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 Portland: The hottest months are usually July and August, with an average temperature of 19°C, while the coldest months are January and February, with an average of -4°C. The snowiest months in Portland are January, December, February and March, with each month seeing an average of 19 cm of snowfall.