If you’re hoping to get lost in the rain on your romantic getaway, take a look at these details about year-round temperatures in North Sioux City: The hottest months are usually July and August, with an average temperature of 22°C, while the coldest months are January and February, with an average of -3°C. The snowiest months in North Sioux City are January, October, February and November, with each month seeing an average of 23 cm of snowfall.