Photo: User:Magicpiano · CC BY-SA 4.0Groton sits near the bottom of U.S. towns for July heat
Deep winter brings January lows near 9°. In January, nights here are colder than in 95% of U.S. towns. December has warmed most since 1901–2000, part of a 1.7° rise. The frost-free window for a garden runs roughly May 15 to September 28.
A year in Groton at a glance
Each month’s typical high and low, and what it brings.
What stands out about Groton’s climate
Compared with towns across the U.S., with Groton’s place in New Hampshire beside it.
What a year in Groton feels like
Typical highs and lows by season and by month, from NOAA’s 30-year normals.
About 133 frost-free days a year
In half of years the last 32° night comes by May 15 and the first by September 28. Frost and day counts come from NOAA’s station at Benton 5 Sw, NH, 22 miles from the town’s center, 220 ft lower.
The 2023 USDA map puts Groton’s center in zone 5b: the coldest night of a typical winter, averaged over 1991–2020, reaches about −15°. Plant labels use the zone; frost dates tell you when to plant.
Freezing nights by month
Average nights at or below 32°
90° days by month
Average days at 90° or more
About 68 inches of snow a winter
Snow, measured at Plymouth, NH, falls mostly in January. Precipitation (rain plus melted snow) adds up to 48 inches a year; October is the wettest month and February the driest. Rain or snow falls on about 141 days a year.
Rain + melted snow by month
Inches of water
Snowfall by month
Inches of snow
Heating and cooling a home in Groton
97% of the work is heating, so the furnace matters far more than the air conditioner. Months averaging under 55° run from October through May.
Degree days add up how far each day’s average falls below (heating) or rises above (cooling) 65° over a year. NOAA normals at Benton 5 Sw, NH.
Living with Groton’s climate
What the numbers mean for a garden, a free afternoon and a bad-weather day.
133 frost-free days in zone 5b. The last frost comes by May 15 in half of years, so many gardeners wait a week or two past that to set out tomatoes. The first fall frost comes by Sep 28.
Months with highs of 62–84° and lows of 40° or more: May, June, July, August and September. 80 miles of trails are waiting.
Parks & trails →Of the yearly building losses FEMA expects in Groton from natural hazards, river flooding is the largest share (85%); heat waves, cold waves, winter storms and ice storms together are 5%. Normals are averages; the hazards page covers the extremes.
Natural hazards →Groton and its neighbors
Rumney has the coldest January nights next door (8°, 1° colder) and Hebron the hottest July afternoons (81°, 3° warmer). Differences under a degree are within what the 5 km grid can tell apart. Tap a town to see its climate.
Climates most like Groton’s, farther away
TownRatings’ own comparison of NOAA 1991–2020 normals, not a NOAA product: places of 5,000+ at least 150 miles away, one per state, closest on January low, July high, precipitation and snow.
| Town | Jan. low | July high | Precip. | Snow |
|---|---|---|---|---|
| Groton, NH | 9° | 79° | 48" | 68" |
| Bucksport, ME | 10° | 79° | 46" | 75" |
| Delhi, NY | 13° | 79° | 46" | 71" |
| Bradford, PA | 15° | 80° | 44" | 75" |
| Litchfield, CT | 15° | 81° | 51" | 59" |
Temperatures and rain come from NOAA’s 5 km grid, so each town gets its own value. Snow and frost-free days come from the nearest weather station, so neighbors often share them.
Warmer than it used to be
The last 30 years in Groton averaged 1.7° warmer than the 1900s. The biggest change is in December (+3.7°).
A bigger shift than in 72% of U.S. towns.
Change by month
The two periods overlap (1991–2000 is in both), which makes the gap a little smaller than it would be between separate periods.
How Groton compares
Against 12,954 U.S. towns of 2,500 or more (one per 5 km climate cell), with Groton’s place among New Hampshire’s.
Groton weather by month
Highs, lows and precipitation from NOAA’s grid at Groton’s center; snow, wet days and snow on the ground from Plymouth, NH. 1991–2020 normals.
| Month | High | Low | Rain + melt | Snow | Wet days | 30-yr range |
|---|---|---|---|---|---|---|
| January | 28° | 9° | 3.4" | 18.0" | 13 | 7° – 26° |
| February | 31° | 10° | 2.9" | 15.7" | 9 | 8° – 27° |
| March | 40° | 19° | 3.4" | 13.5" | 11 | 21° – 38° |
| April | 53° | 30° | 3.9" | 3.4" | 10 | 37° – 46° |
| May | 66° | 41° | 3.9" | 0.0" | 14 | 48° – 59° |
| June | 74° | 50° | 4.7" | 0.0" | 13 | 59° – 66° |
| July | 79° | 55° | 4.8" | 0.0" | 13 | 62° – 71° |
| August | 77° | 54° | 4.0" | 0.0" | 12 | 62° – 69° |
| September | 70° | 46° | 3.9" | 0.0" | 12 | 53° – 62° |
| October | 57° | 36° | 5.2" | 0.3" | 12 | 42° – 54° |
| November | 44° | 27° | 3.8" | 3.2" | 12 | 31° – 40° |
| December | 33° | 16° | 4.2" | 14.2" | 12 | 18° – 34° |
| Year | 54° | 33° | 47.9" | 68.3" | 141 |
How much a month can swing
A normal is an average. February swings the most: from 1991 to 2020 its average ranged from 8° to 27°. August is the most reliable, staying within 6°.
Where Groton’s numbers come from
Normals are 30-year averages, not a forecast. How TownRatings reads climate data →
- Temperatures and precipitation: NOAA’s gridded 1991–2020 normals for the 5 km cell at Groton’s center.
- Snow: Plymouth, NH.
- Frost, freezing nights, 90° and 100° days, heating and cooling: Benton 5 Sw, NH, 22 miles from the town’s center, 220 ft lower; the nearest station that passes our checks for distance, height and agreement with the grid.
- Growing zone: USDA Plant Hardiness Zone Map, 2023. USDA Agricultural Research Service and PRISM Group, Oregon State University, prism.oregonstate.edu/phzm, accessed 8 Oct 2026.
- Then and now: NOAA’s gridded normals for 1901–2000 at the same cell.
- Storms and extremes: FEMA National Risk Index (expected annual losses to buildings).
Common questions about Groton’s climate
What is the weather like in Groton?
A typical July afternoon reaches 79°, a January night drops to 9°, and about 68 inches of snow falls in a normal winter. Colder January nights than 95% of U.S. towns; cooler July afternoons than 95% of U.S. towns.
How cold does it get in Groton in winter?
January nights average 9°. About 173 nights a year reach 32° or below and 24 reach 0° or below. In the coldest January of the last 30 years the month averaged 7°.
How much snow does Groton get?
About 68 inches in a normal winter at Plymouth, NH, most of it in January.
How hot does it get in Groton?
July, with a typical high of 79° and a low of 55°. About 1 days a year reach 90° (Benton 5 Sw, NH).
When is the first and last frost in Groton?
In half of years the last spring frost (32°) comes by May 15 and the first fall frost by September 28, about 133 frost-free days, at Benton 5 Sw, NH.
What growing zone is Groton in?
Zone 5b on the 2023 USDA Plant Hardiness Zone Map: the coldest night of a typical winter reaches about −15°.
What is the best time of year to visit Groton?
By one simple rule (highs of 62–84° and lows of 40° or more), May, June, July, August and September. The rule is ours, not NOAA’s; the month table has the numbers to judge by.
Is Groton getting warmer?
Yes: 1991–2020 averaged 1.7° warmer than 1901–2000 on NOAA’s grid. A bigger shift than 72% of U.S. towns.
Neighbors talk weather
Gardens, snow, and the best days of the year in Groton.
Source: NOAA NCEI U.S. Climate Normals, 1991–2020 and 1901–2000; USDA/PRISM 2023 hardiness zones; FEMA National Risk Index. Today’s forecast: National Weather Service.