Mason City, Iowa climate: Normal weather by month, frost dates and records
Mason City's normal year runs from 7°F January nights to 83°F July afternoons, with 36.3 inches of precipitation and 44 inches of snow a year. (NOAA 1991-2020 normals)
In metric: a yearly mean of 7.6°C, January lows of −14°C, July highs of 28°C, 921 mm of precipitation a year.
- NOAA stationMason City Municipal Airport
- Station IDUSW00014940
- Location43.15°N 93.33°W
- Elevation1,225 ft (373 m)
- From the center6 miles
- Population26,948
On October 23, the normal high in Mason City is 56°F and the normal low 34°F, and the chance of measurable rain or snow is 27%.
Normals describe a typical year at the station, not a forecast. The National Weather Service forecast for Mason City.
- Jan 24° 7°
- Feb 29° 11°
- Mar 42° 24°
- Apr 58° 35°
- May 70° 47°
- Jun 80° 57°
- Jul 83° 61°
- Aug 80° 58°
- Sep 74° 49°
- Oct 60° 37°
- Nov 44° 24°
- Dec 30° 14°
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 Mason City each month?
July is the warmest month, with normal highs of 83°F; January the coldest, with normal lows of 7°F. The most precipitation falls in June (5.39 in), the least in January (0.89 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 | 24°F | 7°F | 15.7°F | 0.89 | 11.3 | 8 | <1 | 31 | 9 h 20 min |
| February | 29°F | 11°F | 20.0°F | 1.22 | 10.0 | 8 | <1 | 27 | 10 h 30 min |
| March | 42°F | 24°F | 32.9°F | 2.29 | 7.0 | 9 | <1 | 25 | 11 h 50 min |
| April | 58°F | 35°F | 46.0°F | 4.15 | 3.0 | 12 | <1 | 12 | 13 h 20 min |
| May | 70°F | 47°F | 58.2°F | 5.15 | 0.3 | 14 | 1 | 1 | 14 h 40 min |
| June | 80°F | 57°F | 68.5°F | 5.39 | 0.0 | 12 | 3 | <1 | 15 h 20 min |
| July | 83°F | 61°F | 71.5°F | 4.43 | 0.0 | 10 | 4 | <1 | 15 h 10 min |
| August | 80°F | 58°F | 68.9°F | 3.79 | 0.0 | 9 | 2 | <1 | 14 h |
| September | 74°F | 49°F | 61.4°F | 3.45 | 0.0 | 9 | 1 | 1 | 12 h 30 min |
| October | 60°F | 37°F | 48.2°F | 2.53 | 0.4 | 9 | <1 | 11 | 11 h 10 min |
| November | 44°F | 24°F | 33.9°F | 1.67 | 3.0 | 8 | <1 | 23 | 9 h 50 min |
| December | 30°F | 14°F | 21.6°F | 1.29 | 9.4 | 8 | <1 | 30 | 9 h |
| Year (annual) | 56°F | 35°F | 45.6°F | 36.25 | 44.4 | 116 | 12 | 161 |
The same normals in °C and millimetres
| Month | High | Low | Mean | Precip. | Snow |
|---|---|---|---|---|---|
| January | −4°C | −14°C | −9.1°C | 23 mm | 29 cm |
| February | −2°C | −11°C | −6.7°C | 31 mm | 25 cm |
| March | 6°C | −5°C | 0.5°C | 58 mm | 18 cm |
| April | 14°C | 1°C | 7.8°C | 105 mm | 8 cm |
| May | 21°C | 8°C | 14.6°C | 131 mm | 1 cm |
| June | 26°C | 14°C | 20.3°C | 137 mm | 0 cm |
| July | 28°C | 16°C | 21.9°C | 113 mm | 0 cm |
| August | 27°C | 14°C | 20.5°C | 96 mm | 0 cm |
| September | 23°C | 9°C | 16.3°C | 88 mm | 0 cm |
| October | 16°C | 3°C | 9.0°C | 64 mm | 1 cm |
| November | 6°C | −4°C | 1.1°C | 42 mm | 8 cm |
| December | −1°C | −10°C | −5.8°C | 33 mm | 24 cm |
Source: NOAA NCEI 1991-2020 monthly normals, station USW00014940; 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 Mason City?
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 (9).
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 USW00014940.
When is the last frost in Mason City?
In Mason City, the last spring frost (32°F) comes after May 3 in half of years and after May 15 in one year in ten; the first autumn frost comes before October 1 in half of years and before September 18 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
- May 31 year in 10 after May 15; 9 in 10 after April 19
- First autumn frost, half of years before
- October 11 year in 10 before September 18; 9 in 10 before October 15
NOAA puts the median frost-free season at 150 days, and the season without a hard freeze (28°F) at 169 days.
A hard freeze (28°F) comes after April 24 in half of springs and before October 11 in half of autumns.
The USDA's 2023 Plant Hardiness Zone Map puts Mason City in zone 5a in ZIP code 50401. By the map's own method, the average of each year's coldest night over 1991-2020, Mason City's NOAA station is in zone 5a: the coldest night of a typical year reaches −19°F (30 complete years).
Frost dates for every NOAA station in Iowa · Frost dates by ZIP code
Source: NOAA NCEI 1991-2020 annual normals (frost probabilities), station USW00014940; 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 Mason City?
In a normal year in Mason City, 12 days a year reach 90°F, 161 nights fall to 32°F or colder and 116 days bring measurable precipitation.
- Days at 90°F or more
- 12a normal year
- Days at 100°F or more
- fewer than 1a normal year
- Nights at 32°F or colder
- 161a normal year
- Days that stay below freezing
- 68high of 32°F or less
- Days with 0.01 inch of precipitation
- 116a normal year
- Days with 1 inch of snow or more
- 13a normal year
The highest temperature in this station's record (since 1948) is 104°F, on July 7, 1980; the lowest is −32°F, on February 2, 1996.
The wettest calendar year on that record is 2018, with 50.01 in; the snowiest season is 1970–71, with 68.5 inches.
Source: NOAA NCEI 1991-2020 annual normals, station USW00014940; records: ACIS (NOAA Regional Climate Centers), station USW00014940. Records use complete months only; a month missing more than three days is left out.
How humid and windy is Mason City, and how clear are its skies?
The summer (June-August) dew point averages 61°F. The muggiest month is July, with an average dew point of 63°F; the driest air comes in January (13°F). March is the windiest month (13.2 mph on average), and August has the most clear or nearly clear hours (70%).
| Month | Dew point | Humidity | Afternoon humidity | Wind | Clear or few clouds | Overcast |
|---|---|---|---|---|---|---|
| January | 13°F | 80% | 74% | 12.1 mph | 48% | 40% |
| February | 19°F | 78% | 69% | 12.5 mph | 49% | 39% |
| March | 31°F | 70% | 52% | 13.2 mph | 50% | 36% |
| April | 40°F | 63% | 45% | 12.7 mph | 52% | 32% |
| May | 52°F | 67% | 48% | 10.7 mph | 55% | 25% |
| June | 61°F | 72% | 54% | 9.4 mph | 64% | 16% |
| July | 63°F | 77% | 57% | 7.7 mph | 64% | 15% |
| August | 59°F | 77% | 55% | 8.1 mph | 70% | 14% |
| September | 45°F | 69% | 46% | 10.0 mph | 65% | 20% |
| October | 33°F | 72% | 53% | 11.5 mph | 55% | 34% |
| November | 22°F | 79% | 67% | 11.8 mph | 51% | 39% |
| December | 13°F | 81% | 74% | 12.1 mph | 50% | 41% |
Source: NOAA NCEI 1991-2020 hourly normals, station USW00014940. Monthly averages of all hours; afternoon humidity at 3 p.m. local standard time; sky as the share of hours NOAA's observations rate clear or few clouds (a dash where NOAA publishes no sky value).
How sunny is Mason City?
Over a year 74% of the sunlight that would reach the ground under clear skies gets through the clouds in the area around Mason City, 4.0 kWh per square metre a day. July is the sunniest month (82%) and December the cloudiest (65%).
| Month | Share of clear-sky sunshine | Sunshine, kWh/m² a day |
|---|---|---|
| January | 70% | 1.9 |
| February | 76% | 3.0 |
| March | 71% | 3.8 |
| April | 69% | 4.8 |
| May | 70% | 5.5 |
| June | 75% | 6.2 |
| July | 82% | 6.5 |
| August | 80% | 5.5 |
| September | 78% | 4.3 |
| October | 70% | 2.9 |
| November | 69% | 1.9 |
| December | 65% | 1.4 |
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 Mason City need?
A normal year in Mason City brings 7,647 heating degree days, 42% more than the median U.S. place (5,373), and 603 cooling degree days, 34% fewer 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 2,628 growing degree days a year above 50°F.
| Month | Heating | Cooling |
|---|---|---|
| January | 1,528 | 0 |
| February | 1,261 | 0 |
| March | 997 | 0 |
| April | 573 | 3 |
| May | 246 | 35 |
| June | 39 | 142 |
| July | 10 | 212 |
| August | 26 | 147 |
| September | 164 | 57 |
| October | 525 | 6 |
| November | 932 | 0 |
| December | 1,345 | 0 |
| Year (annual) | 7,647 | 603 |
Source: NOAA NCEI 1991-2020 monthly normals, station USW00014940. 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 Mason City been warmer than normal lately?
2025 averaged 47.3°F, 1.7°F above the 1991-2020 normal of 45.6°F. 4 of the 5 complete years since 2021 ran warmer than the normal.
| Year | Mean | Against normal | Precip. | Snow |
|---|---|---|---|---|
| 2021 | 47.6°F | +2.0°F | 29.95 | 33.1 |
| 2022 | 44.3°F | −1.3°F | 29.00 | 37.7 |
| 2023 | 47.8°F | +2.2°F | 25.56 | 28.1 |
| 2024 | 49.2°F | +3.6°F | 33.87 | 18.1 |
| 2025 | 47.3°F | +1.7°F | 37.26 | 33.7 |
Over 74 complete years from 1951 to 2025, the station's annual mean temperature rose at a fitted 4.7°F per century (+0.26°C per decade). A fitted rate summarizes the whole record; single years swing well above and below it.
Source: observed years: ACIS, station USW00014940; trend: NOAA GHCN-Monthly v4. A year counts only with all twelve months complete.
How does Mason City's climate compare?
Mason City is warmer than 14 of the other 131 places with their own NOAA record in Iowa, and wetter than 56. Across the 7,247 U.S. stations with normals, its annual mean of 45.6°F is warmer than 22%.
In the Köppen classification computed from these normals, Mason City is Dfb: continental, no dry season, warm 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 Mason City 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.
- Clear Lake, IA7,602 people · 3 mi SW
- Rockwell, IA1,044 people · 14 mi SE
- Ventura, IA701 people · 7 mi W
- Thornton, IA394 people · 15 mi S
- Plymouth, IA368 people · 12 mi NE
- Fertile, IA300 people · 9 mi NW
- Hanlontown, IA200 people · 9 mi N
- Rock Falls, IA143 people · 13 mi E
- Swaledale, IA136 people · 12 mi S
- Burchinal, IA19 people · 7 mi S
- Portland, IA14 people · 10 mi E
Source: Census Bureau 2024 Gazetteer (place centers) and Vintage 2024 population estimates. Distance and direction from the station to each place's center.
What do Mason City's other NOAA stations record?
One more NOAA station keeps 1991-2020 normals in or near Mason City. This page uses Mason City Municipal Airport; the other differs by site and elevation:
| Station | From the center | Elevation | Year | Jan low | Jul high | Precip. | Snow | Last frost |
|---|---|---|---|---|---|---|---|---|
| Mason City station USC00135230 | 1 mi N | 1,105 ft | 45.6°F | 7°F | 82°F | 36.3 | – | April 29 |
Source: NOAA NCEI 1991-2020 normals for each station. Last frost: the median last spring date of 32°F.
Questions about Mason City's climate
What is the coldest month in Mason City?
January, with a normal high of 24°F and a normal low of 7°F. The warmest is July (83°F by day, 61°F at night).
Does it snow in Mason City?
Yes: 44 inches in a normal year, falling on 30 days with 0.1 inch or more, the most in January (11.3 inches).
What is the rainiest month in Mason City?
June, with 5.39 in of precipitation in a normal year; the driest is January with 0.89 in.
What plant hardiness zone is Mason City in?
The USDA's 2023 map puts Mason City in zone 5a in ZIP code 50401. By the same method at Mason City's NOAA station, the coldest night of a typical year reaches −19°F (30 years, 1991-2020): zone 5a.
How late can frost come in Mason City?
In half of years the last 32°F night comes after May 3; in one year in ten it comes after May 15. Waiting until May 15 leaves about a one-in-ten chance of a later frost.
Nearby and next
- Mason City in OctoberThis month day by day, its records and recent years
- Iowa climateThe statewide normals and every place in the state
- Forest City, IA18 miles from this station, 44.9°F a year
- Northwood, IA21 miles from this station, 43.0°F a year
- Britt, IA21 miles from this station, 45.5°F a year
- Osage, IA27 miles from this station, 45.3°F a year
- Compare two placesMonth by month, side by side
Download these normals (CSV) · JSON · How these figures are made