Roundup weather by month
What a typical year looks like in Roundup, Montana: average highs and lows, rain and snow, and the warmest and coldest days on record. Normals are the 1991–2020 averages at Roundup 15 SW, 21 km from Roundup; records cover 2004–2025.
The year at a glance
- Precipitation a year
- 15.1 in384 mm
- Snow a year
- 43 in109 cm
- Last spring freeze
- May 18
- First fall freeze
- Sep 17
- Heating degree days
- 7,900
- Cooling degree days
- 334
Freeze dates are medians (half of years earlier, half later). Degree days use a 65°F base; HVAC design temperatures here are −20°−29° (heating, 99%) and 100°38° (cooling, 1%).
Month by month
Roundup in January
Highs average 36°2° and lows 11°−12°, with 0.53 in13 mm of precipitation and 9 in22 cm of snow in a typical January.
- Record high
- 68°20° (2015)
- Record low
- −44°−42° (2024)
- Heating degree days
- 1288
- Cooling degree days
- 0
Roundup in February
Highs average 39°4° and lows 12°−11°, with 0.4 in10 mm of precipitation and 10 in25 cm of snow in a typical February.
- Record high
- 71°22° (2015)
- Record low
- −43°−42° (2021)
- Heating degree days
- 1102
- Cooling degree days
- 0
Roundup in March
Highs average 48°9° and lows 19°−7°, with 0.91 in23 mm of precipitation and 6 in15 cm of snow in a typical March.
- Record high
- 81°27° (2025)
- Record low
- −39° (2019)
- Heating degree days
- 983
- Cooling degree days
- 0
Roundup in April
Highs average 56°13° and lows 27°−3°, with 1.9 in49 mm of precipitation and 4 in9 cm of snow in a typical April.
- Record high
- 84°29° (2012)
- Record low
- 0°−18° (2022)
- Heating degree days
- 696
- Cooling degree days
- 0
Roundup in May
Highs average 66°19° and lows 37°3°, with 2.4 in61 mm of precipitation and 0.1 in0.3 cm of snow in a typical May.
- Record high
- 92°33° (2006)
- Record low
- 14°−10° (2013)
- Heating degree days
- 422
- Cooling degree days
- 4
Roundup in June
Highs average 76°24° and lows 46°8°, with 3 in76 mm of precipitation in a typical June.
- Record high
- 101°38° (2015)
- Record low
- 30°−1° (2008)
- Heating degree days
- 163
- Cooling degree days
- 29
Roundup in July
Highs average 87°31° and lows 51°11°, with 1.4 in35 mm of precipitation in a typical July.
- Record high
- 109°43° (2021)
- Record low
- 38°3° (2008)
- Heating degree days
- 30
- Cooling degree days
- 155
Roundup in August
Highs average 86°30° and lows 48°9°, with 1.1 in27 mm of precipitation in a typical August.
- Record high
- 105°41° (2024)
- Record low
- 30°−1° (2015)
- Heating degree days
- 59
- Cooling degree days
- 124
Roundup in September
Highs average 75°24° and lows 39°4°, with 1.2 in30 mm of precipitation in a typical September.
- Record high
- 107°42° (2022)
- Record low
- 25°−4° (2004)
- Heating degree days
- 264
- Cooling degree days
- 20
Roundup in OctoberThis month
Highs average 59°15° and lows 29°−2°, with 1.3 in32 mm of precipitation and 4 in9 cm of snow in a typical October.
- Record high
- 95°35° (2011)
- Record low
- −11°−24° (2020)
- Heating degree days
- 653
- Cooling degree days
- 2
Roundup in November
Highs average 46°8° and lows 19°−7°, with 0.57 in14 mm of precipitation and 5 in12 cm of snow in a typical November.
- Record high
- 77°25° (2010)
- Record low
- −22°−30° (2006)
- Heating degree days
- 975
- Cooling degree days
- 0
Roundup in December
Highs average 37°3° and lows 12°−11°, with 0.43 in11 mm of precipitation and 6 in16 cm of snow in a typical December.
- Record high
- 71°22° (2021)
- Record low
- −38°−39° (2016)
- Heating degree days
- 1265
- Cooling degree days
- 0