Roy, Montana climate: Normal weather by month, frost dates and records
Roy's normal year runs from 10°F January nights to 86°F July afternoons, with 13.3 inches of precipitation and 36 inches of snow a year. (NOAA 1991-2020 normals)
In metric: a yearly mean of 7.4°C, January lows of −12°C, July highs of 30°C, 338 mm of precipitation a year.
- NOAA stationRoy (8 mi NE)
- Station IDUSC00247228
- Location47.49°N 108.84°W
- Elevation3,085 ft (940 m)
- Population (census place)133
On October 22, the normal high in Roy is 56°F and the normal low 29°F, and the chance of measurable rain or snow is 15%.
Normals describe a typical year at the station, not a forecast. The National Weather Service forecast for Roy.
- Jan 34° 10°
- Feb 37° 13°
- Mar 48° 22°
- Apr 58° 30°
- May 68° 40°
- Jun 76° 48°
- Jul 86° 54°
- Aug 86° 53°
- Sep 76° 43°
- Oct 60° 32°
- Nov 46° 21°
- Dec 36° 12°
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 Roy each month?
July is the warmest month, with normal highs of 86°F; January the coldest, with normal lows of 10°F. The most precipitation falls in June (2.63 in), the least in February (0.39 in).
| Month | High | Low | Mean | Precip. | Snow | Wet days | 90°F days | Freezing nights | Daylight |
|---|---|---|---|---|---|---|---|---|---|
| January | 34°F | 10°F | 22.3°F | 0.45 | 7.7 | 4 | <1 | 29 | 8 h 50 min |
| February | 37°F | 13°F | 25.3°F | 0.39 | 4.7 | 3 | <1 | 26 | 10 h 10 min |
| March | 48°F | 22°F | 34.9°F | 0.52 | 6.8 | 5 | <1 | 26 | 11 h 50 min |
| April | 58°F | 30°F | 44.1°F | 1.29 | 2.6 | 6 | <1 | 16 | 13 h 30 min |
| May | 68°F | 40°F | 53.7°F | 2.51 | 0.6 | 9 | <1 | 6 | 15 h |
| June | 76°F | 48°F | 62.1°F | 2.63 | 0.0 | 10 | 2 | <1 | 16 h |
| July | 86°F | 54°F | 70.2°F | 1.74 | 0.0 | 8 | 9 | <1 | 15 h 40 min |
| August | 86°F | 53°F | 69.4°F | 1.29 | 0.0 | 5 | 13 | <1 | 14 h 20 min |
| September | 76°F | 43°F | 59.4°F | 0.94 | 0.0 | 5 | 3 | 3 | 12 h 40 min |
| October | 60°F | 32°F | 46.0°F | 0.67 | 1.9 | 4 | <1 | 15 | 11 h |
| November | 46°F | 21°F | 33.3°F | 0.47 | 5.5 | 4 | <1 | 26 | 9 h 20 min |
| December | 36°F | 12°F | 24.1°F | 0.42 | 6.5 | 3 | <1 | 30 | 8 h 30 min |
| Year (annual) | 59°F | 32°F | 45.4°F | 13.32 | 36.3 | 66 | 26 | 177 |
The same normals in °C and millimetres
| Month | High | Low | Mean | Precip. | Snow |
|---|---|---|---|---|---|
| January | 1°C | −12°C | −5.4°C | 11 mm | 20 cm |
| February | 3°C | −10°C | −3.7°C | 10 mm | 12 cm |
| March | 9°C | −6°C | 1.6°C | 13 mm | 17 cm |
| April | 14°C | −1°C | 6.7°C | 33 mm | 7 cm |
| May | 20°C | 4°C | 12.1°C | 64 mm | 2 cm |
| June | 25°C | 9°C | 16.7°C | 67 mm | 0 cm |
| July | 30°C | 12°C | 21.2°C | 44 mm | 0 cm |
| August | 30°C | 12°C | 20.8°C | 33 mm | 0 cm |
| September | 24°C | 6°C | 15.2°C | 24 mm | 0 cm |
| October | 16°C | 0°C | 7.8°C | 17 mm | 5 cm |
| November | 8°C | −6°C | 0.7°C | 12 mm | 14 cm |
| December | 2°C | −11°C | −4.4°C | 11 mm | 17 cm |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00247228; 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 Roy?
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 USC00247228.
When is the last frost in Roy?
In Roy, the last spring frost (32°F) comes after May 14 in half of years and after May 29 in one year in ten; the first autumn frost comes before September 24 in half of years and before September 12 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 141 year in 10 after May 29; 9 in 10 after May 3
- First autumn frost, half of years before
- September 241 year in 10 before September 12; 9 in 10 before October 7
NOAA puts the median frost-free season at 134 days, and the season without a hard freeze (28°F) at 153 days.
A hard freeze (28°F) comes after May 2 in half of springs and before October 2 in half of autumns.
The USDA's 2023 Plant Hardiness Zone Map puts Roy in zone 4b in ZIP code 59471, the nearest ZIP area.
Frost dates for every NOAA station in Montana · Frost dates by ZIP code
Source: NOAA NCEI 1991-2020 annual normals (frost probabilities), station USC00247228; USDA 2023 Plant Hardiness Zone Map, ZIP listings: PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed October 8, 2026. 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 Roy?
In a normal year in Roy, 26 days a year reach 90°F (2 of them 100°F or more), 177 nights fall to 32°F or colder and 66 days bring measurable precipitation.
- Days at 90°F or more
- 26a normal year
- Days at 100°F or more
- 2a normal year
- Nights at 32°F or colder
- 177a normal year
- Days that stay below freezing
- 41high of 32°F or less
- Days with 0.01 inch of precipitation
- 66a normal year
- Days with 1 inch of snow or more
- 14a normal year
The highest temperature in this station's record (since 1942) is 107°F, on August 5, 1961; the lowest is −49°F, on December 22, 1989.
The wettest calendar year on that record is 1978, with 25.15 in; the snowiest season is 1966–67, with 90.0 inches.
Source: NOAA NCEI 1991-2020 annual normals, station USC00247228; records: ACIS (NOAA Regional Climate Centers), station USC00247228. Records use complete months only; a month missing more than three days is left out.
How sunny is Roy?
Over a year 77% of the sunlight that would reach the ground under clear skies gets through the clouds in the area around Roy, 4.0 kWh per square metre a day. July is the sunniest month (87%) and December the cloudiest (67%).
| Month | Share of clear-sky sunshine | Sunshine, kWh/m² a day |
|---|---|---|
| January | 73% | 1.6 |
| February | 75% | 2.6 |
| March | 72% | 3.7 |
| April | 70% | 4.8 |
| May | 72% | 5.8 |
| June | 77% | 6.6 |
| July | 87% | 7.1 |
| August | 85% | 5.9 |
| September | 79% | 4.3 |
| October | 73% | 2.7 |
| November | 71% | 1.7 |
| December | 67% | 1.2 |
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 Roy need?
A normal year in Roy brings 7,566 heating degree days, 41% more than the median U.S. place (5,373), and 449 cooling degree days, 51% 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 2,182 growing degree days a year above 50°F.
| Month | Heating | Cooling |
|---|---|---|
| January | 1,324 | 0 |
| February | 1,113 | 0 |
| March | 933 | 0 |
| April | 629 | 0 |
| May | 357 | 6 |
| June | 132 | 44 |
| July | 28 | 187 |
| August | 38 | 173 |
| September | 203 | 35 |
| October | 592 | 3 |
| November | 951 | 0 |
| December | 1,266 | 0 |
| Year (annual) | 7,566 | 449 |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00247228. 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.
How does Roy's climate compare?
Roy is warmer than 101 of the other 140 places with their own NOAA record in Montana, and wetter than 36. Across the 7,247 U.S. stations with normals, its annual mean of 45.4°F is warmer than 21%.
In the Köppen classification computed from these normals, Roy 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.
Questions about Roy's climate
What is the coldest month in Roy?
January, with a normal high of 34°F and a normal low of 10°F. The warmest is July (86°F by day, 54°F at night).
Does it snow in Roy?
Yes: 36 inches in a normal year, falling on 16 days with 0.1 inch or more, the most in January (7.7 inches).
What is the rainiest month in Roy?
June, with 2.63 in of precipitation in a normal year; the driest is February with 0.39 in.
What plant hardiness zone is Roy in?
The USDA's 2023 map puts Roy in zone 4b in ZIP code 59471, the nearest ZIP area.
How late can frost come in Roy?
In half of years the last 32°F night comes after May 14; in one year in ten it comes after May 29. Waiting until May 29 leaves about a one-in-ten chance of a later frost.
Nearby and next
- Montana climateThe statewide normals and every place in the state
- Sand Creek, MT8 miles from this station, 44.8°F a year
- Valentine, MT19 miles from this station, 43.9°F a year
- Winifred, MT25 miles from this station, 44.0°F a year
- Grass Range, MT32 miles from this station, 45.5°F a year
- Compare two placesMonth by month, side by side
Download these normals (CSV) · JSON · How these figures are made