Lane House · Photo: Smallbones · CC0Summers, winters and rain in Mercersburg all run close to those of most U.S. towns
July afternoons average 87°. Summer afternoons here are warmer than in 62% of U.S. towns. Decade by decade the climate has edged up, 1.5° above 1901–2000. Homes need heating from November to March, the months averaging under 50°.
A year in Mercersburg at a glance
Each month’s typical high and low, and what it brings.
What stands out about Mercersburg’s climate
Compared with towns across the U.S., with Mercersburg’s place in Pennsylvania beside it.
What a year in Mercersburg feels like
Typical highs and lows by season and by month, from NOAA’s 30-year normals.
About 209 frost-free days a year
In half of years the last 32° night comes by April 7 and the first by November 4. Frost and day counts come from NOAA’s station at Hagerstown Washington Co Airport, 13 miles from the town’s center, 130 ft higher.
The 2023 USDA map puts Mercersburg’s center in zone 7a: the coldest night of a typical winter, averaged over 1991–2020, reaches about 4°. 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 31 inches of snow a winter
Snow, measured at Chambersburg 1 Ese, PA, falls mostly in January. Precipitation (rain plus melted snow) adds up to 40 inches a year; May is the wettest month and February the driest. Rain or snow falls on about 117 days a year.
Rain + melted snow by month
Inches of water
Snowfall by month
Inches of snow
Heating and cooling a home in Mercersburg
79% of the work is heating. 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 Hagerstown Washington Co Airport.
Living with Mercersburg’s climate
What the numbers mean for a garden, a free afternoon and a bad-weather day.
209 frost-free days in zone 7a. The last frost comes by Apr 7 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 4.
Months with highs of 62–84° and lows of 40° or more: May, June, September and October. 0.0 miles of trails are waiting.
Parks & trails →Of the yearly building losses FEMA expects in Mercersburg from natural hazards, river flooding is the largest share (70%); heat waves, cold waves, winter storms and ice storms together are 4%. Normals are averages; the hazards page covers the extremes.
Natural hazards →Mercersburg and its neighbors
Every town next door is within a degree of Mercersburg in January and July, closer than the 5 km grid can tell apart. Tap a town to see its climate.
Climates most like Mercersburg’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 |
|---|---|---|---|---|
| Mercersburg, PA | 22° | 87° | 40" | 31" |
| Obetz, OH | 22° | 86° | 41" | 28" |
| Chatham, IL | 20° | 86° | 39" | 22" |
| Fort Wright, KY | 24° | 87° | 45" | 23" |
| Excelsior Springs, MO | 19° | 87° | 40" | 19" |
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 Mercersburg averaged 1.5° warmer than the 1900s. The biggest change is in December (+2.6°).
A bigger shift than in 62% 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 Mercersburg compares
Against 12,954 U.S. towns of 2,500 or more (one per 5 km climate cell), with Mercersburg’s place among Pennsylvania’s.
Mercersburg weather by month
Highs, lows and precipitation from NOAA’s grid at Mercersburg’s center; snow, wet days and snow on the ground from Chambersburg 1 Ese, PA. 1991–2020 normals.
| Month | High | Low | Rain + melt | Snow | Wet days | Snow on ground | 30-yr range |
|---|---|---|---|---|---|---|---|
| January | 40° | 22° | 2.6" | 10.0" | 10 | 11 | 22° – 39° |
| February | 44° | 23° | 2.1" | 8.0" | 9 | 11 | 22° – 41° |
| March | 53° | 30° | 3.3" | 6.0" | 10 | 5 | 36° – 51° |
| April | 65° | 40° | 3.6" | 0.3" | 11 | 0 | 48° – 58° |
| May | 74° | 49° | 4.1" | 0.0" | 12 | 0 | 57° – 68° |
| June | 83° | 59° | 3.8" | 0.0" | 11 | 0 | 67° – 74° |
| July | 87° | 63° | 3.8" | 0.0" | 10 | 0 | 70° – 78° |
| August | 85° | 61° | 3.5" | 0.0" | 9 | 0 | 69° – 77° |
| September | 78° | 54° | 4.0" | 0.0" | 9 | 0 | 63° – 70° |
| October | 67° | 42° | 3.2" | 0.0" | 9 | 0 | 51° – 61° |
| November | 54° | 33° | 3.1" | 1.0" | 8 | 0 | 37° – 49° |
| December | 44° | 26° | 3.3" | 5.5" | 9 | 5 | 25° – 44° |
| Year | 64° | 42° | 40.4" | 30.8" | 117 | 31 |
How much a month can swing
A normal is an average. February swings the most: from 1991 to 2020 its average ranged from 22° to 41°. September is the most reliable, staying within 6°.
Where Mercersburg’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 Mercersburg’s center.
- Snow: Chambersburg 1 Ese, PA.
- Frost, freezing nights, 90° and 100° days, heating and cooling: Hagerstown Washington Co Airport, 13 miles from the town’s center, 130 ft higher; 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 Mercersburg’s climate
What is the weather like in Mercersburg?
A typical July afternoon reaches 87°, a January night drops to 22°, and about 31 inches of snow falls in a normal winter. Milder January nights than 51% of U.S. towns; hotter July afternoons than 62% of U.S. towns.
How cold does it get in Mercersburg in winter?
January nights average 22°. About 93 nights a year reach 32° or below. In the coldest January of the last 30 years the month averaged 22°.
How much snow does Mercersburg get?
About 31 inches in a normal winter at Chambersburg 1 Ese, PA, most of it in January, with snow on the ground about 31 days a year.
How hot does it get in Mercersburg?
July, with a typical high of 87° and a low of 63°. About 24 days a year reach 90° (Hagerstown Washington Co Airport).
When is the first and last frost in Mercersburg?
In half of years the last spring frost (32°) comes by April 7 and the first fall frost by November 4, about 209 frost-free days, at Hagerstown Washington Co Airport.
What growing zone is Mercersburg in?
Zone 7a on the 2023 USDA Plant Hardiness Zone Map: the coldest night of a typical winter reaches about 4°.
What is the best time of year to visit Mercersburg?
By one simple rule (highs of 62–84° and lows of 40° or more), May, June, September and October. The rule is ours, not NOAA’s; the month table has the numbers to judge by.
Is Mercersburg getting warmer?
Yes: 1991–2020 averaged 1.5° warmer than 1901–2000 on NOAA’s grid. A bigger shift than 62% of U.S. towns.
Neighbors talk weather
Gardens, snow, and the best days of the year in Mercersburg.
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.