Keystone, SD climate
Keystone has cold, snowy winters and pleasant summers, with very little rain. A typical July afternoon reaches 81°, a January night drops to 14°, and about 59 inches of snow falls in a normal winter.
NOAA 1991-2020 climate normals Updated once a decadeWhat a year in Keystone feels like
Winter
Spring
Summer
Fall
Keystone weather by month
Average highs, lows, rain and snow for every month, from NOAA’s 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 | 12 | 0 | 60° – 73° |
| August | 80° | 53° | 2.3" | 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 |
“Wet days” have at least 0.01" of rain or melted snow. “Snow on ground” counts days with 1" or more. The 30-year range is the coldest and warmest that month’s average temperature got between 1991 and 2020.
Rain and snow in Keystone
Keystone gets 22 inches of rain and melted snow a year. May is the wettest month and January the driest. Rain or snow falls on about 102 days a year. Snow covers the ground about 66 days of the year.
About 138 frost-free days a year
In half of years the last 32° night comes by May 15 and the first one by October 1. That leaves about 138 frost-free days for gardens, shorter than 90% of U.S. towns.
Heating and cooling a home in Keystone
Engineers use “degree days” to estimate how hard a furnace or air conditioner works. In Keystone, 95% of that work is heating and 5% is cooling, so the furnace matters far more than the air conditioner.
Degree days measure how far each day’s average temperature falls below or rises above 65°, added up over a year. Source: NOAA station normals.
How Keystone compares
Compared with every U.S. town and city on TownTapestry, each counted once.
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°). The shift is larger than in 62% of U.S. towns.
Change by month1991–2020 average minus 1901–2000 average, at Keystone’s spot on NOAA’s grid
How much a month can swing
A normal is an average, and real years wander around it. March swings the most: between 1991 and 2020 its average temperature ranged from 22° to 45°. August is the most reliable, staying within 9°.
Common questions about Keystone’s climate
What is the coldest month in Keystone?
February, with a typical high of 38° and a low of 14°.
What is the hottest month in Keystone?
July, with a typical high of 81° and a low of 55°. About 6 days a year reach 90°.
How much snow does Keystone get?
About 59 inches in a normal winter, most of it in April.
When is the first frost in Keystone?
In half of years the first 32° night comes by October 1, and the last spring frost by May 15.
What is the rainiest month in Keystone?
May, with 4.3 inches of rain and melted snow. The year totals 22 inches.
Temperatures and rainfall come from NOAA’s gridded climate normals for Keystone itself (about a 3-mile square). Snow, frost dates and day counts come from NOAA’s weather station at Mt Rushmore Nmem, SD (2 mi) away. Normals are 30-year averages, not a forecast. Source: NOAA NCEI U.S. Climate Normals, 1991–2020 and 1901–2000.