.