Darien, Connecticut, like much of southern New England and metropolitan New York, experiences cold, snowy winters and humid, mildly hot summers. Average annual precipitation for the town (including melted snowfall) is 48 inches per year, while snowfall totals average around 28 to 37 inches annually (rarely falling outside of November and March); the average US city receives 25 inches of snow annually The number of days with any measurable precipitation is 101. On average, there are 176 sunny days per year in Darien, Connecticut. The July high is around 85 degrees. The January low is 20. Our comfort index, which is based on humidity during the hot months, is a 44 out of 100, where higher is more comfortable. The US average on the comfort index is 44.

Darien's local weather is strongly influenced by its location on the shores of Long Island Sound. Darien is often subject to strong winds and heavy precipitation from nor'easters and tropical storms, which occasionally results in flooding along the coast and small streams. In addition, due to the moderating effects of the Sound, summer afternoon temperatures in Darien are often several degrees cooler than location further inland, while winter temperatures usually warmer. In fact, it is not unusual for winter storms to drop rain and sleet over Darien, while locations less than five miles north in New Canaan and northern Stamford receive snow.