Climate Fact: Two Tales of American Snowfall

Two divergent stories are beginning to emerge about America’s snowfall.  While one study showed that American snowfall might decline in the future, another found that the biggest snow-producers – extreme snowstorms – have increased.  In fact, there have been twice as many extreme snowstorms in the past half century as there were in the preceding one.  These findings seem to contradict one another, so how can they both be right?  The answer boils down to snow’s ingredients – water vapor and cold temperatures – and how our climate system influences them.  Our planet’s rising thermostat has enabled the atmosphere to hold more water vapor, or “storm fuel”, and storms with exceptionally heavy precipitation have become more common as a result.  When the air is cold enough, this precipitation falls as snow, which may explain why scientists have seen an increase of powerful snowstorms.  However, a higher planetary temperature makes it harder for that precipitation to fall as snow, so a greater percentage of it falls as rain rather than snow.  This explains why average snowfall can decrease even as heavy snowstorms become more common.

Photo courtesy of UCAR.

(Sources: Kapnick, S. and T. Delworth, 2013.  “Controls of Global Snow Under a Changed Climate.”  Journal of Climate, doi: 10.1175/JCLI-D-12-05528.1, in press; Kunkel, K.E. et al. 2012, “Monitoring and Understanding Trends in Extreme Storms: State of Knowledge.”  Bulletin of the American Meteorological Society, doi: 10.1175/BAMS-D-11-02262.1, in press.)

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