Olney, Illinois climate: Normal weather by month, frost dates and records
Olney's normal year runs from 21°F January nights to 87°F July afternoons, with 48.8 inches of precipitation and 11 inches of snow a year. (NOAA 1991-2020 normals)
In metric: a yearly mean of 12.3°C, January lows of −6°C, July highs of 30°C, 1,239 mm of precipitation a year.
- NOAA stationOlney (2 mi S)
- Station IDUSC00116446
- Location38.70°N 88.08°W
- Elevation459 ft (140 m)
- From the center2 miles
- Population8,431
On October 23, the normal high in Olney is 65°F and the normal low 42°F, and the chance of measurable rain or snow is 31%.
Normals describe a typical year at the station, not a forecast. The National Weather Service forecast for Olney.
- Jan 38° 21°
- Feb 43° 24°
- Mar 53° 32°
- Apr 66° 43°
- May 75° 53°
- Jun 84° 62°
- Jul 87° 66°
- Aug 86° 64°
- Sep 80° 56°
- Oct 69° 44°
- Nov 54° 34°
- Dec 42° 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 in Olney each month?
July is the warmest month, with normal highs of 87°F; January the coldest, with normal lows of 21°F. The most precipitation falls in May (5.60 in), the least in February (2.57 in).
| Month | High | Low | Mean | Precip. | Snow | Wet days | 90°F days | Freezing nights | Daylight |
|---|---|---|---|---|---|---|---|---|---|
| January | 38°F | 21°F | 29.3°F | 3.52 | 3.6 | 11 | <1 | 26 | 9 h 40 min |
| February | 43°F | 24°F | 33.3°F | 2.57 | 2.6 | 9 | <1 | 21 | 10 h 40 min |
| March | 53°F | 32°F | 42.9°F | 4.21 | 1.1 | 12 | <1 | 15 | 11 h 50 min |
| April | 66°F | 43°F | 54.2°F | 5.02 | 0.0 | 11 | <1 | 4 | 13 h 10 min |
| May | 75°F | 53°F | 64.2°F | 5.60 | 0.0 | 13 | 1 | <1 | 14 h 20 min |
| June | 84°F | 62°F | 73.2°F | 4.79 | 0.0 | 11 | 7 | <1 | 14 h 50 min |
| July | 87°F | 66°F | 76.2°F | 4.96 | 0.0 | 9 | 11 | <1 | 14 h 40 min |
| August | 86°F | 64°F | 74.8°F | 3.19 | 0.0 | 8 | 9 | <1 | 13 h 40 min |
| September | 80°F | 56°F | 68.1°F | 3.31 | 0.0 | 8 | 4 | <1 | 12 h 30 min |
| October | 69°F | 44°F | 56.4°F | 3.83 | 0.0 | 9 | <1 | 3 | 11 h 20 min |
| November | 54°F | 34°F | 43.7°F | 4.26 | 0.5 | 10 | <1 | 14 | 10 h 10 min |
| December | 42°F | 26°F | 34.0°F | 3.50 | 2.7 | 11 | <1 | 22 | 9 h 30 min |
| Year (annual) | 65°F | 44°F | 54.2°F | 48.76 | 10.5 | 120 | 32 | 105 |
The same normals in °C and millimetres
| Month | High | Low | Mean | Precip. | Snow |
|---|---|---|---|---|---|
| January | 3°C | −6°C | −1.5°C | 89 mm | 9 cm |
| February | 6°C | −5°C | 0.7°C | 65 mm | 7 cm |
| March | 12°C | 0°C | 6.1°C | 107 mm | 3 cm |
| April | 19°C | 6°C | 12.3°C | 128 mm | 0 cm |
| May | 24°C | 12°C | 17.9°C | 142 mm | 0 cm |
| June | 29°C | 17°C | 22.9°C | 122 mm | 0 cm |
| July | 30°C | 19°C | 24.6°C | 126 mm | 0 cm |
| August | 30°C | 18°C | 23.8°C | 81 mm | 0 cm |
| September | 27°C | 13°C | 20.1°C | 84 mm | 0 cm |
| October | 20°C | 7°C | 13.6°C | 97 mm | 0 cm |
| November | 12°C | 1°C | 6.5°C | 108 mm | 1 cm |
| December | 6°C | −4°C | 1.1°C | 89 mm | 7 cm |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00116446; 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 Olney?
Normal highs sit between 65°F and 85°F in April, May, June, September and October. Of those, September has the fewest days with rain (8).
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 USC00116446.
When is the last frost in Olney?
In Olney, the last spring frost (32°F) comes after April 15 in half of years and after May 3 in one year in ten; the first autumn frost comes before October 23 in half of years and before October 8 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 151 year in 10 after May 3; 9 in 10 after April 1
- First autumn frost, half of years before
- October 231 year in 10 before October 8; 9 in 10 before November 3
NOAA puts the median frost-free season at 189 days, and the season without a hard freeze (28°F) at 211 days.
A hard freeze (28°F) comes after April 3 in half of springs and before November 1 in half of autumns.
The USDA's 2023 Plant Hardiness Zone Map puts Olney in zone 6b in ZIP code 62450, the nearest ZIP area. By the map's own method, the average of each year's coldest night over 1991-2020, Olney's NOAA station is in zone 6b: the coldest night of a typical year reaches −3°F (27 complete years).
Frost dates for every NOAA station in Illinois · Frost dates by ZIP code
Source: NOAA NCEI 1991-2020 annual normals (frost probabilities), station USC00116446; 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 in Olney?
In a normal year in Olney, 32 days a year reach 90°F (1 of them 100°F or more), 105 nights fall to 32°F or colder and 120 days bring measurable precipitation.
- Days at 90°F or more
- 32a normal year
- Days at 100°F or more
- 1a normal year
- Nights at 32°F or colder
- 105a normal year
- Days that stay below freezing
- 22high of 32°F or less
- Days with 0.01 inch of precipitation
- 120a normal year
- Days with 1 inch of snow or more
- 4a normal year
The highest temperature in this station's record (since 1896) is 112°F, on July 15, 1936; the lowest is −25°F, on February 2, 1951.
The wettest calendar year on that record is 2011, with 66.87 in; the snowiest season is 1917–18, with 37.0 inches.
Source: NOAA NCEI 1991-2020 annual normals, station USC00116446; records: ACIS (NOAA Regional Climate Centers), station USC00116446. Records use complete months only; a month missing more than three days is left out.
How sunny is Olney?
Over a year 75% of the sunlight that would reach the ground under clear skies gets through the clouds in the area around Olney, 4.2 kWh per square metre a day. August is the sunniest month (83%) and December the cloudiest (63%).
| Month | Share of clear-sky sunshine | Sunshine, kWh/m² a day |
|---|---|---|
| January | 65% | 2.0 |
| February | 66% | 2.8 |
| March | 67% | 3.7 |
| April | 73% | 5.0 |
| May | 73% | 5.6 |
| June | 82% | 6.5 |
| July | 83% | 6.3 |
| August | 83% | 5.7 |
| September | 81% | 4.7 |
| October | 76% | 3.4 |
| November | 71% | 2.4 |
| December | 63% | 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 much heating and cooling does Olney need?
A normal year in Olney brings 5,102 heating degree days, 5% fewer than the median U.S. place (5,373), and 1,195 cooling degree days, 32% 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 3,829 growing degree days a year above 50°F.
| Month | Heating | Cooling |
|---|---|---|
| January | 1,106 | 0 |
| February | 888 | 0 |
| March | 690 | 3 |
| April | 340 | 15 |
| May | 117 | 92 |
| June | 10 | 257 |
| July | 1 | 348 |
| August | 2 | 305 |
| September | 53 | 146 |
| October | 294 | 28 |
| November | 640 | 2 |
| December | 961 | 0 |
| Year (annual) | 5,102 | 1,195 |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00116446. 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 Olney been warmer than normal lately?
2025 averaged 55.5°F, 1.3°F above the 1991-2020 normal of 54.2°F. 4 of the 5 complete years since 2021 ran warmer than the normal.
| Year | Mean | Against normal | Precip. | Snow |
|---|---|---|---|---|
| 2021 | 55.5°F | +1.3°F | 45.43 | 18.8 |
| 2022 | 54.2°F | at normal | 50.48 | 10.5 |
| 2023 | 56.3°F | +2.0°F | 38.92 | 2.7 |
| 2024 | 56.9°F | +2.7°F | 51.57 | 6.2 |
| 2025 | 55.5°F | +1.3°F | 46.56 | 20.6 |
Over 110 complete years from 1888 to 2025, the station's annual mean temperature rose at a fitted 1.5°F per century (+0.08°C per decade). A fitted rate summarizes the whole record; single years swing well above and below it.
Source: observed years: ACIS, station USC00116446; trend: NOAA GHCN-Monthly v4. A year counts only with all twelve months complete.
How does Olney's climate compare?
Olney is warmer than 110 of the other 143 places with their own NOAA record in Illinois, and wetter than 132. Across the 7,247 U.S. stations with normals, its annual mean of 54.2°F is warmer than 58%.
In the Köppen classification computed from these normals, Olney is Dfa: continental, 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 Olney share this climate record?
6 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.
- Noble, IL613 people · 7 mi W
- Dundas, IL264 people · 9 mi N
- Parkersburg, IL186 people · 8 mi S
- Claremont, IL157 people · 6 mi E
- Calhoun, IL154 people · 4 mi SE
- West Liberty, IL37 people · 11 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 Olney's climate
What is the coldest month in Olney?
January, with a normal high of 38°F and a normal low of 21°F. The warmest is July (87°F by day, 66°F at night).
Does it snow in Olney?
Yes: 11 inches in a normal year, falling on 8 days with 0.1 inch or more, the most in January (3.6 inches).
What is the rainiest month in Olney?
May, with 5.60 in of precipitation in a normal year; the driest is February with 2.57 in.
What plant hardiness zone is Olney in?
The USDA's 2023 map puts Olney in zone 6b in ZIP code 62450, the nearest ZIP area. By the same method at Olney's NOAA station, the coldest night of a typical year reaches −3°F (27 years, 1991-2020): zone 6b.
How late can frost come in Olney?
In half of years the last 32°F night comes after April 15; in one year in ten it comes after May 3. Waiting until May 3 leaves about a one-in-ten chance of a later frost.
Nearby and next
- Illinois climateThe statewide normals and every place in the state
- Newton, IL21 miles from this station, 54.5°F a year
- Flora, IL22 miles from this station, 55.0°F a year
- Albion, IL22 miles from this station, 56.6°F a year
- Fairfield, IL25 miles from this station, 57.1°F a year
- Compare two placesMonth by month, side by side
Download these normals (CSV) · JSON · How these figures are made