Many persons awoke to frosty lawns on the morning of September 15 as the first frost arrives a week or two earlier than the median dates over much of central and southern Minnesota. See the daily Minimum Temperature maps for frost monitoring.
With the recent heat that Minnesota has been experiencing throughout the first half of September, temperatures took a dramatic plunge when a cold front arrived by the 13th and many communities throughout the state had record to near record low temperatures by the morning of September 15.
The Twin Cities International Airport tied the record low of 36 set back in 1964 on September 15 when the temperature dropped to 36 degrees. Many suburbs outside of the urban heat island reported their first freezing temperatures of the year. The Crystal Airport reported a low of 31 degrees. Even some areas in southern Minnesota hit the freezing point or lower including Mankato at 32 degrees, Waseca at 28 degrees, and Rochester at 31 degrees, all records for this date.
Several areas in northern Minnesota recorded some impressive records also. Embarrass and International Falls each bottomed out at 19 degrees. Several other areas including Bemidji, Park Rapids, Hibbing, and Tower recorded record lows in the 20’s also.
The culprit behind these low temperatures was clear skies with extremely low dew points, and calm winds throughout the state. A strong high pressure system more typical of winter allowed these factors to exist.
Ryan Stepaniak - Climatology Volunteer assisted with this report