Frost and Freeze Products - And Dates of Occurrence (Updated 9/22)

 With the official arrival of fall, the growing season over north-central and northeastern South Dakota and west-central Minnesota will gradually be coming to an end.  Although most locations have yet to fall below 32F so far this fall, freezing temperatures will gradually arrive and pose a threat for many agricultural interests. 

The NWS in Aberdeen will issue several products to alert users for the potential for frost or freeze conditions.  These products will be issued until the following:

1)   a hard freeze occurs over a majority of the area

2)  until October 15th (statistical end of the growing season) 


 Descriptions of the NWS Products: 

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.


Average Dates of First Frost and Freeze:

Below is a table that summarizes the date when temperatures of a given threshold are expected to be met.  For example, in Aberdeen, the average (or mean) date when temperatures are first expected to fall to 32F occurs on September 22nd.  Similarly, 90 percent of time, temperatures in Aberdeen will have fallen at or below 28F by October 15th.


ABERDEEN 36F 32F 28F 24F
90th 25-Sep 7-Oct 15-Oct 30-Oct
75th 21-Sep 29-Sep 9-Oct 20-Oct
50th 15-Sep 22-Sep 30-Sep 11-Oct
Mean 13-Sep 22-Sep 1-Oct 11-Oct
PIERRE 36F 32F 28F 24F
90th 2-Oct 18-Oct 28-Oct 7-Nov
75th 29-Sep 10-Oct 22-Oct 31-Oct
50th 21-Sep 4-Oct 12-Oct 23-Oct
Mean 22-Sep 4-Oct 13-Oct 22-Oct
WATERTOWN  36F 32F 28F 24F
90th 27-Sep 7-Oct 14-Oct 29-Oct
75th 21-Sep 1-Oct 10-Oct 21-Oct
50th 16-Sep 24-Sep 3-Oct 10-Oct
Mean 13-Sep 23-Sep 3-Oct 11-Oct
MOBRIDGE 36F 32F 28F 24F
90th 4-Oct 13-Oct 26-Oct 5-Nov
75th 27-Sep 7-Oct 16-Oct 30-Oct
50th 18-Sep 28-Sep 6-Oct 22-Oct
Mean 19-Sep 29-Sep 6-Oct 19-Oct


El Nino Conditions and Freezing Temperatures:

With El Nino conditions forecast to strengthen over the eastern Pacific Ocean, what effect might this have on the date when temperatures first fall below freezing over the area?  Based on statistical research by South Dakota State University, average freeze dates over the area do show a slight trend to be later than normal during El Nino years than non El Nino years (3 to 7 days later).  Note: at several locations, the trend for later than normal freeze dates are not significant, and there have been El Nino years with earlier than normal freeze dates. 

Based on current forecasts, it appears as though a later than average first freeze will occur over at least north-central and northeastern South Dakota.   Recall that the average first 32F temperature normally occurs on September 22nd in Aberdeen, September 23rd in Watertown, and on September 29th in Mobridge.      

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