Norristown, Pennsylvania climate: Normal weather by month, frost dates and records
Norristown's normal year runs from 23°F January nights to 89°F July afternoons, with 50.6 inches of precipitation and 25 inches of snow a year. (NOAA 1991-2020 normals)
In metric: a yearly mean of 12.8°C, January lows of −5°C, July highs of 32°C, 1,287 mm of precipitation a year.
- NOAA stationNorristown
- Station IDUSC00366370
- Location40.11°N 75.34°W
- Elevation62 ft (19 m)
- From the centerunder 1 mile
- Population36,075
On October 23, the normal high in Norristown is 66°F and the normal low 42°F, and the chance of measurable rain or snow is 34%.
Normals describe a typical year at the station, not a forecast. The National Weather Service forecast for Norristown.
- Jan 42° 23°
- Feb 44° 25°
- Mar 52° 32°
- Apr 65° 42°
- May 75° 52°
- Jun 84° 62°
- Jul 89° 67°
- Aug 87° 65°
- Sep 80° 58°
- Oct 68° 45°
- Nov 57° 35°
- Dec 46° 28°
Each month: normal high (large) and low, °F. Fill: the month's normal mean, colder blue to hotter red.
What is the weather like in Norristown each month?
July is the warmest month, with normal highs of 89°F; January the coldest, with normal lows of 23°F. The most precipitation falls in August (4.98 in), the least in February (2.98 in).
Each month has its own page with the day-by-day normals, the month's records and its recent years:
| Month | High | Low | Mean | Precip. | Snow | Wet days | 90°F days | Freezing nights | Daylight |
|---|---|---|---|---|---|---|---|---|---|
| January | 42°F | 23°F | 32.1°F | 3.66 | 6.8 | 11 | <1 | 26 | 9 h 40 min |
| February | 44°F | 25°F | 34.1°F | 2.98 | 10.9 | 9 | <1 | 24 | 10 h 40 min |
| March | 52°F | 32°F | 41.8°F | 4.41 | 3.0 | 11 | <1 | 17 | 11 h 50 min |
| April | 65°F | 42°F | 53.1°F | 3.90 | 0.2 | 13 | 1 | 3 | 13 h 10 min |
| May | 75°F | 52°F | 63.4°F | 4.25 | 0.0 | 14 | 3 | <1 | 14 h 20 min |
| June | 84°F | 62°F | 73.0°F | 4.20 | 0.0 | 12 | 7 | <1 | 15 h |
| July | 89°F | 67°F | 77.7°F | 4.70 | 0.0 | 11 | 15 | <1 | 14 h 50 min |
| August | 87°F | 65°F | 75.9°F | 4.98 | 0.0 | 10 | 10 | <1 | 13 h 50 min |
| September | 80°F | 58°F | 68.8°F | 4.91 | 0.0 | 9 | 4 | <1 | 12 h 30 min |
| October | 68°F | 45°F | 56.5°F | 4.32 | 0.1 | 11 | <1 | 1 | 11 h 10 min |
| November | 57°F | 35°F | 45.9°F | 3.61 | 0.1 | 9 | <1 | 12 | 10 h |
| December | 46°F | 28°F | 37.3°F | 4.73 | 4.2 | 11 | <1 | 23 | 9 h 20 min |
| Year (annual) | 66°F | 44°F | 55.0°F | 50.65 | 25.3 | 131 | 39 | 107 |
The same normals in °C and millimetres
| Month | High | Low | Mean | Precip. | Snow |
|---|---|---|---|---|---|
| January | 5°C | −5°C | 0.1°C | 93 mm | 17 cm |
| February | 6°C | −4°C | 1.2°C | 76 mm | 28 cm |
| March | 11°C | 0°C | 5.4°C | 112 mm | 8 cm |
| April | 18°C | 5°C | 11.7°C | 99 mm | 1 cm |
| May | 24°C | 11°C | 17.4°C | 108 mm | 0 cm |
| June | 29°C | 17°C | 22.8°C | 107 mm | 0 cm |
| July | 32°C | 19°C | 25.4°C | 119 mm | 0 cm |
| August | 30°C | 18°C | 24.4°C | 126 mm | 0 cm |
| September | 27°C | 14°C | 20.4°C | 125 mm | 0 cm |
| October | 20°C | 7°C | 13.6°C | 110 mm | 0 cm |
| November | 14°C | 2°C | 7.7°C | 92 mm | 0 cm |
| December | 8°C | −2°C | 2.9°C | 120 mm | 11 cm |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00366370; 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.
When is the best weather to visit Norristown?
Normal highs sit between 65°F and 85°F in May, June, September and October. Of those, September has the fewest days with rain (9).
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 USC00366370.
When is the last frost in Norristown?
In Norristown, the last spring frost (32°F) comes after April 8 in half of years and after April 23 in one year in ten; the first autumn frost comes before October 31 in half of years and before October 14 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 81 year in 10 after April 23; 9 in 10 after March 28
- First autumn frost, half of years before
- October 311 year in 10 before October 14; 9 in 10 before November 12
NOAA puts the median frost-free season at 203 days, and the season without a hard freeze (28°F) at 224 days.
A hard freeze (28°F) comes after March 31 in half of springs and before November 10 in half of autumns.
The USDA's 2023 Plant Hardiness Zone Map puts Norristown in zone 7a in ZIP code 19401.
Frost dates for every NOAA station in Pennsylvania · Frost dates by ZIP code
Source: NOAA NCEI 1991-2020 annual normals (frost probabilities), station USC00366370; USDA 2023 Plant Hardiness Zone Map, ZIP listings: PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed October 8, 2026. 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 in Norristown?
In a normal year in Norristown, 39 days a year reach 90°F (2 of them 100°F or more), 107 nights fall to 32°F or colder and 131 days bring measurable precipitation.
- Days at 90°F or more
- 39a normal year
- Days at 100°F or more
- 2a normal year
- Nights at 32°F or colder
- 107a normal year
- Days that stay below freezing
- 14high of 32°F or less
- Days with 0.01 inch of precipitation
- 131a normal year
- Days with 1 inch of snow or more
- 6a normal year
The highest temperature in this station's record (since 1951) is 108°F, on July 24, 2011; the lowest is −12°F, on January 18, 1982.
The wettest calendar year on that record is 2018, with 69.98 in; the snowiest season is 2002–03, with 50.0 inches.
Source: NOAA NCEI 1991-2020 annual normals, station USC00366370; records: ACIS (NOAA Regional Climate Centers), station USC00366370. Records use complete months only; a month missing more than three days is left out.
How sunny is Norristown?
Over a year 72% of the sunlight that would reach the ground under clear skies gets through the clouds in the area around Norristown, 3.9 kWh per square metre a day. July is the sunniest month (79%) and December the cloudiest (63%).
| Month | Share of clear-sky sunshine | Sunshine, kWh/m² a day |
|---|---|---|
| January | 65% | 1.9 |
| February | 68% | 2.7 |
| March | 67% | 3.6 |
| April | 70% | 4.8 |
| May | 69% | 5.3 |
| June | 74% | 5.9 |
| July | 79% | 6.0 |
| August | 77% | 5.2 |
| September | 75% | 4.2 |
| October | 69% | 3.0 |
| November | 70% | 2.1 |
| December | 63% | 1.6 |
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 much heating and cooling does Norristown need?
A normal year in Norristown brings 4,869 heating degree days, 9% fewer than the median U.S. place (5,373), and 1,254 cooling degree days, 38% more than the median (908). Six months need 300 or more heating degree days, a monthly mean of about 55°F or colder. For gardens and crops, NOAA counts 3,815 growing degree days a year above 50°F.
| Month | Heating | Cooling |
|---|---|---|
| January | 1,018 | 0 |
| February | 865 | 0 |
| March | 718 | 0 |
| April | 370 | 15 |
| May | 127 | 79 |
| June | 13 | 253 |
| July | 0 | 394 |
| August | 1 | 338 |
| September | 42 | 156 |
| October | 283 | 20 |
| November | 572 | 0 |
| December | 859 | 0 |
| Year (annual) | 4,869 | 1,254 |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00366370. 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.
Has Norristown been warmer than normal lately?
2025 averaged 53.7°F, 1.3°F below the 1991-2020 normal of 55.0°F. 1 of the 3 complete years since 2022 ran warmer than the normal.
| Year | Mean | Against normal | Precip. | Snow |
|---|---|---|---|---|
| 2022 | 54.0°F | −1.0°F | 48.13 | 16.0 |
| 2023 | 55.8°F | +0.8°F | 50.89 | 0.0 |
| 2025 | 53.7°F | −1.3°F | 40.76 | – |
Over 36 complete years from 1954 to 2025, the station's annual mean temperature rose at a fitted 4.2°F per century (+0.23°C per decade). A fitted rate summarizes the whole record; single years swing well above and below it.
Source: observed years: ACIS, station USC00366370; trend: NOAA GHCN-Monthly v4. A year counts only with all twelve months complete.
How does Norristown's climate compare?
Norristown is warmer than 104 of the other 107 places with their own NOAA record in Pennsylvania, and wetter than 96. Across the 7,247 U.S. stations with normals, its annual mean of 55.0°F is warmer than 60%.
In the Köppen classification computed from these normals, Norristown is Cfa: temperate, no dry season, hot 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 Norristown share this climate record?
14 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.
- King of Prussia, PA25,025 people · 2 mi SW
- Conshohocken, PA9,342 people · 3 mi SE
- Villanova, PA8,431 people · 5 mi S
- Plymouth Meeting, PA6,990 people · 3 mi E
- Wayne, PA6,902 people · 6 mi SW
- Blue Bell, PA6,450 people · 4 mi NE
- Bryn Mawr, PA5,777 people · 6 mi S
- Trooper, PA5,408 people · 4 mi NW
- Bridgeport, PA5,401 people · 0 mi SW
- St. Davids, PA3,950 people · 5 mi S
- Rosemont, PA3,722 people · 5 mi S
- Swedeland, PA1,725 people · 2 mi S
- West Conshohocken, PA1,508 people · 3 mi S
- Swedesburg, PA805 people · 1 mi SE
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 Norristown's climate
What is the coldest month in Norristown?
January, with a normal high of 42°F and a normal low of 23°F. The warmest is July (89°F by day, 67°F at night).
Does it snow in Norristown?
Yes: 25 inches in a normal year, falling on 10 days with 0.1 inch or more, the most in February (10.9 inches).
What is the rainiest month in Norristown?
August, with 4.98 in of precipitation in a normal year; the driest is February with 2.98 in.
What plant hardiness zone is Norristown in?
The USDA's 2023 map puts Norristown in zone 7a in ZIP code 19401.
How late can frost come in Norristown?
In half of years the last 32°F night comes after April 8; in one year in ten it comes after April 23. Waiting until April 23 leaves about a one-in-ten chance of a later frost.
Nearby and next
- Norristown in OctoberThis month day by day, its records and recent years
- Pennsylvania climateThe statewide normals and every place in the state
- Phoenixville, PA8 miles from this station, 54.4°F a year
- Graterford (1 mi E), PA9 miles from this station, 52.4°F a year
- Willow Grove, PA12 miles from this station, 54.0°F a year
- Phila Franklin Inst, PA14 miles from this station, 57.7°F a year
- Compare two placesMonth by month, side by side
Download these normals (CSV) · JSON · How these figures are made