The waters that surround the Saint John area, specifically in the Bay of Fundy and harbour Saint John, never freeze in the winter. The weather, however, can get very cold during the winter months. January and February are the the coldest months of the year, which makes it the least popular month for tourists.

July and August are the warmest months in Saint John, and the warmest time of the day is early afternoon; in the evening as the sun drops the wind will shift from off shore to onshore and lends to having cool evenings and some dew on most  days.  The Bay of Fundy is the world's best natural air conditioning unit and provides cooling breezes at night and little need for air conditioning near the bay.

From May through July, the most important weather element is the wind direction.  The Bay of Fundy water never gets above 15°C (60°F).  When the wind is south or east, it chills the city and the immediate Fundy coast.  From late afternoon through the night and past noon next day, thick sea fog blows in, dropping temperatures to about 10°C (50°F), very slightly milder in July, accompanied by drizzle, occasional showers, and clammy humidity.  Although tourist brochures sometimes describe this euphemistically as "cooling fog," most find it unpleasant for outdoor activity, and sometimes even hazardous for driving.  Worse, this sort of weather can hang on for as long as two weeks at a time in some years, broken by a couple days of dry air before the next period of sea winds.  Perhaps it will not surprise you to learn that the fog horn was invented in Saint John in 1810.

(If the fog seems miserable to you, only about 20 kilometers (10 miles) inland it's sunny and much warmer on such days.  The contrast may amaze you.)

If you are lucky to get days when the wind is west or northwest, the days of May through July can be very pleasant with the temperatures climbing into the 20s C (70s F, with an occasional 80). In spring, the due-north and northeast wind has been known to blow in unseasonably cold air.

August and September are the most pleasant months, the least likely to get sea fog.  Early autumn is not a bad time either.  The weather can be either warm or cool, but almost always pleasant.  September is the city's best-kept weather secret, usually crisp and dry.  About once a year, the tail end of a tropical storm brushes the area around this time, and if it coincides with your visit you'll get a rainy, windy day, likely with power outages. 

The fall colors are at the peak from the fourth week of September to the second week of October, when the reds fall.  The yellows and oranges last through the third week and into the fourth.  By November 1, all will be gone, except for the oaks and the tamarack, a deciduous conifer that turns its needles a golden yellow and sheds them in early November.

Most of Saint John’s severe storms (both snow and rain) occur during the autumn and winter months. Some of these storms have the capability of producing freezing rain.

Despite the cold winters in Saint John, there are still plenty of things for visitors to see and do which take place indoors.

For current weather conditions, forecasts, and up-to-date weather warnings, check Environment Canada's Saint John weather page. This page is also available in imperial units.

For a very detailed picture of the climate, including snowfall, snow depths, sunshine, rainfall, and more, see Environment Canada's Saint John climate page.