Climateby Month

Keystone, SD climate by month

NOAA 1991-2020 normals · 4,335 ft elevation

Keystone has mild summers and cold and snowy winters. Highs peak at 79°F in July and fall to 36°F in January. The wettest month is May (about 13 wet days) and the driest is November (about 5). Normal snowfall is about 61 in a year. By our comfort score the best month is June.

Warmest month
79°F
July normal high
Coldest month
11°F
February normal low
Wet days a year
103
21.5 in of precipitation
Snow a year
60.9 in
normal snowfall

How warm is Keystone?

Normal highs range from 36°F in January to 79°F in July.

0°20°40°60°80° January: normal high 36°F (2°C), low 11°F (-12°C) 36° 11° February: normal high 36°F (2°C), low 11°F (-12°C) March: normal high 44°F (7°C), low 19°F (-7°C) April: normal high 51°F (11°C), low 26°F (-3°C) May: normal high 60°F (16°C), low 36°F (2°C) June: normal high 71°F (22°C), low 45°F (7°C) July: normal high 79°F (26°C), low 51°F (11°C) 79° 51° August: normal high 78°F (26°C), low 49°F (9°C) September: normal high 69°F (21°C), low 40°F (4°C) October: normal high 55°F (13°C), low 29°F (-2°C) November: normal high 45°F (7°C), low 20°F (-7°C) December: normal high 37°F (3°C), low 13°F (-11°C) JFMAMJJASOND

Bars run from the normal low to the normal high for each month.

How rainy is Keystone?

May has the most wet days (about 13); the year brings about 22 in of precipitation.

January: 6 wet days February: 7 wet days March: 8 wet days April: 10 wet days May: 13 wet days 13 June: 13 wet days July: 12 wet days August: 9 wet days September: 7 wet days October: 7 wet days November: 5 wet days 5 December: 5 wet days JFMAMJJASOND

Wet day: at least 0.01 in of rain or melted snow, counted from daily records 1991-2020.

How much does it snow?

Normal snowfall is 60.9 in a year, most of it in April.

January: 5.7 in of snow February: 8.2 in of snow March: 10.5 in of snow April: 12.8 in of snow 12.8 May: 4.5 in of snow June: 0.2 in of snow July: 0.0 in of snow 0.0 August: 0.0 in of snow September: 0.8 in of snow October: 6.3 in of snow November: 6.5 in of snow December: 5.4 in of snow JFMAMJJASOND

How humid is Keystone?

Muggy days peak in July, at about 1 days.

January: 0 muggy days 0 February: 0 muggy days March: 0 muggy days April: 0 muggy days May: 0 muggy days June: 0 muggy days July: 1 muggy days 1 August: 0 muggy days September: 0 muggy days October: 0 muggy days November: 0 muggy days December: 0 muggy days JFMAMJJASOND

Muggy day: daily mean dew point of 65°F or higher, from hourly observations 1991-2020 at Rapid City Regional Airport, 21 mi ENE of the city center (the nearest airport with complete hourly records).

How much daylight?

Daylight ranges from about 9.0 hours in December to 15.4 hours in June.

January: 9.3 hours of daylight February: 10.5 hours of daylight March: 11.9 hours of daylight April: 13.5 hours of daylight May: 14.8 hours of daylight June: 15.4 hours of daylight 15.4 July: 15.1 hours of daylight August: 13.9 hours of daylight September: 12.5 hours of daylight October: 11.0 hours of daylight November: 9.7 hours of daylight December: 9.0 hours of daylight 9.0 JFMAMJJASOND
See all numbers
Monthly climate normals and day counts for Keystone, 1991-2020
MonthHighLowPrecip.Wet daysSnowMuggy daysDaylight
January 36°F11°F 0.3 in6 5.7 in 0 9.3 h
February 36°F11°F 0.6 in7 8.2 in 0 10.5 h
March 44°F19°F 1.1 in8 10.5 in 0 11.9 h
April 51°F26°F 2.3 in10 12.8 in 0 13.5 h
May 60°F36°F 4.3 in13 4.5 in 0 14.8 h
June 71°F45°F 3.5 in13 0.2 in 0 15.4 h
July 79°F51°F 3.1 in12 0.0 in 1 15.1 h
August 78°F49°F 2.4 in9 0.0 in 0 13.9 h
September 69°F40°F 1.6 in7 0.8 in 0 12.5 h
October 55°F29°F 1.6 in7 6.3 in 0 11.0 h
November 45°F20°F 0.5 in5 6.5 in 0 9.7 h
December 37°F13°F 0.4 in5 5.4 in 0 9.0 h

High and low: NOAA 1991-2020 normal daily high and low. Wet days: at least 0.01 in of rain or melted snow. Muggy days: daily mean dew point 65°F or higher.

Best months to visit Keystone

By our comfort score, the best month is June.

Comfort score by month (0-100) and its parts, in days per month
MonthScoreComfortableNotable rainHot or cold
Jan 330119
Feb 350217
Mar 442312
Apr 53567
May 651082
Jun 751681
Jul 691373
Aug 711552
Sep 701541
Oct 55845
Nov 412211
Dec 330118

Score = 40 × share of comfortable days + 25 × share of days without notable rain + 20 × share of days neither hot (90°F+) nor cold (high 40°F or below) + 15 × daylight. How the score works.

Frost dates in Keystone

The last spring frost typically comes around May 28, and the first fall frost around Sep 18, leaving 112 frost-free days in a typical year.

Frost and freeze dates for Keystone
Typical date1 year in 10
Last spring frost (32°F)May 28after Jun 11
First fall frost (32°F)Sep 18before Sep 4
Last hard freeze (28°F)May 15after May 28
First hard freeze (28°F)Sep 29before Sep 14
Frost-free season112 daysunder 91 days

"Typical" is the date with a 50% chance of a later spring frost (or earlier fall frost). Planting after the "1 year in 10" spring date gives a 90% chance of no further frost. The Old Farmer's Almanac publishes 30% dates, which fall between our typical and 1-in-10 dates.

Station: Pactola Dam (USC00396427), NOAA 1991-2020 freeze probabilities. Frost dates for every city in South Dakota.

Hottest and coldest readings, 1991-2020

The highest reading was 101°F (July 30, 2006, and 1 other day); the lowest was -34°F (February 3, 1996, and 1 other day).

From the temperature station's daily records with NOAA quality flags removed. Not an all-time record.

Near Keystone

Similar climates elsewhere

Where the numbers come from

  • Temperature, rain, snowfall, snow depth and frost dates: Pactola Dam (USC00396427), 12 mi NNW of the city center, 4,720 ft (385 ft higher than the city). NOAA normals and daily records, 1991-2020.
  • Humidity and wind by hour: Custer Co Airport (USW00094032), 15 mi SW of the city center, 5,545 ft (1,210 ft higher than the city). NOAA normals and daily records, 1991-2020.
  • Cloud cover: Ellsworth AFB (USW00024006), 24 mi NE of the city center, 3,215 ft (1,120 ft lower than the city). NOAA normals and daily records, 1991-2020.
  • Daily humidity and wind: Rapid City Regional Airport (726620-24090), 21 mi ENE of the city center, 3,162 ft (1,173 ft lower than the city). Hourly observations, 1991-2020.

Distances from the city center (USGS). Methodology · Report an error