St. Mary weather by month
What a typical year looks like in St. Mary, Montana: average highs and lows, rain and snow, and the warmest and coldest days on record. Normals are the 1991–2020 averages at St. Mary 1 Ssw, 0 km from St. Mary; records cover 2003–2026.
The year at a glance
- Precipitation a year
- 26.1 in663 mm
- Snow a year
- Rare
- Last spring freeze
- Jun 5
- First fall freeze
- Sep 1
- Heating degree days
- 9,283
- Cooling degree days
- 21
Freeze dates are medians (half of years earlier, half later). Degree days use a 65°F base; HVAC design temperatures here are −21°−29° (heating, 99%) and 85°29° (cooling, 1%).
Month by month
St. Mary in January
Highs average 32°0° and lows 15°−9°, with 2.1 in53 mm of precipitation in a typical January.
- Record high
- 58°14° (2024)
- Record low
- −41° (2024)
- Heating degree days
- 1294
- Cooling degree days
- 0
St. Mary in February
Highs average 31°0° and lows 15°−10°, with 2.1 in52 mm of precipitation in a typical February.
- Record high
- 58°14° (2026)
- Record low
- −38°−39° (2021)
- Heating degree days
- 1177
- Cooling degree days
- 0
St. Mary in March
Highs average 38°3° and lows 20°−7°, with 2.5 in64 mm of precipitation in a typical March.
- Record high
- 66°19° (2004)
- Record low
- −36°−38° (2019)
- Heating degree days
- 1124
- Cooling degree days
- 0
St. Mary in April
Highs average 46°8° and lows 28°−2°, with 2.5 in62 mm of precipitation in a typical April.
- Record high
- 73°23° (2023)
- Record low
- −8°−22° (2018)
- Heating degree days
- 848
- Cooling degree days
- 0
St. Mary in May
Highs average 56°13° and lows 35°2°, with 2.8 in72 mm of precipitation in a typical May.
- Record high
- 81°27° (2025)
- Record low
- 15°−9° (2009)
- Heating degree days
- 602
- Cooling degree days
- 0
St. Mary in June
Highs average 63°17° and lows 42°5°, with 3.1 in78 mm of precipitation in a typical June.
- Record high
- 91°33° (2021)
- Record low
- 29°−2° (2004)
- Heating degree days
- 383
- Cooling degree days
- 1
St. Mary in July
Highs average 73°23° and lows 46°8°, with 1.2 in30 mm of precipitation in a typical July.
- Record high
- 96°36° (2007)
- Record low
- 33°1° (2008)
- Heating degree days
- 175
- Cooling degree days
- 11
St. Mary in August
Highs average 73°23° and lows 45°7°, with 1.3 in33 mm of precipitation in a typical August.
- Record high
- 94°34° (2018)
- Record low
- 29°−2° (2012)
- Heating degree days
- 196
- Cooling degree days
- 8
St. Mary in September
Highs average 63°17° and lows 39°4°, with 1.6 in41 mm of precipitation in a typical September.
- Record high
- 91°33° (2022)
- Record low
- 12°−11° (2019)
- Heating degree days
- 424
- Cooling degree days
- 1
St. Mary in OctoberThis month
Highs average 49°9° and lows 32°0°, with 2.2 in55 mm of precipitation in a typical October.
- Record high
- 78°26° (2008)
- Record low
- −9°−23° (2020)
- Heating degree days
- 764
- Cooling degree days
- 0
St. Mary in November
Highs average 37°3° and lows 25°−4°, with 2.7 in69 mm of precipitation in a typical November.
- Record high
- 64°18° (2010)
- Record low
- −22°−30° (2014)
- Heating degree days
- 1020
- Cooling degree days
- 0
St. Mary in December
Highs average 31°−1° and lows 17°−8°, with 2.1 in54 mm of precipitation in a typical December.
- Record high
- 60°16° (2020)
- Record low
- −43°−42° (2022)
- Heating degree days
- 1276
- Cooling degree days
- 0