Romeoville, Illinois climate: Normal weather by month, frost dates and records
Romeoville's normal year runs from 16°F January nights to 85°F July afternoons, with 41.1 inches of precipitation and 33 inches of snow a year. (NOAA 1991-2020 normals)
In metric: a yearly mean of 10.5°C, January lows of −9°C, July highs of 29°C, 1,045 mm of precipitation a year.
- NOAA stationRomeoville Weather Office
- Station IDUSC00117457
- Location41.60°N 88.08°W
- Elevation660 ft (201 m)
- From the center2 miles
- Population41,177
On October 22, the normal high in Romeoville is 61°F and the normal low 41°F, and the chance of measurable rain or snow is 33%.
Normals describe a typical year at the station, not a forecast. The National Weather Service forecast for Romeoville.
- Jan 32° 16°
- Feb 36° 20°
- Mar 49° 30°
- Apr 61° 40°
- May 72° 50°
- Jun 82° 60°
- Jul 85° 65°
- Aug 83° 63°
- Sep 76° 55°
- Oct 64° 44°
- Nov 49° 32°
- Dec 37° 22°
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 Romeoville each month?
July is the warmest month, with normal highs of 85°F; January the coldest, with normal lows of 16°F. The most precipitation falls in May (4.81 in), the least in February (1.98 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 | 32°F | 16°F | 23.9°F | 2.19 | 10.6 | 10 | <1 | 28 | 9 h 30 min |
| February | 36°F | 20°F | 28.0°F | 1.98 | 8.7 | 10 | <1 | 25 | 10 h 30 min |
| March | 49°F | 30°F | 39.1°F | 2.71 | 4.2 | 11 | <1 | 20 | 11 h 50 min |
| April | 61°F | 40°F | 50.3°F | 4.11 | 0.9 | 12 | <1 | 5 | 13 h 20 min |
| May | 72°F | 50°F | 61.4°F | 4.81 | 0.0 | 14 | 1 | <1 | 14 h 30 min |
| June | 82°F | 60°F | 70.9°F | 4.68 | 0.0 | 12 | 4 | <1 | 15 h 10 min |
| July | 85°F | 65°F | 74.6°F | 4.50 | 0.0 | 10 | 6 | <1 | 15 h |
| August | 83°F | 63°F | 72.8°F | 4.36 | 0.0 | 10 | 3 | <1 | 13 h 50 min |
| September | 76°F | 55°F | 65.9°F | 3.31 | 0.0 | 8 | 2 | <1 | 12 h 30 min |
| October | 64°F | 44°F | 53.7°F | 3.67 | 0.1 | 11 | <1 | 3 | 11 h 10 min |
| November | 49°F | 32°F | 40.4°F | 2.67 | 1.2 | 9 | <1 | 15 | 9 h 50 min |
| December | 37°F | 22°F | 29.4°F | 2.15 | 7.5 | 11 | <1 | 27 | 9 h 10 min |
| Year (annual) | 60°F | 41°F | 50.9°F | 41.14 | 33.2 | 127 | 16 | 123 |
The same normals in °C and millimetres
| Month | High | Low | Mean | Precip. | Snow |
|---|---|---|---|---|---|
| January | 0°C | −9°C | −4.5°C | 56 mm | 27 cm |
| February | 2°C | −7°C | −2.2°C | 50 mm | 22 cm |
| March | 9°C | −1°C | 3.9°C | 69 mm | 11 cm |
| April | 16°C | 4°C | 10.2°C | 104 mm | 2 cm |
| May | 22°C | 10°C | 16.3°C | 122 mm | 0 cm |
| June | 28°C | 16°C | 21.6°C | 119 mm | 0 cm |
| July | 29°C | 18°C | 23.7°C | 114 mm | 0 cm |
| August | 28°C | 17°C | 22.7°C | 111 mm | 0 cm |
| September | 25°C | 13°C | 18.8°C | 84 mm | 0 cm |
| October | 18°C | 6°C | 12.1°C | 93 mm | 0 cm |
| November | 9°C | 0°C | 4.7°C | 68 mm | 3 cm |
| December | 3°C | −6°C | −1.4°C | 55 mm | 19 cm |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00117457; 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 Romeoville?
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 (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 USC00117457.
When is the last frost in Romeoville?
In Romeoville, the last spring frost (32°F) comes after April 20 in half of years and after May 6 in one year in ten; the first autumn frost comes before October 22 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 201 year in 10 after May 6; 9 in 10 after April 7
- First autumn frost, half of years before
- October 221 year in 10 before October 7; 9 in 10 before November 3
NOAA puts the median frost-free season at 184 days, and the season without a hard freeze (28°F) at 206 days.
A hard freeze (28°F) comes after April 8 in half of springs and before November 1 in half of autumns.
The USDA's 2023 Plant Hardiness Zone Map puts Romeoville in zone 6a in ZIP code 60446. By the map's own method, the average of each year's coldest night over 1991-2020, Romeoville's NOAA station is in zone 5b: the coldest night of a typical year reaches −11°F (29 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 Illinois · Frost dates by ZIP code
Source: NOAA NCEI 1991-2020 annual normals (frost probabilities), station USC00117457; 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 Romeoville?
In a normal year in Romeoville, 16 days a year reach 90°F, 123 nights fall to 32°F or colder and 127 days bring measurable precipitation.
- Days at 90°F or more
- 16a normal year
- Days at 100°F or more
- fewer than 1a normal year
- Nights at 32°F or colder
- 123a normal year
- Days that stay below freezing
- 43high of 32°F or less
- Days with 0.01 inch of precipitation
- 127a normal year
- Days with 1 inch of snow or more
- 10a normal year
The highest temperature in this station's record (since 1992) is 102°F, on July 24, 2005; the lowest is −24°F, on January 16, 2009.
The wettest calendar year on that record is 2019, with 56.81 in; the snowiest season is 2013–14, with 76.7 inches.
Source: NOAA NCEI 1991-2020 annual normals, station USC00117457; records: ACIS (NOAA Regional Climate Centers), station USC00117457. Records use complete months only; a month missing more than three days is left out.
How sunny is Romeoville?
Over a year 73% of the sunlight that would reach the ground under clear skies gets through the clouds in the area around Romeoville, 3.9 kWh per square metre a day. July is the sunniest month (81%) and January the cloudiest (61%).
| Month | Share of clear-sky sunshine | Sunshine, kWh/m² a day |
|---|---|---|
| January | 61% | 1.7 |
| February | 65% | 2.6 |
| March | 67% | 3.6 |
| April | 70% | 4.8 |
| May | 71% | 5.5 |
| June | 77% | 6.1 |
| July | 81% | 6.2 |
| August | 80% | 5.4 |
| September | 80% | 4.5 |
| October | 71% | 3.0 |
| November | 67% | 2.0 |
| December | 61% | 1.5 |
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 Romeoville need?
A normal year in Romeoville brings 6,063 heating degree days, 13% more than the median U.S. place (5,373), and 947 cooling degree days, 4% 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 3,305 growing degree days a year above 50°F.
| Month | Heating | Cooling |
|---|---|---|
| January | 1,274 | 0 |
| February | 1,036 | 0 |
| March | 806 | 3 |
| April | 448 | 7 |
| May | 180 | 67 |
| June | 23 | 200 |
| July | 2 | 300 |
| August | 5 | 248 |
| September | 80 | 106 |
| October | 368 | 17 |
| November | 738 | 0 |
| December | 1,104 | 0 |
| Year (annual) | 6,063 | 947 |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00117457. 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 Romeoville been warmer than normal lately?
2025 averaged 51.0°F, 0.1°F above the 1991-2020 normal of 50.9°F. 4 of the 5 complete years since 2021 ran warmer than the normal.
| Year | Mean | Against normal | Precip. | Snow |
|---|---|---|---|---|
| 2021 | 52.3°F | +1.4°F | 33.23 | 45.4 |
| 2022 | 50.0°F | −0.9°F | 37.65 | 34.7 |
| 2023 | 52.4°F | +1.5°F | 38.40 | 13.4 |
| 2024 | 53.9°F | +3.0°F | 41.62 | 19.3 |
| 2025 | 51.0°F | +0.1°F | 31.50 | 30.8 |
Source: observed years: ACIS, station USC00117457. A year counts only with all twelve months complete.
How does Romeoville's climate compare?
Romeoville is warmer than 54 of the other 143 places with their own NOAA record in Illinois, and wetter than 91. Across the 7,247 U.S. stations with normals, its annual mean of 50.9°F is warmer than 44%.
In the Köppen classification computed from these normals, Romeoville 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 Romeoville share this climate record?
11 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.
- Bolingbrook, ILalso near: Lisle (9 mi, 49.2°F a year); Wheaton (9 mi, 51.1°F a year)74,756 people · 6 mi N
- Plainfield, IL48,881 people · 8 mi W
- Lockport, IL26,915 people · 3 mi E
- Homer Glen, IL24,852 people · 7 mi E
- Crest Hill, IL20,223 people · 3 mi SW
- Fairmont, IL2,409 people · 3 mi SE
- Crystal Lawns, IL1,965 people · 5 mi SW
- Lockport Heights, IL984 people · 3 mi E
- Bonnie Brae, IL844 people · 3 mi E
- Sunnyland, IL829 people · 4 mi SW
- Marley, IL111 people · 9 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 Romeoville's climate
What is the coldest month in Romeoville?
January, with a normal high of 32°F and a normal low of 16°F. The warmest is July (85°F by day, 65°F at night).
Does it snow in Romeoville?
Yes: 33 inches in a normal year, falling on 26 days with 0.1 inch or more, the most in January (10.6 inches).
What is the rainiest month in Romeoville?
May, with 4.81 in of precipitation in a normal year; the driest is February with 1.98 in.
What plant hardiness zone is Romeoville in?
The USDA's 2023 map puts Romeoville in zone 6a in ZIP code 60446. By the same method at Romeoville's NOAA station, the coldest night of a typical year reaches −11°F (29 years, 1991-2020): zone 5b.
How late can frost come in Romeoville?
In half of years the last 32°F night comes after April 20; in one year in ten it comes after May 6. Waiting until May 6 leaves about a one-in-ten chance of a later frost.
Nearby and next
- Romeoville in OctoberThis month day by day, its records and recent years
- Illinois climateThe statewide normals and every place in the state
- Joliet, IL7 miles from this station, 50.4°F a year
- Little Red School House, IL13 miles from this station, 51.4°F a year
- Lisle, IL14 miles from this station, 49.2°F a year
- Wheaton, IL14 miles from this station, 51.1°F a year
- Compare two placesMonth by month, side by side
Download these normals (CSV) · JSON · How these figures are made