May is one of the warmer months of the year in Great Falls, with average highs near 17.9°C and lows around 4.6°C (mean 11.3°C). It is a relatively wet time of year, averaging 72 mm of rainfall and 59% relative humidity across the period.
May is one of the warmer months of the year in Great Falls. Across 45 years of records, the warmest May in Great Falls was 2023 — when the month averaged 14.5°C — while the coldest was 2010 at 8.2°C. Typical May days reach 17.9°C with nights near 4.6°C. The long-term May temperature trend is broadly flat.
May is a relatively wet time of year in Great Falls, averaging 72 mm of rainfall. The wettest May on record was 1981 with 170 mm, while the driest was 2001 at 21 mm.
Relative humidity in Great Falls during May averages 59%. The most humid May was 1996 at 68%, and the least humid was 2001 at 44%.
May receives about 5.8 kWh/m²/day of solar energy in Great Falls. The sunniest May was 2001 at 6.9 kWh/m²/day, and the cloudiest was 2008 at 5.
Average wind speed in Great Falls during May is 2.5 m/s. The windiest Mays were 1984 and 2001 at 3.1 m/s, while the calmest was 2023 at 1.9 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 11.4°C | 11.2°C | 11.4°C | 11.0°C | 11.5°C | +0.1°C |
| Avg High | 18.3°C | 18.1°C | 18.1°C | 17.3°C | 18.0°C | -0.3°C |
| Avg Low | 4.6°C | 4.4°C | 4.6°C | 4.6°C | 5.1°C | +0.5°C |
| Avg Rain | 75 mm | 70 mm | 59 mm | 78 mm | 78 mm | +2 mm |
May temperatures in Great Falls have risen by about 0.9°C between 1981–1985 and 2021–2025.
May has ranged from a record low of -7.6°C (2009) to a record high of 32.6°C (1988).
Rainfall in May is a relatively wet time of year, averaging 72 mm, with a wettest year of 170 mm.
Daytime highs and overnight lows have shifted differently — highs fell about 0.1°C per decade while lows rose 0.2°C per decade, narrowing the gap between day and night.
A good time to visit Great Falls
May is a good time to visit Great Falls, with days averaging 17.9°C and nights around 4.6°C (mean 11.3°C, warmer than Great Falls's yearly average) and moderate rainfall. July and August are marginally more temperate, but May still suits most travellers.
| Year | Avg High | Avg Temp | Avg Low | Hottest Day | Coldest Day | Rainfall | Humidity | Wind | Solar |
|---|---|---|---|---|---|---|---|---|---|
| 2025 | 20.7°C | 13.6°C | 6.6°C | 32.2°C | -0.1°C | 64 mm | 57% | 2.1 m/s | 6.2 |
| 2024 | 16.0°C | 10.2°C | 4.3°C | 27.9°C | -2.6°C | 92 mm | 62% | 2.9 m/s | 5.5 |
| 2023 🔥 | 21.0°C | 14.5°C | 7.9°C | 28.9°C | 1.8°C | 82 mm | 64% | 1.9 m/s | 5.8 |
| 2022 | 16.7°C | 10.2°C | 3.7°C | 23.9°C | -2.0°C | 34 mm | 55% | 2.8 m/s | 5.9 |
| 2021 | 15.6°C | 9.5°C | 3.3°C | 28.2°C | -5.3°C | 118 mm | 62% | 2.4 m/s | 5.7 |
| 2020 | 17.7°C | 11.1°C | 4.5°C | 30.0°C | -0.6°C | 77 mm | 62% | 2.6 m/s | 6 |
| 2019 | 16.1°C | 10.1°C | 4.1°C | 25.8°C | -5.1°C | 71 mm | 65% | 2.5 m/s | 5.2 |
| 2018 | 20.5°C | 14.2°C | 7.8°C | 26.9°C | 0.8°C | 88 mm | 64% | 2.2 m/s | 5.8 |
| 2017 | 19.6°C | 12.6°C | 5.7°C | 29.7°C | 0.2°C | 53 mm | 58% | 2.3 m/s | 6.4 |
| 2016 | 17.7°C | 11.2°C | 4.7°C | 27.7°C | -1.6°C | 78 mm | 60% | 2.6 m/s | 5.6 |
| 2015 | 17.4°C | 10.9°C | 4.5°C | 24.0°C | -0.7°C | 78 mm | 61% | 2.4 m/s | 5.4 |
| 2014 | 17.6°C | 11.2°C | 4.7°C | 28.5°C | -4.1°C | 38 mm | 61% | 2 m/s | 6 |
| 2013 | 18.5°C | 12.2°C | 5.9°C | 29.4°C | -2.3°C | 85 mm | 59% | 2.5 m/s | 5.5 |
| 2012 | 16.9°C | 10.2°C | 3.5°C | 29.8°C | -2.4°C | 75 mm | 58% | 2.7 m/s | 6 |
| 2011 | 14.4°C | 8.8°C | 3.2°C | 22.7°C | -1.7°C | 105 mm | 67% | 2.8 m/s | 5.3 |
| 2010 ❄️ | 14.1°C | 8.2°C | 2.3°C | 26.9°C | -4.8°C | 106 mm | 64% | 2.8 m/s | 5.1 |
| 2009 | 18.4°C | 11.4°C | 4.4°C | 28.7°C | -7.6°C | 33 mm | 56% | 2.6 m/s | 6.8 |
| 2008 | 16.9°C | 10.7°C | 4.5°C | 29.6°C | -2.7°C | 110 mm | 62% | 2.6 m/s | 5 |
| 2007 | 19.2°C | 12.4°C | 5.5°C | 27.8°C | -1.1°C | 77 mm | 59% | 2.5 m/s | 5.9 |
| 2006 | 19.6°C | 12.9°C | 6.1°C | 31.1°C | -2.7°C | 57 mm | 54% | 2.5 m/s | 6.3 |
| 2005 | 17.6°C | 10.7°C | 3.8°C | 23.4°C | -5.3°C | 37 mm | 58% | 2.5 m/s | 6 |
| 2004 | 15.6°C | 9.7°C | 3.8°C | 25.7°C | -4.6°C | 81 mm | 61% | 2.8 m/s | 5.4 |
| 2003 | 17.4°C | 10.9°C | 4.4°C | 32.6°C | -2.1°C | 54 mm | 60% | 2.4 m/s | 5.8 |
| 2002 | 16.7°C | 9.7°C | 2.7°C | 31.5°C | -4.9°C | 63 mm | 56% | 2.7 m/s | 5.8 |
| 2001 | 21.1°C | 13.4°C | 5.8°C | 32.1°C | -1.9°C | 21 mm | 44% | 3.1 m/s | 6.9 |
| 2000 | 18.5°C | 11.9°C | 5.2°C | 27.1°C | -0.7°C | 62 mm | 52% | 2.7 m/s | 5.9 |
| 1999 | 16.9°C | 10.3°C | 3.7°C | 29.7°C | -2.7°C | 58 mm | 56% | 2.7 m/s | 6.1 |
| 1998 | 20.1°C | 12.9°C | 5.7°C | 28.0°C | 1.2°C | 64 mm | 52% | 2.6 m/s | 6.6 |
| 1997 | 18.5°C | 11.6°C | 4.6°C | 28.4°C | -2.4°C | 81 mm | 62% | 2.3 m/s | 6 |
| 1996 | 14.3°C | 8.4°C | 2.5°C | 19.2°C | -3.3°C | 78 mm | 68% | 2.3 m/s | 5.2 |
| 1995 | 16.5°C | 9.7°C | 2.9°C | 27.4°C | -4.5°C | 88 mm | 62% | 2.2 m/s | 5.5 |
| 1994 | 19.8°C | 12.8°C | 5.8°C | 28.4°C | 1.9°C | 52 mm | 59% | 2.3 m/s | 5.8 |
| 1993 | 20.8°C | 13.4°C | 6.0°C | 29.8°C | -0.3°C | 76 mm | 58% | 2.3 m/s | 6.2 |
| 1992 | 21.0°C | 13.3°C | 5.6°C | 30.0°C | -0.8°C | 49 mm | 49% | 2.5 m/s | 6.5 |
| 1991 | 16.7°C | 10.3°C | 3.9°C | 24.6°C | -4.3°C | 69 mm | 62% | 2.4 m/s | 5.6 |
| 1990 | 16.1°C | 9.6°C | 3.1°C | 25.1°C | -4.2°C | 86 mm | 63% | 2.4 m/s | 5.8 |
| 1989 | 17.2°C | 10.5°C | 3.8°C | 26.5°C | -0.7°C | 61 mm | 60% | 2.8 m/s | 5.6 |
| 1988 | 21.3°C | 13.5°C | 5.8°C | 32.6°C | -0.8°C | 58 mm | 50% | 2.7 m/s | 5.7 |
| 1987 | 20.8°C | 13.9°C | 7.0°C | 29.0°C | -1.0°C | 67 mm | 55% | 2.5 m/s | 5.8 |
| 1986 | 18.3°C | 11.3°C | 4.4°C | 31.8°C | -2.1°C | 59 mm | 60% | 2.6 m/s | 5.7 |
| 1985 | 20.8°C | 13.6°C | 6.4°C | 29.1°C | 1.0°C | 56 mm | 53% | 2.4 m/s | 6 |
| 1984 | 16.7°C | 10.0°C | 3.2°C | 30.6°C | -0.7°C | 38 mm | 55% | 3.1 m/s | 6 |
| 1983 | 16.9°C | 10.2°C | 3.5°C | 28.0°C | -5.1°C | 62 mm | 59% | 2.5 m/s | — |
| 1982 | 15.4°C | 8.9°C | 2.4°C | 28.0°C | -3.0°C | 108 mm | 62% | 2.7 m/s | — |
| 1981 🌧️ | 16.9°C | 11.0°C | 5.1°C | 23.6°C | -0.4°C | 170 mm | 67% | 2.3 m/s | — |
Actual recorded May data for each year, 1981–2025 — sourced from NASA POWER.
The average high in May is around 17.9°C with lows near 4.6°C (mean 11.3°C), based on 45 years of NASA POWER data.
May averages 72 mm of rainfall in Great Falls, a relatively wet time of year. The wettest on record was 170 mm in 1981.
The hottest May reached 32.6°C in 1988. The coldest dipped to -7.6°C in 2009.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average May temperatures have risen by about 0.9°C. Daytime highs moved from 17.3°C to 18°C and overnight lows from 4.1°C to 5.2°C over the same span.
May is one of the warmer months of the year in Great Falls and a relatively wet time of year, so plan for around 17.9°C daytime highs and 4.6°C at night.
Not quite — May is the 8th coolest month in Great Falls, averaging 11.3°C.
For May in Great Falls, pack warm layers and a jacket for chilly mornings, with typical highs of 17.9°C and lows of 4.6°C. Bring an umbrella or light rain jacket too.
Relative humidity in May averages 59% — moderately humid.
Average wind speed in May is 2.5 m/s. The windiest May on record averaged 3.1 m/s (1984).
The wettest May on record was 1981 with 170 mm. On average, May sees 72 mm.
All figures are derived from NASA POWER (Prediction Of Worldwide Energy Resources), based on MERRA-2 satellite reanalysis, covering 1981–2025.
Explore how the weather in Great Falls behaves each May, based on 45 years of NASA POWER climate data from 1981 to 2025. This page breaks down average temperatures, rainfall, humidity, wind and solar radiation for May specifically, along with year-by-year records and how the month has changed over the decades.
