South Dennis has some of the coolest summers among U.S. towns
Nights in January average 24°. Seasons differ by 55°, from the coldest nights to the warmest afternoons. Its January nights stay gentler than in 61% of U.S. towns. Homes need heating from November to April, the months averaging under 50°.
A year in South Dennis at a glance
Each month’s typical high and low, and what it brings.
What stands out about South Dennis’ climate
Compared with towns across the U.S., with South Dennis’ place in Massachusetts beside it.
What a year in South Dennis feels like
Typical highs and lows by season and by month, from NOAA’s 30-year normals.
About 204 frost-free days a year
In half of years the last 32° night comes by April 13 and the first by November 3. Frost and day counts come from NOAA’s station at W Harwich, MA, 3 miles from the town’s center, at about the same height.
The 2023 USDA map puts South Dennis’ center in zone 7a: the coldest night of a typical winter, averaged over 1991–2020, reaches about 5°. Plant labels use the zone; frost dates tell you when to plant.
Freezing nights by month
Average nights at or below 32°
About 22 inches of snow a winter
Snow, measured at Hyannis, MA, falls mostly in January. Precipitation (rain plus melted snow) adds up to 45 inches a year; December is the wettest month and July the driest. Rain or snow falls on about 113 days a year.
Rain + melted snow by month
Inches of water
Snowfall by month
Inches of snow
Heating and cooling a home in South Dennis
93% of the work is heating, so the furnace matters far more than the air conditioner. Months averaging under 55° run from October through April.
Degree days add up how far each day’s average falls below (heating) or rises above (cooling) 65° over a year. NOAA normals at W Harwich, MA.
Living with South Dennis’ climate
What the numbers mean for a garden, a free afternoon and a bad-weather day.
204 frost-free days in zone 7a. The last frost comes by Apr 13 in half of years, so many gardeners wait a week or two past that to set out tomatoes. The first fall frost comes by Nov 3.
Months with highs of 62–84° and lows of 40° or more: May, June, July, August, September and October. 19 miles of trails are waiting.
Parks & trails →Of the yearly building losses FEMA expects in South Dennis from natural hazards, river flooding is the largest share (64%); heat waves, cold waves, winter storms and ice storms together are 1%. Normals are averages; the hazards page covers the extremes.
Natural hazards →South Dennis and its neighbors
Every town next door is within a degree of South Dennis in January and July, closer than the 5 km grid can tell apart. Tap a town to see its climate.
Climates most like South Dennis’, 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 |
|---|---|---|---|---|
| South Dennis, MA | 24° | 79° | 45" | 22" |
| Princeton, WV | 23° | 82° | 41" | 24" |
| Galax, VA | 25° | 82° | 48" | 17" |
| Center Moriches, NY | 24° | 82° | 46" | 32" |
| Atlantic City, NJ | 28° | 83° | 45" | 17" |
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 South Dennis averaged 2.0° warmer than the 1900s. The biggest change is in December (+3.5°).
A bigger shift than in 91% 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 South Dennis compares
Against 12,954 U.S. towns of 2,500 or more (one per 5 km climate cell), with South Dennis’ place among Massachusetts’.
South Dennis weather by month
Highs, lows and precipitation from NOAA’s grid at South Dennis’ center; snow, wet days and snow on the ground from Hyannis, MA. 1991–2020 normals.
| Month | High | Low | Rain + melt | Snow | Wet days | Snow on ground | 30-yr range |
|---|---|---|---|---|---|---|---|
| January | 39° | 24° | 3.9" | 9.5" | 10 | 5 | 23° – 38° |
| February | 40° | 25° | 3.3" | 6.3" | 10 | 7 | 23° – 38° |
| March | 45° | 30° | 4.4" | 3.6" | 10 | 3 | 32° – 43° |
| April | 54° | 38° | 4.1" | 0.0" | 11 | 0 | 42° – 49° |
| May | 63° | 47° | 3.2" | 0.0" | 10 | 0 | 50° – 59° |
| June | 72° | 56° | 3.3" | 0.0" | 9 | 0 | 60° – 68° |
| July | 79° | 63° | 2.5" | 0.0" | 7 | 0 | 67° – 75° |
| August | 78° | 62° | 3.4" | 0.0" | 8 | 0 | 67° – 74° |
| September | 72° | 56° | 3.8" | 0.0" | 8 | 0 | 61° – 67° |
| October | 62° | 46° | 4.4" | 0.0" | 10 | 0 | 51° – 60° |
| November | 53° | 38° | 4.0" | 0.0" | 10 | 0 | 41° – 49° |
| December | 44° | 30° | 4.7" | 2.1" | 12 | 2 | 31° – 46° |
| Year | 58° | 43° | 44.9" | 21.5" | 113 | 16 |
How much a month can swing
A normal is an average. January swings the most: from 1991 to 2020 its average ranged from 23° to 38°. September is the most reliable, staying within 7°.
Where South Dennis’ 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 South Dennis’ center.
- Snow: Hyannis, MA.
- Frost, freezing nights, 90° and 100° days, heating and cooling: W Harwich, MA, 3 miles from the town’s center, at about the same height; 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 South Dennis’ climate
What is the weather like in South Dennis?
A typical July afternoon reaches 79°, a January night drops to 24°, and about 22 inches of snow falls in a normal winter. Milder January nights than 61% of U.S. towns; cooler July afternoons than 95% of U.S. towns.
How cold does it get in South Dennis in winter?
January nights average 24°. About 94 nights a year reach 32° or below. In the coldest January of the last 30 years the month averaged 23°.
How much snow does South Dennis get?
About 22 inches in a normal winter at Hyannis, MA, most of it in January, with snow on the ground about 16 days a year.
How hot does it get in South Dennis?
July, with a typical high of 79°. 90° days are rare: none in a normal year at W Harwich, MA.
When is the first and last frost in South Dennis?
In half of years the last spring frost (32°) comes by April 13 and the first fall frost by November 3, about 204 frost-free days, at W Harwich, MA.
What growing zone is South Dennis in?
Zone 7a on the 2023 USDA Plant Hardiness Zone Map: the coldest night of a typical winter reaches about 5°.
What is the best time of year to visit South Dennis?
By one simple rule (highs of 62–84° and lows of 40° or more), May, June, July, August, September and October. The rule is ours, not NOAA’s; the month table has the numbers to judge by.
Is South Dennis getting warmer?
Yes: 1991–2020 averaged 2.0° warmer than 1901–2000 on NOAA’s grid. A bigger shift than 91% of U.S. towns.
Neighbors talk weather
Gardens, snow, and the best days of the year in South Dennis.
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.