Rosebud Battlefield-Where the Girl Saved Her Brother · Photo: Phil Konstantin · Public domainMidwinter lows in Forty Mile Colony sink below those of 93% of U.S. towns
Peak summer warmth arrives in July, with afternoons near 89°. It is a dry place: less rain and snow fall here than on 93% of U.S. towns. Compared with 1901–2000, the average now sits 1.3° higher. Garden planting can start around May 21; autumn frost returns near September 17.
A year in Forty Mile Colony at a glance
Each month’s typical high and low, and what it brings.
What stands out about Forty Mile Colony’s climate
Compared with towns across the U.S., with Forty Mile Colony’s place in Montana beside it.
What a year in Forty Mile Colony feels like
Typical highs and lows by season and by month, from NOAA’s 30-year normals.
About 117 frost-free days a year
In half of years the last 32° night comes by May 21 and the first by September 17. Frost and day counts come from NOAA’s station at Wyola 1 Sw, MT, 11 miles from the town’s center, 300 ft higher.
The 2023 USDA map puts Forty Mile Colony’s center in zone 4b: the coldest night of a typical winter, averaged over 1991–2020, reaches about −25°. 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 15 inches of rain a year
May is the wettest month and January the driest.
Rain + melted snow by month
Inches of water
Heating and cooling a home in Forty Mile Colony
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 Wyola 1 Sw, MT.
Living with Forty Mile Colony’s climate
What the numbers mean for a garden, a free afternoon and a bad-weather day.
117 frost-free days in zone 4b. The last frost comes by May 21 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 17.
Months with highs of 62–84° and lows of 40° or more: June and September.
Parks & trails →Of the yearly building losses FEMA expects in Forty Mile Colony from natural hazards, river flooding is the largest share (50%); heat waves, cold waves, winter storms and ice storms together are 16%. Normals are averages; the hazards page covers the extremes.
Natural hazards →Forty Mile Colony and similar climates
TownRatings has no climate map of the towns around Forty Mile Colony yet.
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 Forty Mile Colony averaged 1.3° warmer than the 1900s. The biggest change is in January (+4.1°).
A smaller shift than in 52% 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 Forty Mile Colony compares
Against 12,954 U.S. towns of 2,500 or more (one per 5 km climate cell), with Forty Mile Colony’s place among Montana’s.
Forty Mile Colony weather by month
Highs, lows and precipitation from NOAA’s grid at Forty Mile Colony’s center. 1991–2020 normals.
| Month | High | Low | Rain + melt | 30-yr range |
|---|---|---|---|---|
| January | 36° | 10° | 0.6" | 14° – 33° |
| February | 39° | 13° | 0.7" | 8° – 36° |
| March | 50° | 22° | 0.9" | 25° – 46° |
| April | 59° | 30° | 1.8" | 39° – 49° |
| May | 68° | 39° | 2.7" | 49° – 59° |
| June | 79° | 48° | 2.0" | 57° – 69° |
| July | 89° | 54° | 1.1" | 60° – 77° |
| August | 87° | 51° | 0.8" | 63° – 75° |
| September | 76° | 42° | 1.5" | 53° – 65° |
| October | 61° | 30° | 1.6" | 37° – 52° |
| November | 47° | 20° | 0.8" | 22° – 44° |
| December | 36° | 11° | 0.6" | 14° – 30° |
| Year | 61° | 31° | 15.0" |
How much a month can swing
A normal is an average. February swings the most: from 1991 to 2020 its average ranged from 8° to 36°. May is the most reliable, staying within 10°.
Where Forty Mile Colony’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 Forty Mile Colony’s center.
- Frost, freezing nights, 90° and 100° days, heating and cooling: Wyola 1 Sw, MT, 11 miles from the town’s center, 300 ft higher; 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 Forty Mile Colony’s climate
What is the weather like in Forty Mile Colony?
A typical July afternoon reaches 89°, a January night drops to 10°. Colder January nights than 93% of U.S. towns; hotter July afternoons than 73% of U.S. towns.
How cold does it get in Forty Mile Colony in winter?
January nights average 10°. About 197 nights a year reach 32° or below and 21 reach 0° or below. In the coldest January of the last 30 years the month averaged 14°.
How hot does it get in Forty Mile Colony?
July, with a typical high of 89° and a low of 54°. About 39 days a year reach 90° and 5 reach 100° (Wyola 1 Sw, MT).
When is the first and last frost in Forty Mile Colony?
In half of years the last spring frost (32°) comes by May 21 and the first fall frost by September 17, about 117 frost-free days, at Wyola 1 Sw, MT.
What growing zone is Forty Mile Colony in?
Zone 4b on the 2023 USDA Plant Hardiness Zone Map: the coldest night of a typical winter reaches about −25°.
What is the best time of year to visit Forty Mile Colony?
By one simple rule (highs of 62–84° and lows of 40° or more), June and September. The rule is ours, not NOAA’s; the month table has the numbers to judge by.
Is Forty Mile Colony getting warmer?
Yes: 1991–2020 averaged 1.3° warmer than 1901–2000 on NOAA’s grid. A smaller shift than 52% of U.S. towns.
Neighbors talk weather
Gardens, snow, and the best days of the year in Forty Mile Colony.
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.