May is one of the warmer months of the year in Boise, with average highs near 20.7°C and lows around 7°C (mean 13.9°C). It is about average for rainfall, averaging 40 mm of rainfall and 53% relative humidity across the period.
May is one of the warmer months of the year in Boise. Across 45 years of records, the warmest May in Boise was 1992 — when the month averaged 17.6°C — while the coldest was 2010 at 10.1°C. Typical May days reach 20.7°C with nights near 7°C. The long-term trend is warming, about 0.2°C per decade.
May is about average for rainfall in Boise, averaging 40 mm of rainfall. The wettest May on record was 1998 with 130 mm, while the driest was 1992 at 5 mm.
Relative humidity in Boise during May averages 53%. The most humid May was 1998 at 63%, and the least humid was 1992 at 38%.
May receives about 6.7 kWh/m²/day of solar energy in Boise. The sunniest May was 1992 at 7.6 kWh/m²/day, and the cloudiest were 1994, 1998 and 2010 at 5.9.
Average wind speed in Boise during May is 2.3 m/s. The windiest May was 1991 at 2.8 m/s, while the calmest was 2023 at 1.7 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 13.2°C | 13.7°C | 14.6°C | 13.7°C | 13.9°C | +0.7°C |
| Avg High | 20.2°C | 20.5°C | 21.6°C | 20.4°C | 20.7°C | +0.5°C |
| Avg Low | 6.2°C | 6.9°C | 7.5°C | 7.0°C | 7.2°C | +1°C |
| Avg Rain | 31 mm | 51 mm | 35 mm | 37 mm | 45 mm | +14 mm |
May temperatures in Boise have risen by about 1.3°C between 1981–1985 and 2021–2025.
May has ranged from a record low of -3.7°C (1999) to a record high of 37.7°C (2003).
Rainfall in May is about average for rainfall, averaging 40 mm, with a wettest year of 130 mm.
A good time to visit Boise
May is a good time to visit Boise, with days averaging 20.7°C and nights around 7°C (mean 13.9°C, warmer than Boise's yearly average) and moderate rainfall. August and July 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 | 22.6°C | 15.3°C | 7.9°C | 36.6°C | 1.5°C | 23 mm | 52% | 2.5 m/s | 7.1 |
| 2024 | 19.4°C | 12.5°C | 5.6°C | 29.7°C | 0.7°C | 36 mm | 55% | 2.5 m/s | 7.2 |
| 2023 | 22.7°C | 16.3°C | 9.9°C | 31.4°C | 3.5°C | 54 mm | 57% | 1.7 m/s | 6.5 |
| 2022 | 17.8°C | 11.7°C | 5.6°C | 29.6°C | -1.6°C | 79 mm | 59% | 2.5 m/s | 6.2 |
| 2021 | 20.9°C | 13.8°C | 6.8°C | 31.2°C | 0.9°C | 21 mm | 48% | 2.5 m/s | 7 |
| 2020 | 20.9°C | 14.0°C | 7.2°C | 35.6°C | 1.2°C | 58 mm | 51% | 2.3 m/s | 6.6 |
| 2019 | 19.8°C | 13.9°C | 8.0°C | 28.9°C | 0.2°C | 69 mm | 58% | 1.8 m/s | 6.3 |
| 2018 | 22.6°C | 16.1°C | 9.7°C | 28.9°C | 1.0°C | 44 mm | 59% | 1.9 m/s | 6.5 |
| 2017 | 20.6°C | 13.6°C | 6.7°C | 30.6°C | 0.0°C | 25 mm | 57% | 2.2 m/s | 7 |
| 2016 | 21.2°C | 14.4°C | 7.5°C | 28.5°C | 2.1°C | 32 mm | 54% | 2.3 m/s | 6.8 |
| 2015 | 21.5°C | 15.2°C | 8.9°C | 31.5°C | 3.0°C | 46 mm | 54% | 2 m/s | 6.3 |
| 2014 | 22.1°C | 14.8°C | 7.5°C | 29.8°C | 0.5°C | 17 mm | 49% | 2.3 m/s | 7.3 |
| 2013 | 22.3°C | 14.9°C | 7.6°C | 33.0°C | -2.7°C | 16 mm | 45% | 2.4 m/s | 6.9 |
| 2012 | 20.4°C | 13.3°C | 6.2°C | 30.9°C | -1.0°C | 23 mm | 48% | 2.3 m/s | 6.8 |
| 2011 | 17.1°C | 10.7°C | 4.2°C | 27.0°C | -1.2°C | 50 mm | 62% | 2.6 m/s | 6.1 |
| 2010 ❄️ | 16.2°C | 10.1°C | 3.9°C | 27.4°C | -2.1°C | 47 mm | 55% | 2.7 m/s | 5.9 |
| 2009 | 22.7°C | 15.2°C | 7.8°C | 34.7°C | -0.5°C | 38 mm | 47% | 2.1 m/s | 7.1 |
| 2008 | 21.0°C | 14.0°C | 7.0°C | 32.7°C | -2.9°C | 29 mm | 50% | 2.5 m/s | 6.7 |
| 2007 | 23.1°C | 15.5°C | 8.0°C | 30.4°C | -0.6°C | 10 mm | 43% | 2.5 m/s | 7.4 |
| 2006 | 21.8°C | 14.9°C | 7.9°C | 32.2°C | -0.8°C | 36 mm | 52% | 2 m/s | 7.1 |
| 2005 | 20.7°C | 14.1°C | 7.4°C | 30.5°C | 2.2°C | 87 mm | 57% | 2.1 m/s | 6 |
| 2004 | 20.3°C | 13.8°C | 7.3°C | 30.8°C | 2.0°C | 58 mm | 52% | 2.1 m/s | 6.3 |
| 2003 | 20.9°C | 14.0°C | 7.0°C | 37.7°C | -1.0°C | 43 mm | 54% | 2 m/s | 6.8 |
| 2002 | 20.9°C | 13.7°C | 6.5°C | 33.2°C | -3.0°C | 10 mm | 47% | 2.5 m/s | 7.1 |
| 2001 | 23.7°C | 15.9°C | 8.1°C | 34.9°C | -1.0°C | 15 mm | 40% | 2.5 m/s | 7.3 |
| 2000 | 21.3°C | 14.6°C | 7.9°C | 28.6°C | 0.3°C | 27 mm | 51% | 2.3 m/s | 6.4 |
| 1999 | 19.2°C | 12.1°C | 5.0°C | 31.8°C | -3.7°C | 22 mm | 51% | 2.5 m/s | 7.2 |
| 1998 🌧️ | 18.0°C | 12.2°C | 6.4°C | 27.5°C | 0.7°C | 130 mm | 63% | 2 m/s | 5.9 |
| 1997 | 23.5°C | 16.3°C | 9.1°C | 30.8°C | 0.1°C | 25 mm | 51% | 2 m/s | 7.1 |
| 1996 | 18.0°C | 11.8°C | 5.6°C | 26.2°C | -2.3°C | 61 mm | 59% | 2.2 m/s | 6.6 |
| 1995 | 18.8°C | 12.6°C | 6.3°C | 28.1°C | 0.5°C | 70 mm | 61% | 2 m/s | 6.3 |
| 1994 | 22.4°C | 15.5°C | 8.6°C | 30.4°C | 2.8°C | 38 mm | 51% | 1.9 m/s | 5.9 |
| 1993 | 23.1°C | 15.9°C | 8.6°C | 30.1°C | -0.1°C | 31 mm | 55% | 2.5 m/s | 6.5 |
| 1992 🔥 | 25.5°C | 17.6°C | 9.7°C | 31.5°C | 1.7°C | 5 mm | 38% | 2.2 m/s | 7.6 |
| 1991 | 18.1°C | 11.3°C | 4.6°C | 25.7°C | 1.1°C | 59 mm | 56% | 2.8 m/s | 6 |
| 1990 | 18.8°C | 12.0°C | 5.3°C | 28.6°C | -0.2°C | 71 mm | 53% | 2.5 m/s | 6.6 |
| 1989 | 19.8°C | 12.7°C | 5.6°C | 28.6°C | 0.5°C | 20 mm | 53% | 2.4 m/s | 6.9 |
| 1988 | 21.0°C | 13.8°C | 6.7°C | 32.0°C | -1.6°C | 32 mm | 48% | 2.6 m/s | 6.5 |
| 1987 | 23.1°C | 16.1°C | 9.1°C | 32.9°C | 1.1°C | 34 mm | 46% | 2.1 m/s | 6.6 |
| 1986 | 20.6°C | 13.5°C | 6.3°C | 34.7°C | -0.4°C | 31 mm | 55% | 2.5 m/s | 6.6 |
| 1985 | 22.0°C | 14.7°C | 7.4°C | 31.4°C | -0.3°C | 37 mm | 48% | 2.2 m/s | 6.9 |
| 1984 | 18.6°C | 11.7°C | 4.8°C | 32.5°C | -1.7°C | 30 mm | 58% | 2.5 m/s | 6.2 |
| 1983 | 19.1°C | 12.6°C | 6.0°C | 33.4°C | -1.8°C | 37 mm | 59% | 2.3 m/s | — |
| 1982 | 19.0°C | 11.9°C | 4.8°C | 28.0°C | -1.5°C | 18 mm | 56% | 2.5 m/s | — |
| 1981 | 18.6°C | 12.0°C | 5.4°C | 27.5°C | -0.9°C | 41 mm | 57% | 2.6 m/s | — |
Actual recorded May data for each year, 1981–2025 — sourced from NASA POWER.
The average high in May is around 20.7°C with lows near 7°C (mean 13.9°C), based on 45 years of NASA POWER data.
May averages 40 mm of rainfall in Boise, about average for rainfall. The wettest on record was 130 mm in 1998.
The hottest May reached 37.7°C in 2003. The coldest dipped to -3.7°C in 1999.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average May temperatures have risen by about 1.3°C. Daytime highs moved from 19.5°C to 20.7°C and overnight lows from 5.7°C to 7.2°C over the same span.
May is one of the warmer months of the year in Boise and about average for rainfall, so plan for around 20.7°C daytime highs and 7°C at night.
Not quite — May is the 8th coolest month in Boise, averaging 13.9°C.
For May in Boise, pack warm layers and a jacket for chilly mornings, with typical highs of 20.7°C and lows of 7°C.
Relative humidity in May averages 53% — relatively dry.
Average wind speed in May is 2.3 m/s. The windiest May on record averaged 2.8 m/s (1991).
The wettest May on record was 1998 with 130 mm. On average, May sees 40 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 Boise 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.
