Harrisburg, Illinois climate: Normal weather by month, frost dates and records
Harrisburg's normal year runs from 24°F January nights to 89°F July afternoons, with 47.6 inches of precipitation a year. (NOAA 1991-2020 normals)
In metric: a yearly mean of 14.1°C, January lows of −4°C, July highs of 32°C, 1,209 mm of precipitation a year.
- NOAA stationHarrisburg
- Station IDUSC00113879
- Location37.74°N 88.52°W
- Elevation365 ft (111 m)
- Population7,937
On October 23, the normal high in Harrisburg is 68°F and the normal low 43°F, and the chance of measurable rain or snow is 23%.
Normals describe a typical year at the station, not a forecast. The National Weather Service forecast for Harrisburg.
- Jan 43° 24°
- Feb 48° 28°
- Mar 58° 36°
- Apr 69° 46°
- May 78° 57°
- Jun 86° 65°
- Jul 89° 68°
- Aug 88° 66°
- Sep 82° 57°
- Oct 71° 45°
- Nov 57° 36°
- Dec 47° 29°
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 Harrisburg each month?
July is the warmest month, with normal highs of 89°F; January the coldest, with normal lows of 24°F. The most precipitation falls in April (5.26 in), the least in September (3.10 in).
| Month | High | Low | Mean | Precip. | Wet days | 90°F days | Freezing nights | Daylight |
|---|---|---|---|---|---|---|---|---|
| January | 43°F | 24°F | 33.4°F | 3.79 | 8 | <1 | 25 | 9 h 50 min |
| February | 48°F | 28°F | 38.0°F | 3.13 | 6 | <1 | 20 | 10 h 50 min |
| March | 58°F | 36°F | 47.1°F | 4.90 | 9 | <1 | 13 | 11 h 50 min |
| April | 69°F | 46°F | 57.6°F | 5.26 | 11 | <1 | 3 | 13 h 10 min |
| May | 78°F | 57°F | 67.3°F | 4.31 | 9 | 1 | <1 | 14 h 10 min |
| June | 86°F | 65°F | 75.5°F | 4.92 | 8 | 9 | <1 | 14 h 50 min |
| July | 89°F | 68°F | 78.7°F | 3.49 | 7 | 14 | <1 | 14 h 30 min |
| August | 88°F | 66°F | 76.9°F | 3.58 | 6 | 13 | <1 | 13 h 40 min |
| September | 82°F | 57°F | 69.8°F | 3.10 | 6 | 5 | <1 | 12 h 30 min |
| October | 71°F | 45°F | 58.3°F | 3.76 | 6 | <1 | 3 | 11 h 20 min |
| November | 57°F | 36°F | 46.8°F | 3.97 | 8 | <1 | 12 | 10 h 10 min |
| December | 47°F | 29°F | 37.8°F | 3.38 | 8 | <1 | 21 | 9 h 30 min |
| Year (annual) | 68°F | 47°F | 57.3°F | 47.59 | 92 | 43 | 95 |
The same normals in °C and millimetres
| Month | High | Low | Mean | Precip. |
|---|---|---|---|---|
| January | 6°C | −4°C | 0.8°C | 96 mm |
| February | 9°C | −2°C | 3.3°C | 80 mm |
| March | 15°C | 2°C | 8.4°C | 124 mm |
| April | 21°C | 8°C | 14.2°C | 134 mm |
| May | 26°C | 14°C | 19.6°C | 109 mm |
| June | 30°C | 18°C | 24.2°C | 125 mm |
| July | 32°C | 20°C | 25.9°C | 89 mm |
| August | 31°C | 19°C | 24.9°C | 91 mm |
| September | 28°C | 14°C | 21.0°C | 79 mm |
| October | 22°C | 7°C | 14.6°C | 96 mm |
| November | 14°C | 2°C | 8.2°C | 101 mm |
| December | 8°C | −2°C | 3.2°C | 86 mm |
NOAA publishes no 1991-2020 snowfall normal for this station. The nearest record that keeps one, Rosiclare (19 miles away), gets 3 inches of snow in a normal year; elevation and distance can change that.
Source: NOAA NCEI 1991-2020 monthly normals, station USC00113879; 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 Harrisburg?
Normal highs sit between 65°F and 85°F in April, May, September and October. Of those, October has the fewest days with rain (6).
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 USC00113879.
When is the last frost in Harrisburg?
In Harrisburg, the last spring frost (32°F) comes after April 7 in half of years and after April 25 in one year in ten; the first autumn frost comes before October 26 in half of years and before October 10 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 71 year in 10 after April 25; 9 in 10 after March 21
- First autumn frost, half of years before
- October 261 year in 10 before October 10; 9 in 10 before November 8
NOAA puts the median frost-free season at 202 days, and the season without a hard freeze (28°F) at 226 days.
A hard freeze (28°F) comes after March 26 in half of springs and before November 6 in half of autumns.
The USDA's 2023 Plant Hardiness Zone Map puts Harrisburg in zone 7a in ZIP code 62965, the nearest ZIP area.
Frost dates for every NOAA station in Illinois · Frost dates by ZIP code
Source: NOAA NCEI 1991-2020 annual normals (frost probabilities), station USC00113879; 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 Harrisburg?
In a normal year in Harrisburg, 43 days a year reach 90°F (1 of them 100°F or more), 95 nights fall to 32°F or colder and 92 days bring measurable precipitation.
- Days at 90°F or more
- 43a normal year
- Days at 100°F or more
- 1a normal year
- Nights at 32°F or colder
- 95a normal year
- Days that stay below freezing
- 14high of 32°F or less
- Days with 0.01 inch of precipitation
- 92a normal year
The highest temperature in this station's record (since 1888) is 113°F, on July 13, 1936; the lowest is −23°F, on February 2, 1951.
The wettest calendar year on that record is 1957, with 64.92 in; the snowiest season is 1977–78, with 54.5 inches.
Source: NOAA NCEI 1991-2020 annual normals, station USC00113879; records: ACIS (NOAA Regional Climate Centers), station USC00113879. Records use complete months only; a month missing more than three days is left out.
How sunny is Harrisburg?
Over a year 75% of the sunlight that would reach the ground under clear skies gets through the clouds in the area around Harrisburg, 4.2 kWh per square metre a day. August is the sunniest month (83%) and December the cloudiest (64%).
| Month | Share of clear-sky sunshine | Sunshine, kWh/m² a day |
|---|---|---|
| January | 64% | 2.1 |
| February | 64% | 2.8 |
| March | 67% | 3.8 |
| April | 73% | 5.1 |
| May | 74% | 5.7 |
| June | 82% | 6.5 |
| July | 83% | 6.3 |
| August | 83% | 5.7 |
| September | 81% | 4.8 |
| October | 76% | 3.5 |
| November | 72% | 2.5 |
| December | 64% | 1.8 |
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 Harrisburg need?
A normal year in Harrisburg brings 4,299 heating degree days, 20% fewer than the median U.S. place (5,373), and 1,522 cooling degree days, 68% more than the median (908). Five months need 300 or more heating degree days, a monthly mean of about 55°F or colder. For gardens and crops, NOAA counts 4,395 growing degree days a year above 50°F.
| Month | Heating | Cooling |
|---|---|---|
| January | 978 | 0 |
| February | 756 | 0 |
| March | 563 | 8 |
| April | 260 | 36 |
| May | 66 | 139 |
| June | 5 | 322 |
| July | 0 | 426 |
| August | 2 | 370 |
| September | 37 | 183 |
| October | 242 | 34 |
| November | 548 | 3 |
| December | 842 | 0 |
| Year (annual) | 4,299 | 1,522 |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00113879. 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 Harrisburg been warmer than normal lately?
2024 averaged 59.0°F, 1.7°F above the 1991-2020 normal of 57.3°F. 2 of the 3 complete years since 2021 ran warmer than the normal.
| Year | Mean | Against normal | Precip. |
|---|---|---|---|
| 2021 | 57.4°F | +0.1°F | – |
| 2022 | 56.7°F | −0.6°F | – |
| 2024 | 59.0°F | +1.7°F | – |
Over 74 complete years from 1899 to 2024, the station's annual mean temperature rose at a fitted 0.2°F per century (+0.01°C per decade). A fitted rate summarizes the whole record; single years swing well above and below it.
Source: observed years: ACIS, station USC00113879; trend: NOAA GHCN-Monthly v4. A year counts only with all twelve months complete.
How does Harrisburg's climate compare?
Harrisburg is warmer than 139 of the other 143 places with their own NOAA record in Illinois, and wetter than 127. Across the 7,247 U.S. stations with normals, its annual mean of 57.3°F is warmer than 67%.
In the Köppen classification computed from these normals, Harrisburg 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 Harrisburg share this climate record?
8 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.
- Eldorado, IL3,583 people · 7 mi NE
- Carrier Mills, IL1,600 people · 7 mi SW
- Galatia, IL787 people · 9 mi NW
- Pittsburg, IL561 people · 18 mi W
- Equality, IL506 people · 10 mi E
- Crab Orchard, IL359 people · 16 mi W
- Raleigh, IL278 people · 6 mi N
- Muddy, IL57 people · 2 mi N
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 Harrisburg's climate
What is the coldest month in Harrisburg?
January, with a normal high of 43°F and a normal low of 24°F. The warmest is July (89°F by day, 68°F at night).
Does it snow in Harrisburg?
Yes. NOAA publishes no 1991-2020 snowfall normal for Harrisburg's NOAA station; the nearest record that keeps one, Rosiclare (19 miles away), records 3 inches of snow in a normal year.
What is the rainiest month in Harrisburg?
April, with 5.26 in of precipitation in a normal year; the driest is September with 3.10 in.
What plant hardiness zone is Harrisburg in?
The USDA's 2023 map puts Harrisburg in zone 7a in ZIP code 62965, the nearest ZIP area.
How late can frost come in Harrisburg?
In half of years the last 32°F night comes after April 7; in one year in ten it comes after April 25. Waiting until April 25 leaves about a one-in-ten chance of a later frost.
Nearby and next
- Illinois climateThe statewide normals and every place in the state
- Rosiclare, IL19 miles from this station, 54.8°F a year
- Dixon Springs Agricultural Center, IL22 miles from this station, 57.2°F a year
- McLeansboro, IL24 miles from this station, 55.4°F a year
- J.T. Myers Locks & Dam, IN29 miles from this station, 56.8°F a year
- Compare two placesMonth by month, side by side
Download these normals (CSV) · JSON · How these figures are made