Frost dates for Romeoville WFO, IL
At Romeoville WFO, the median last spring frost (32°F) is Apr 20 and the median first fall frost is Oct 22, for a typical growing season of 184 days. For a 90% chance that the last frost has passed, wait until May 6. Nearby ZIP codes are in USDA hardiness zones 5b to 6a.
- Apr 20Last spring frost (median)50% chance of 32°F after this date
- May 6Safer planting date10% chance of 32°F after this date
- Oct 22First fall frost (median)50% chance of 32°F by this date
- 184 daysGrowing season (median)between 32°F freezes
Last spring frost dates
The chance that the temperature drops to the threshold after each date.
| Temperature | 90% chance later | 50% chance later | 10% chance later |
|---|---|---|---|
| 36°F | Apr 17 | May 1 | May 17 |
| 32°F | Apr 7 | Apr 20 | May 6 |
| 28°F | Mar 27 | Apr 8 | Apr 23 |
| 24°F | Mar 13 | Mar 30 | Apr 12 |
First fall frost dates
The chance that the temperature has dropped to the threshold by each date.
| Temperature | 10% chance by | 50% chance by | 90% chance by |
|---|---|---|---|
| 36°F | Sep 28 | Oct 12 | Oct 24 |
| 32°F | Oct 7 | Oct 22 | Nov 3 |
| 28°F | Oct 19 | Nov 1 | Nov 15 |
| 24°F | Nov 1 | Nov 12 | Nov 26 |
Growing season length
Days between the last spring and first fall freeze, as the length reached in 9, 5 and 1 out of 10 years.
| Temperature | 9 in 10 years at least | 5 in 10 years at least | 1 in 10 years at least |
|---|---|---|---|
| 36°F | 142 days | 162 days | 180 days |
| 32°F | 162 days | 184 days | 202 days |
| 28°F | 186 days | 206 days | 226 days |
| 24°F | 211 days | 230 days | 252 days |
Chance of a freeze in any year
| Temperature | Chance per year |
|---|---|
| 36°F | 100% |
| 32°F | 100% |
| 28°F | 100% |
| 24°F | 100% |
ZIP codes whose closest station is this one
| ZIP | Hardiness zone | Avg. extreme low | Distance |
|---|---|---|---|
| 60441 | 6a | -10 to -5°F | 3 km |
| 60446 | 6a | -10 to -5°F | 3 km |
| 60403 | 6a | -10 to -5°F | 5 km |
| 60490 | 6a | -10 to -5°F | 9 km |
| 60491 | 6a | -10 to -5°F | 10 km |
| 60440 | 6a | -10 to -5°F | 11 km |
| 60544 | 5b | -15 to -10°F | 11 km |
| 60586 | 5b | -15 to -10°F | 13 km |
| 60585 | 5b | -15 to -10°F | 13 km |
| 60448 | 6a | -10 to -5°F | 18 km |
Not the official USDA Plant Hardiness Zone Map. Zones shown here are the values published in the USDA-ARS / Oregon State University PRISM Group 2023 ZIP code tables, shown unaltered. For the official interactive map, visit planthardiness.ars.usda.gov.
About this station
- NOAA station ID USC00117457, at 41.6042, -88.0850, elevation 201 m (660 ft).
- Data quality: Representative (10+ years), 23 years of freeze data.
- Average days per year at or below 32°F: 123.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Joliet Brandon Rd Dam (11 km)
- Little Red School Hse (21 km)
- Lisle-Morton Arboretum (23 km)
- Wheaton 3 SE (23 km)
- Aurora (27 km)
- Channahon Dresden Isl Dam (28 km)
- Chicago Midway Airport 3sw (30 km)
- Chicago Midway Airport (34 km)
Sources
- NOAA National Centers for Environmental Information, U.S. Climate Normals 1991–2020, annual/seasonal normals by station (version 1.0.1), file dated June 27, 2023; documentation.
- USDA Agricultural Research Service and PRISM Group, Oregon State University, 2023 Plant Hardiness Zone Map ZIP code tables (CONUS, Alaska, Hawaii, Puerto Rico), files dated November 17, 2023. Data © PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed November 1, 2026. Official map: planthardiness.ars.usda.gov.
- U.S. Census Bureau, 2024 Gazetteer ZIP Code Tabulation Areas file, dated August 30, 2024 (ZIP centroids used to find the nearest station).
Freeze dates are 30-year probabilities, not forecasts. Check your local forecast before planting tender plants.