These tiles are published and intended for use in the map Historic date of first snow.These base map tiles cover the North American extent and include data which represent the historic date by which there’s a 50% chance at least 0.1” of snow will have accumulated, based on each location’s snowfall history from 1981-2010. Map based on an analysis of the current U.S. Climate Normals by Mike Squires, National Centers for Environmental Information.  White indicates places where there is a year-round chance of snow. Shades of blue and purple show places where the first day of snow historically falls between August 1st and December 31st, while dark gray shows places where, historically, the first snow doesn't take place until January 1st or later. Empty circles showing background gray indicate places where snow is so infrequent that there is not enough data to calculate a statistical first date of snow. While the map shows the historic date of first snow, the actual conditions this year may vary widely from this map because current weather patterns will determine the first snow of the year. For a more detailed assessment of the historic date of first snow, please see this Climate.gov blog post by Deke Arndt, NOAA NCEI scientist. For a broad overview of NOAA's 1981–2010 Climate Normals, see NOAA's 1981-2010 U.S. Climate Normals: An Overview published in the Bulletin of the American Meteorological Society, or for a detailed description of snow Normals, seeNOAA's 1981-2010 U.S. Climate Normals: Monthly Precipitation, Snowfall, and Snow Depth published in the Journal of Applied Meteorology and Climatology.

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