Groton, CT Climate: Temperature & Rain by Month
Temperature and precipitation from NOAA NCEI 1991–2020 normals →, plus PlainClimate's derived comfort score
30-year climate normals (1991-2020) from Groton's primary NOAA station, GROTON.
The climate verdict for Groton
Water is the standout signal in Groton, Connecticut: 48.9 inches of precipitation in a normal year. Against that wet profile, NOAA records an annual average of 52°F. Its climate comfort score of 63/100 (good) lands mid-pack nationally, exceeding 46% of station-mapped location scores.
- 52°F
- average temperature, NOAA 1991-2020 normal
- 63/100
- comfort score, above 46% of station-mapped location scores
- 48.9"
- annual precipitation · 25" snow
- 208 days
- growing season, frost-free days
Groton: NOAA 1991-2020 normals describe a typical year, not a forecast. Method: /methodology.
Normals record plate
Sheet USC00063207 · Groton, CT 52°F mean · 48.9" precip
TEMP-COOL · RANK-MID · PHOTO-FINISH · PRCP-MID · SWING-MID · COMF-MID · LOAD-HEAT · STN-1 · BOOK-FULL
- TEMP-COOL 52°F
- RANK-MID #3,431
- PHOTO-FINISH ≈ Olive Hill
- PRCP-MID 48.9"
- SWING-MID 42°F
- COMF-MID 63/100
- LOAD-HEAT 5,333 HDD
- STN-1 USC00063207
- BOOK-FULL 6/6 fields
Nearest mean-temperature peer: Olive Hill, KY (+ 0 °F mean)
Instrument codes from this station's NOAA 1991–2020 normals, mean temperature, corpus warmth rank, photo-finish peer station, precipitation band, seasonal swing, comfort composite, degree-day load, and field book, not a livability rating.
Mean-temperature neighbourhood
Nationwide NOAA normal poles and nearest peers, not a reprint of every CT station list.
- Groton (this station) 52°F
- Cold Grants, NM 52°F
- Hot Shirley Brookha…, NY 52°F
- Near Olive Hill, KY 52°F
- Near Spencer, WV 52°F
Climate Living Index · Groton
Groton: 59/100 · grade C
Groton publishes 5 of 6 Living Index dimensions (NOAA annual/seasonal normals · NOAA daily multivariate normals); 1 missing weight rescale to 100.
PlainClimate-derived for Groton, not an official NOAA rating. Rankings still use Comfort Score 63/100 (separate formula). Breakpoints and limits.
| Dimension | Station value | Score |
|---|---|---|
| Normal heat + freeze calendar | 104 calendar days | 74/100 · B |
| Frost-free season | 208 days/year | 70/100 · B |
| Precipitation balance | 48.9 in · 13.9 from 35 in | 51/100 · D |
| Annual temperature balance | 52.3°F · 15.2° from 67.5°F | 50/100 · D |
| Snowfall burden | 24.5 inches/year | 44/100 · D |
Groton · 2026-08-04 · NOAA NCEI Climate Normals · method · Comfort Score method.
Groton is a continental Köppen climate: Dfa
Coldest-month mean 31.3°F and warmest-month mean 73.4°F place this station in continental, no dry season, hot summer climates (Dfa). Class Dfa is the Peel et al. (2007) label for this station's monthly mean temperature and precipitation normals: continental, specifically continental, no dry season, hot summer.
- Köppen code
- Dfa
- Group
- Continental
- Warmest month
- 73.4°F
- Coldest month
- 31.3°F
Source: official public datasets monthly normals (1991–2020) at the city’s primary station. This is a station classification, not a mapped regional consensus.
National standing · heating-led station
Where Groton sits across the climate record
Three NOAA fields for Groton's primary station, temperature, precipitation, and seasonal swing, are ranked against every station-mapped normal that carries the same field.
- Annual temperature
- 50th percentile warmth
- Mid-pack annual mean versus 6,861 station normals.
- Annual precipitation
- Top 22% wettest
- Groton's annual total ranks in the wetter third of 6,352 measured normals.
- Seasonal temperature swing
- 45th percentile swing
- Typical seasonal amplitude versus 6,861 complete station-years.
How Groton compares across U.S. station-mapped locations
Groton's comfort score vs. all station-mapped locations
PlainClimate composite comfort index (1–100), NOAA 1991–2020 normals
63 46th percentile score exceeds 46% of 6,189 station-mapped location scores
- 0–10: 0 station-mapped locations (0%). Below this entry.
- 10–20: 0 station-mapped locations (0%). Below this entry.
- 20–30: 96 station-mapped locations (2%). Below this entry.
- 30–40: 280 station-mapped locations (5%). Below this entry.
- 40–50: 1,113 station-mapped locations (18%). Below this entry.
- 50–60: 1,329 station-mapped locations (21%). Below this entry.
- 60–70: 1,236 station-mapped locations (20%). This entry sits in this band.
- 70–80: 650 station-mapped locations (11%). Above this entry.
- 80–90: 921 station-mapped locations (15%). Above this entry.
- 90–100: 564 station-mapped locations (9%). Above this entry.
Source NOAA U.S. Climate Normals, PlainClimate comfort index · 1991–2020
Groton's measured station temperature trend
MethodologyAcross 112 complete annual observations from 1872 to 2024, GROTON warmed at a fitted rate of 0.18°C per decade. The line shows the fitted change relative to its first year, not raw year-to-year temperatures or a forecast.
- Groton primary station fitted change +0.18 °C/decade
Monthly Temperatures
Average daily high and low temperatures by month
| Month | Avg High | Avg Low | Mean | Precip | Snow | Freeze Days | 90°F+ Days |
|---|---|---|---|---|---|---|---|
| January | 39°F (4°C) | 24°F (-5°C) | 31°F (0°C) | 3.9" | 5.8" | 25.5 | 0.0 |
| February | 41°F (5°C) | 25°F (-4°C) | 33°F (0°C) | 3.4" | 8.3" | 22.6 | 0.0 |
| March | 47°F (8°C) | 32°F (0°C) | 40°F (4°C) | 4.9" | 3.9" | 17.7 | 0.0 |
| April | 57°F (14°C) | 41°F (5°C) | 49°F (9°C) | 4.4" | 0.8" | 4.1 | 0.0 |
| May | 66°F (19°C) | 50°F (10°C) | 58°F (15°C) | 3.7" | 0.0" | 0.0 | 0.0 |
| June | 75°F (24°C) | 59°F (15°C) | 67°F (20°C) | 3.9" | 0.0" | 0.0 | 0.4 |
| July | 81°F (27°C) | 66°F (19°C) | 73°F (23°C) | 3.4" | 0.0" | 0.0 | 1.8 |
| August | 80°F (27°C) | 65°F (18°C) | 73°F (23°C) | 4.2" | 0.0" | 0.0 | 0.7 |
| September | 74°F (23°C) | 58°F (14°C) | 66°F (19°C) | 4.3" | 0.0" | 0.0 | 0.1 |
| October | 63°F (17°C) | 47°F (8°C) | 55°F (13°C) | 4.4" | 0.0" | 1.1 | 0.0 |
| November | 53°F (12°C) | 38°F (3°C) | 46°F (8°C) | 3.8" | 0.5" | 9.5 | 0.0 |
| December | 44°F (7°C) | 30°F (-1°C) | 37°F (3°C) | 4.6" | 5.2" | 20.9 | 0.0 |
The year, day by day
Summer here tops out rather than builds: the warmest normal high is 81°F around July 17, short of 90°F on every date, while 104 dates carry a normal low at or below freezing, the coldest 23°F near January 24.
The freezing stretch
The normal low stays at or below 32°F into March 18, then returns to freezing around December 6, covering 104 dates in all.
Derived from the normal daily minimum. This is a different measure from the 50%-probability frost dates shown elsewhere on this page, which come from NOAA’s frost product.
Where the wet dates fall
The likeliest wet date is December 14, when 40% of years recorded at least a hundredth of an inch. The driest is August 25 at 30%. Summed across the calendar, that is about 128 wet dates a year.
The widest day
May 12 carries the biggest normal gap between afternoon and dawn, 17°F between the normal high and the normal low.
Look up any date
Any date's 1991–2020 normal for Groton.
Where Groton Stands Nationally
Among the steadiest day-night climates ranked: even the widest normal daily swing holds to roughly 17°F.
Groton earns one nationally notable standing (outer quintile) against 6,860 NOAA 1991–2020 normals stations, middle-of-the-pack metrics stay silent here.
Monthly Precipitation
Average monthly rainfall and snowfall
Snow: 5.8"
11.4 days with precipitation
Snow: 8.3"
9.7 days with precipitation
Snow: 3.9"
11.5 days with precipitation
Snow: 0.8"
11.6 days with precipitation
11.9 days with precipitation
9.5 days with precipitation
9.7 days with precipitation
9.3 days with precipitation
10.2 days with precipitation
10.4 days with precipitation
Snow: 0.5"
10.0 days with precipitation
Snow: 5.2"
12.4 days with precipitation
Groton spreads its precipitation across the year
Neither half of the year dominates here: June through August take 24% of the annual total and December through February 24%, with neither reaching the 35% that would mark a distinct wet season. Groton has no dry season to plan around, though it does carry a 42.1°F seasonal spread.
The gap between the wettest and driest month still matters: March averages 4.9" and July 3.4". The three wettest months together take 28% of the year, against the 25% a perfectly flat distribution would give them.
Shares are computed from this station's own 1991-2020 monthly precipitation normals. "Spread across the year" means neither the June-August nor the December-February share reaches 35%; it describes an average year, not the variability of any single one.
When it rains in Groton, it arrives in quantity
48.9" of precipitation falls across only about 128 wet days here, averaging 0.38 inches each. Fewer days carry more water: the year's total is delivered in comparatively heavy events rather than persistent damp.
- Days with measurable precipitation
- about 128 a year, 35% of all days
- Average depth per wet day
- 0.38 inches
- Most wet days
- December, about 12
- Fewest wet days
- August, about 9
A wet day is one recording at least 0.01 inches. These are 1991-2020 normals: they describe an average year, and a per-day average is not a forecast of any individual storm.
Winter brings real snow to Groton
Groton averages 24.5 inches of snowfall a year, with February the snowiest month on the normals, spread across roughly 10 days that record measurable snow. That is depth accumulating on the ground, which is why it can exceed the annual precipitation figure: precipitation counts the liquid the snow melts down to, and fresh snow is mostly air.
- Annual snowfall: 24.5 inches of depth.
- Days recording measurable snow: about 10 a year.
- At a rough ten-to-one melt ratio, snow accounts for on the order of 5% of the year's precipitation.
NOAA 1991-2020 normals. The ten-to-one ratio is a convention, not a measurement: real ratios vary with temperature, so treat the share as an order of magnitude rather than an exact split.
Frost Dates & Growing Season
First Fall Freeze
November 2
50% probability date
Last Spring Freeze
April 8
50% probability date
Growing Season
208 days
Heating & Cooling Degree Days
Annual totals indicate energy demand for heating and cooling
Heating Degree Days
5,333
Higher = more heating needed
Cooling Degree Days
721
Higher = more cooling needed
Warmest Month
July
Coldest Month
January
Nationwide similar cities
Other rankable U.S. places outside CT closest to Groton on two NOAA annual-normal axes (mean temperature and annual precipitation). Chip rows use distinct link sets.
Closest by average temperature
Nearest out-of-state peers by annual mean temperature (52°F here).
- Albany, MO 52°F · 0.0°F off
- Avondale, PA 52°F · 0.0°F off
- Benkelman, NE 52°F · 0.0°F off
- Bremerton, WA 52°F · 0.0°F off
Closest by annual precipitation
Nearest out-of-state peers by annual precipitation (48.9" here), excluding temperature-peer places.
- Sand Point, AK 48.9" · 0.0" off
- Calico Rock, AR 48.9" · 0.0" off
- Paris, TX 48.9" · 0.0" off
- Rumford, ME 48.9" · 0.0" off
Snow and freeze rhythm
When cold and snow define Groton
heating led · wet · mid swing
Groton's energy balance leans toward cold weather: 5,333 annual heating degree days against 721 for cooling. Its 42.1°F seasonal range still makes the monthly rows more useful than the annual average alone.
Groton's frost-free season lasts about 208 days, a middle-length window whose endpoints matter more than the annual average. It describes freeze probability, not year-specific planting conditions.
-
1. Groton coldest normal
January
The monthly mean of 31°F (0°C) sits near freezing, so cold nights and above-freezing afternoons share the same month.
-
2. Groton typical freeze period
January through December
The station reports average freezing days from January through December.
-
3. Groton snow peak
February
Groton averages 24.5 inches of snow a year, with February the snowiest month on the normals.
Questions about Groton's climate
How much snow does Groton get? ▼
How cold does Groton get in winter? ▼
How much energy does heating and cooling require in Groton? ▼
Data Sources
Data source: NOAA U.S. Climate Normals v1.0.1 (1991-2020). All figures on this page are from Groton's primary station: GROTON (USC00063207). For informational purposes only.
Place identity: U.S. Census Bureau 2024 Gazetteer places. The 2024 Census Gazetteer identifies the exact name-and-state match as an incorporated place (GEOID 0934180). Match rule for Groton: exact normalized name + state only, no fuzzy expansion, so nearby differently spelled facilities stay unmatched.
On this page every temperature, precipitation, and derived score for Groton comes from its primary NOAA station record. No figure on this page is typed in by an editor - each value is rendered from NOAA 1991-2020 U.S. Climate Normals. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error. Data current as of 1991–2020 normals.