Groton, Connecticut climate: Normal weather by month, frost dates and records
Groton's normal year runs from 23°F January nights to 80°F July afternoons, with 39.3 inches of precipitation a year. (NOAA 1991-2020 normals)
In metric: a yearly mean of 10.8°C, January lows of −5°C, July highs of 27°C, 998 mm of precipitation a year.
- NOAA stationGroton New London Airport
- Station IDUSW00014707
- Location41.33°N 72.05°W
- Elevation10 ft (3 m)
- Population10,160
On October 14, the normal high in Groton is 64°F and the normal low 46°F, and the chance of measurable rain or snow is 31%.
Normals describe a typical year at the station, not a forecast. The National Weather Service forecast for Groton.
- Jan 38° 23°
- Feb 40° 25°
- Mar 47° 31°
- Apr 56° 39°
- May 65° 49°
- Jun 74° 58°
- Jul 80° 65°
- Aug 79° 64°
- Sep 74° 57°
- Oct 63° 46°
- Nov 53° 37°
- Dec 44° 29°
Each month: normal high (large) and low, °F. Fill: the month's normal mean, colder blue to hotter red.
What is the weather like in Groton each month?
July is the warmest month, with normal highs of 80°F; January the coldest, with normal lows of 23°F. The most precipitation falls in September (3.83 in), the least in February (2.20 in).
Each month has its own page with the day-by-day normals, the month's records and its recent years:
| Month | High | Low | Mean | Precip. | Wet days | 90°F days | Freezing nights | Daylight |
|---|---|---|---|---|---|---|---|---|
| January | 38°F | 23°F | 30.8°F | 2.68 | 9 | <1 | 25 | 9 h 30 min |
| February | 40°F | 25°F | 32.4°F | 2.20 | 8 | <1 | 24 | 10 h 40 min |
| March | 47°F | 31°F | 38.6°F | 3.82 | 9 | <1 | 19 | 11 h 50 min |
| April | 56°F | 39°F | 47.6°F | 3.58 | 11 | <1 | 5 | 13 h 20 min |
| May | 65°F | 49°F | 56.8°F | 3.31 | 12 | <1 | <1 | 14 h 30 min |
| June | 74°F | 58°F | 66.0°F | 3.30 | 11 | <1 | <1 | 15 h 10 min |
| July | 80°F | 65°F | 72.3°F | 3.24 | 10 | 1 | <1 | 14 h 50 min |
| August | 79°F | 64°F | 71.5°F | 3.32 | 10 | 1 | <1 | 13 h 50 min |
| September | 74°F | 57°F | 65.2°F | 3.83 | 9 | <1 | <1 | 12 h 30 min |
| October | 63°F | 46°F | 54.4°F | 3.66 | 10 | <1 | 2 | 11 h 10 min |
| November | 53°F | 37°F | 45.1°F | 3.24 | 9 | <1 | 10 | 9 h 50 min |
| December | 44°F | 29°F | 36.5°F | 3.13 | 10 | <1 | 22 | 9 h 10 min |
| Year (annual) | 59°F | 44°F | 51.4°F | 39.31 | 116 | 2 | 107 |
The same normals in °C and millimetres
| Month | High | Low | Mean | Precip. |
|---|---|---|---|---|
| January | 3°C | −5°C | −0.7°C | 68 mm |
| February | 5°C | −4°C | 0.2°C | 56 mm |
| March | 8°C | −1°C | 3.7°C | 97 mm |
| April | 13°C | 4°C | 8.7°C | 91 mm |
| May | 18°C | 9°C | 13.8°C | 84 mm |
| June | 23°C | 15°C | 18.9°C | 84 mm |
| July | 27°C | 18°C | 22.4°C | 82 mm |
| August | 26°C | 18°C | 21.9°C | 84 mm |
| September | 23°C | 14°C | 18.4°C | 97 mm |
| October | 17°C | 8°C | 12.4°C | 93 mm |
| November | 12°C | 3°C | 7.3°C | 82 mm |
| December | 7°C | −2°C | 2.5°C | 80 mm |
NOAA publishes no 1991-2020 snowfall normal for this station. Groton's own co-op station Groton station does: 25 inches of snow in a normal year (see the other stations below).
Source: NOAA NCEI 1991-2020 monthly normals, station USW00014707; annual normals. Wet days: 0.01 inch or more; 90°F days and freezing nights: NOAA's day counts. Daylight: sunrise to sunset on the 15th, computed from the latitude.
When is the best weather to visit Groton?
Normal highs sit between 65°F and 85°F in June, July, August and September. Of those, September has the fewest days with rain (9).
That is a measurement, not a recommendation: it counts the months whose normal afternoon high sits between 65°F and 85°F, where a light layer is enough by day.
Source: NOAA NCEI 1991-2020 monthly normals, station USW00014707.
When is the last frost in Groton?
In Groton, the last spring frost (32°F) comes after April 16 in half of years and after April 30 in one year in ten; the first autumn frost comes before October 28 in half of years and before October 13 in one year in ten.
Frost-free in half of yearsFrost in 1 to 9 years out of 10Frost most years
- Last spring frost, half of years after
- April 161 year in 10 after April 30; 9 in 10 after April 3
- First autumn frost, half of years before
- October 281 year in 10 before October 13; 9 in 10 before November 12
NOAA puts the median frost-free season at 194 days, and the season without a hard freeze (28°F) at 220 days.
A hard freeze (28°F) comes after April 3 in half of springs and before November 9 in half of autumns.
The USDA's 2023 Plant Hardiness Zone Map puts Groton in zone 7a in ZIP code 06340. By the map's own method, the average of each year's coldest night over 1991-2020, Groton's NOAA station is in zone 7a: the coldest night of a typical year reaches 3°F (20 complete years).
Frost dates for every NOAA station in Connecticut · Frost dates by ZIP code
Source: NOAA NCEI 1991-2020 annual normals (frost probabilities), station USW00014707; USDA 2023 Plant Hardiness Zone Map, ZIP listings: PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed October 8, 2026; the station zone: ACIS daily lows, 1991-2020. A 10% date means one year in ten has a frost after it in spring or before it in autumn.
How hot and how cold does it get in Groton?
In a normal year in Groton, 2 days a year reach 90°F, 107 nights fall to 32°F or colder and 116 days bring measurable precipitation.
- Days at 90°F or more
- 2a normal year
- Days at 100°F or more
- fewer than 1a normal year
- Nights at 32°F or colder
- 107a normal year
- Days that stay below freezing
- 18high of 32°F or less
- Days with 0.01 inch of precipitation
- 116a normal year
The highest temperature in this station's record (since 1999) is 101°F, on July 6, 2010; the lowest is −8°F, on February 14, 2016.
The wettest calendar year on that record is 2019, with 54.40 in.
Source: NOAA NCEI 1991-2020 annual normals, station USW00014707; records: ACIS (NOAA Regional Climate Centers), station USW00014707. Records use complete months only; a month missing more than three days is left out.
How sunny is Groton?
Over a year 73% of the sunlight that would reach the ground under clear skies gets through the clouds in the area around Groton, 3.9 kWh per square metre a day. July is the sunniest month (79%) and December the cloudiest (67%).
| Month | Share of clear-sky sunshine | Sunshine, kWh/m² a day |
|---|---|---|
| January | 70% | 1.9 |
| February | 70% | 2.7 |
| March | 69% | 3.7 |
| April | 71% | 4.9 |
| May | 70% | 5.5 |
| June | 74% | 5.9 |
| July | 79% | 6.0 |
| August | 79% | 5.3 |
| September | 78% | 4.4 |
| October | 71% | 2.9 |
| November | 72% | 2.1 |
| December | 67% | 1.5 |
Source: NASA POWER solar climatology, 2001-2020 (CERES SYN1deg). Satellite-based, for the 1-degree cell (about 100 km across) around the station, so it describes the area rather than the airport.
How much heating and cooling does Groton need?
A normal year in Groton brings 5,521 heating degree days, 3% more than the median U.S. place (5,373), and 608 cooling degree days, 33% fewer than the median (908). Seven months need 300 or more heating degree days, a monthly mean of about 55°F or colder. For gardens and crops, NOAA counts 2,786 growing degree days a year above 50°F.
| Month | Heating | Cooling |
|---|---|---|
| January | 1,060 | 0 |
| February | 913 | 0 |
| March | 817 | 0 |
| April | 521 | 1 |
| May | 261 | 7 |
| June | 52 | 82 |
| July | 2 | 228 |
| August | 5 | 207 |
| September | 71 | 77 |
| October | 336 | 7 |
| November | 599 | 0 |
| December | 885 | 0 |
| Year (annual) | 5,521 | 608 |
Source: NOAA NCEI 1991-2020 monthly normals, station USW00014707. A degree day is one degree of a day's mean temperature below 65°F (heating) or above it (cooling); utilities use them to estimate energy use.
Has Groton been warmer than normal lately?
2023 averaged 54.6°F, 3.2°F above the 1991-2020 normal of 51.4°F. 2 of the 2 complete years since 2021 ran warmer than the normal.
| Year | Mean | Against normal | Precip. |
|---|---|---|---|
| 2021 | 52.1°F | +0.7°F | 38.39 |
| 2023 | 54.6°F | +3.2°F | – |
Source: observed years: ACIS, station USW00014707. A year counts only with all twelve months complete.
How does Groton's climate compare?
Groton is warmer than 8 of the other 12 places with their own NOAA record in Connecticut, and wetter than 0. Across the 7,247 U.S. stations with normals, its annual mean of 51.4°F is warmer than 47%.
In the Köppen classification computed from these normals, Groton is Dfa: continental, no dry season, hot summer. What the classes mean.
Places with the most similar year elsewhere
Measured month by month on the normal high, low and precipitation, among places of 20,000 or more people in other states:
Source: NOAA NCEI 1991-2020 normals for every station PlainClimate covers. Similarity: the root-mean-square difference of the 36 monthly figures, precipitation weighted so an inch counts like 6°F.
Which places near Groton share this climate record?
7 places have no NOAA station with 1991-2020 normals of their own, and this station is the nearest full record. A place's own climate can differ from these figures, by several degrees where it sits much higher or lower than the station, nearer the coast, or inside a large city's heat; for the larger places the next nearest records are named with their yearly mean, so the spread around them is visible, and places of 50,000 or more have their own page with NOAA's gridded normals.
- New London, CT28,081 people · 2 mi W
- Conning Towers-Nautilus Park, CT8,590 people · 4 mi N
- Long Hill, CT4,292 people · 2 mi N
- Waterford, CT19,910 people · 4 mi W
- Misquamicut, RI355 people · 12 mi E
- Watch Hill, RI224 people · 11 mi E
- Fishers Island, NY53 people · 5 mi SE
Source: Census Bureau 2024 Gazetteer (place centers) and Vintage 2024 population estimates. Distance and direction from the station to each place's center.
What do Groton's other NOAA stations record?
One more NOAA station keeps 1991-2020 normals in or near Groton. This page uses Groton New London Airport; the other differs by site and elevation:
| Station | From this station | Elevation | Year | Jan low | Jul high | Precip. | Snow | Last frost |
|---|---|---|---|---|---|---|---|---|
| Groton station USC00063207 | 2 mi N | 40 ft | 52.3°F | 24°F | 81°F | 48.9 | 25 | April 8 |
Source: NOAA NCEI 1991-2020 normals for each station. Last frost: the median last spring date of 32°F.
Questions about Groton's climate
What is the coldest month in Groton?
January, with a normal high of 38°F and a normal low of 23°F. The warmest is July (80°F by day, 65°F at night).
Does it snow in Groton?
Yes. NOAA publishes no 1991-2020 snowfall normal for Groton's NOAA station; Groton's own co-op station Groton station records 25 inches of snow in a normal year.
What is the rainiest month in Groton?
September, with 3.83 in of precipitation in a normal year; the driest is February with 2.20 in.
What plant hardiness zone is Groton in?
The USDA's 2023 map puts Groton in zone 7a in ZIP code 06340. By the same method at Groton's NOAA station, the coldest night of a typical year reaches 3°F (20 years, 1991-2020): zone 7a.
How late can frost come in Groton?
In half of years the last 32°F night comes after April 16; in one year in ten it comes after April 30. Waiting until April 30 leaves about a one-in-ten chance of a later frost.
Nearby and next
- Groton in OctoberThis month day by day, its records and recent years
- Connecticut climateThe statewide normals and every place in the state
- Westerly, RI13 miles from this station, 52.5°F a year
- Norwich, CT14 miles from this station, 51.8°F a year
- Orient, NY17 miles from this station, 53.0°F a year
- Montauk, NY19 miles from this station, 53.0°F a year
- Compare two placesMonth by month, side by side
Download these normals (CSV) · JSON · How these figures are made