Keystone, SD weather in May
In May, Keystone sees highs around 60°F and lows around 36°F: cool, with frequent rain and some snow. Rain or snow falls on about 13 days. Snowfall averages about 4.5 in.
- Normal high
- 60°F
- Normal low
- 36°F
- Wet days
- 13
- 4.3 in total
- Snowfall
- 4.5 in
- snow on the ground 1 day
How May changes from start to finish
| May 1 | May 31 | |
|---|---|---|
| Normal high | 54°F | 66°F |
| Normal low | 30°F | 42°F |
| Chance of a wet day | 40% | 45% |
| Sunrise / sunset | 5:45 am / 7:56 pm | 5:14 am / 8:28 pm |
| Daylight | 14.2 h | 15.2 h |
Chance of a wet day: average for the first and last 7 days of the month. Times are local clock time (Mountain Time).
A typical May day
- 6 am44°Fdew point 35°F
- 9 am52°Fdew point 35°F
- Noon56°Fdew point 35°F
- 3 pm56°Fdew point 35°F
- 6 pm53°Fdew point 36°F
- 9 pm46°Fdew point 36°F
NOAA hourly normals (local standard time) from Custer Co Airport (15 mi away); average wind 7 mph; clear or few clouds in 38% of daytime hours, mostly cloudy or overcast in 50%.
What kind of days to expect
- Comfortable dayshigh 65-80°F and dew point under 60°F10 of 31
- Hot dayshigh 90°F or more0 of 31
- Muggy daysdaily mean dew point 65°F or more0 of 31
- Wet daysat least 0.01 in of rain or melted snow13 of 31
- Notable rainat least 0.10 in8 of 31
- Freezing nightslow 32°F or below11 of 31
- Snow on the groundsnow depth 1 in or more1 of 31
Average days per May, counted from daily records for each year 1991-2020.
Rain and snow in May
Normal precipitation is 4.3 in; a dry May brings about 2.4 in and a wet one about 5.6 in (25th and 75th percentiles). About 3 days bring half an inch or more, and about 1 an inch or more. Normal snowfall is 4.5 in, with about 1 day of an inch or more.
How May varies from year to year
- Warmest May, 1991-20201994: average high 67°F
- Coolest May2019: average high 52°F
- Wettest May2015: 9.5 in
- Driest May2009: 0.9 in
- Highest reading89°F (May 20, 2009)
- Lowest reading15°F (May 3, 2005)
From the station's daily records with NOAA quality flags removed; most recent date shown when a reading repeats.
May compared with April and June
| April | May | June | |
|---|---|---|---|
| Normal high | 51°F | 60°F | 71°F |
| Normal low | 26°F | 36°F | 45°F |
| Wet days | 10 | 13 | 13 |
| Comfortable days | 5 | 10 | 16 |
| Daylight | 13.5 h | 14.8 h | 15.4 h |
Highs change by +9°F from April and +11°F into June.
Nearby alternatives in May
- Warmer: Rapid City, SD16 mi · high 67°F · 13 wet days
- Drier: Medora, ND209 mi · high 67°F · 10 wet days
How Keystone ranks in May
- Normal high364th warmest of 378 cities; 4th of 4 in South Dakota
- Wet days347th driest of 378
- Comfortable days217th most of 339
What to pack for Keystone in May
- A warm jacket – lows near 36°F, highs near 60°F
- A rain jacket or umbrella – rain or snow on about 13 days
- Waterproof boots – about 4.5 in of snow in a typical year
Frost in May
The last spring frost typically comes around May 28; in 1 year in 10 it comes after Jun 11. All frost dates for Keystone.
Heating and cooling
May has 525 heating degree days and 1 cooling degree days (base 65°F), 6% of the year's total heating and cooling demand.
Questions
How cold is Keystone in May?
The normal high is 60°F and the normal low is 36°F. From 1991 to 2020 the coldest May reading was 15°F (May 3, 2005).
Does it rain a lot in Keystone in May?
About 13 days in May have at least 0.01 in of precipitation, and the normal total is 4.3 in. The wettest May in 1991-2020 was in 2015 (9.5 in); the driest was in 2009 (0.9 in).
Does it snow in Keystone in May?
Yes. Normal snowfall in May is 4.5 in, and snow covers the ground on about 1 day.
Is May a good time to visit Keystone?
May ranks 5th of 12 months on our comfort score for Keystone (65 out of 100). It has about 10 comfortable days. The best month is June.
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.