Frost dates for Mason City Muni Airport, IA
At Mason City Muni Airport, the median last spring frost (32°F) is May 3 and the median first fall frost is Oct 1, for a typical growing season of 150 days. For a 90% chance that the last frost has passed, wait until May 15. Nearby ZIP codes are in USDA hardiness zone 5a.
- May 3Last spring frost (median)50% chance of 32°F after this date
- May 15Safer planting date10% chance of 32°F after this date
- Oct 1First fall frost (median)50% chance of 32°F by this date
- 150 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 30 | May 11 | May 25 |
| 32°F | Apr 19 | May 3 | May 15 |
| 28°F | Apr 9 | Apr 24 | May 7 |
| 24°F | Mar 30 | Apr 13 | Apr 29 |
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 10 | Sep 24 | Oct 5 |
| 32°F | Sep 18 | Oct 1 | Oct 15 |
| 28°F | Sep 27 | Oct 11 | Oct 23 |
| 24°F | Oct 7 | Oct 22 | Nov 3 |
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 | 134 days | 150 days |
| 32°F | 131 days | 150 days | 168 days |
| 28°F | 149 days | 169 days | 187 days |
| 24°F | 170 days | 189 days | 208 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 |
|---|---|---|---|
| 50428 | 5a | -20 to -15°F | 5 km |
| 50482 | 5a | -20 to -15°F | 13 km |
| 50444 | 5a | -20 to -15°F | 17 km |
| 50477 | 5a | -20 to -15°F | 19 km |
| 50479 | 5a | -20 to -15°F | 25 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 USW00014940, at 43.1544, -93.3269, elevation 373 m (1,225 ft).
- Data quality: Standard (24+ years of data), 29 years of freeze data.
- Average days per year at or below 32°F: 160.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Mason City (11 km)
- Forest City 2 NNE (29 km)
- Northwood (33 km)
- Britt 3e (34 km)
- Osage (44 km)
- Hampton (45 km)
- Charles City (54 km)
- Clarion (59 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.