A storm system unique to the New England region is called a Nor'easter. A Nor'easter is a powerful storm system that forms in the Gulf of Mexico and slowly moves up the East Coast. It dumps a lot of rain on the northeast coast and a huge amount of snow inland, especially on higher elevations. It has similar precipitation amounts to January except that in July the precipitation only falls as rain. Most of the rain falls in downpours that result from thunderstorms.
Thunderstorms form because the air is fairly warm and humid.
Warm air and humidity are two important ingredients for thunderstorms. Aside from the thunderstorms, July is a mostly sunny month for the Northeast. The coldest recorded temperature is -52 degrees Fahrenheit in Old Forge, New York on February 18, 1979. For more climate data, look at the Weather Research Center site. Climate data is listed for many cities, including temperature and precipitation information.