According to the National Weather Service, on February 23rd, 1981 the high temperature in Sioux Falls soared to 70 degrees. That tied the record set on the same day in 1958 for the warmest temperature on record in Sioux Falls for the month of February and is also the earliest in the year that the temp has hit 70 degrees.

Source: http://www.crh.noaa.gov/fsd/?n=fsdtrivia02

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