Roundup, Montana climate: Normal weather by month, frost dates and records
Roundup's normal year runs from 13°F January nights to 89°F July afternoons, with 14.9 inches of precipitation and 24 inches of snow a year. (NOAA 1991-2020 normals)
In metric: a yearly mean of 8.1°C, January lows of −10°C, July highs of 32°C, 378 mm of precipitation a year.
- NOAA stationRoundup
- Station IDUSC00247214
- Location46.44°N 108.53°W
- Elevation3,200 ft (975 m)
- Population2,017
On October 22, the normal high in Roundup is 58°F and the normal low 29°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 Roundup.
- Jan 37° 13°
- Feb 41° 15°
- Mar 51° 22°
- Apr 60° 30°
- May 69° 39°
- Jun 78° 48°
- Jul 89° 54°
- Aug 88° 51°
- Sep 77° 42°
- Oct 61° 32°
- Nov 47° 22°
- Dec 37° 14°
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 Roundup each month?
July is the warmest month, with normal highs of 89°F; January the coldest, with normal lows of 13°F. The most precipitation falls in June (2.89 in), the least in January (0.37 in).
| Month | High | Low | Mean | Precip. | Snow | Wet days | 90°F days | Freezing nights | Daylight |
|---|---|---|---|---|---|---|---|---|---|
| January | 37°F | 13°F | 25.1°F | 0.37 | 5.2 | 4 | <1 | 27 | 9 h |
| February | 41°F | 15°F | 27.8°F | 0.42 | 3.9 | 4 | <1 | 25 | 10 h 20 min |
| March | 51°F | 22°F | 36.3°F | 0.71 | 4.4 | 5 | <1 | 25 | 11 h 50 min |
| April | 60°F | 30°F | 44.9°F | 1.71 | 1.4 | 8 | <1 | 15 | 13 h 30 min |
| May | 69°F | 39°F | 54.2°F | 2.55 | 0.1 | 10 | 1 | 4 | 15 h |
| June | 78°F | 48°F | 63.1°F | 2.89 | 0.0 | 11 | 4 | <1 | 15 h 50 min |
| July | 89°F | 54°F | 71.2°F | 1.70 | 0.0 | 7 | 18 | <1 | 15 h 30 min |
| August | 88°F | 51°F | 69.5°F | 1.21 | 0.0 | 5 | 16 | <1 | 14 h 10 min |
| September | 77°F | 42°F | 59.6°F | 1.20 | 0.0 | 5 | 5 | 2 | 12 h 40 min |
| October | 61°F | 32°F | 46.3°F | 1.22 | 1.0 | 7 | <1 | 12 | 11 h |
| November | 47°F | 22°F | 34.2°F | 0.49 | 2.8 | 4 | <1 | 24 | 9 h 30 min |
| December | 37°F | 14°F | 25.7°F | 0.41 | 5.6 | 5 | <1 | 29 | 8 h 40 min |
| Year (annual) | 61°F | 32°F | 46.5°F | 14.88 | 24.4 | 74 | 44 | 163 |
The same normals in °C and millimetres
| Month | High | Low | Mean | Precip. | Snow |
|---|---|---|---|---|---|
| January | 3°C | −10°C | −3.8°C | 9 mm | 13 cm |
| February | 5°C | −9°C | −2.3°C | 11 mm | 10 cm |
| March | 10°C | −5°C | 2.4°C | 18 mm | 11 cm |
| April | 16°C | −1°C | 7.2°C | 43 mm | 4 cm |
| May | 21°C | 4°C | 12.3°C | 65 mm | 0 cm |
| June | 26°C | 9°C | 17.3°C | 73 mm | 0 cm |
| July | 32°C | 12°C | 21.8°C | 43 mm | 0 cm |
| August | 31°C | 11°C | 20.8°C | 31 mm | 0 cm |
| September | 25°C | 6°C | 15.3°C | 30 mm | 0 cm |
| October | 16°C | 0°C | 7.9°C | 31 mm | 3 cm |
| November | 8°C | −6°C | 1.2°C | 12 mm | 7 cm |
| December | 3°C | −10°C | −3.5°C | 10 mm | 14 cm |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00247214; 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 Roundup?
Normal highs sit between 65°F and 85°F in May, June and September. Of those, September has the fewest days with rain (5).
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 USC00247214.
When is the last frost in Roundup?
In Roundup, the last spring frost (32°F) comes after May 20 in half of years and after June 2 in one year in ten; the first autumn frost comes before September 21 in half of years and before September 5 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 201 year in 10 after June 2; 9 in 10 after May 6
- First autumn frost, half of years before
- September 211 year in 10 before September 5; 9 in 10 before October 4
NOAA puts the median frost-free season at 124 days, and the season without a hard freeze (28°F) at 146 days.
A hard freeze (28°F) comes after May 7 in half of springs and before October 1 in half of autumns.
The USDA's 2023 Plant Hardiness Zone Map puts Roundup in zone 4b in ZIP code 59072, the nearest ZIP area. By the map's own method, the average of each year's coldest night over 1991-2020, Roundup's NOAA station is in zone 4b: the coldest night of a typical year reaches −24°F (26 complete years).
Frost dates for every NOAA station in Montana · Frost dates by ZIP code
Source: NOAA NCEI 1991-2020 annual normals (frost probabilities), station USC00247214; 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 Roundup?
In a normal year in Roundup, 44 days a year reach 90°F (6 of them 100°F or more), 163 nights fall to 32°F or colder and 74 days bring measurable precipitation.
- Days at 90°F or more
- 44a normal year
- Days at 100°F or more
- 6a normal year
- Nights at 32°F or colder
- 163a normal year
- Days that stay below freezing
- 31high of 32°F or less
- Days with 0.01 inch of precipitation
- 74a normal year
- Days with 1 inch of snow or more
- 10a normal year
The highest temperature in this station's record (since 1914) is 111°F, on July 15, 2002; the lowest is −44°F, on December 24, 1983.
The wettest calendar year on that record is 2014, with 19.09 in; the snowiest season is 1919–20, with 123.0 inches.
Source: NOAA NCEI 1991-2020 annual normals, station USC00247214; records: ACIS (NOAA Regional Climate Centers), station USC00247214. Records use complete months only; a month missing more than three days is left out.
How sunny is Roundup?
Over a year 76% of the sunlight that would reach the ground under clear skies gets through the clouds in the area around Roundup, 4.0 kWh per square metre a day. July is the sunniest month (87%) and December the cloudiest (66%).
| Month | Share of clear-sky sunshine | Sunshine, kWh/m² a day |
|---|---|---|
| January | 72% | 1.7 |
| February | 74% | 2.6 |
| March | 71% | 3.7 |
| April | 68% | 4.8 |
| May | 71% | 5.8 |
| June | 77% | 6.7 |
| July | 87% | 7.1 |
| August | 85% | 5.9 |
| September | 79% | 4.4 |
| October | 73% | 2.8 |
| November | 71% | 1.8 |
| December | 66% | 1.3 |
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 Roundup need?
A normal year in Roundup brings 7,193 heating degree days, 34% more than the median U.S. place (5,373), and 482 cooling degree days, 47% fewer than the median (908). Eight months need 300 or more heating degree days, a monthly mean of about 55°F or colder. For gardens and crops, NOAA counts 2,260 growing degree days a year above 50°F.
| Month | Heating | Cooling |
|---|---|---|
| January | 1,235 | 0 |
| February | 1,042 | 0 |
| March | 888 | 0 |
| April | 602 | 0 |
| May | 342 | 8 |
| June | 111 | 52 |
| July | 20 | 212 |
| August | 34 | 174 |
| September | 196 | 36 |
| October | 581 | 1 |
| November | 924 | 0 |
| December | 1,218 | 0 |
| Year (annual) | 7,193 | 482 |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00247214. 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 Roundup been warmer than normal lately?
Over 49 complete years from 1919 to 2017, the station's annual mean temperature rose at a fitted 2.1°F per century (+0.12°C per decade). A fitted rate summarizes the whole record; single years swing well above and below it.
Source: trend: NOAA GHCN-Monthly v4. A year counts only with all twelve months complete.
How does Roundup's climate compare?
Roundup is warmer than 121 of the other 140 places with their own NOAA record in Montana, and wetter than 64. Across the 7,247 U.S. stations with normals, its annual mean of 46.5°F is warmer than 25%.
In the Köppen classification computed from these normals, Roundup is BSk: cold semi-arid steppe. 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.
Which places near Roundup share this climate record?
3 places have no NOAA station with 1991-2020 normals of their own, and this station is the nearest full record. A place's own climate can differ from these figures, by several degrees where it sits much higher or lower than the station, nearer the coast, or inside a large city's heat; for the larger places the next nearest records are named with their yearly mean, so the spread around them is visible, and places of 50,000 or more have their own page with NOAA's gridded normals.
- Klein, MT292 people · 3 mi S
- Camp Three, MT70 people · 2 mi NW
- Kilby Butte Colony, MT0 people · 9 mi E
Source: Census Bureau 2024 Gazetteer (place centers) and Vintage 2024 population estimates. Distance and direction from the station to each place's center.
What do Roundup's other NOAA stations record?
One more NOAA station keeps 1991-2020 normals in or near Roundup. This page uses Roundup; the other differs by site and elevation:
| Station | From this station | Elevation | Year | Jan low | Jul high | Precip. | Snow | Last frost |
|---|---|---|---|---|---|---|---|---|
| Roundup (15 mi SW) USC00247220 | 13 mi SW | 3,386 ft | 44.2°F | 11°F | 87°F | 15.1 | 43 | May 22 |
Source: NOAA NCEI 1991-2020 normals for each station. Last frost: the median last spring date of 32°F.
Questions about Roundup's climate
What is the coldest month in Roundup?
January, with a normal high of 37°F and a normal low of 13°F. The warmest is July (89°F by day, 54°F at night).
Does it snow in Roundup?
Yes: 24 inches in a normal year, falling on 14 days with 0.1 inch or more, the most in December (5.6 inches).
What is the rainiest month in Roundup?
June, with 2.89 in of precipitation in a normal year; the driest is January with 0.37 in.
What plant hardiness zone is Roundup in?
The USDA's 2023 map puts Roundup in zone 4b in ZIP code 59072, the nearest ZIP area. By the same method at Roundup's NOAA station, the coldest night of a typical year reaches −24°F (26 years, 1991-2020): zone 4b.
How late can frost come in Roundup?
In half of years the last 32°F night comes after May 20; in one year in ten it comes after June 2. Waiting until June 2 leaves about a one-in-ten chance of a later frost.
Nearby and next
- Montana climateThe statewide normals and every place in the state
- Flatwillow (4 mi ENE), MT27 miles from this station, 46.5°F a year
- Pompeys Pillar (15 mi N), MT30 miles from this station, 44.2°F a year
- Melstone, MT34 miles from this station, 47.2°F a year
- Ryegate, MT36 miles from this station, 46.2°F a year
- Compare two placesMonth by month, side by side
Download these normals (CSV) · JSON · How these figures are made