By Climate Central

As the world warms, the overall area of North America covered by snow is decreasing. One reason is that an increasing percentage of winter precipitation is falling as rain instead of snow in many locations. A Climate Central report found that between sea level and 5,000 feet in elevation, a smaller percentage of winter precipitation is falling as snow in the western U.S. The subsequent decline in snowpack affects reservoir levels and irrigation, as the melting snow provides water for the Westin the dry summer months.

 

 

Snowfall trends (inches per year)

However, the relationship is more complex at the local level. Rising temperatures can cause some individual storms to produce more snow. That’s because for every 1°F rise in temperature, the atmosphere can hold 4 percent more water. This, in turn, means more water is available to fall as snow or rain.

In the Great Lakes region, warming is leading to more snow in some of the downstream areas. When the lakes go longer without forming ice, that allows for increased evaporation, and the potential for more lake-effect snow.

Nationwide, more than 40 percent of counties have had their biggest 2-day snow totals since 1980. Our analysis excluded counties where the 2-day snowfall record was less than 3 inches. So even if the average amount of snow at the local level may be trending down, the snow that falls may come in larger batches. This is notable in the northeastern cities, where the biggest storms are usually nor’easters, which tap into the Atlantic Ocean for moisture. As the Washington Post’s Capital Weather Gang has pointed out:

• Seven of Washington, D.C.’s top 10 snowstorms since 1889 have occurred since 1979.
• All five of Philadelphia’s highest snowfalls have occurred since 1983. Its top three have happened since 1996.
• In New York City, seven of the nine biggest snows have occurred since 1996. Three of the top five have come in the past decade.
• Eight of Boston’s top 10 snowstorms have come since 1978. Half have occurred since 2003. 

Methodology: total snowfall is over the period from July - June in areas which average at least 10 inches of snow per year. Data is from the Applied Climate Information System.

 

This originally appeared on Climate Central.