Interior, South Dakota climate: Normal weather by month, frost dates and records
Interior's normal year runs from 14°F January nights to 91°F July afternoons, with 19.6 inches of precipitation and 38 inches of snow a year. (NOAA 1991-2020 normals)
In metric: a yearly mean of 10.2°C, January lows of −10°C, July highs of 33°C, 498 mm of precipitation a year.
- NOAA stationInterior (3 mi NE)
- Station IDUSC00394184
- Location43.75°N 101.94°W
- Elevation2,440 ft (744 m)
- Population65
On October 22, the normal high in Interior is 62°F and the normal low 35°F, and the chance of measurable rain or snow is 19%.
Normals describe a typical year at the station, not a forecast. The National Weather Service forecast for Interior.
- Jan 37° 14°
- Feb 41° 16°
- Mar 53° 26°
- Apr 62° 35°
- May 72° 46°
- Jun 83° 56°
- Jul 91° 62°
- Aug 91° 60°
- Sep 82° 51°
- Oct 65° 38°
- Nov 50° 25°
- Dec 39° 17°
Each month: normal high (large) and low, °F. Fill: the month's normal mean, colder blue to hotter red.
What is the weather like in Interior each month?
July is the warmest month, with normal highs of 91°F; January the coldest, with normal lows of 14°F. The most precipitation falls in May (3.62 in), the least in January (0.46 in).
| Month | High | Low | Mean | Precip. | Snow | Wet days | 90°F days | Freezing nights | Daylight |
|---|---|---|---|---|---|---|---|---|---|
| January | 37°F | 14°F | 25.7°F | 0.46 | 5.5 | 4 | <1 | 29 | 9 h 20 min |
| February | 41°F | 16°F | 28.5°F | 0.55 | 6.4 | 5 | <1 | 25 | 10 h 30 min |
| March | 53°F | 26°F | 39.1°F | 1.16 | 5.9 | 6 | <1 | 22 | 11 h 50 min |
| April | 62°F | 35°F | 48.4°F | 2.26 | 6.4 | 9 | <1 | 11 | 13 h 20 min |
| May | 72°F | 46°F | 58.9°F | 3.62 | 0.5 | 10 | 2 | 2 | 14 h 40 min |
| June | 83°F | 56°F | 69.2°F | 3.46 | 0.0 | 10 | 7 | <1 | 15 h 30 min |
| July | 91°F | 62°F | 76.8°F | 2.23 | 0.0 | 8 | 18 | <1 | 15 h 10 min |
| August | 91°F | 60°F | 75.3°F | 1.81 | 0.0 | 7 | 18 | <1 | 14 h |
| September | 82°F | 51°F | 66.2°F | 1.39 | 0.0 | 6 | 8 | <1 | 12 h 30 min |
| October | 65°F | 38°F | 51.6°F | 1.59 | 1.9 | 7 | 1 | 8 | 11 h 10 min |
| November | 50°F | 25°F | 37.6°F | 0.53 | 3.7 | 4 | <1 | 22 | 9 h 40 min |
| December | 39°F | 17°F | 27.8°F | 0.54 | 7.7 | 5 | <1 | 28 | 9 h |
| Year (annual) | 64°F | 37°F | 50.4°F | 19.60 | 38.0 | 80 | 53 | 146 |
The same normals in °C and millimetres
| Month | High | Low | Mean | Precip. | Snow |
|---|---|---|---|---|---|
| January | 3°C | −10°C | −3.5°C | 12 mm | 14 cm |
| February | 5°C | −9°C | −1.9°C | 14 mm | 16 cm |
| March | 11°C | −3°C | 3.9°C | 29 mm | 15 cm |
| April | 17°C | 2°C | 9.1°C | 57 mm | 16 cm |
| May | 22°C | 8°C | 14.9°C | 92 mm | 1 cm |
| June | 28°C | 13°C | 20.7°C | 88 mm | 0 cm |
| July | 33°C | 17°C | 24.9°C | 57 mm | 0 cm |
| August | 33°C | 16°C | 24.1°C | 46 mm | 0 cm |
| September | 28°C | 10°C | 19.0°C | 35 mm | 0 cm |
| October | 19°C | 3°C | 10.9°C | 40 mm | 5 cm |
| November | 10°C | −4°C | 3.1°C | 13 mm | 9 cm |
| December | 4°C | −9°C | −2.3°C | 14 mm | 20 cm |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00394184; annual normals. Wet days: 0.01 inch or more; 90°F days and freezing nights: NOAA's day counts. Daylight: sunrise to sunset on the 15th, computed from the latitude.
When is the best weather to visit Interior?
Normal highs sit between 65°F and 85°F in May, June, September and October. Of those, September has the fewest days with rain (6).
That is a measurement, not a recommendation: it counts the months whose normal afternoon high sits between 65°F and 85°F, where a light layer is enough by day.
Source: NOAA NCEI 1991-2020 monthly normals, station USC00394184.
When is the last frost in Interior?
In Interior, the last spring frost (32°F) comes after May 5 in half of years and after May 20 in one year in ten; the first autumn frost comes before October 7 in half of years and before September 23 in one year in ten.
Frost-free in half of yearsFrost in 1 to 9 years out of 10Frost most years
- Last spring frost, half of years after
- May 51 year in 10 after May 20; 9 in 10 after April 22
- First autumn frost, half of years before
- October 71 year in 10 before September 23; 9 in 10 before October 20
NOAA puts the median frost-free season at 152 days, and the season without a hard freeze (28°F) at 173 days.
A hard freeze (28°F) comes after April 25 in half of springs and before October 15 in half of autumns.
The USDA's 2023 Plant Hardiness Zone Map puts Interior in zone 5a in ZIP code 57750, the nearest ZIP area. By the map's own method, the average of each year's coldest night over 1991-2020, Interior's NOAA station is in zone 5a: the coldest night of a typical year reaches −16°F (22 complete years).
Frost dates for every NOAA station in South Dakota · Frost dates by ZIP code
Source: NOAA NCEI 1991-2020 annual normals (frost probabilities), station USC00394184; USDA 2023 Plant Hardiness Zone Map, ZIP listings: PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed October 8, 2026; the station zone: ACIS daily lows, 1991-2020. A 10% date means one year in ten has a frost after it in spring or before it in autumn.
How hot and how cold does it get in Interior?
In a normal year in Interior, 53 days a year reach 90°F (11 of them 100°F or more), 146 nights fall to 32°F or colder and 80 days bring measurable precipitation.
- Days at 90°F or more
- 53a normal year
- Days at 100°F or more
- 11a normal year
- Nights at 32°F or colder
- 146a normal year
- Days that stay below freezing
- 36high of 32°F or less
- Days with 0.01 inch of precipitation
- 80a normal year
- Days with 1 inch of snow or more
- 13a normal year
The highest temperature in this station's record (since 1949) is 115°F, on July 25, 2026; the lowest is −31°F, on February 2, 1996.
The wettest calendar year on that record is 1998, with 27.07 in; the snowiest season is 2022–23, with 85.5 inches.
Source: NOAA NCEI 1991-2020 annual normals, station USC00394184; records: ACIS (NOAA Regional Climate Centers), station USC00394184. Records use complete months only; a month missing more than three days is left out.
How sunny is Interior?
Over a year 79% of the sunlight that would reach the ground under clear skies gets through the clouds in the area around Interior, 4.3 kWh per square metre a day. July is the sunniest month (87%) and April the cloudiest (72%).
| Month | Share of clear-sky sunshine | Sunshine, kWh/m² a day |
|---|---|---|
| January | 75% | 2.0 |
| February | 74% | 2.9 |
| March | 72% | 4.0 |
| April | 72% | 5.0 |
| May | 75% | 6.1 |
| June | 82% | 6.9 |
| July | 87% | 7.0 |
| August | 86% | 6.0 |
| September | 83% | 4.8 |
| October | 76% | 3.2 |
| November | 76% | 2.2 |
| December | 72% | 1.7 |
Source: NASA POWER solar climatology, 2001-2020 (CERES SYN1deg). Satellite-based, for the 1-degree cell (about 100 km across) around the station, so it describes the area rather than the airport.
How much heating and cooling does Interior need?
A normal year in Interior brings 6,331 heating degree days, 18% more than the median U.S. place (5,373), and 1,057 cooling degree days, 16% more than the median (908). Seven months need 300 or more heating degree days, a monthly mean of about 55°F or colder. For gardens and crops, NOAA counts 3,313 growing degree days a year above 50°F.
| Month | Heating | Cooling |
|---|---|---|
| January | 1,220 | 0 |
| February | 1,022 | 0 |
| March | 802 | 0 |
| April | 501 | 4 |
| May | 231 | 42 |
| June | 41 | 167 |
| July | 3 | 367 |
| August | 10 | 331 |
| September | 97 | 131 |
| October | 430 | 14 |
| November | 822 | 0 |
| December | 1,153 | 0 |
| Year (annual) | 6,331 | 1,057 |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00394184. A degree day is one degree of a day's mean temperature below 65°F (heating) or above it (cooling); utilities use them to estimate energy use.
Has Interior been warmer than normal lately?
2024 averaged 54.5°F, 4.1°F above the 1991-2020 normal of 50.4°F. 3 of the 3 complete years since 2022 ran warmer than the normal.
| Year | Mean | Against normal | Precip. | Snow |
|---|---|---|---|---|
| 2022 | 50.5°F | +0.1°F | 14.35 | 45.0 |
| 2023 | 52.3°F | +1.9°F | 21.95 | 66.5 |
| 2024 | 54.5°F | +4.1°F | 15.03 | 21.0 |
Over 43 complete years from 1957 to 2024, the station's annual mean temperature rose at a fitted 5.0°F per century (+0.28°C per decade). A fitted rate summarizes the whole record; single years swing well above and below it.
Source: observed years: ACIS, station USC00394184; trend: NOAA GHCN-Monthly v4. A year counts only with all twelve months complete.
How does Interior's climate compare?
Interior is warmer than 99 of the other 99 places with their own NOAA record in South Dakota, and wetter than 23. Across the 7,247 U.S. stations with normals, its annual mean of 50.4°F is warmer than 42%.
In the Köppen classification computed from these normals, Interior is Dfa: continental, no dry season, hot summer. What the classes mean.
Places with the most similar year elsewhere
Measured month by month on the normal high, low and precipitation, among places of 20,000 or more people in other states:
Source: NOAA NCEI 1991-2020 normals for every station PlainClimate covers. Similarity: the root-mean-square difference of the 36 monthly figures, precipitation weighted so an inch counts like 6°F.
Questions about Interior's climate
What is the coldest month in Interior?
January, with a normal high of 37°F and a normal low of 14°F. The warmest is July (91°F by day, 62°F at night).
Does it snow in Interior?
Yes: 38 inches in a normal year, falling on 17 days with 0.1 inch or more, the most in December (7.7 inches).
What is the rainiest month in Interior?
May, with 3.62 in of precipitation in a normal year; the driest is January with 0.46 in.
What plant hardiness zone is Interior in?
The USDA's 2023 map puts Interior in zone 5a in ZIP code 57750, the nearest ZIP area. By the same method at Interior's NOAA station, the coldest night of a typical year reaches −16°F (22 years, 1991-2020): zone 5a.
How late can frost come in Interior?
In half of years the last 32°F night comes after May 5; in one year in ten it comes after May 20. Waiting until May 20 leaves about a one-in-ten chance of a later frost.
Nearby and next
- South Dakota climateThe statewide normals and every place in the state
- Cottonwood, SD16 miles from this station, 46.1°F a year
- Kyle, SD24 miles from this station, 47.3°F a year
- Philip, SD27 miles from this station, 47.6°F a year
- Longvalley, SD30 miles from this station, 49.0°F a year
- Compare two placesMonth by month, side by side
Download these normals (CSV) · JSON · How these figures are made