Frost dates for Northwood, IA
At Northwood, the median last spring frost (32°F) is May 4 and the median first fall frost is Oct 4, for a typical growing season of 152 days. For a 90% chance that the last frost has passed, wait until May 16. Nearby ZIP codes are in USDA hardiness zone 5a.
- May 4Last spring frost (median)50% chance of 32°F after this date
- May 16Safer planting date10% chance of 32°F after this date
- Oct 4First fall frost (median)50% chance of 32°F by this date
- 152 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 | May 1 | May 13 | May 27 |
| 32°F | Apr 21 | May 4 | May 16 |
| 28°F | Apr 9 | Apr 24 | May 7 |
| 24°F | Apr 1 | Apr 14 | Apr 28 |
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 13 | Sep 25 | Oct 7 |
| 32°F | Sep 20 | Oct 4 | Oct 17 |
| 28°F | Oct 1 | Oct 13 | Oct 25 |
| 24°F | Oct 10 | Oct 22 | Nov 4 |
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 | 116 days | 133 days | 151 days |
| 32°F | 135 days | 152 days | 169 days |
| 28°F | 153 days | 172 days | 190 days |
| 24°F | 173 days | 191 days | 209 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 |
|---|---|---|---|
| 50459 | 5a | -20 to -15°F | 3 km |
| 50448 | 5a | -20 to -15°F | 10 km |
| 50426 | 5a | -20 to -15°F | 17 km |
| 50440 | 5a | -20 to -15°F | 17 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 USC00136103, at 43.4386, -93.2253, elevation 363 m (1,190 ft).
- Data quality: Standard (24+ years of data), 26 years of freeze data.
- Average days per year at or below 32°F: 164.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Mason City (31 km)
- Mason City Muni Airport (33 km)
- Forest City 2 NNE (37 km)
- Osage (38 km)
- Britt 3e (56 km)
- Charles City (61 km)
- Hampton (76 km)
- Allison (84 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.