Photo: TravelingOtter · CC BY 2.0Keystone’s winters are colder and snowier than most of the U.S.
A typical July afternoon reaches 81°, a January night drops to 14°, and about 59 inches of snow falls in a normal winter.
A year in Keystone at a glance
Each month’s typical high and low, and what it brings.
What stands out about Keystone’s climate
Compared with towns across the U.S., with Keystone’s place in South Dakota beside it.
What a year in Keystone feels like
Typical highs and lows by season and by month, from NOAA’s 30-year normals.
About 102 frost-free days a year
In half of years the last 32° night comes by June 1 and the first by September 10. Frost and day counts come from NOAA’s station at Hill City, SD, 7 miles from the town’s center, 380 ft higher.
The 2023 USDA map puts Keystone’s center in zone 5a: the coldest night of a typical winter, averaged over 1991–2020, reaches about −17°. 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 59 inches of snow a winter
Snow, measured at Mt Rushmore Nmem, SD, falls mostly in April. Precipitation (rain plus melted snow) adds up to 22 inches a year; May is the wettest month and January the driest. Rain or snow falls on about 102 days a year.
Rain + melted snow by month
Inches of water
Snowfall by month
Inches of snow
Heating and cooling a home in Keystone
97% of the work is heating, so the furnace matters far more than the air conditioner. Months averaging under 55° run from October through May.
Degree days add up how far each day’s average falls below (heating) or rises above (cooling) 65° over a year. NOAA normals at Hill City, SD.
Living with Keystone’s climate
What the numbers mean for a garden, a free afternoon and a bad-weather day.
102 frost-free days in zone 5a. The last frost comes by Jun 1 in half of years, so many gardeners wait a week or two past that to set out tomatoes. The first fall frost comes by Sep 10.
Months with highs of 62–84° and lows of 40° or more: June, July, August and September. 2.1 miles of trails are waiting.
Parks & trails →Of the yearly building losses FEMA expects in Keystone from natural hazards, river flooding is the largest share (44%); heat waves, cold waves, winter storms and ice storms together are 5%. Normals are averages; the hazards page covers the extremes.
Natural hazards →Keystone and similar climates
TownRatings has no climate map of the towns around Keystone yet.
Climates most like Keystone’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 |
|---|---|---|---|---|
| Keystone, SD | 14° | 81° | 22" | 59" |
| Columbia Falls, MT | 18° | 82° | 20" | 54" |
| Gleneagle, CO | 14° | 84° | 21" | 55" |
| Sheboygan Falls, WI | 13° | 80° | 32" | 45" |
| Laramie, WY | 12° | 81° | 12" | 64" |
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 Keystone averaged 1.4° warmer than the 1900s. The biggest change is in January (+4.0°).
A bigger shift than in 51% 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 Keystone compares
Against 12,954 U.S. towns of 2,500 or more (one per 5 km climate cell), with Keystone’s place among South Dakota’s.
Keystone weather by month
Highs, lows and precipitation from NOAA’s grid at Keystone’s center; snow, wet days and snow on the ground from Mt Rushmore Nmem, SD. 1991–2020 normals.
| Month | High | Low | Rain + melt | Snow | Wet days | Snow on ground | 30-yr range |
|---|---|---|---|---|---|---|---|
| January | 38° | 14° | 0.4" | 7.2" | 5 | 15 | 18° – 35° |
| February | 38° | 14° | 0.6" | 8.9" | 6 | 13 | 12° – 35° |
| March | 46° | 22° | 1.1" | 9.6" | 7 | 10 | 22° – 45° |
| April | 53° | 29° | 2.4" | 13.1" | 10 | 6 | 34° – 47° |
| May | 62° | 39° | 4.3" | 1.5" | 14 | 1 | 45° – 56° |
| June | 73° | 48° | 3.5" | 0.2" | 13 | 0 | 54° – 67° |
| July | 81° | 55° | 3.3" | 0.0" | 12 | 0 | 60° – 73° |
| August | 80° | 53° | 2.3" | 0.0" | 11 | 0 | 61° – 70° |
| September | 71° | 44° | 1.6" | 0.9" | 8 | 0 | 51° – 63° |
| October | 57° | 32° | 1.6" | 4.9" | 7 | 3 | 36° – 50° |
| November | 46° | 22° | 0.6" | 6.4" | 5 | 7 | 25° – 44° |
| December | 38° | 15° | 0.4" | 6.6" | 5 | 12 | 17° – 32° |
| Year | 57° | 32° | 22.1" | 59.3" | 102 | 66 |
How much a month can swing
A normal is an average. March swings the most: from 1991 to 2020 its average ranged from 22° to 45°. August is the most reliable, staying within 9°.
Where Keystone’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 Keystone’s center.
- Snow: Mt Rushmore Nmem, SD (NOAA station in town).
- Frost, freezing nights, 90° and 100° days, heating and cooling: Hill City, SD, 7 miles from the town’s center, 380 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 Keystone’s climate
What is the weather like in Keystone?
A typical July afternoon reaches 81°, a January night drops to 14°, and about 59 inches of snow falls in a normal winter. Colder January nights than 87% of U.S. towns; cooler July afternoons than 88% of U.S. towns.
How cold does it get in Keystone in winter?
February nights average 14°. About 212 nights a year reach 32° or below and 26 reach 0° or below. In the coldest February of the last 30 years the month averaged 12°.
How much snow does Keystone get?
About 59 inches in a normal winter at Mt Rushmore Nmem, SD, most of it in April, with snow on the ground about 66 days a year.
How hot does it get in Keystone?
July, with a typical high of 81° and a low of 55°. About 8 days a year reach 90° (Hill City, SD).
When is the first and last frost in Keystone?
In half of years the last spring frost (32°) comes by June 1 and the first fall frost by September 10, about 102 frost-free days, at Hill City, SD.
What growing zone is Keystone in?
Zone 5a on the 2023 USDA Plant Hardiness Zone Map: the coldest night of a typical winter reaches about −17°.
What is the best time of year to visit Keystone?
By one simple rule (highs of 62–84° and lows of 40° or more), June, July, August and September. The rule is ours, not NOAA’s; the month table has the numbers to judge by.
Is Keystone getting warmer?
Yes: 1991–2020 averaged 1.4° warmer than 1901–2000 on NOAA’s grid. A bigger shift than 51% of U.S. towns.
Neighbors talk weather
Gardens, snow, and the best days of the year in Keystone.
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.