Iroquois sits near the bottom of U.S. towns for winter warmth
High summer brings afternoon highs near 85°. The year swings widely: the coldest month’s nights and the warmest month’s afternoons are 80° apart. It is a dry place: less rain and snow fall here than on 88% of U.S. towns. Plan time outside for May, June, August and September, when highs sit at 70–82°.
A year in Iroquois at a glance
Each month’s typical high and low, and what it brings.
What stands out about Iroquois’ climate
Compared with towns across the U.S., with Iroquois’ place in South Dakota beside it.
What a year in Iroquois feels like
Typical highs and lows by season and by month, from NOAA’s 30-year normals.
About 151 frost-free days a year
In half of years the last 32° night comes by May 5 and the first by October 4. Frost and day counts come from NOAA’s station at De Smet, SD, 15 miles from the town’s center, 310 ft higher.
The 2023 USDA map puts Iroquois’ center in zone 4b: the coldest night of a typical winter, averaged over 1991–2020, reaches about −21°. 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 39 inches of snow a winter
Snow, measured at Iroquois, SD, falls mostly in December. Precipitation (rain plus melted snow) adds up to 24 inches a year; June is the wettest month and January the driest. Rain or snow falls on about 72 days a year.
Rain + melted snow by month
Inches of water
Snowfall by month
Inches of snow
Heating and cooling a home in Iroquois
94% 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 De Smet, SD.
Living with Iroquois’ climate
What the numbers mean for a garden, a free afternoon and a bad-weather day.
151 frost-free days in zone 4b. The last frost comes by May 5 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 4.
Months with highs of 62–84° and lows of 40° or more: May, June, August and September. 0.5 miles of trails are waiting.
Parks & trails →Cold waves are 28% of the yearly building losses FEMA expects in Iroquois from natural hazards, the largest share. Normals are averages; the hazards page covers the extremes.
Natural hazards →Iroquois and its neighbors
Every town next door is within a degree of Iroquois in January and July, closer than the 5 km grid can tell apart. Tap a town to see its climate.
Climates most like Iroquois’, 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 |
|---|---|---|---|---|
| Iroquois, SD | 5° | 85° | 24" | 39" |
| Spencer, IA | 7° | 84° | 31" | 43" |
| Bismarck, ND | 3° | 84° | 18" | 51" |
| New Ulm, MN | 6° | 83° | 30" | 38" |
| Wayne, NE | 11° | 85° | 29" | 32" |
Temperatures and rain come from NOAA’s 5 km grid, so each town gets its own value. Snow and frost-free days come from the nearest weather station, so neighbors often share them.
Warmer than it used to be
The last 30 years in Iroquois averaged 1.1° warmer than the 1900s. The biggest change is in January (+3.1°).
A smaller shift than in 70% 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 Iroquois compares
Against 12,954 U.S. towns of 2,500 or more (one per 5 km climate cell), with Iroquois’ place among South Dakota’s.
Iroquois weather by month
Highs, lows and precipitation from NOAA’s grid at Iroquois’ center; snow, wet days and snow on the ground from Iroquois, SD. 1991–2020 normals.
| Month | High | Low | Rain + melt | Snow | Wet days | Snow on ground | 30-yr range |
|---|---|---|---|---|---|---|---|
| January | 25° | 5° | 0.5" | 6.7" | 5 | 25 | 3° – 30° |
| February | 30° | 10° | 0.7" | 6.4" | 5 | 17 | 5° – 32° |
| March | 43° | 22° | 1.1" | 6.5" | 5 | 10 | 22° – 47° |
| April | 57° | 33° | 2.4" | 4.6" | 7 | 2 | 36° – 52° |
| May | 70° | 46° | 3.1" | 0.0" | 9 | 0 | 53° – 65° |
| June | 79° | 57° | 3.9" | 0.0" | 8 | 0 | 63° – 72° |
| July | 85° | 61° | 3.2" | 0.0" | 8 | 0 | 65° – 80° |
| August | 82° | 59° | 3.0" | 0.0" | 7 | 0 | 65° – 75° |
| September | 75° | 50° | 2.4" | 0.0" | 6 | 0 | 55° – 68° |
| October | 60° | 36° | 2.0" | 1.2" | 5 | 1 | 39° – 52° |
| November | 43° | 22° | 0.9" | 5.0" | 4 | 4 | 22° – 42° |
| December | 29° | 11° | 0.6" | 8.6" | 5 | 18 | 6° – 27° |
| Year | 57° | 34° | 23.8" | 39.0" | 72 | 76 |
How much a month can swing
A normal is an average. February swings the most: from 1991 to 2020 its average ranged from 5° to 32°. August is the most reliable, staying within 9°.
Where Iroquois’ 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 Iroquois’ center.
- Snow: Iroquois, SD (NOAA station in town).
- Frost, freezing nights, 90° and 100° days, heating and cooling: De Smet, SD, 15 miles from the town’s center, 310 ft higher; 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 Iroquois’ climate
What is the weather like in Iroquois?
A typical July afternoon reaches 85°, a January night drops to 5°, and about 39 inches of snow falls in a normal winter. Colder January nights than 98% of U.S. towns; cooler July afternoons than 52% of U.S. towns.
How cold does it get in Iroquois in winter?
January nights average 5°. About 165 nights a year reach 32° or below and 27 reach 0° or below. In the coldest January of the last 30 years the month averaged 3°.
How much snow does Iroquois get?
About 39 inches in a normal winter at Iroquois, SD, most of it in December, with snow on the ground about 76 days a year.
How hot does it get in Iroquois?
July, with a typical high of 85° and a low of 61°. About 10 days a year reach 90° (De Smet, SD).
When is the first and last frost in Iroquois?
In half of years the last spring frost (32°) comes by May 5 and the first fall frost by October 4, about 151 frost-free days, at De Smet, SD.
What growing zone is Iroquois in?
Zone 4b on the 2023 USDA Plant Hardiness Zone Map: the coldest night of a typical winter reaches about −21°.
What is the best time of year to visit Iroquois?
By one simple rule (highs of 62–84° and lows of 40° or more), May, June, August and September. The rule is ours, not NOAA’s; the month table has the numbers to judge by.
Is Iroquois getting warmer?
Yes: 1991–2020 averaged 1.1° warmer than 1901–2000 on NOAA’s grid. A smaller shift than 70% of U.S. towns.
Neighbors talk weather
Gardens, snow, and the best days of the year in Iroquois.
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.