Signer's House and Matthew Thornton Cemetery · Photo: Jane023 · CC BY-SA 4.0Winter nights in Merrimack are colder than in 86% of U.S. towns
Expect July afternoons of about 84°. By July afternoons alone, it runs cooler than 62% of U.S. towns. Decade by decade the climate has edged up, 1.9° above 1901–2000. The frost-free window for a garden runs roughly April 30 to October 12.
A year in Merrimack at a glance
Each month’s typical high and low, and what it brings.
What stands out about Merrimack’s climate
Compared with towns across the U.S., with Merrimack’s place in New Hampshire beside it.
What a year in Merrimack feels like
Typical highs and lows by season and by month, from NOAA’s 30-year normals.
About 165 frost-free days a year
In half of years the last 32° night comes by April 30 and the first by October 12. Frost and day counts come from NOAA’s station at Nashua 2 Nnw, NH, 5 miles from the town’s center, at about the same height.
The 2023 USDA map puts Merrimack’s center in zone 6a: the coldest night of a typical winter, averaged over 1991–2020, reaches about −8°. 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 53 inches of snow a winter
Snow, measured at Nashua 2 Nnw, NH, is heaviest from January through February, about 15 inches a month. Precipitation (rain plus melted snow) adds up to 45 inches a year; October is the wettest month and February the driest. Rain or snow falls on about 120 days a year.
Rain + melted snow by month
Inches of water
Snowfall by month
Inches of snow
Heating and cooling a home in Merrimack
91% 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 Nashua 2 Nnw, NH.
Living with Merrimack’s climate
What the numbers mean for a garden, a free afternoon and a bad-weather day.
165 frost-free days in zone 6a. The last frost comes by Apr 30 in half of years, so many gardeners wait a week or two past that to set out tomatoes. The first fall frost comes by Oct 12.
Months with highs of 62–84° and lows of 40° or more: May, June, July, August and September. 57 miles of trails are waiting.
Parks & trails →Of the yearly building losses FEMA expects in Merrimack from natural hazards, river flooding is the largest share (68%); heat waves, cold waves, winter storms and ice storms together are 5%. Normals are averages; the hazards page covers the extremes.
Natural hazards →Merrimack and its neighbors
Every town next door is within a degree of Merrimack in January and July, closer than the 5 km grid can tell apart. Tap a town to see its climate.
Climates most like Merrimack’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 |
|---|---|---|---|---|
| Merrimack, NH | 15° | 84° | 45" | 53" |
| New Paltz, NY | 18° | 84° | 46" | 59" |
| Franklin, PA | 19° | 83° | 45" | 54" |
| Ontario, OH | 17° | 82° | 42" | 49" |
| Plymouth, IN | 17° | 83° | 40" | 55" |
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 Merrimack averaged 1.9° warmer than the 1900s. The biggest change is in December (+3.6°).
A bigger shift than in 83% 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 Merrimack compares
Against 12,954 U.S. towns of 2,500 or more (one per 5 km climate cell), with Merrimack’s place among New Hampshire’s.
Merrimack weather by month
Highs, lows and precipitation from NOAA’s grid at Merrimack’s center; snow, wet days and snow on the ground from Nashua 2 Nnw, NH. 1991–2020 normals.
| Month | High | Low | Rain + melt | Snow | Wet days | 30-yr range |
|---|---|---|---|---|---|---|
| January | 34° | 15° | 3.1" | 14.7" | 9 | 14° – 32° |
| February | 37° | 16° | 3.0" | 14.5" | 8 | 13° – 33° |
| March | 45° | 24° | 3.9" | 10.1" | 9 | 28° – 44° |
| April | 59° | 35° | 3.9" | 0.7" | 11 | 43° – 51° |
| May | 70° | 45° | 3.6" | 0.0" | 12 | 52° – 63° |
| June | 79° | 55° | 4.1" | 0.0" | 11 | 63° – 70° |
| July | 84° | 60° | 3.7" | 0.0" | 10 | 67° – 75° |
| August | 82° | 59° | 3.7" | 0.0" | 9 | 67° – 74° |
| September | 74° | 51° | 4.0" | 0.0" | 9 | 59° – 67° |
| October | 62° | 39° | 4.6" | 0.0" | 11 | 46° – 58° |
| November | 50° | 30° | 3.7" | 1.7" | 10 | 35° – 45° |
| December | 39° | 21° | 4.1" | 11.2" | 10 | 24° – 40° |
| Year | 59° | 37° | 45.4" | 52.9" | 120 |
How much a month can swing
A normal is an average. February swings the most: from 1991 to 2020 its average ranged from 13° to 33°. August is the most reliable, staying within 6°.
Where Merrimack’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 Merrimack’s center.
- Snow: Nashua 2 Nnw, NH.
- Frost, freezing nights, 90° and 100° days, heating and cooling: Nashua 2 Nnw, NH, 5 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 Merrimack’s climate
What is the weather like in Merrimack?
A typical July afternoon reaches 84°, a January night drops to 15°, and about 53 inches of snow falls in a normal winter. Colder January nights than 86% of U.S. towns; cooler July afternoons than 62% of U.S. towns.
How cold does it get in Merrimack in winter?
January nights average 15°. About 155 nights a year reach 32° or below and 8 reach 0° or below. In the coldest January of the last 30 years the month averaged 14°.
How much snow does Merrimack get?
About 53 inches in a normal winter at Nashua 2 Nnw, NH, heaviest from January through February, about 15 inches a month.
How hot does it get in Merrimack?
July, with a typical high of 84° and a low of 60°. About 15 days a year reach 90° (Nashua 2 Nnw, NH).
When is the first and last frost in Merrimack?
In half of years the last spring frost (32°) comes by April 30 and the first fall frost by October 12, about 165 frost-free days, at Nashua 2 Nnw, NH.
What growing zone is Merrimack in?
Zone 6a on the 2023 USDA Plant Hardiness Zone Map: the coldest night of a typical winter reaches about −8°.
What is the best time of year to visit Merrimack?
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 Merrimack getting warmer?
Yes: 1991–2020 averaged 1.9° warmer than 1901–2000 on NOAA’s grid. A bigger shift than 83% of U.S. towns.
Neighbors talk weather
Gardens, snow, and the best days of the year in Merrimack.
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.