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 Tri-Cities: The hottest months are usually July and August, with an average temperature of 21°C, while the coldest months are December and January, with an average of 3°C. The snowiest months in Tri-Cities are February, March, January and April, with each month seeing an average of 13 inches of snowfall.