Locally, a heat wave consists of 3 or more consecutive days of 90+ degree farenheit high temperatures.
In the greater Boston Area of eastern Massachusetts, weather is highly volatile and variable. It's primarily driven by the direction of the prevailing winds and their interaction with the Gulf Stream.
There is no such thing as an "average" weather day here. Averages are backward-looking statistical analysis of some quantitative weather measurements. There is insufficent data, or too few data points, to glean a reliable probability model for our weather.
If the scientists knew all there is to know about climate, weather forecasters wouldn't need spaghetti charts to plot the multitude of courses a storm could take in the days ahead.