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.
Mike Fowle - Science and Operations Officer