Massachusetts is located in the northeastern United States, where continental and oceanic weather systems converge. This position means the experience of summer does not always align neatly with the calendar, causing confusion about its true timing. Understanding when the season truly begins and ends requires distinguishing between the official dates and the actual climate patterns of the area.
Defining Summer: Calendar vs. Climate
The question of “when is summer” has two answers, depending on whether one consults an astronomer or a meteorologist. The astronomical definition is based on the Earth’s orbit and its tilt relative to the sun. Astronomical summer begins with the Summer Solstice (around June 20th or 21st) and concludes with the Autumnal Equinox (around September 22nd or 23rd).
This calendar-based timing marks the period of maximum sunlight but does not perfectly capture the warmest part of the year. Meteorologists use a simpler, fixed-date system for seasonal planning and data comparison. Meteorological summer runs from June 1st through August 31st, grouping the three warmest months together. This June-August window is the most reliable framework for residents and visitors expecting peak warmth.
Typical Summer Weather Patterns
The core of Massachusetts summer, primarily July and August, is characterized by a humid continental climate. This brings consistently warm and sticky conditions, with average high temperatures in July often exceeding 80°F. Overnight lows commonly stay above 60°F, and the inland sections, particularly the western and central parts of the state, tend to experience the highest temperatures.
Coastal areas, including Boston and Cape Cod, benefit from the moderating effect of the Atlantic Ocean and the daily sea breeze. While Boston’s average July high is around 82°F, a location like Nantucket sees a cooler average high closer to 76°F. Humidity levels are high, with moisture originating from Gulf of Mexico air masses influencing the region.
The heat and humidity often fuel convective thunderstorms, with the state averaging about 30 days of activity annually. Occasional heat waves push daytime temperatures into the 90s Fahrenheit, sometimes reaching 100°F during intense periods. The late summer and early fall period also carries the risk of tropical systems, which can bring heavy rain and strong winds as they move up the Atlantic seaboard.
The Transition Periods: Late Spring and Early Fall
The edges of summer, late spring and early fall, are marked by greater temperature variability compared to the stability of July and August. Late May and early June can deliver delightful, fair weather, but they are often unpredictable. Days in late May might feel like mid-summer, with temperatures soaring into the 80s, only to be followed by a sharp drop due to cold ocean waters pushing inland.
Early to mid-September often retains warm conditions, especially along the immediate coast. Although the meteorological season has ended, the average temperature in September remains comfortable, with highs often in the low 70s Fahrenheit. By mid-September, the first hints of fall color begin to appear as the region prepares for cooler temperatures and the foliage display.