By David Bailey
MINNEAPOLIS (Reuters) - Don't put away those mittens and wooly socks just yet.
Midwesterners dreaming of an early spring - after one of the warmest winters on record - could be in for a shock this weekend when below-zero temperatures and bitter wind chills are due to strike parts of North Dakota and Minnesota.
The National Weather Service is forecasting temperatures to reach 10 below zero Fahrenheit in Grand Forks, North Dakota, into Friday morning and 2 below zero eastward across to Duluth, Minnesota, with wind chills of up to 35 below zero.
The forecast signals a harsh return to reality for residents spoiled by a relatively mild winter, not only in the Midwest, but across much of the country.
Overall, the lower 48 U.S. states through December and January had the fourth warmest average temperature on record, a sharp contrast to heavy snow and cold temperatures last winter that contributed to spring and summer flooding in many regions.
Across the contiguous 48 states, the average temperature in December and January was 3.8 degrees above average, with much of the warmth across the northern and eastern United States.
Twenty-two states from Montana to Maine had December-January temperatures that ranked in their top 10 warmest on record.
Through Tuesday, the Minneapolis-St. Paul metropolitan area has had the warmest average temperature for the December through February period in more than 130 years, according to the state climatology office.
The cold snap is expected to be a temporary interruption of that trend, with a return to above normal temperatures in most cases, said meteorologist Tony Zaleski from the National Weather Service in the Twin Cities.
"It is going to be pretty much similar. Maybe not the same degrees in temperature, but it will still be above average, probably by at least 10 degrees in most cases," Zaleski said.
The state climatogy office said the average Twin Cities temperature from December 1 through February 7 was 27 degrees. That is just below the record 29 degrees average for the three-month period from December through February in the winter of 1877 to 1878.
The warmer temperatures across the United States have had a mixed impact, leaving retailers struggling to sell winter clothing and equipment, but preparing for earlier demand for other materials such as lawn care equipment.
Home heating days, a measure of demand for home heating, were sharply lower than normal through January and the lesser snowfall cut snow-plowing costs for some communities.
While the contiguous U.S. states have enjoyed warmer temperatures, Alaska has not. Several towns in Alaska set record low average temperatures in January, including Nome at 16.6 degrees below zero.
(Reporting by David Bailey; Editing by Paul Thomasch)