Petersburg, Illinois climate: Normal weather by month, frost dates and records
Petersburg's normal year runs from 17°F January nights to 86°F July afternoons, with 37.6 inches of precipitation and 15 inches of snow a year. (NOAA 1991-2020 normals)
In metric: a yearly mean of 11.3°C, January lows of −8°C, July highs of 30°C, 956 mm of precipitation a year.
- NOAA stationPetersburg (1 mi E)
- Station IDUSC00116765
- Location40.02°N 89.83°W
- Elevation600 ft (183 m)
- From the centerunder 1 mile
- Population2,156
On October 23, the normal high in Petersburg is 63°F and the normal low 40°F, and the chance of measurable rain or snow is 28%.
Normals describe a typical year at the station, not a forecast. The National Weather Service forecast for Petersburg.
- Jan 34° 17°
- Feb 39° 21°
- Mar 51° 30°
- Apr 64° 41°
- May 74° 53°
- Jun 82° 62°
- Jul 86° 65°
- Aug 85° 63°
- Sep 79° 55°
- Oct 66° 43°
- Nov 52° 32°
- Dec 39° 23°
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 Petersburg each month?
July is the warmest month, with normal highs of 86°F; January the coldest, with normal lows of 17°F. The most precipitation falls in May (4.61 in), the least in February (1.75 in).
| Month | High | Low | Mean | Precip. | Snow | Wet days | 90°F days | Freezing nights | Daylight |
|---|---|---|---|---|---|---|---|---|---|
| January | 34°F | 17°F | 25.9°F | 2.02 | 5.4 | 9 | <1 | 27 | 9 h 40 min |
| February | 39°F | 21°F | 29.9°F | 1.75 | 2.7 | 7 | <1 | 24 | 10 h 40 min |
| March | 51°F | 30°F | 40.6°F | 2.51 | 1.4 | 10 | <1 | 18 | 11 h 50 min |
| April | 64°F | 41°F | 52.5°F | 4.09 | 0.5 | 11 | <1 | 7 | 13 h 10 min |
| May | 74°F | 53°F | 63.5°F | 4.61 | 0.0 | 11 | 1 | <1 | 14 h 20 min |
| June | 82°F | 62°F | 72.3°F | 4.14 | 0.0 | 9 | 5 | <1 | 15 h |
| July | 86°F | 65°F | 75.5°F | 3.87 | 0.0 | 8 | 8 | <1 | 14 h 50 min |
| August | 85°F | 63°F | 73.6°F | 3.66 | 0.0 | 8 | 2 | <1 | 13 h 50 min |
| September | 79°F | 55°F | 66.9°F | 3.12 | 0.0 | 7 | 4 | <1 | 12 h 30 min |
| October | 66°F | 43°F | 54.7°F | 3.19 | 0.0 | 9 | <1 | 4 | 11 h 10 min |
| November | 52°F | 32°F | 41.8°F | 2.76 | 1.2 | 8 | <1 | 17 | 10 h |
| December | 39°F | 23°F | 30.9°F | 1.93 | 4.0 | 8 | <1 | 24 | 9 h 20 min |
| Year (annual) | 63°F | 42°F | 52.3°F | 37.65 | 15.2 | 104 | 19 | 121 |
The same normals in °C and millimetres
| Month | High | Low | Mean | Precip. | Snow |
|---|---|---|---|---|---|
| January | 1°C | −8°C | −3.4°C | 51 mm | 14 cm |
| February | 4°C | −6°C | −1.2°C | 44 mm | 7 cm |
| March | 10°C | −1°C | 4.8°C | 64 mm | 4 cm |
| April | 18°C | 5°C | 11.4°C | 104 mm | 1 cm |
| May | 23°C | 12°C | 17.5°C | 117 mm | 0 cm |
| June | 28°C | 17°C | 22.4°C | 105 mm | 0 cm |
| July | 30°C | 19°C | 24.2°C | 98 mm | 0 cm |
| August | 29°C | 17°C | 23.1°C | 93 mm | 0 cm |
| September | 26°C | 13°C | 19.4°C | 79 mm | 0 cm |
| October | 19°C | 6°C | 12.6°C | 81 mm | 0 cm |
| November | 11°C | 0°C | 5.4°C | 70 mm | 3 cm |
| December | 4°C | −5°C | −0.6°C | 49 mm | 10 cm |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00116765; 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 Petersburg?
Normal highs sit between 65°F and 85°F in May, June, August, September and October. Of those, September has the fewest days with rain (7).
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 USC00116765.
When is the last frost in Petersburg?
In Petersburg, the last spring frost (32°F) comes after April 13 in half of years and after April 28 in one year in ten; the first autumn frost comes before October 21 in half of years and before October 7 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 131 year in 10 after April 28; 9 in 10 after March 31
- First autumn frost, half of years before
- October 211 year in 10 before October 7; 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 210 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 Petersburg in zone 6a in ZIP code 62675, 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 USC00116765; 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 Petersburg?
In a normal year in Petersburg, 19 days a year reach 90°F, 121 nights fall to 32°F or colder and 104 days bring measurable precipitation.
- Days at 90°F or more
- 19a normal year
- Days at 100°F or more
- fewer than 1a normal year
- Nights at 32°F or colder
- 121a normal year
- Days that stay below freezing
- 31high of 32°F or less
- Days with 0.01 inch of precipitation
- 104a normal year
- Days with 1 inch of snow or more
- 6a normal year
Source: NOAA NCEI 1991-2020 annual normals, station USC00116765.
How sunny is Petersburg?
Over a year 74% of the sunlight that would reach the ground under clear skies gets through the clouds in the area around Petersburg, 4.1 kWh per square metre a day. July is the sunniest month (83%) and December the cloudiest (62%).
| Month | Share of clear-sky sunshine | Sunshine, kWh/m² a day |
|---|---|---|
| January | 64% | 1.9 |
| February | 67% | 2.8 |
| March | 68% | 3.7 |
| April | 71% | 4.9 |
| May | 72% | 5.6 |
| June | 79% | 6.3 |
| July | 83% | 6.4 |
| August | 81% | 5.6 |
| September | 81% | 4.7 |
| October | 73% | 3.2 |
| November | 70% | 2.2 |
| December | 62% | 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 Petersburg need?
A normal year in Petersburg brings 5,644 heating degree days, 5% more than the median U.S. place (5,373), and 1,056 cooling degree days, 16% more 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 3,563 growing degree days a year above 50°F.
| Month | Heating | Cooling |
|---|---|---|
| January | 1,213 | 0 |
| February | 982 | 0 |
| March | 758 | 0 |
| April | 385 | 10 |
| May | 126 | 79 |
| June | 8 | 225 |
| July | 1 | 325 |
| August | 3 | 269 |
| September | 70 | 125 |
| October | 342 | 21 |
| November | 698 | 2 |
| December | 1,058 | 0 |
| Year (annual) | 5,644 | 1,056 |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00116765. 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 Petersburg been warmer than normal lately?
2025 averaged 53.8°F, 1.5°F above the 1991-2020 normal of 52.3°F. 4 of the 5 complete years since 2021 ran warmer than the normal.
| Year | Mean | Against normal | Precip. | Snow |
|---|---|---|---|---|
| 2021 | 54.0°F | +1.7°F | 47.72 | 22.9 |
| 2022 | 52.1°F | −0.2°F | 37.01 | 33.1 |
| 2023 | 54.3°F | +2.0°F | 29.26 | 4.8 |
| 2024 | 55.1°F | +2.8°F | 40.58 | 13.8 |
| 2025 | 53.8°F | +1.5°F | 26.63 | 32.4 |
Source: observed years: ACIS, station USC00116765. A year counts only with all twelve months complete.
How does Petersburg's climate compare?
Petersburg is warmer than 80 of the other 143 places with their own NOAA record in Illinois, and wetter than 24. Across the 7,247 U.S. stations with normals, its annual mean of 52.3°F is warmer than 51%.
In the Köppen classification computed from these normals, Petersburg 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 Petersburg 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.
- Lake Petersburg, IL769 people · 2 mi SW
- Greenview, IL724 people · 7 mi NE
- Chandlerville, IL519 people · 17 mi W
- Tallula, IL424 people · 7 mi SW
- Oakford, IL228 people · 9 mi NW
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 Petersburg's climate
What is the coldest month in Petersburg?
January, with a normal high of 34°F and a normal low of 17°F. The warmest is July (86°F by day, 65°F at night).
Does it snow in Petersburg?
Yes: 15 inches in a normal year, falling on 13 days with 0.1 inch or more, the most in January (5.4 inches).
What is the rainiest month in Petersburg?
May, with 4.61 in of precipitation in a normal year; the driest is February with 1.75 in.
What plant hardiness zone is Petersburg in?
The USDA's 2023 map puts Petersburg in zone 6a in ZIP code 62675, the nearest ZIP area.
How late can frost come in Petersburg?
In half of years the last 32°F night comes after April 13; in one year in ten it comes after April 28. Waiting until April 28 leaves about a one-in-ten chance of a later frost.
Nearby and next
- Illinois climateThe statewide normals and every place in the state
- Athens, IL6 miles from this station, 52.0°F a year
- Mason City, IL14 miles from this station, 51.7°F a year
- Springfield, IL14 miles from this station, 54.0°F a year
- Havana, IL23 miles from this station, 52.5°F a year
- Compare two placesMonth by month, side by side
Download these normals (CSV) · JSON · How these figures are made