St. Mary, Montana climate: Normal weather by month, frost dates and records
St. Mary's normal year runs from 15°F February nights to 73°F July afternoons, with 26.1 inches of precipitation a year. (NOAA 1991-2020 normals)
In metric: a yearly mean of 4.2°C, February lows of −10°C, July highs of 23°C, 663 mm of precipitation a year.
- NOAA stationSt. Mary (1 mi SSW)
- Station IDUSW00004130
- Location48.74°N 113.43°W
- Elevation4,555 ft (1,388 m)
- Population (census place)209
On October 22, the normal high in St. Mary is 46°F and the normal low 30°F, and the chance of measurable rain or snow is 42%.
Normals describe a typical year at the station, not a forecast. The National Weather Service forecast for St. Mary.
- Jan 32° 15°
- Feb 31° 15°
- Mar 38° 20°
- Apr 46° 28°
- May 56° 35°
- Jun 63° 42°
- Jul 73° 46°
- Aug 73° 45°
- Sep 63° 39°
- Oct 49° 32°
- Nov 37° 25°
- Dec 31° 17°
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 St. Mary each month?
July is the warmest month, with normal highs of 73°F; February the coldest, with normal lows of 15°F. The most precipitation falls in June (3.07 in), the least in July (1.20 in).
| Month | High | Low | Mean | Precip. | Wet days | 90°F days | Freezing nights | Daylight |
|---|---|---|---|---|---|---|---|---|
| January | 32°F | 15°F | 23.2°F | 2.07 | 15 | <1 | 27 | 8 h 40 min |
| February | 31°F | 15°F | 23.0°F | 2.06 | 14 | <1 | 26 | 10 h 10 min |
| March | 38°F | 20°F | 28.8°F | 2.50 | 16 | <1 | 25 | 11 h 50 min |
| April | 46°F | 28°F | 36.8°F | 2.45 | 15 | <1 | 21 | 13 h 40 min |
| May | 56°F | 35°F | 45.6°F | 2.83 | 13 | <1 | 11 | 15 h 10 min |
| June | 63°F | 42°F | 52.3°F | 3.07 | 13 | <1 | 2 | 16 h 10 min |
| July | 73°F | 46°F | 59.7°F | 1.20 | 8 | 1 | <1 | 15 h 50 min |
| August | 73°F | 45°F | 58.9°F | 1.28 | 8 | <1 | 1 | 14 h 30 min |
| September | 63°F | 39°F | 50.9°F | 1.63 | 9 | <1 | 6 | 12 h 40 min |
| October | 49°F | 32°F | 40.4°F | 2.17 | 12 | <1 | 15 | 10 h 50 min |
| November | 37°F | 25°F | 31.0°F | 2.70 | 14 | <1 | 21 | 9 h 10 min |
| December | 31°F | 17°F | 23.8°F | 2.13 | 14 | <1 | 27 | 8 h 20 min |
| Year (annual) | 49°F | 30°F | 39.5°F | 26.09 | 151 | 1 | 181 |
The same normals in °C and millimetres
| Month | High | Low | Mean | Precip. |
|---|---|---|---|---|
| January | 0°C | −9°C | −4.9°C | 53 mm |
| February | 0°C | −10°C | −5.0°C | 52 mm |
| March | 3°C | −7°C | −1.8°C | 64 mm |
| April | 8°C | −2°C | 2.7°C | 62 mm |
| May | 13°C | 2°C | 7.6°C | 72 mm |
| June | 17°C | 5°C | 11.3°C | 78 mm |
| July | 23°C | 8°C | 15.4°C | 30 mm |
| August | 23°C | 7°C | 14.9°C | 33 mm |
| September | 17°C | 4°C | 10.5°C | 41 mm |
| October | 9°C | 0°C | 4.7°C | 55 mm |
| November | 3°C | −4°C | −0.6°C | 69 mm |
| December | −1°C | −8°C | −4.6°C | 54 mm |
NOAA publishes no 1991-2020 snowfall normal for this station, and no record within 25 miles keeps one, so snow is left out here rather than estimated.
Source: NOAA NCEI 1991-2020 monthly normals, station USW00004130; 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 St. Mary?
Normal highs sit between 65°F and 85°F in July and August. Of those, August has the fewest days with rain (8).
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 USW00004130.
When is the last frost in St. Mary?
In St. Mary, the last spring frost (32°F) comes after June 3 in half of years and after June 23 in one year in ten; the first autumn frost comes before September 8 in half of years and before August 22 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
- June 31 year in 10 after June 23; 9 in 10 after May 19
- First autumn frost, half of years before
- September 81 year in 10 before August 22; 9 in 10 before September 26
NOAA puts the median frost-free season at 94 days, and the season without a hard freeze (28°F) at 131 days.
A hard freeze (28°F) comes after May 14 in half of springs and before September 25 in half of autumns.
The USDA's 2023 Plant Hardiness Zone Map puts St. Mary in zone 4b in ZIP code 59434, the nearest ZIP area. By the map's own method, the average of each year's coldest night over 1991-2020, St. Mary's NOAA station is in zone 4a: the coldest night of a typical year reaches −28°F (17 complete years); the map interpolates between stations and terrain, so the station and the ZIP area can differ by half a zone.
Frost dates for every NOAA station in Montana · Frost dates by ZIP code
Source: NOAA NCEI 1991-2020 annual normals (frost probabilities), station USW00004130; USDA 2023 Plant Hardiness Zone Map, ZIP listings: PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed October 8, 2026; the station zone: ACIS daily lows, 1991-2020. 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 St. Mary?
In a normal year in St. Mary, 1 day a year reaches 90°F, 181 nights fall to 32°F or colder and 151 days bring measurable precipitation.
- Days at 90°F or more
- 1a normal year
- Days at 100°F or more
- fewer than 1a normal year
- Nights at 32°F or colder
- 181a normal year
- Days that stay below freezing
- 61high of 32°F or less
- Days with 0.01 inch of precipitation
- 151a normal year
The highest temperature in this station's record (since 2003) is 96°F, on July 23, 2007; the lowest is −43°F, on December 22, 2022.
The wettest calendar year on that record is 2025, with 30.27 in.
Source: NOAA NCEI 1991-2020 annual normals, station USW00004130; records: ACIS (NOAA Regional Climate Centers), station USW00004130. Records use complete months only; a month missing more than three days is left out.
How sunny is St. Mary?
Over a year 73% of the sunlight that would reach the ground under clear skies gets through the clouds in the area around St. Mary, 3.8 kWh per square metre a day. July is the sunniest month (86%) and December the cloudiest (62%).
| Month | Share of clear-sky sunshine | Sunshine, kWh/m² a day |
|---|---|---|
| January | 65% | 1.3 |
| February | 73% | 2.4 |
| March | 68% | 3.5 |
| April | 68% | 4.7 |
| May | 69% | 5.6 |
| June | 73% | 6.3 |
| July | 86% | 7.1 |
| August | 82% | 5.8 |
| September | 76% | 4.1 |
| October | 69% | 2.5 |
| November | 62% | 1.4 |
| December | 62% | 1.0 |
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 St. Mary need?
A normal year in St. Mary brings 9,282 heating degree days, 73% more than the median U.S. place (5,373), and 21 cooling degree days, 98% fewer than the median (908). Ten months need 300 or more heating degree days, a monthly mean of about 55°F or colder. For gardens and crops, NOAA counts 867 growing degree days a year above 50°F.
| Month | Heating | Cooling |
|---|---|---|
| January | 1,294 | 0 |
| February | 1,177 | 0 |
| March | 1,124 | 0 |
| April | 848 | 0 |
| May | 602 | 0 |
| June | 383 | 1 |
| July | 175 | 11 |
| August | 196 | 8 |
| September | 424 | 1 |
| October | 764 | 0 |
| November | 1,020 | 0 |
| December | 1,276 | 0 |
| Year (annual) | 9,282 | 21 |
Source: NOAA NCEI 1991-2020 monthly normals, station USW00004130. 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.
Has St. Mary been warmer than normal lately?
2025 averaged 41.3°F, 1.8°F above the 1991-2020 normal of 39.5°F. 4 of the 5 complete years since 2021 ran warmer than the normal.
| Year | Mean | Against normal | Precip. |
|---|---|---|---|
| 2021 | 40.0°F | +0.5°F | 24.23 |
| 2022 | 39.2°F | −0.3°F | 26.88 |
| 2023 | 41.6°F | +2.1°F | 20.28 |
| 2024 | 41.2°F | +1.7°F | 22.94 |
| 2025 | 41.3°F | +1.8°F | 30.27 |
Source: observed years: ACIS, station USW00004130. A year counts only with all twelve months complete.
How does St. Mary's climate compare?
St. Mary is warmer than 11 of the other 140 places with their own NOAA record in Montana, and wetter than 126. Across the 7,247 U.S. stations with normals, its annual mean of 39.5°F is warmer than 5%.
In the Köppen classification computed from these normals, St. Mary is Dfb: continental, no dry season, warm summer. 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.
Which places near St. Mary share this climate record?
Babb has no NOAA station with 1991-2020 normals of its own, and this station is the nearest full record. A place's own climate can differ from these figures, by several degrees where it sits much higher or lower than the station, nearer the coast, or inside a large city's heat; for the larger places the next nearest records are named with their yearly mean, so the spread around them is visible, and places of 50,000 or more have their own page with NOAA's gridded normals.
- Babb, MT279 people · 10 mi N
Source: Census Bureau 2024 Gazetteer (place centers) and Vintage 2024 population estimates. Distance and direction from the station to each place's center.
What do St. Mary's other NOAA stations record?
One more NOAA station keeps 1991-2020 normals in or near St. Mary. This page uses St. Mary (1 mi SSW); the other differs by site and elevation:
| Station | From this station | Elevation | Year | Jan low | Jul high | Precip. | Snow | Last frost |
|---|---|---|---|---|---|---|---|---|
| St Mary station USC00247292 | in town | 4,560 ft | 39.1°F | 12°F | 75°F | – | – | June 12 |
Source: NOAA NCEI 1991-2020 normals for each station. Last frost: the median last spring date of 32°F.
Questions about St. Mary's climate
What is the coldest month in St. Mary?
February, with a normal high of 31°F and a normal low of 15°F. The warmest is July (73°F by day, 46°F at night).
What is the rainiest month in St. Mary?
June, with 3.07 in of precipitation in a normal year; the driest is July with 1.20 in.
What plant hardiness zone is St. Mary in?
The USDA's 2023 map puts St. Mary in zone 4b in ZIP code 59434, the nearest ZIP area. By the same method at St. Mary's NOAA station, the coldest night of a typical year reaches −28°F (17 years, 1991-2020): zone 4a.
How late can frost come in St. Mary?
In half of years the last 32°F night comes after June 3; in one year in ten it comes after June 23. Waiting until June 23 leaves about a one-in-ten chance of a later frost.
Nearby and next
- Montana climateThe statewide normals and every place in the state
- East Glacier, MT22 miles from this station, 38.8°F a year
- West Glacier, MT30 miles from this station, 43.1°F a year
- Del Bonita, MT34 miles from this station, 40.1°F a year
- Hungry Horse, MT39 miles from this station, 44.4°F a year
- Compare two placesMonth by month, side by side
Download these normals (CSV) · JSON · How these figures are made