South Mountain, Pennsylvania climate: Climate normals at a NOAA weather station
South Mountain's normal year runs from 21°F January nights to 81°F July afternoons, with 48.6 inches of precipitation and 33 inches of snow a year. (NOAA 1991-2020 normals)
In metric: a yearly mean of 10.0°C, January lows of −6°C, July highs of 27°C, 1,233 mm of precipitation a year.
- NOAA stationSouth Mountain
- Station IDUSC00368308
- Location39.85°N 77.50°W
- Elevation1,520 ft (463 m)
On October 23, the normal high in South Mountain is 59°F and the normal low 40°F, and the chance of measurable rain or snow is 30%.
Normals describe a typical year at the station, not a forecast. The National Weather Service forecast for South Mountain.
- Jan 36° 21°
- Feb 39° 21°
- Mar 47° 28°
- Apr 59° 38°
- May 69° 49°
- Jun 77° 58°
- Jul 81° 62°
- Aug 79° 60°
- Sep 73° 53°
- Oct 61° 43°
- Nov 50° 33°
- Dec 40° 26°
Each month: normal high (large) and low, °F. Fill: the month's normal mean, colder blue to hotter red.
What is the weather like at South Mountain each month?
July is the warmest month, with normal highs of 81°F; January the coldest, with normal lows of 21°F. The most precipitation falls in September (5.07 in), the least in February (2.91 in).
| Month | High | Low | Mean | Precip. | Snow | Wet days | 90°F days | Freezing nights | Daylight |
|---|---|---|---|---|---|---|---|---|---|
| January | 36°F | 21°F | 28.1°F | 3.69 | 10.6 | 10 | <1 | 27 | 9 h 40 min |
| February | 39°F | 21°F | 30.1°F | 2.91 | 9.5 | 9 | <1 | 25 | 10 h 40 min |
| March | 47°F | 28°F | 37.1°F | 4.38 | 6.5 | 11 | <1 | 22 | 11 h 50 min |
| April | 59°F | 38°F | 48.8°F | 4.18 | 0.6 | 12 | <1 | 9 | 13 h 10 min |
| May | 69°F | 49°F | 58.7°F | 4.69 | 0.0 | 13 | <1 | 1 | 14 h 20 min |
| June | 77°F | 58°F | 67.3°F | 4.64 | 0.0 | 12 | <1 | <1 | 15 h |
| July | 81°F | 62°F | 71.1°F | 3.94 | 0.0 | 11 | 2 | <1 | 14 h 40 min |
| August | 79°F | 60°F | 69.7°F | 3.85 | 0.0 | 11 | 1 | <1 | 13 h 50 min |
| September | 73°F | 53°F | 63.0°F | 5.07 | 0.0 | 10 | <1 | <1 | 12 h 30 min |
| October | 61°F | 43°F | 52.0°F | 4.09 | 0.0 | 10 | <1 | 4 | 11 h 10 min |
| November | 50°F | 33°F | 41.6°F | 3.30 | 0.6 | 8 | <1 | 16 | 10 h |
| December | 40°F | 26°F | 32.8°F | 3.82 | 5.2 | 10 | <1 | 25 | 9 h 20 min |
| Year (annual) | 59°F | 41°F | 50.0°F | 48.56 | 33.0 | 127 | 3 | 129 |
The same normals in °C and millimetres
| Month | High | Low | Mean | Precip. | Snow |
|---|---|---|---|---|---|
| January | 2°C | −6°C | −2.2°C | 94 mm | 27 cm |
| February | 4°C | −6°C | −1.1°C | 74 mm | 24 cm |
| March | 8°C | −2°C | 2.8°C | 111 mm | 17 cm |
| April | 15°C | 3°C | 9.3°C | 106 mm | 2 cm |
| May | 21°C | 9°C | 14.8°C | 119 mm | 0 cm |
| June | 25°C | 14°C | 19.6°C | 118 mm | 0 cm |
| July | 27°C | 17°C | 21.7°C | 100 mm | 0 cm |
| August | 26°C | 16°C | 20.9°C | 98 mm | 0 cm |
| September | 23°C | 12°C | 17.2°C | 129 mm | 0 cm |
| October | 16°C | 6°C | 11.1°C | 104 mm | 0 cm |
| November | 10°C | 0°C | 5.3°C | 84 mm | 2 cm |
| December | 4°C | −4°C | 0.4°C | 97 mm | 13 cm |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00368308; annual normals. Wet days: 0.01 inch or more; 90°F days and freezing nights: NOAA's day counts. Daylight: sunrise to sunset on the 15th, computed from the latitude.
Which months are mildest at South Mountain?
Normal highs sit between 65°F and 85°F in May, June, July, August and September. Of those, September has the fewest days with rain (10).
That is a measurement, not a recommendation: it counts the months whose normal afternoon high sits between 65°F and 85°F, where a light layer is enough by day.
Source: NOAA NCEI 1991-2020 monthly normals, station USC00368308.
When is the last frost at South Mountain?
In South Mountain, the last spring frost (32°F) comes after April 27 in half of years and after May 14 in one year in ten; the first autumn frost comes before October 20 in half of years and before October 6 in one year in ten.
Frost-free in half of yearsFrost in 1 to 9 years out of 10Frost most years
- Last spring frost, half of years after
- April 271 year in 10 after May 14; 9 in 10 after April 13
- First autumn frost, half of years before
- October 201 year in 10 before October 6; 9 in 10 before November 2
NOAA puts the median frost-free season at 177 days, and the season without a hard freeze (28°F) at 202 days.
A hard freeze (28°F) comes after April 13 in half of springs and before November 1 in half of autumns.
The USDA's 2023 Plant Hardiness Zone Map puts South Mountain in zone 7a in ZIP code 17261, the nearest ZIP area. By the map's own method, the average of each year's coldest night over 1991-2020, the station is in zone 6b: the coldest night of a typical year reaches 0°F (19 complete years); the map interpolates between stations and terrain, so the station and the ZIP area can differ by half a zone.
Frost dates for every NOAA station in Pennsylvania · Frost dates by ZIP code
Source: NOAA NCEI 1991-2020 annual normals (frost probabilities), station USC00368308; USDA 2023 Plant Hardiness Zone Map, ZIP listings: PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed October 8, 2026; the station zone: ACIS daily lows, 1991-2020. A 10% date means one year in ten has a frost after it in spring or before it in autumn.
How hot and how cold does it get at South Mountain?
In a normal year in South Mountain, 3 days a year reach 90°F, 129 nights fall to 32°F or colder and 127 days bring measurable precipitation.
- Days at 90°F or more
- 3a normal year
- Days at 100°F or more
- fewer than 1a normal year
- Nights at 32°F or colder
- 129a normal year
- Days that stay below freezing
- 34high of 32°F or less
- Days with 0.01 inch of precipitation
- 127a normal year
- Days with 1 inch of snow or more
- 11a normal year
Source: NOAA NCEI 1991-2020 annual normals, station USC00368308.
How sunny is it at South Mountain?
Over a year 73% of the sunlight that would reach the ground under clear skies gets through the clouds at South Mountain, 4.0 kWh per square metre a day. July is the sunniest month (79%) and January the cloudiest (65%).
| Month | Share of clear-sky sunshine | Sunshine, kWh/m² a day |
|---|---|---|
| January | 65% | 2.0 |
| February | 68% | 2.8 |
| March | 68% | 3.8 |
| April | 71% | 4.9 |
| May | 71% | 5.4 |
| June | 77% | 6.1 |
| July | 79% | 6.0 |
| August | 78% | 5.3 |
| September | 75% | 4.3 |
| October | 72% | 3.1 |
| November | 72% | 2.3 |
| December | 66% | 1.7 |
Source: NASA POWER solar climatology, 2001-2020 (CERES SYN1deg). Satellite-based, for the 1-degree cell (about 100 km across) around the station, so it describes the area rather than the airport.
How many heating and cooling degree days does South Mountain record?
A normal year at South Mountain brings 5,995 heating degree days, 12% more than the median U.S. place (5,373), and 570 cooling degree days, 37% fewer than the median (908). Seven months need 300 or more heating degree days, a monthly mean of about 55°F or colder. For gardens and crops, NOAA counts 2,756 growing degree days a year above 50°F.
| Month | Heating | Cooling |
|---|---|---|
| January | 1,145 | 0 |
| February | 979 | 0 |
| March | 863 | 0 |
| April | 490 | 5 |
| May | 221 | 27 |
| June | 45 | 114 |
| July | 8 | 198 |
| August | 15 | 161 |
| September | 119 | 59 |
| October | 409 | 6 |
| November | 704 | 0 |
| December | 998 | 0 |
| Year (annual) | 5,995 | 570 |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00368308. A degree day is one degree of a day's mean temperature below 65°F (heating) or above it (cooling); utilities use them to estimate energy use.
How does South Mountain's climate compare?
South Mountain is warmer than 45 of the 108 places with their own NOAA record in Pennsylvania, and wetter than 90. Across the 7,247 U.S. stations with normals, its annual mean of 50.0°F is warmer than 40%.
In the Köppen classification computed from these normals, South Mountain is Dfb: continental, no dry season, warm summer. What the classes mean.
Places with the most similar year elsewhere
Measured month by month on the normal high, low and precipitation, among places of 20,000 or more people in other states:
Source: NOAA NCEI 1991-2020 normals for every station PlainClimate covers. Similarity: the root-mean-square difference of the 36 monthly figures, precipitation weighted so an inch counts like 6°F.
Which places near South Mountain share this climate record?
5 places have no NOAA station with 1991-2020 normals of their own, and this station is the nearest full record. A place's own climate can differ from these figures, by several degrees where it sits much higher or lower than the station, nearer the coast, or inside a large city's heat; for the larger places the next nearest records are named with their yearly mean, so the spread around them is visible, and places of 50,000 or more have their own page with NOAA's gridded normals.
- Mont Alto, PA1,563 people · 3 mi W
- Highfield-Cascade, MD1,079 people · 10 mi S
- Sabillasville, MD350 people · 11 mi S
- Ringgold, MD81 people · 10 mi S
- Fort Ritchie, MD0 people · 10 mi S
Source: Census Bureau 2024 Gazetteer (place centers) and Vintage 2024 population estimates. Distance and direction from the station to each place's center.
Questions about South Mountain's climate
What is the coldest month at South Mountain?
January, with a normal high of 36°F and a normal low of 21°F. The warmest is July (81°F by day, 62°F at night).
Does it snow at South Mountain?
Yes: 33 inches in a normal year, falling on 13 days with 0.1 inch or more, the most in January (10.6 inches).
What is the rainiest month at South Mountain?
September, with 5.07 in of precipitation in a normal year; the driest is February with 2.91 in.
What plant hardiness zone is South Mountain in?
The USDA's 2023 map puts South Mountain in zone 7a in ZIP code 17261, the nearest ZIP area. By the same method at the station, the coldest night of a typical year reaches 0°F (19 years, 1991-2020): zone 6b.
How late can frost come at South Mountain?
In half of years the last 32°F night comes after April 27; in one year in ten it comes after May 14. Waiting until May 14 leaves about a one-in-ten chance of a later frost.
Nearby and next
- Pennsylvania climateThe statewide normals and every place in the state
- Cashtown, PA9 miles from this station, 51.3°F a year
- Chambersburg, PA9 miles from this station, 52.9°F a year
- Smithsburg, MD14 miles from this station, 52.3°F a year
- Catoctin Mountain Park, MD14 miles from this station, 53.4°F a year
- Compare two placesMonth by month, side by side
Download these normals (CSV) · JSON · How these figures are made