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Will it freeze in Mason City in the next 7 nights?
The earliest overnight low at or below 32°F in the available NWS frost forecast is Tonight: 31°F (Thu, Nov 5, 6:00 PM CST to Fri, Nov 6, 6:00 AM CST).
Tonight: forecast low 31°F. Freeze.
NWS forecast period: Thu, Nov 5, 6:00 PM CST to Fri, Nov 6, 6:00 AM CST.
5 of the next 7 nights are forecast at 36°F or colder, cold enough for frost on exposed plants.
- Tonight 31°F Freeze · Mostly Cloudy
- Fri, Nov 6 25°F Hard freeze · Partly Cloudy
- Sat, Nov 7 33°F Frost possible · Partly Cloudy
- Sun, Nov 8 35°F Frost possible · Clear
- Mon, Nov 9 37°F Above 36°F · Mostly Clear
- Tue, Nov 10 36°F Frost possible · Partly Cloudy
- Wed, Nov 11 37°F Above 36°F · Partly Cloudy
Overnight lows from the National Weather Service forecast for this location. This covers the available forecast window, not the first freeze of the whole season. Frost can form above 32°F on clear, calm nights.
Frost and freeze probabilities
Freeze dates shift from year to year. Spring percentages describe the chance of a freeze after the stated date; fall percentages describe the chance of a freeze by that date. The 10% spring date is the cautious one: a later freeze happens about 1 year in 10.
These dates describe historical probabilities, not this year’s forecast or the earliest and latest possible freezes. Different weather stations or probability thresholds can produce different published dates for the same city.
Average first hard freeze in Mason City
The median first fall hard-freeze date (28°F) is October 18, from NOAA’s 1991–2020 Climate Normals at Mason City. This is the 50% probability date, not a forecast for this year.
| Temperature | Last spring date 90% · 50% · 10% chance of a later freeze | First fall date 10% · 50% · 90% chance of an earlier freeze | Season |
|---|---|---|---|
| 36°F frost possible | Apr 25 · May 7 · May 19 | Sep 17 · Sep 30 · Oct 12 | 144 days |
| 32°F freeze | Apr 14 · Apr 29 · May 9 | Sep 25 · Oct 7 · Oct 21 | 161 days |
| 28°F hard freeze | Apr 3 · Apr 18 · Apr 30 | Oct 1 · Oct 18 · Oct 31 | 181 days |
Average high temperature by month
1991–2020 normals at Mason City
Average low temperature by month
Months with lows near or below freezing carry frost risk
Where these frost dates come from
The frost dates for Mason City, IA come from the nearest weather station with freeze statistics in NOAA’s 1991–2020 Climate Normals: Mason City (station USC00135230, elevation 1,105 ft), 1.1 mi from Mason City. Local conditions (valleys, hilltops, distance to water, city heat) can shift frost dates by days or weeks. The hardiness zone is from the 2023 USDA Plant Hardiness Zone Map (USDA ARS and Oregon State University PRISM). See our methodology.
Frost dates near Mason City
| City | Distance | Last spring frost | First fall frost |
|---|---|---|---|
| Clear Lake, IA | 8.7 mi | May 3 | Oct 1 |
| Charles City, IA | 27 mi | Apr 30 | Oct 6 |
| Albert Lea, MN | 36 mi | Apr 27 | Oct 9 |
| Austin, MN | 38 mi | Apr 30 | Oct 5 |
| Iowa Falls, IA | 43 mi | Apr 28 | Oct 10 |
| Waverly, IA | 47 mi | Apr 27 | Oct 10 |
| Algona, IA | 52 mi | Apr 30 | Oct 6 |
| Webster City, IA | 57 mi | May 3 | Oct 2 |
| Cedar Falls, IA | 58 mi | Apr 27 | Oct 10 |
| Stewartville, MN | 61 mi | Apr 30 | Oct 6 |
Frequently asked questions
When is the last frost in Mason City?
On average, the last spring frost (32°F) in Mason City is around April 29. In about 1 year in 10 it comes after May 9, and in 9 years in 10 it comes after April 14.
When is the first frost in Mason City?
The first fall frost (32°F) usually arrives around October 7. There’s a 10% chance of a freeze by September 25 and a 90% chance by October 21.
Can it frost in Mason City after the last frost date?
Yes. Frost can form on clear, calm nights even when the air stays above 32°F. Temperatures of 36°F or lower, cold enough for frost on exposed plants, have a 50% chance of occurring after May 7.
What growing zone is Mason City?
Mason City is in USDA Plant Hardiness Zone 5a (average annual extreme minimum temperature −20 to −15°F), based on the 2023 USDA map for ZIP code 50401. See growing zones in Iowa.
More: all Iowa frost dates · Iowa growing zones · UV index today in Mason City · frost vs. freeze