Photo: Royalbroil · CC BY-SA 3.0Hardly any U.S. towns see fresher July days than St. Mary
Deep winter brings January lows near 13°. In January, nights here are colder than in 90% of U.S. towns. Since 1901–2000, the year has warmed by 1.9°, most of all in January. Homes need heating from October to May, the months averaging under 50°.
A year in St. Mary at a glance
Each month’s typical high and low, and what it brings.
What stands out about St. Mary’s climate
Compared with towns across the U.S., with St. Mary’s place in Montana beside it.
What a year in St. Mary feels like
Typical highs and lows by season and by month, from NOAA’s 30-year normals.
About 82 frost-free days a year
In half of years the last 32° night comes by June 12 and the first by September 5. Day counts come from NOAA’s station at St. Mary 1 Ssw, MT, 0.3 miles from the town’s center, at about the same height; frost dates and degree days from St Mary, MT, 0.3 miles away.
The 2023 USDA map puts St. Mary’s center in zone 4b: the coldest night of a typical winter, averaged over 1991–2020, reaches about −24°. Plant labels use the zone; frost dates tell you when to plant.
Freezing nights by month
Average nights at or below 32°
About 25 inches of rain a year
June is the wettest month and July the driest.
Rain + melted snow by month
Inches of water
Heating and cooling a home in St. Mary
99% of the work is heating, so the furnace matters far more than the air conditioner. Months averaging under 55° run from September through June.
Degree days add up how far each day’s average falls below (heating) or rises above (cooling) 65° over a year. NOAA normals at St Mary, MT.
Living with St. Mary’s climate
What the numbers mean for a garden, a free afternoon and a bad-weather day.
82 frost-free days in zone 4b. The last frost comes by Jun 12 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 5.
Months with highs of 62–84° and lows of 40° or more: June, July and August. 1.5 miles of trails are waiting.
Parks & trails →Cold waves are 41% of the yearly building losses FEMA expects in St. Mary from natural hazards, the largest share. Normals are averages; the hazards page covers the extremes.
Natural hazards →St. Mary and similar climates
TownRatings has no climate map of the towns around St. Mary 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 St. Mary averaged 1.9° warmer than the 1900s. The biggest change is in January (+5.1°).
A bigger shift than in 87% 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 St. Mary compares
Against 12,954 U.S. towns of 2,500 or more (one per 5 km climate cell), with St. Mary’s place among Montana’s.
St. Mary weather by month
Highs, lows and precipitation from NOAA’s grid at St. Mary’s center. 1991–2020 normals.
| Month | High | Low | Rain + melt | 30-yr range |
|---|---|---|---|---|
| January | 31° | 13° | 1.9" | 11° – 30° |
| February | 33° | 13° | 1.8" | 1° – 33° |
| March | 40° | 19° | 2.1" | 16° – 37° |
| April | 48° | 27° | 2.1" | 32° – 44° |
| May | 58° | 34° | 2.7" | 41° – 51° |
| June | 65° | 41° | 3.7" | 50° – 59° |
| July | 75° | 45° | 1.4" | 51° – 68° |
| August | 75° | 43° | 1.4" | 54° – 63° |
| September | 65° | 37° | 1.8" | 47° – 56° |
| October | 50° | 30° | 2.1" | 34° – 47° |
| November | 38° | 22° | 2.2" | 20° – 39° |
| December | 31° | 15° | 1.9" | 12° – 30° |
| Year | 51° | 28° | 25.2" |
How much a month can swing
A normal is an average. February swings the most: from 1991 to 2020 its average ranged from 1° to 33°. September is the most reliable, staying within 8°.
Where St. Mary’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 St. Mary’s center.
- Frost dates, heating and cooling: St Mary, MT, 0.3 miles away.
- Freezing nights, 90° and 100° days: St. Mary 1 Ssw, 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 St. Mary’s climate
What is the weather like in St. Mary?
A typical July afternoon reaches 75°, a January night drops to 13°. Colder January nights than 90% of U.S. towns; cooler July afternoons than 98% of U.S. towns.
How cold does it get in St. Mary in winter?
January nights average 13°. About 181 nights a year reach 32° or below and 25 reach 0° or below. In the coldest January of the last 30 years the month averaged 11°.
How hot does it get in St. Mary?
July, with a typical high of 75°. 90° days are rare: none in a normal year at St Mary, MT.
When is the first and last frost in St. Mary?
In half of years the last spring frost (32°) comes by June 12 and the first fall frost by September 5, about 82 frost-free days, at St Mary, MT.
What growing zone is St. Mary in?
Zone 4b on the 2023 USDA Plant Hardiness Zone Map: the coldest night of a typical winter reaches about −24°.
What is the best time of year to visit St. Mary?
By one simple rule (highs of 62–84° and lows of 40° or more), June, July and August. The rule is ours, not NOAA’s; the month table has the numbers to judge by.
Is St. Mary getting warmer?
Yes: 1991–2020 averaged 1.9° warmer than 1901–2000 on NOAA’s grid. A bigger shift than 87% of U.S. towns.
Neighbors talk weather
Gardens, snow, and the best days of the year in St. Mary.
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.