The most pleasant months of the year for the 57439 zip code are June, August and September. In the 57439 zip code, there are 4 comfortable months with high temperatures in the range of 70-85°. July is the hottest month for the 57439 zip code with an average high temperature of 83.4°, which ranks it as cooler than most places in South Dakota. February is the snowiest month in the 57439 zip code with 6.9 inches of snow, and 7 months of the year have significant snowfall. But there some days when the humidity becomes unpleasant, especially in July and August.