Groton (CT) Temperature by Month
The average annual maximum temperature in Groton, Connecticut, United States of America is 15°C (59°F), with daytime highs ranging from 4°C (39°F) in January to 27°C (81°F) in July. This page covers monthly averages, day-night differences, and how Groton compares to cities worldwide.
Groton Monthly Temperatures
Visitors to Groton will encounter a climate influenced by big temperature differences across the year. Nighttime temperatures range from 19°C (66°F) in July to -5°C (23°F) in January.
The chart below illustrates the average maximum day and minimum night temperatures in Groton by month:
The coldest point of the day usually falls between 4 AM and 6 AM, with temperatures peaking around 3 PM. July, the city's warmest month, gets 293 hours of sunshine.
The chart below shows the average temperature throughout the year:
Temperature: Groton vs the United States of America
The map below shows the annual temperature across the United States of America. You can also select individual months if you want to compare a specific time of year.
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Groton vs World: Temperature Compared
Groton's average annual maximum temperature is 15°C (59°F). To put that in context, here's how it compares to a few well-known destinations:
Seville, Spain averages 23°C (73°F) a year — one of the warmer cities in Western Europe, with long hot summers.
Interlaken, Switzerland averages 8°C (46°F) a year, with cold winters and cool summers thanks to its Alpine setting.
Seoul, South Korea averages 18°C (64°F) a year, with four clear seasons, cold winters, and hot humid summers.
Tokyo, Japan averages 21°C (70°F) a year, with hot summers, cool winters, and a well-defined cherry blossom spring.
What Does the Temperature Feel Like in Groton?
Temperature alone doesn't tell the whole story — humidity plays a big role in how warm or cold it actually feels. High humidity in summer makes the heat feel more intense, particularly once temperatures climb above 25°C. In winter, the same humidity can make cold air feel sharper than the thermometer suggests.
In the cooler months, when temperatures drop below 10°C, high humidity makes the cold feel more cutting than it would in dry conditions.
In Groton, January is the coolest month, with average highs of 4°C (39°F) and humidity around 64% — considered high. In July, the warmest month, temperatures average 27°C (81°F) with 68% humidity — conditions that feel high. For a full picture, see our humidity page.
Climate temperature data is typically calculated as a 30-year average. This smooths out year-to-year variability and gives a more reliable picture of what a place is actually like, rather than what happened in any single unusual year.
The readings come from a range of sources — land-based weather stations, ocean buoys, ships, and satellites. That data is collected by weather services around the world, then pooled, quality-checked, and averaged to produce the climate records you see here.
Seasonal temperature shifts influence more than just how warm it feels — they also drive changes in rainfall, cloud cover, and wind patterns throughout the year.
Warmer air holds more moisture, which tends to mean heavier or more frequent rain during the warmer months. When temperatures drop in winter, any precipitation that does fall is more likely to come as snow or sleet, though in Groton this rarely lasts long on the ground.
For more on Groton's weather — including monthly rainfall, sunshine hours, and humidity — visit our Groton climate page.
