Hardly any U.S. towns see harsher January nights than Rocky Boy West
On a normal July day the thermometer tops out near 85°. By precipitation alone, it ranks drier than 94% of U.S. towns. Since 1901–2000, the year has warmed by 1.7°, most of all in January. Warm coats and heating bills mark the months from October to April, when means dip under 50°.
A year in Rocky Boy West at a glance
Each month’s typical high and low, and what it brings.
What stands out about Rocky Boy West’s climate
Compared with towns across the U.S., with Rocky Boy West’s place in Montana beside it.
What a year in Rocky Boy West feels like
Typical highs and lows by season and by month, from NOAA’s 30-year normals.
About 128 frost-free days a year
In half of years the last 32° night comes by May 17 and the first by September 25. Frost and day counts come from NOAA’s station at Big Sandy, MT, 12 miles from the town’s center, at about the same height.
The 2023 USDA map puts Rocky Boy West’s center in zone 4a: the coldest night of a typical winter, averaged over 1991–2020, reaches about −29°. Plant labels use the zone; frost dates tell you when to plant.
Freezing nights by month
Average nights at or below 32°
90° days by month
Average days at 90° or more
About 35 inches of snow a winter
Snow, measured at Ft Assiniboine, MT, falls mostly in February. Precipitation (rain plus melted snow) adds up to 14 inches a year; June is the wettest month and February the driest. Rain or snow falls on about 88 days a year.
Rain + melted snow by month
Inches of water
Snowfall by month
Inches of snow
Heating and cooling a home in Rocky Boy West
94% of the work is heating, so the furnace matters far more than the air conditioner. Months averaging under 55° run from October through May.
Degree days add up how far each day’s average falls below (heating) or rises above (cooling) 65° over a year. NOAA normals at Big Sandy, MT.
Living with Rocky Boy West’s climate
What the numbers mean for a garden, a free afternoon and a bad-weather day.
128 frost-free days in zone 4a. The last frost comes by May 17 in half of years, so many gardeners wait a week or two past that to set out tomatoes. The first fall frost comes by Sep 25.
Months with highs of 62–84° and lows of 40° or more: June, August and September. 3.0 miles of trails are waiting.
Parks & trails →Of the yearly building losses FEMA expects in Rocky Boy West from natural hazards, river flooding is the largest share (43%); heat waves, cold waves, winter storms and ice storms together are 40%. Normals are averages; the hazards page covers the extremes.
Natural hazards →Rocky Boy West and similar climates
TownRatings has no climate map of the towns around Rocky Boy West yet.
Climates most like Rocky Boy West’s, farther away
TownRatings’ own comparison of NOAA 1991–2020 normals, not a NOAA product: places of 5,000+ at least 150 miles away, one per state, closest on January low, July high, precipitation and snow.
| Town | Jan. low | July high | Precip. | Snow |
|---|---|---|---|---|
| Rocky Boy West, MT | 7° | 85° | 14" | 35" |
| Dickinson, ND | 5° | 83° | 16" | 35" |
| Taos, NM | 11° | 84° | 13" | 28" |
| Gypsum, CO | 11° | 86° | 14" | 39" |
| Green River, WY | 9° | 87° | 9" | 39" |
Temperatures and precipitation come from NOAA’s 5 km grid; snow and day counts from the stations named on this page.
Warmer than it used to be
The last 30 years in Rocky Boy West averaged 1.7° warmer than the 1900s. The biggest change is in January (+4.9°).
A bigger shift than in 71% of U.S. towns.
Change by month
The two periods overlap (1991–2000 is in both), which makes the gap a little smaller than it would be between separate periods.
How Rocky Boy West compares
Against 12,954 U.S. towns of 2,500 or more (one per 5 km climate cell), with Rocky Boy West’s place among Montana’s.
Rocky Boy West weather by month
Highs, lows and precipitation from NOAA’s grid at Rocky Boy West’s center; snow, wet days and snow on the ground from Ft Assiniboine, MT. 1991–2020 normals.
| Month | High | Low | Rain + melt | Snow | Wet days | 30-yr range |
|---|---|---|---|---|---|---|
| January | 29° | 7° | 0.4" | 6.4" | 7 | 5° – 33° |
| February | 34° | 10° | 0.4" | 7.3" | 5 | −4° – 36° |
| March | 45° | 20° | 0.5" | 4.0" | 5 | 14° – 40° |
| April | 57° | 30° | 1.1" | 2.7" | 8 | 38° – 47° |
| May | 67° | 39° | 2.2" | 0.7" | 11 | 49° – 59° |
| June | 75° | 48° | 3.0" | 0.0" | 13 | 58° – 66° |
| July | 85° | 53° | 1.7" | 0.0" | 8 | 59° – 76° |
| August | 84° | 51° | 1.1" | 0.0" | 7 | 62° – 73° |
| September | 72° | 41° | 1.2" | 0.0" | 7 | 52° – 63° |
| October | 57° | 30° | 1.0" | 1.9" | 7 | 36° – 50° |
| November | 42° | 19° | 0.6" | 5.2" | 6 | 18° – 40° |
| December | 32° | 10° | 0.4" | 6.4" | 5 | 7° – 31° |
| Year | 56° | 30° | 13.6" | 34.6" | 88 |
How much a month can swing
A normal is an average. February swings the most: from 1991 to 2020 its average ranged from -4° to 36°. June is the most reliable, staying within 8°.
Where Rocky Boy West’s numbers come from
Normals are 30-year averages, not a forecast. How TownRatings reads climate data →
- Temperatures and precipitation: NOAA’s gridded 1991–2020 normals for the 5 km cell at Rocky Boy West’s center.
- Snow: Ft Assiniboine, MT.
- Frost, freezing nights, 90° and 100° days, heating and cooling: Big Sandy, MT, 12 miles from the town’s center, at about the same height; the nearest station that passes our checks for distance, height and agreement with the grid.
- Growing zone: USDA Plant Hardiness Zone Map, 2023. USDA Agricultural Research Service and PRISM Group, Oregon State University, prism.oregonstate.edu/phzm, accessed 8 Oct 2026.
- Then and now: NOAA’s gridded normals for 1901–2000 at the same cell.
- Storms and extremes: FEMA National Risk Index (expected annual losses to buildings).
Common questions about Rocky Boy West’s climate
What is the weather like in Rocky Boy West?
A typical July afternoon reaches 85°, a January night drops to 7°, and about 35 inches of snow falls in a normal winter. Colder January nights than 96% of U.S. towns; cooler July afternoons than 52% of U.S. towns.
How cold does it get in Rocky Boy West in winter?
January nights average 7°. About 180 nights a year reach 32° or below and 29 reach 0° or below. In the coldest January of the last 30 years the month averaged 5°.
How much snow does Rocky Boy West get?
About 35 inches in a normal winter at Ft Assiniboine, MT, most of it in February.
How hot does it get in Rocky Boy West?
July, with a typical high of 85° and a low of 53°. About 28 days a year reach 90° and 2 reach 100° (Big Sandy, MT).
When is the first and last frost in Rocky Boy West?
In half of years the last spring frost (32°) comes by May 17 and the first fall frost by September 25, about 128 frost-free days, at Big Sandy, MT.
What growing zone is Rocky Boy West in?
Zone 4a on the 2023 USDA Plant Hardiness Zone Map: the coldest night of a typical winter reaches about −29°.
What is the best time of year to visit Rocky Boy West?
By one simple rule (highs of 62–84° and lows of 40° or more), June, August and September. The rule is ours, not NOAA’s; the month table has the numbers to judge by.
Is Rocky Boy West getting warmer?
Yes: 1991–2020 averaged 1.7° warmer than 1901–2000 on NOAA’s grid. A bigger shift than 71% of U.S. towns.
Neighbors talk weather
Gardens, snow, and the best days of the year in Rocky Boy West.
Source: NOAA NCEI U.S. Climate Normals, 1991–2020 and 1901–2000; USDA/PRISM 2023 hardiness zones; FEMA National Risk Index. Today’s forecast: National Weather Service.