Waterloo, Iowa climate: Normal weather by month, frost dates and records
Waterloo's normal year runs from 11°F January nights to 85°F July afternoons, with 36.3 inches of precipitation and 39 inches of snow a year. (NOAA 1991-2020 normals)
In metric: a yearly mean of 9.4°C, January lows of −12°C, July highs of 29°C, 922 mm of precipitation a year.
- NOAA stationWaterloo Municipal Airport
- Station IDUSW00094910
- Location42.55°N 92.40°W
- Elevation868 ft (265 m)
- Population67,477
On October 23, the normal high in Waterloo is 59°F and the normal low 37°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 Waterloo.
- Jan 28° 11°
- Feb 33° 15°
- Mar 47° 27°
- Apr 61° 38°
- May 73° 50°
- Jun 82° 61°
- Jul 85° 64°
- Aug 83° 61°
- Sep 77° 52°
- Oct 63° 40°
- Nov 47° 28°
- Dec 34° 17°
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 Waterloo each month?
July is the warmest month, with normal highs of 85°F; January the coldest, with normal lows of 11°F. The most precipitation falls in June (5.72 in), the least in January (1.10 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 | 28°F | 11°F | 19.4°F | 1.10 | 10.1 | 8 | <1 | 30 | 9 h 20 min |
| February | 33°F | 15°F | 23.9°F | 1.14 | 9.3 | 8 | <1 | 26 | 10 h 30 min |
| March | 47°F | 27°F | 36.7°F | 1.98 | 4.6 | 10 | <1 | 23 | 11 h 50 min |
| April | 61°F | 38°F | 49.4°F | 4.04 | 1.7 | 12 | <1 | 10 | 13 h 20 min |
| May | 73°F | 50°F | 61.5°F | 4.61 | 0.1 | 13 | 1 | 1 | 14 h 30 min |
| June | 82°F | 61°F | 71.5°F | 5.72 | 0.0 | 12 | 4 | <1 | 15 h 20 min |
| July | 85°F | 64°F | 74.5°F | 4.34 | 0.0 | 9 | 6 | <1 | 15 h |
| August | 83°F | 61°F | 71.9°F | 4.17 | 0.0 | 9 | 3 | <1 | 14 h |
| September | 77°F | 52°F | 64.6°F | 3.14 | 0.0 | 9 | 2 | 1 | 12 h 30 min |
| October | 63°F | 40°F | 51.6°F | 2.76 | 0.3 | 9 | <1 | 9 | 11 h 10 min |
| November | 47°F | 28°F | 37.4°F | 1.85 | 3.1 | 8 | <1 | 22 | 9 h 50 min |
| December | 34°F | 17°F | 25.3°F | 1.44 | 9.9 | 8 | <1 | 29 | 9 h 10 min |
| Year (annual) | 59°F | 39°F | 49.0°F | 36.29 | 39.1 | 114 | 15 | 151 |
The same normals in °C and millimetres
| Month | High | Low | Mean | Precip. | Snow |
|---|---|---|---|---|---|
| January | −2°C | −12°C | −7.0°C | 28 mm | 26 cm |
| February | 0°C | −9°C | −4.5°C | 29 mm | 24 cm |
| March | 8°C | −3°C | 2.6°C | 50 mm | 12 cm |
| April | 16°C | 3°C | 9.7°C | 103 mm | 4 cm |
| May | 23°C | 10°C | 16.4°C | 117 mm | 0 cm |
| June | 28°C | 16°C | 21.9°C | 145 mm | 0 cm |
| July | 29°C | 18°C | 23.6°C | 110 mm | 0 cm |
| August | 28°C | 16°C | 22.2°C | 106 mm | 0 cm |
| September | 25°C | 11°C | 18.1°C | 80 mm | 0 cm |
| October | 17°C | 5°C | 10.9°C | 70 mm | 1 cm |
| November | 8°C | −2°C | 3.0°C | 47 mm | 8 cm |
| December | 1°C | −8°C | −3.7°C | 37 mm | 25 cm |
Source: NOAA NCEI 1991-2020 monthly normals, station USW00094910; 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 Waterloo?
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 USW00094910.
When is the last frost in Waterloo?
In Waterloo, the last spring frost (32°F) comes after April 27 in half of years and after May 10 in one year in ten; the first autumn frost comes before October 10 in half of years and before September 26 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
- April 271 year in 10 after May 10; 9 in 10 after April 11
- First autumn frost, half of years before
- October 101 year in 10 before September 26; 9 in 10 before October 21
NOAA puts the median frost-free season at 165 days, and the season without a hard freeze (28°F) at 185 days.
A hard freeze (28°F) comes after April 16 in half of springs and before October 20 in half of autumns.
The USDA's 2023 Plant Hardiness Zone Map puts Waterloo in zone 5a across its 4 ZIP code areas (5a in 50701, the largest). By the map's own method, the average of each year's coldest night over 1991-2020, Waterloo's NOAA station is in zone 5a: the coldest night of a typical year reaches −20°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 USW00094910; 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.
What hardiness zone is each Waterloo ZIP code in?
The USDA's 2023 map gives each ZIP code area one zone. Waterloo's 4 ZIP code areas are all in zone 5a. Each ZIP's frost dates are in the frost tool.
Source: USDA 2023 Plant Hardiness Zone Map, ZIP listings: PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed October 8, 2026; ZIP areas in the place: Census Bureau 2020 ZCTA-to-place relationship file. A ZIP area counts when at least a tenth of its land (and 0.5 km²) lies in the place.
How hot and how cold does it get in Waterloo?
In a normal year in Waterloo, 15 days a year reach 90°F, 151 nights fall to 32°F or colder and 114 days bring measurable precipitation.
- Days at 90°F or more
- 15a normal year
- Days at 100°F or more
- fewer than 1a normal year
- Nights at 32°F or colder
- 151a normal year
- Days that stay below freezing
- 58high of 32°F or less
- Days with 0.01 inch of precipitation
- 114a normal year
- Days with 1 inch of snow or more
- 12a normal year
The highest temperature in Waterloo's official record (kept by the National Weather Service since 1895) is 112°F, on July 14, 1936; the lowest is −34°F, on January 16, 2009.
The wettest calendar year on that record is 2018, with 54.15 in; the snowiest season is 2018–19, with 60.0 inches.
Source: NOAA NCEI 1991-2020 annual normals, station USW00094910; records: ACIS (NOAA Regional Climate Centers), NWS threaded record ALOthr. Records use complete months only; a month missing more than three days is left out.
How humid and windy is Waterloo, and how clear are its skies?
The summer (June-August) dew point averages 62°F. The muggiest month is July, with an average dew point of 63°F; the driest air comes in January (14°F). March is the windiest month (11.7 mph on average), and August has the most clear or nearly clear hours (73%).
| Month | Dew point | Humidity | Afternoon humidity | Wind | Clear or few clouds | Overcast |
|---|---|---|---|---|---|---|
| January | 14°F | 78% | 69% | 10.0 mph | 51% | 39% |
| February | 20°F | 75% | 63% | 10.8 mph | 52% | 39% |
| March | 31°F | 65% | 47% | 11.7 mph | 52% | 35% |
| April | 41°F | 62% | 45% | 11.2 mph | 55% | 32% |
| May | 54°F | 67% | 49% | 9.1 mph | 60% | 23% |
| June | 63°F | 71% | 54% | 8.1 mph | 70% | 13% |
| July | 63°F | 74% | 55% | 6.9 mph | 71% | 12% |
| August | 60°F | 75% | 54% | 7.4 mph | 73% | 14% |
| September | 46°F | 68% | 46% | 8.8 mph | 69% | 20% |
| October | 34°F | 70% | 51% | 10.0 mph | 57% | 33% |
| November | 23°F | 77% | 63% | 10.1 mph | 52% | 39% |
| December | 15°F | 79% | 70% | 10.0 mph | 53% | 40% |
Source: NOAA NCEI 1991-2020 hourly normals, station USW00094910. 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 Waterloo?
Over a year 74% of the sunlight that would reach the ground under clear skies gets through the clouds in the area around Waterloo, 4.0 kWh per square metre a day. July is the sunniest month (81%) and December the cloudiest (66%). Among the 459 U.S. places of 50,000 or more, that ranks tied 330th (with 21 others) in sunshine.
| Month | Share of clear-sky sunshine | Sunshine, kWh/m² a day |
|---|---|---|
| January | 70% | 1.9 |
| February | 76% | 3.0 |
| March | 72% | 3.9 |
| April | 69% | 4.8 |
| May | 71% | 5.6 |
| June | 76% | 6.2 |
| July | 81% | 6.3 |
| August | 80% | 5.5 |
| September | 79% | 4.4 |
| October | 71% | 3.0 |
| November | 70% | 2.0 |
| December | 66% | 1.6 |
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 Waterloo need?
A normal year in Waterloo brings 6,714 heating degree days, 25% more than the median U.S. place (5,373), and 918 cooling degree days, 1% more 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 3,194 growing degree days a year above 50°F.
| Month | Heating | Cooling |
|---|---|---|
| January | 1,412 | 0 |
| February | 1,151 | 0 |
| March | 879 | 1 |
| April | 475 | 7 |
| May | 173 | 64 |
| June | 18 | 213 |
| July | 3 | 297 |
| August | 10 | 225 |
| September | 109 | 97 |
| October | 428 | 13 |
| November | 828 | 0 |
| December | 1,229 | 0 |
| Year (annual) | 6,714 | 918 |
Source: NOAA NCEI 1991-2020 monthly normals, station USW00094910. 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 Waterloo been warmer than normal lately?
2025 averaged 49.8°F, 0.8°F above the 1991-2020 normal of 49.0°F. 4 of the 5 complete years since 2021 ran warmer than the normal.
| Year | Mean | Against normal | Precip. | Snow |
|---|---|---|---|---|
| 2021 | 50.2°F | +1.2°F | 24.87 | 42.8 |
| 2022 | 47.6°F | −1.4°F | 34.04 | 35.4 |
| 2023 | 51.5°F | +2.5°F | 22.63 | 23.0 |
| 2024 | 52.4°F | +3.4°F | 40.95 | 32.7 |
| 2025 | 49.8°F | +0.8°F | 35.46 | 34.2 |
Over 66 complete years from 1952 to 2025, the station's annual mean temperature rose at a fitted 3.4°F per century (+0.19°C per decade). A fitted rate summarizes the whole record; single years swing well above and below it.
Source: observed years: ACIS, station USW00094910; trend: NOAA GHCN-Monthly v4. A year counts only with all twelve months complete.
How does Waterloo's climate compare?
Waterloo is warmer than 87 of the other 131 places with their own NOAA record in Iowa, and wetter than 57. Across the 7,247 U.S. stations with normals, its annual mean of 49.0°F is warmer than 36%.
In the Köppen classification computed from these normals, Waterloo is Dfa: continental, no dry season, hot 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 Waterloo share this climate record?
12 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.
- Cedar Falls, IA41,417 people · 4 mi SW
- Waverly, IA10,576 people · 12 mi N
- Evansdale, IA4,515 people · 9 mi SE
- Hudson, IA2,916 people · 9 mi S
- Denver, IA1,955 people · 9 mi NE
- Elk Run Heights, IA1,061 people · 9 mi SE
- Janesville, IA1,052 people · 7 mi NW
- Dunkerton, IA840 people · 12 mi E
- Gilbertville, IA792 people · 13 mi SE
- Raymond, IA754 people · 11 mi SE
- Washburn, IA658 people · 12 mi SE
- New Hartford, IA555 people · 11 mi W
Source: Census Bureau 2024 Gazetteer (place centers) and Vintage 2024 population estimates. Distance and direction from the station to each place's center.
Questions about Waterloo's climate
What is the coldest month in Waterloo?
January, with a normal high of 28°F and a normal low of 11°F. The warmest is July (85°F by day, 64°F at night).
Does it snow in Waterloo?
Yes: 39 inches in a normal year, falling on 27 days with 0.1 inch or more, the most in January (10.1 inches).
What is the rainiest month in Waterloo?
June, with 5.72 in of precipitation in a normal year; the driest is January with 1.10 in.
What plant hardiness zone is Waterloo in?
The USDA's 2023 map puts Waterloo in zone 5a across its 4 ZIP code areas (5a in 50701, the largest). By the same method at Waterloo's NOAA station, the coldest night of a typical year reaches −20°F (30 years, 1991-2020): zone 5a.
How late can frost come in Waterloo?
In half of years the last 32°F night comes after April 27; in one year in ten it comes after May 10. Waiting until May 10 leaves about a one-in-ten chance of a later frost.
Nearby and next
- Waterloo in OctoberThis month day by day, its records and recent years
- Iowa climateThe statewide normals and every place in the state
- Tripoli, IA19 miles from this station, 46.4°F a year
- Grundy Center, IA22 miles from this station, 47.1°F a year
- Allison, IA25 miles from this station, 46.7°F a year
- Oelwein, IA25 miles from this station, 46.3°F a year
- Compare two placesMonth by month, side by side
Download these normals (CSV) · JSON · How these figures are made