Snow is blanketing over half the U.S. less than three weeks from spring's official arrival, marking one of the most expansive early-March snow covers in 15 years.

As of March 4, 56.7 percent of the contiguous U.S. had snow on the ground, according to an analysis by NOAA's National Operational Hydrologic Remote Sensing Center.

This aerial extent of snow cover was only exceeded twice before in early March, once on Mar. 3, 2014 (57.3 percent coverage) and again on Mar. 1-2, 2015 (up to 63.4 percent coverage). NOHRSC's dataset dates to 2003.

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This was a more expansive snow cover than any December (peak of 46.7 percent coverage on Dec. 10) or January (peak of 51.3 percent on Jan. 22) day this season. Only February 21 (58.8 percent) had more expansive coverage this winter than early March.

Another NOAA analysis had a record expansive early-March North American snow cover extent of 17.28 million square kilometers in data going back to 2005.

A number of factors have contributed to this expansive snow blanket.

February was the snowiest on record in at least two dozen locations from the West to the upper Midwest. Even typically snow-covered locations had impressive early-March snowpacks.

Baxter State Park, Maine, had an 84-inch snowpack on March 5, according to the National Weather Service.

In California's Sierra Nevada mountains, a SNOTEL station at Independence Lake just north of Truckee, had an estimated 165 inches (almost 14 feet) of snow cover March 4, double their average for the date, second only to 2017's 186-inch snow cover.

This past weekend, Winter Storm Scott laid down a footprint of snow from the Plains and Midwest to the Northeast. Oklahoma City's Will Rogers World Airport officially had a trace of snow on the ground both Mar. 3 and 4. Louisville International Airport reported 1 inch of snow on the ground Mar. 4.

Scott also unleashed an arctic blast in its wake, featuring some all-time March record cold in some parts of the Plains which helped the snow stick around.

That's typically not the case throughout March.

Lower 48 snow cover area diminishes on average from about 37 percent on the first of the month, to just under 17 percent at month's end, according to the NOHRSC database.

March average highs warm above freezing in most of the Lower 48 states outside mountain areas thanks to increasing daylight and more effective heating of the ground by a sun that's higher in the sky.

(MORE: Itching For Spring? Here's When Temperatures Typically Warm Up)

So, while March certainly offers some notable snowstorms, snow cover often doesn't stick around as long.

(MORE: 4 Reasons Why March is Still a Winter Month)