If you’re looking forward to lots of outings with your partner, take a look at these details about year-round temperatures in Watertown: The hottest months are usually July and August, with an average temperature of 21°C, while the coldest months are January and February, with an average of 0°C. The snowiest months in Watertown are January, February, March and April, with each month seeing an average of 13 cm of snowfall.