Average Dates of Last Frost and Freeze

Although average monthly temperatures in March and April continued to be generally below normal, the growing season is well underway across most portions of north-central and northeastern South Dakota and west central Minnesota.  As such, freezing temperatures may begin to pose a threat for many agricultural interests. 

Based on statistical research, the NWS in Aberdeen will begin issuing several products to alert users for the potential for frost or freeze conditions.  These products will begin being issued on and after May 15th.  Descriptions of the products are provided below:


Freeze Watch:   Issued when conditions are favorable for temperatures to fall below 32 degrees Fahrenheit  during the next 12 to 48 hours resulting in the possibility for significant damage to unprotected vegetation. 

Freeze Warning:  Issued when confidence is high that temperatures will fall below 32 degrees Fahrenheit within the next 24 hours resulting in significant damage to unprotected vegetation. 

Frost Advisory:  Issued when conditions are favorable for temperatures to drop between 33 and 36 degrees Fahrenheit resulting in the possibility of widespread frost near the surface.  Unprotected vegetation may be damaged. 


 Below is a table that summarizes the date when the last temperature of a given threshold is expected to be reached.  For example, in Aberdeen, the average (or mean) date when temperatures are no longer expected to fall below 32F occurs on May 13th.  Similarily, 90 percent of time, temperatures will no longer fall to 32F after May 27th (in other words it's very rare to see low temperatures below 32F after May 27th).   Graphics are also provided below.  



ABERDEEN   36 32 28 24
  90th 7-Jun 27-May 18-May 9-May
  75th 29-May 19-May 12-May 1-May
  50th 24-May 13-May 3-May 19-Apr
  Mean 23-May 13-May 3-May 21-Apr
PIERRE   36 32 28 24
  90th 27-May 16-May 10-May 4-May
  75th 20-May 13-May 2-May 24-Apr
  50th 13-May 7-May 23-Apr 14-Apr
  Mean 13-May 5-May 25-Apr 15-Apr
WATERTOWN  36 32 28 24
  90th 11-Jun 1-Jun 20-May 10-May
  75th 4-Jun 24-May 12-May 2-May
  50th 25-May 16-May 4-May 21-Apr
  Mean 26-May 16-May 4-May 23-Apr
MOBRIDGE   36 32 28 24
  90th 1-Jun 22-May 15-May 29-Apr
  75th 24-May 14-May 7-May 28-Apr
  50th 17-May 9-May 28-Apr 15-Apr
  Mean 18-May 8-May 29-Apr 18-Apr



Mike Fowle - Science and Operations Officer


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