St. Marie, Montana climate: Normal weather by month, frost dates and records
St. Marie's normal year runs from 6°F January nights to 85°F July afternoons, with 11.8 inches of precipitation a year. (NOAA 1991-2020 normals)
In metric: a yearly mean of 6.1°C, January lows of −15°C, July highs of 29°C, 299 mm of precipitation a year.
- NOAA stationSt Marie
- Station IDUSW00094010
- Location48.41°N 106.51°W
- Elevation2,756 ft (840 m)
- Population (census place)319
On October 23, the normal high in St. Marie is 53°F and the normal low 30°F, and the chance of measurable rain or snow is 15%.
Normals describe a typical year at the station, not a forecast. The National Weather Service forecast for St. Marie.
- Jan 24° 6°
- Feb 28° 9°
- Mar 41° 20°
- Apr 56° 31°
- May 67° 41°
- Jun 75° 51°
- Jul 85° 57°
- Aug 84° 56°
- Sep 73° 46°
- Oct 57° 33°
- Nov 39° 20°
- Dec 27° 9°
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. Marie each month?
July is the warmest month, with normal highs of 85°F; January the coldest, with normal lows of 6°F. The most precipitation falls in June (3.08 in), the least in December (0.16 in).
| Month | High | Low | Mean | Precip. | Wet days | 90°F days | Freezing nights | Daylight |
|---|---|---|---|---|---|---|---|---|
| January | 24°F | 6°F | 15.0°F | 0.25 | 3 | <1 | 30 | 8 h 40 min |
| February | 28°F | 9°F | 18.3°F | 0.20 | 3 | <1 | 28 | 10 h 10 min |
| March | 41°F | 20°F | 30.6°F | 0.23 | 3 | <1 | 27 | 11 h 50 min |
| April | 56°F | 31°F | 43.5°F | 0.82 | 6 | <1 | 17 | 13 h 40 min |
| May | 67°F | 41°F | 53.8°F | 1.94 | 9 | <1 | 5 | 15 h 10 min |
| June | 75°F | 51°F | 62.7°F | 3.08 | 11 | 1 | <1 | 16 h |
| July | 85°F | 57°F | 70.6°F | 1.57 | 7 | 9 | <1 | 15 h 40 min |
| August | 84°F | 56°F | 69.8°F | 1.32 | 6 | 8 | <1 | 14 h 20 min |
| September | 73°F | 46°F | 59.3°F | 0.99 | 6 | 2 | 1 | 12 h 40 min |
| October | 57°F | 33°F | 44.8°F | 0.95 | 6 | <1 | 14 | 11 h |
| November | 39°F | 20°F | 29.8°F | 0.26 | 3 | <1 | 26 | 9 h 20 min |
| December | 27°F | 9°F | 18.3°F | 0.16 | 3 | <1 | 31 | 8 h 20 min |
| Year (annual) | 55°F | 32°F | 43.0°F | 11.77 | 67 | 21 | 179 |
The same normals in °C and millimetres
| Month | High | Low | Mean | Precip. |
|---|---|---|---|---|
| January | −4°C | −15°C | −9.4°C | 6 mm |
| February | −2°C | −13°C | −7.6°C | 5 mm |
| March | 5°C | −7°C | −0.8°C | 6 mm |
| April | 13°C | −1°C | 6.4°C | 21 mm |
| May | 19°C | 5°C | 12.1°C | 49 mm |
| June | 24°C | 10°C | 17.1°C | 78 mm |
| July | 29°C | 14°C | 21.4°C | 40 mm |
| August | 29°C | 13°C | 21.0°C | 34 mm |
| September | 23°C | 8°C | 15.2°C | 25 mm |
| October | 14°C | 1°C | 7.1°C | 24 mm |
| November | 4°C | −6°C | −1.2°C | 7 mm |
| December | −3°C | −13°C | −7.6°C | 4 mm |
NOAA publishes no 1991-2020 snowfall normal for this station. The nearest record that keeps one, Glasgow (14 miles away), gets 41 inches of snow in a normal year; elevation and distance can change that.
Source: NOAA NCEI 1991-2020 monthly normals, station USW00094010; 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. Marie?
Normal highs sit between 65°F and 85°F in May, June, July, August and September. Of those, September has the fewest days with rain (6).
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 USW00094010.
When is the last frost in St. Marie?
In St. Marie, the last spring frost (32°F) comes after May 13 in half of years and after May 26 in one year in ten; the first autumn frost comes before September 27 in half of years and before September 13 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
- May 131 year in 10 after May 26; 9 in 10 after May 2
- First autumn frost, half of years before
- September 271 year in 10 before September 13; 9 in 10 before October 9
NOAA puts the median frost-free season at 134 days, and the season without a hard freeze (28°F) at 154 days.
A hard freeze (28°F) comes after May 3 in half of springs and before October 5 in half of autumns.
The USDA's 2023 Plant Hardiness Zone Map puts St. Marie in zone 4a in ZIP code 59231. By the map's own method, the average of each year's coldest night over 1991-2020, St. Marie's NOAA station is in zone 4a: the coldest night of a typical year reaches −26°F (15 complete years).
Frost dates for every NOAA station in Montana · Frost dates by ZIP code
Source: NOAA NCEI 1991-2020 annual normals (frost probabilities), station USW00094010; 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. Marie?
In a normal year in St. Marie, 21 days a year reach 90°F (1 of them 100°F or more), 179 nights fall to 32°F or colder and 67 days bring measurable precipitation.
- Days at 90°F or more
- 21a normal year
- Days at 100°F or more
- 1a normal year
- Nights at 32°F or colder
- 179a normal year
- Days that stay below freezing
- 75high of 32°F or less
- Days with 0.01 inch of precipitation
- 67a normal year
Source: NOAA NCEI 1991-2020 annual normals, station USW00094010.
How sunny is St. Marie?
Over a year 78% of the sunlight that would reach the ground under clear skies gets through the clouds in the area around St. Marie, 4.0 kWh per square metre a day. July is the sunniest month (86%) and December the cloudiest (68%).
| Month | Share of clear-sky sunshine | Sunshine, kWh/m² a day |
|---|---|---|
| January | 75% | 1.5 |
| February | 78% | 2.6 |
| March | 75% | 3.8 |
| April | 73% | 4.9 |
| May | 75% | 6.0 |
| June | 77% | 6.5 |
| July | 86% | 6.9 |
| August | 85% | 5.7 |
| September | 79% | 4.2 |
| October | 75% | 2.7 |
| November | 72% | 1.6 |
| December | 68% | 1.1 |
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. Marie need?
A normal year in St. Marie brings 8,452 heating degree days, 57% more than the median U.S. place (5,373), and 487 cooling degree days, 46% fewer than the median (908). Eight months need 300 or more heating degree days, a monthly mean of about 55°F or colder. For gardens and crops, NOAA counts 2,220 growing degree days a year above 50°F.
| Month | Heating | Cooling |
|---|---|---|
| January | 1,550 | 0 |
| February | 1,308 | 0 |
| March | 1,068 | 0 |
| April | 647 | 0 |
| May | 355 | 8 |
| June | 122 | 53 |
| July | 19 | 194 |
| August | 35 | 184 |
| September | 215 | 45 |
| October | 630 | 2 |
| November | 1,056 | 0 |
| December | 1,448 | 0 |
| Year (annual) | 8,452 | 487 |
Source: NOAA NCEI 1991-2020 monthly normals, station USW00094010. 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. Marie been warmer than normal lately?
2025 averaged 44.1°F, 1.1°F above the 1991-2020 normal of 43.0°F.
| Year | Mean | Against normal | Precip. |
|---|---|---|---|
| 2025 | 44.1°F | +1.1°F | 9.06 |
Source: observed years: ACIS, station USW00094010. A year counts only with all twelve months complete.
How does St. Marie's climate compare?
St. Marie is warmer than 46 of the other 140 places with their own NOAA record in Montana, and wetter than 11. Across the 7,247 U.S. stations with normals, its annual mean of 43.0°F is warmer than 12%.
In the Köppen classification computed from these normals, St. Marie is BSk: cold semi-arid steppe. 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.
Questions about St. Marie's climate
What is the coldest month in St. Marie?
January, with a normal high of 24°F and a normal low of 6°F. The warmest is July (85°F by day, 57°F at night).
Does it snow in St. Marie?
Yes. NOAA publishes no 1991-2020 snowfall normal for St. Marie's NOAA station; the nearest record that keeps one, Glasgow (14 miles away), records 41 inches of snow in a normal year.
What is the rainiest month in St. Marie?
June, with 3.08 in of precipitation in a normal year; the driest is December with 0.16 in.
What plant hardiness zone is St. Marie in?
The USDA's 2023 map puts St. Marie in zone 4a in ZIP code 59231. By the same method at St. Marie's NOAA station, the coldest night of a typical year reaches −26°F (15 years, 1991-2020): zone 4a.
How late can frost come in St. Marie?
In half of years the last 32°F night comes after May 13; in one year in ten it comes after May 26. Waiting until May 26 leaves about a one-in-ten chance of a later frost.
Nearby and next
- Montana climateThe statewide normals and every place in the state
- Glasgow, MT14 miles from this station, 43.9°F a year
- Nashua, MT21 miles from this station, 44.3°F a year
- Opheim (12 mi SSE), MT22 miles from this station, 35.5°F a year
- Fort Peck, MT28 miles from this station, 46.5°F a year
- Compare two placesMonth by month, side by side
Download these normals (CSV) · JSON · How these figures are made