Merchants' National Bank · Photo: Einar Einarsson Kvaran aka Carptrash · CC BY-SA 3.0Grinnell has colder winter nights than 92% of U.S. towns
On a normal July day the thermometer tops out near 84°. The wettest month is June; the driest is January. Precipitation is light here, less than falls on 69% of U.S. towns. Garden chairs stay out from May to October, the months with highs of 62–84°.
A year in Grinnell at a glance
Each month’s typical high and low, and what it brings.
What stands out about Grinnell’s climate
Compared with towns across the U.S., with Grinnell’s place in Iowa beside it.
What a year in Grinnell feels like
Typical highs and lows by season and by month, from NOAA’s 30-year normals.
About 155 frost-free days a year
In half of years the last 32° night comes by May 3 and the first by October 6. Frost and day counts come from NOAA’s station at Grinnell 3 Sw, IA, 1.6 miles from the town’s center, at about the same height.
The 2023 USDA map puts Grinnell’s center in zone 5b: the coldest night of a typical winter, averaged over 1991–2020, reaches about −14°. Plant labels use the zone; frost dates tell you when to plant.
Freezing nights by month
Average nights at or below 32°
90° days by month
Average days at 90° or more
About 31 inches of snow a winter
Snow, measured at Grinnell 3 Sw, IA, is heaviest from January through February, about 9 inches a month. Precipitation (rain plus melted snow) adds up to 38 inches a year; June is the wettest month and January the driest. Rain or snow falls on about 115 days a year.
Rain + melted snow by month
Inches of water
Snowfall by month
Inches of snow
Heating and cooling a home in Grinnell
91% of the work is heating, so the furnace matters far more than the air conditioner. Months averaging under 55° run from October through April.
Degree days add up how far each day’s average falls below (heating) or rises above (cooling) 65° over a year. NOAA normals at Grinnell 3 Sw, IA.
Living with Grinnell’s climate
What the numbers mean for a garden, a free afternoon and a bad-weather day.
155 frost-free days in zone 5b. The last frost comes by May 3 in half of years, so many gardeners wait a week or two past that to set out tomatoes. The first fall frost comes by Oct 6.
Months with highs of 62–84° and lows of 40° or more: May, June, July, August, September and October. 5.1 miles of trails are waiting.
Parks & trails →Of the yearly building losses FEMA expects in Grinnell from natural hazards, tornadoes are the largest share (27%); heat waves, cold waves, winter storms and ice storms together are 15%. Normals are averages; the hazards page covers the extremes.
Natural hazards →Grinnell and similar climates
TownRatings has no climate map of the towns around Grinnell yet.
Climates most like Grinnell’s, farther away
TownRatings’ own comparison of NOAA 1991–2020 normals, not a NOAA product: places of 5,000+ at least 150 miles away, one per state, closest on January low, July high, precipitation and snow.
| Town | Jan. low | July high | Precip. | Snow |
|---|---|---|---|---|
| Grinnell, IA | 12° | 84° | 38" | 31" |
| Freeport, IL | 12° | 83° | 38" | 35" |
| Evansville, WI | 12° | 83° | 38" | 36" |
| Winona, MN | 8° | 83° | 36" | 38" |
| Lakes of the Four Seasons, IN | 16° | 83° | 40" | 27" |
Temperatures and precipitation come from NOAA’s 5 km grid; snow and day counts from the stations named on this page.
Warmer than it used to be
The last 30 years in Grinnell averaged 0.8° warmer than the 1900s. The biggest change is in December (+2.4°).
A smaller shift than in 92% of U.S. towns.
Change by month
The two periods overlap (1991–2000 is in both), which makes the gap a little smaller than it would be between separate periods.
How Grinnell compares
Against 12,954 U.S. towns of 2,500 or more (one per 5 km climate cell), with Grinnell’s place among Iowa’s.
Grinnell weather by month
Highs, lows and precipitation from NOAA’s grid at Grinnell’s center; snow, wet days and snow on the ground from Grinnell 3 Sw, IA. 1991–2020 normals.
| Month | High | Low | Rain + melt | Snow | Wet days | 30-yr range |
|---|---|---|---|---|---|---|
| January | 28° | 12° | 1.0" | 9.0" | 8 | 11° – 33° |
| February | 33° | 16° | 1.2" | 9.1" | 8 | 13° – 36° |
| March | 47° | 27° | 2.1" | 3.4" | 9 | 29° – 51° |
| April | 60° | 38° | 3.8" | 0.6" | 12 | 40° – 56° |
| May | 71° | 49° | 5.1" | 0.0" | 13 | 54° – 68° |
| June | 80° | 59° | 5.6" | 0.0" | 12 | 67° – 74° |
| July | 84° | 63° | 4.3" | 0.0" | 9 | 67° – 79° |
| August | 82° | 60° | 4.3" | 0.0" | 11 | 66° – 77° |
| September | 75° | 52° | 3.7" | 0.0" | 9 | 58° – 69° |
| October | 62° | 40° | 2.9" | 0.5" | 10 | 46° – 56° |
| November | 47° | 28° | 2.0" | 1.5" | 7 | 29° – 48° |
| December | 34° | 17° | 1.5" | 6.9" | 8 | 10° – 35° |
| Year | 59° | 38° | 37.6" | 31.0" | 115 |
How much a month can swing
A normal is an average. December swings the most: from 1991 to 2020 its average ranged from 10° to 35°. June is the most reliable, staying within 7°.
Where Grinnell’s numbers come from
Normals are 30-year averages, not a forecast. How TownRatings reads climate data →
- Temperatures and precipitation: NOAA’s gridded 1991–2020 normals for the 5 km cell at Grinnell’s center.
- Snow: Grinnell 3 Sw, IA (NOAA station in town).
- Frost, freezing nights, 90° and 100° days, heating and cooling: Grinnell 3 Sw, IA, 1.6 miles from the town’s center, at about the same height; the nearest station that passes our checks for distance, height and agreement with the grid.
- Growing zone: USDA Plant Hardiness Zone Map, 2023. USDA Agricultural Research Service and PRISM Group, Oregon State University, prism.oregonstate.edu/phzm, accessed 8 Oct 2026.
- Then and now: NOAA’s gridded normals for 1901–2000 at the same cell.
- Storms and extremes: FEMA National Risk Index (expected annual losses to buildings).
Common questions about Grinnell’s climate
What is the weather like in Grinnell?
A typical July afternoon reaches 84°, a January night drops to 12°, and about 31 inches of snow falls in a normal winter. Colder January nights than 92% of U.S. towns; cooler July afternoons than 65% of U.S. towns.
How cold does it get in Grinnell in winter?
January nights average 12°. About 157 nights a year reach 32° or below and 19 reach 0° or below. In the coldest January of the last 30 years the month averaged 11°.
How much snow does Grinnell get?
About 31 inches in a normal winter at Grinnell 3 Sw, IA, heaviest from January through February, about 9 inches a month.
How hot does it get in Grinnell?
July, with a typical high of 84° and a low of 63°. About 11 days a year reach 90° (Grinnell 3 Sw, IA).
When is the first and last frost in Grinnell?
In half of years the last spring frost (32°) comes by May 3 and the first fall frost by October 6, about 155 frost-free days, at Grinnell 3 Sw, IA.
What growing zone is Grinnell in?
Zone 5b on the 2023 USDA Plant Hardiness Zone Map: the coldest night of a typical winter reaches about −14°.
What is the best time of year to visit Grinnell?
By one simple rule (highs of 62–84° and lows of 40° or more), May, June, July, August, September and October. The rule is ours, not NOAA’s; the month table has the numbers to judge by.
Is Grinnell getting warmer?
Yes: 1991–2020 averaged 0.8° warmer than 1901–2000 on NOAA’s grid. A smaller shift than 92% of U.S. towns.
Neighbors talk weather
Gardens, snow, and the best days of the year in Grinnell.
Source: NOAA NCEI U.S. Climate Normals, 1991–2020 and 1901–2000; USDA/PRISM 2023 hardiness zones; FEMA National Risk Index. Today’s forecast: National Weather Service.