Grinnell, Iowa climate: Normal weather by month, frost dates and records
Grinnell's normal year runs from 10°F January nights to 83°F July afternoons, with 38.2 inches of precipitation and 31 inches of snow a year. (NOAA 1991-2020 normals)
In metric: a yearly mean of 8.6°C, January lows of −12°C, July highs of 29°C, 970 mm of precipitation a year.
- NOAA stationGrinnell (3 mi SW)
- Station IDUSC00133473
- Location41.72°N 92.75°W
- Elevation905 ft (276 m)
- From the center2 miles
- Population9,495
On October 24, the normal high in Grinnell is 58°F and the normal low 35°F, and the chance of measurable rain or snow is 29%.
Normals describe a typical year at the station, not a forecast. The National Weather Service forecast for Grinnell.
- Jan 28° 10°
- Feb 33° 14°
- Mar 46° 25°
- Apr 59° 35°
- May 70° 47°
- Jun 80° 58°
- Jul 83° 62°
- Aug 81° 59°
- Sep 75° 50°
- Oct 62° 38°
- Nov 47° 26°
- Dec 34° 16°
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 Grinnell each month?
July is the warmest month, with normal highs of 83°F; January the coldest, with normal lows of 10°F. The most precipitation falls in June (5.53 in), the least in January (1.10 in).
| Month | High | Low | Mean | Precip. | Snow | Wet days | 90°F days | Freezing nights | Daylight |
|---|---|---|---|---|---|---|---|---|---|
| January | 28°F | 10°F | 19.3°F | 1.10 | 9.0 | 8 | <1 | 30 | 9 h 30 min |
| February | 33°F | 14°F | 23.3°F | 1.55 | 9.1 | 8 | <1 | 27 | 10 h 30 min |
| March | 46°F | 25°F | 35.4°F | 2.22 | 3.4 | 9 | <1 | 24 | 11 h 50 min |
| April | 59°F | 35°F | 47.3°F | 3.90 | 0.6 | 12 | <1 | 12 | 13 h 20 min |
| May | 70°F | 47°F | 58.5°F | 5.09 | 0.0 | 13 | <1 | 2 | 14 h 30 min |
| June | 80°F | 58°F | 68.6°F | 5.53 | 0.0 | 12 | 2 | <1 | 15 h 10 min |
| July | 83°F | 62°F | 72.5°F | 3.96 | 0.0 | 9 | 5 | <1 | 15 h |
| August | 81°F | 59°F | 70.2°F | 4.37 | 0.0 | 11 | 3 | <1 | 13 h 50 min |
| September | 75°F | 50°F | 62.7°F | 3.71 | 0.0 | 9 | 1 | 1 | 12 h 30 min |
| October | 62°F | 38°F | 50.2°F | 3.21 | 0.5 | 10 | <1 | 9 | 11 h 10 min |
| November | 47°F | 26°F | 36.6°F | 1.95 | 1.5 | 7 | <1 | 22 | 9 h 50 min |
| December | 34°F | 16°F | 25.2°F | 1.60 | 6.9 | 8 | <1 | 29 | 9 h 10 min |
| Year (annual) | 58°F | 37°F | 47.5°F | 38.19 | 31.0 | 115 | 11 | 157 |
The same normals in °C and millimetres
| Month | High | Low | Mean | Precip. | Snow |
|---|---|---|---|---|---|
| January | −2°C | −12°C | −7.1°C | 28 mm | 23 cm |
| February | 1°C | −10°C | −4.8°C | 39 mm | 23 cm |
| March | 8°C | −4°C | 1.9°C | 56 mm | 9 cm |
| April | 15°C | 2°C | 8.5°C | 99 mm | 2 cm |
| May | 21°C | 8°C | 14.7°C | 129 mm | 0 cm |
| June | 26°C | 14°C | 20.3°C | 140 mm | 0 cm |
| July | 29°C | 17°C | 22.5°C | 101 mm | 0 cm |
| August | 27°C | 15°C | 21.2°C | 111 mm | 0 cm |
| September | 24°C | 10°C | 17.1°C | 94 mm | 0 cm |
| October | 17°C | 3°C | 10.1°C | 82 mm | 1 cm |
| November | 8°C | −3°C | 2.6°C | 50 mm | 4 cm |
| December | 1°C | −9°C | −3.8°C | 41 mm | 18 cm |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00133473; 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 Grinnell?
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 USC00133473.
When is the last frost in Grinnell?
In Grinnell, the last spring frost (32°F) comes after May 3 in half of years and after May 17 in one year in ten; the first autumn frost comes before October 6 in half of years and before September 22 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 17; 9 in 10 after April 19
- First autumn frost, half of years before
- October 61 year in 10 before September 22; 9 in 10 before October 20
NOAA puts the median frost-free season at 155 days, and the season without a hard freeze (28°F) at 175 days.
A hard freeze (28°F) comes after April 23 in half of springs and before October 17 in half of autumns.
The USDA's 2023 Plant Hardiness Zone Map puts Grinnell in zone 5b in ZIP code 50112, the nearest ZIP area. By the map's own method, the average of each year's coldest night over 1991-2020, Grinnell's NOAA station is in zone 5a: the coldest night of a typical year reaches −17°F (28 complete years); the map interpolates between stations and terrain, so the station and the ZIP area can differ by half a zone.
Frost dates for every NOAA station in Iowa · Frost dates by ZIP code
Source: NOAA NCEI 1991-2020 annual normals (frost probabilities), station USC00133473; 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 Grinnell?
In a normal year in Grinnell, 11 days a year reach 90°F, 157 nights fall to 32°F or colder and 115 days bring measurable precipitation.
- Days at 90°F or more
- 11a normal year
- Days at 100°F or more
- fewer than 1a normal year
- Nights at 32°F or colder
- 157a normal year
- Days that stay below freezing
- 55high of 32°F or less
- Days with 0.01 inch of precipitation
- 115a normal year
- Days with 1 inch of snow or more
- 11a normal year
The highest temperature in this station's record (since 1893) is 110°F, on August 8, 1934; the lowest is −35°F, on February 4, 1996.
The wettest calendar year on that record is 2010, with 57.51 in; the snowiest season is 1959–60, with 63.5 inches.
Source: NOAA NCEI 1991-2020 annual normals, station USC00133473; records: ACIS (NOAA Regional Climate Centers), station USC00133473. Records use complete months only; a month missing more than three days is left out.
How sunny is Grinnell?
Over a year 75% of the sunlight that would reach the ground under clear skies gets through the clouds in the area around Grinnell, 4.1 kWh per square metre a day. July is the sunniest month (81%) and December the cloudiest (66%).
| Month | Share of clear-sky sunshine | Sunshine, kWh/m² a day |
|---|---|---|
| January | 69% | 2.0 |
| February | 74% | 3.0 |
| March | 70% | 3.8 |
| April | 70% | 4.8 |
| May | 72% | 5.6 |
| June | 77% | 6.2 |
| July | 81% | 6.3 |
| August | 80% | 5.5 |
| September | 81% | 4.6 |
| October | 73% | 3.1 |
| November | 71% | 2.1 |
| 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 Grinnell need?
A normal year in Grinnell brings 7,038 heating degree days, 31% more than the median U.S. place (5,373), and 692 cooling degree days, 24% 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 2,803 growing degree days a year above 50°F.
| Month | Heating | Cooling |
|---|---|---|
| January | 1,418 | 0 |
| February | 1,168 | 0 |
| March | 918 | 1 |
| April | 536 | 3 |
| May | 238 | 37 |
| June | 40 | 149 |
| July | 7 | 242 |
| August | 20 | 181 |
| September | 140 | 71 |
| October | 466 | 9 |
| November | 852 | 0 |
| December | 1,235 | 0 |
| Year (annual) | 7,038 | 692 |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00133473. 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 Grinnell been warmer than normal lately?
2024 averaged 51.4°F, 3.9°F above the 1991-2020 normal of 47.5°F. 2 of the 2 complete years since 2023 ran warmer than the normal.
| Year | Mean | Against normal | Precip. | Snow |
|---|---|---|---|---|
| 2023 | 50.5°F | +3.0°F | 28.48 | – |
| 2024 | 51.4°F | +3.9°F | 42.20 | 28.8 |
Over 78 complete years from 1906 to 2024, the station's annual mean temperature rose at a fitted 2.9°F per century (+0.16°C per decade). A fitted rate summarizes the whole record; single years swing well above and below it.
Source: observed years: ACIS, station USC00133473; trend: NOAA GHCN-Monthly v4. A year counts only with all twelve months complete.
How does Grinnell's climate compare?
Grinnell is warmer than 56 of the other 131 places with their own NOAA record in Iowa, and wetter than 98. Across the 7,247 U.S. stations with normals, its annual mean of 47.5°F is warmer than 30%.
In the Köppen classification computed from these normals, Grinnell 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 Grinnell share this climate record?
7 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.
- Montezuma, IA1,421 people · 15 mi SE
- Sully, IA891 people · 11 mi SW
- Gilman, IA530 people · 11 mi N
- Lynnville, IA382 people · 10 mi S
- Malcom, IA257 people · 10 mi E
- Oakland Acres, IA178 people · 4 mi W
- Searsboro, IA129 people · 10 mi S
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 Grinnell's climate
What is the coldest month in Grinnell?
January, with a normal high of 28°F and a normal low of 10°F. The warmest is July (83°F by day, 62°F at night).
Does it snow in Grinnell?
Yes: 31 inches in a normal year, falling on 20 days with 0.1 inch or more, the most in February (9.1 inches).
What is the rainiest month in Grinnell?
June, with 5.53 in of precipitation in a normal year; the driest is January with 1.10 in.
What plant hardiness zone is Grinnell in?
The USDA's 2023 map puts Grinnell in zone 5b in ZIP code 50112, the nearest ZIP area. By the same method at Grinnell's NOAA station, the coldest night of a typical year reaches −17°F (28 years, 1991-2020): zone 5a.
How late can frost come in Grinnell?
In half of years the last 32°F night comes after May 3; in one year in ten it comes after May 17. Waiting until May 17 leaves about a one-in-ten chance of a later frost.
Nearby and next
- Iowa climateThe statewide normals and every place in the state
- Newton, IA14 miles from this station, 48.6°F a year
- Toledo, IA24 miles from this station, 47.3°F a year
- Belle Plaine, IA27 miles from this station, 48.2°F a year
- Oskaloosa, IA28 miles from this station, 50.1°F a year
- Compare two placesMonth by month, side by side
Download these normals (CSV) · JSON · How these figures are made