WASHINGTON -- We've become weather wimps.
As the world warms, the United States is getting fewer bitter cold spells like this week's. So when a deep freeze strikes, it seems more unprecedented than it really is.
An Associated Press analysis of daily national winter temperature - averaged into one figure for the Lower 48 states - shows that since 1900 cold extremes like this week's happen about once every four years.
Government meteorologist Greg Carbin created a database of the winter daily national temperature average going back to 1900. And Monday was the first time since 1979 that the national average temperature dropped below 18 degrees.
In 27 distinct cold snaps over 115 years, that's by far the longest the U.S. has gone without getting this frigid.