Photo: USGS · Public domainMidwinter lows in Sweet Grass sink below those of 94% of U.S. towns
Peak summer warmth arrives in July, with afternoons near 80°. Precipitation peaks in June and eases off in December. Its yearly precipitation falls short of 94% of U.S. towns. Seedlings are safe outdoors from about May 15, with the first autumn frost due around September 25.
A year in Sweet Grass at a glance
Each month’s typical high and low, and what it brings.
What stands out about Sweet Grass’ climate
Compared with towns across the U.S., with Sweet Grass’ place in Montana beside it.
What a year in Sweet Grass feels like
Typical highs and lows by season and by month, from NOAA’s 30-year normals.
About 132 frost-free days a year
In half of years the last 32° night comes by May 15 and the first by September 25. Frost and day counts come from NOAA’s station at Sweetgrass, MT, 0.3 miles from the town’s center, at about the same height.
The 2023 USDA map puts Sweet Grass’ center in zone 4a: the coldest night of a typical winter, averaged over 1991–2020, reaches about −27°. 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 14 inches of rain a year
June is the wettest month and December the driest.
Rain + melted snow by month
Inches of water
Heating and cooling a home in Sweet Grass
96% 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 Sweetgrass, MT.
Living with Sweet Grass’ climate
What the numbers mean for a garden, a free afternoon and a bad-weather day.
132 frost-free days in zone 4a. The last frost comes by May 15 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, July, August and September.
Parks & trails →Cold waves are 49% of the yearly building losses FEMA expects in Sweet Grass from natural hazards, the largest share. Normals are averages; the hazards page covers the extremes.
Natural hazards →Sweet Grass and similar climates
TownRatings has no climate map of the towns around Sweet Grass 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 Sweet Grass averaged 1.8° warmer than the 1900s. The biggest change is in January (+5.6°).
A bigger shift than in 76% 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 Sweet Grass compares
Against 12,954 U.S. towns of 2,500 or more (one per 5 km climate cell), with Sweet Grass’ place among Montana’s.
Sweet Grass weather by month
Highs, lows and precipitation from NOAA’s grid at Sweet Grass’ center. 1991–2020 normals.
| Month | High | Low | Rain + melt | 30-yr range |
|---|---|---|---|---|
| January | 32° | 10° | 0.4" | 6° – 35° |
| February | 34° | 11° | 0.4" | −3° – 36° |
| March | 43° | 19° | 0.6" | 13° – 40° |
| April | 53° | 29° | 1.3" | 35° – 46° |
| May | 64° | 38° | 2.1" | 46° – 57° |
| June | 71° | 45° | 3.8" | 55° – 63° |
| July | 80° | 50° | 1.3" | 56° – 73° |
| August | 80° | 49° | 1.3" | 58° – 69° |
| September | 69° | 41° | 1.3" | 51° – 62° |
| October | 55° | 30° | 0.9" | 36° – 49° |
| November | 41° | 19° | 0.6" | 17° – 40° |
| December | 33° | 11° | 0.3" | 9° – 33° |
| Year | 55° | 29° | 14.2" |
How much a month can swing
A normal is an average. February swings the most: from 1991 to 2020 its average ranged from -3° to 36°. June is the most reliable, staying within 8°.
Where Sweet Grass’ 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 Sweet Grass’ center.
- Frost, freezing nights, 90° and 100° days, heating and cooling: Sweetgrass, MT, 0.3 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 Sweet Grass’ climate
What is the weather like in Sweet Grass?
A typical July afternoon reaches 80°, a January night drops to 10°. Colder January nights than 94% of U.S. towns; cooler July afternoons than 90% of U.S. towns.
How cold does it get in Sweet Grass in winter?
January nights average 10°. About 179 nights a year reach 32° or below and 28 reach 0° or below. In the coldest January of the last 30 years the month averaged 6°.
How hot does it get in Sweet Grass?
July, with a typical high of 80° and a low of 50°. About 16 days a year reach 90° (Sweetgrass, MT).
When is the first and last frost in Sweet Grass?
In half of years the last spring frost (32°) comes by May 15 and the first fall frost by September 25, about 132 frost-free days, at Sweetgrass, MT.
What growing zone is Sweet Grass in?
Zone 4a on the 2023 USDA Plant Hardiness Zone Map: the coldest night of a typical winter reaches about −27°.
What is the best time of year to visit Sweet Grass?
By one simple rule (highs of 62–84° and lows of 40° or more), June, July, August and September. The rule is ours, not NOAA’s; the month table has the numbers to judge by.
Is Sweet Grass getting warmer?
Yes: 1991–2020 averaged 1.8° warmer than 1901–2000 on NOAA’s grid. A bigger shift than 76% of U.S. towns.
Neighbors talk weather
Gardens, snow, and the best days of the year in Sweet Grass.
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.