Climate Insights for Groton

The climate in Groton is cool. The average annual temperature is 9°C and approximately 1300mm of precipitation falls per year. Groton receives a notable amount of rainfall throughout the year, including during its driest month. Groton is in the Northern Hemisphere. Summer begins at the end of June and lasts through September. The summer months are: July, August, June. The coldest months are January, February, December, when temperatures can drop to -7°C. Groton experiences heavy snowfall, typically from January through December.

Temperatures in Groton vary considerably across the year, with a 34°C difference between the coldest and warmest months. The warmest month is July, when average highs reach 27°C and the mean temperature sits around 22°C. The coldest month is January, when overnight lows fall to -7°C and the daily average is -4°C. On average, daily temperatures fluctuate by about 9°C between overnight lows and afternoon highs. The sharpest temperature change occurs between October and November, with a 7°C shift in average temperatures.

Groton is a fairly wet location, receiving approximately 1300mm of precipitation annually, which averages out to around 108mm per month. The wettest month is October, averaging 148mm of rainfall. May and April also tend to see above-average precipitation. The driest month is September, with just 88mm. That's 60mm less than October, the wettest month. Rainfall is relatively evenly distributed throughout the year, so there is no pronounced dry or wet season to plan around. Groton receives heavy snowfall, accumulating around 231cm annually from January through December. The snowiest month is December, with approximately 51cm. Winter travel should account for significant snow cover.

Groton is relatively calm, with an average annual wind speed of 3km/h. For context, sustained winds below 12km/h are generally light, while anything above 25km/h is considered strong. The windiest month is January, averaging 4km/h, though still comfortable for most outdoor activities. The calmest conditions occur in July, with average winds dropping to 2km/h, making it an ideal period for wind-sensitive activities. There is moderate seasonal variation in wind speed, with a 2km/h gap between the calmest and windiest months.

It is currently spring in Groton, which began on March 20, 2026. Groton is in the Northern Hemisphere, where spring begins in March, summer in June, autumn in September, and winter in December. The warmest period peaks in July at around 27°C, while the coldest stretch bottoms out in January near -7°C. Summer is next, beginning on June 21, 2026 — 7 days from now.

The best time to visit Groton is during September, when the weather is most comfortable for travellers. During these months, average temperatures hover around 17°C with modest rainfall averaging 88mm per month. By contrast, July can be uncomfortably hot with highs reaching 27°C, while January is the coldest period with lows dropping to -7°C. Despite being the best months overall, some rain is still likely — pack a waterproof layer and plan a mix of indoor and outdoor activities.

The table below shows monthly climate averages for Groton based on historical weather data. Min and max temperatures represent typical overnight lows and afternoon highs for each month, shown in degrees Celsius (°C). Precipitation is measured in millimetres (mm) and indicates the average total rainfall per month. Snow is measured in centimetres (cm) and reflects average monthly snowfall accumulation. Wind speed is the average sustained speed in kilometres per hour (km/h). All values are based on averages from over 10 years of historical weather data. The current month is highlighted for quick reference.