May is one of the warmer months of the year in Portland, with average highs near 12°C and lows around 8°C (mean 10°C). It is about average for rainfall, averaging 98 mm of rainfall and 86% relative humidity across the period.
May is one of the warmer months of the year in Portland. Across 45 years of records, the warmest Mays in Portland were 2010 and 2012 — when the month averaged 12.1°C — while the coldest was 2005 at 8.1°C. Typical May days reach 12°C with nights near 8°C. The long-term trend is warming, about 0.4°C per decade.
May is about average for rainfall in Portland, averaging 98 mm of rainfall. The wettest May on record was 1984 with 250 mm, while the driest was 1992 at 29 mm.
Relative humidity in Portland during May averages 86%. The most humid May was 2011 at 91%, and the least humid was 2023 at 80%.
May receives about 5.3 kWh/m²/day of solar energy in Portland. The sunniest May was 2020 at 6.6 kWh/m²/day, and the cloudiest was 1984 at 4.2.
Average wind speed in Portland during May is 2.9 m/s. The windiest May was 2020 at 3.5 m/s, while the calmest were 1992 and 2003 at 2.3 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 9.6°C | 9.5°C | 9.7°C | 10.8°C | 10.9°C | +1.3°C |
| Avg High | 11.7°C | 11.6°C | 11.6°C | 12.8°C | 12.8°C | +1.1°C |
| Avg Low | 7.6°C | 7.4°C | 7.6°C | 8.8°C | 9.0°C | +1.4°C |
| Avg Rain | 113 mm | 89 mm | 115 mm | 93 mm | 73 mm | -40 mm |
May temperatures in Portland have risen by about 1.4°C between 1981–1985 and 2021–2025.
May has ranged from a record low of 1.9°C (1985) to a record high of 23.2°C (2010).
Rainfall in May is about average for rainfall, averaging 98 mm, with a wettest year of 250 mm.
A good time to visit Portland
May is a good time to visit Portland, with days averaging 12°C and nights around 8°C (mean 10°C, warmer than Portland's yearly average) and higher 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 | 11.9°C | 10.1°C | 8.4°C | 16.2°C | 5.6°C | 145 mm | 89% | 3 m/s | 4.5 |
| 2024 | 13.1°C | 11.5°C | 10.0°C | 18.1°C | 6.9°C | 52 mm | 89% | 2.5 m/s | 5 |
| 2023 | 13.3°C | 11.1°C | 8.8°C | 18.5°C | 5.0°C | 96 mm | 80% | 3.2 m/s | 6.5 |
| 2022 | 12.9°C | 11.1°C | 9.3°C | 18.6°C | 5.0°C | 41 mm | 86% | 2.8 m/s | 6.1 |
| 2021 | 13.5°C | 11.5°C | 9.6°C | 20.0°C | 6.6°C | 47 mm | 82% | 2.8 m/s | 5.7 |
| 2020 | 11.9°C | 9.8°C | 7.7°C | 18.2°C | 3.0°C | 56 mm | 82% | 3.5 m/s | 6.6 |
| 2019 | 11.3°C | 9.5°C | 7.6°C | 16.4°C | 4.7°C | 116 mm | 87% | 2.9 m/s | 4.9 |
| 2018 | 13.7°C | 11.6°C | 9.4°C | 20.4°C | 5.5°C | 39 mm | 87% | 2.7 m/s | 5.9 |
| 2017 | 11.4°C | 9.7°C | 8.1°C | 19.0°C | 5.0°C | 166 mm | 88% | 2.9 m/s | 4.6 |
| 2016 | 12.5°C | 10.5°C | 8.5°C | 19.7°C | 4.9°C | 50 mm | 86% | 2.8 m/s | 5.3 |
| 2015 | 13.6°C | 11.1°C | 8.7°C | 17.7°C | 4.6°C | 43 mm | 86% | 2.8 m/s | 6 |
| 2014 | 12.3°C | 10.3°C | 8.4°C | 18.1°C | 5.2°C | 101 mm | 88% | 2.7 m/s | 5.1 |
| 2013 | 12.9°C | 10.8°C | 8.8°C | 20.5°C | 5.9°C | 135 mm | 87% | 2.8 m/s | 5.5 |
| 2012 | 13.7°C | 12.1°C | 10.5°C | 20.4°C | 5.5°C | 142 mm | 90% | 2.5 m/s | 4.9 |
| 2011 | 11.8°C | 10.2°C | 8.5°C | 19.1°C | 6.0°C | 88 mm | 91% | 3.2 m/s | 4.5 |
| 2010 🔥 | 14.3°C | 12.1°C | 9.8°C | 23.2°C | 4.5°C | 50 mm | 83% | 2.9 m/s | 6.2 |
| 2009 | 12.2°C | 10.4°C | 8.6°C | 19.9°C | 6.4°C | 117 mm | 87% | 2.9 m/s | 4.9 |
| 2008 | 12.3°C | 10.2°C | 8.1°C | 16.3°C | 3.7°C | 38 mm | 83% | 2.9 m/s | 5.8 |
| 2007 | 12.8°C | 10.5°C | 8.1°C | 21.7°C | 4.8°C | 83 mm | 85% | 2.7 m/s | 5.9 |
| 2006 | 11.7°C | 10.1°C | 8.4°C | 18.5°C | 6.3°C | 242 mm | 89% | 3.4 m/s | 4.6 |
| 2005 ❄️ | 9.7°C | 8.1°C | 6.4°C | 13.6°C | 3.5°C | 177 mm | 88% | 3.2 m/s | 4.4 |
| 2004 | 11.5°C | 9.4°C | 7.3°C | 18.0°C | 3.9°C | 130 mm | 88% | 2.9 m/s | 5.3 |
| 2003 | 10.5°C | 8.6°C | 6.8°C | 15.9°C | 3.7°C | 97 mm | 89% | 2.3 m/s | 4.6 |
| 2002 | 11.5°C | 9.3°C | 7.0°C | 15.3°C | 3.6°C | 122 mm | 83% | 3.3 m/s | 5.6 |
| 2001 | 12.4°C | 10.2°C | 8.1°C | 20.9°C | 4.8°C | 37 mm | 84% | 2.5 m/s | 5.7 |
| 2000 | 11.8°C | 9.7°C | 7.6°C | 17.8°C | 3.3°C | 104 mm | 86% | 3 m/s | 5.1 |
| 1999 | 12.7°C | 10.6°C | 8.5°C | 18.1°C | 5.0°C | 102 mm | 86% | 2.5 m/s | 6.2 |
| 1998 | 12.9°C | 10.8°C | 8.6°C | 18.6°C | 4.6°C | 109 mm | 87% | 2.8 m/s | 5.6 |
| 1997 | 10.4°C | 8.5°C | 6.7°C | 14.1°C | 3.4°C | 76 mm | 85% | 3.3 m/s | 5 |
| 1996 | 11.8°C | 9.7°C | 7.6°C | 18.7°C | 4.0°C | 103 mm | 84% | 2.8 m/s | 5.4 |
| 1995 | 10.8°C | 8.8°C | 6.7°C | 16.5°C | 1.9°C | 81 mm | 86% | 2.7 m/s | 4.9 |
| 1994 | 10.6°C | 8.6°C | 6.6°C | 15.8°C | 3.7°C | 127 mm | 87% | 3.2 m/s | 5.4 |
| 1993 | 11.9°C | 9.7°C | 7.6°C | 18.4°C | 4.4°C | 34 mm | 86% | 2.6 m/s | 5.4 |
| 1992 | 10.9°C | 8.5°C | 6.2°C | 19.6°C | 2.4°C | 29 mm | 83% | 2.3 m/s | 6 |
| 1991 | 13.6°C | 11.3°C | 8.9°C | 20.3°C | 5.7°C | 87 mm | 86% | 2.7 m/s | 5.6 |
| 1990 | 10.1°C | 8.3°C | 6.4°C | 13.6°C | 3.6°C | 141 mm | 87% | 3.1 m/s | 4.9 |
| 1989 | 12.1°C | 10.2°C | 8.4°C | 16.8°C | 4.6°C | 202 mm | 90% | 3 m/s | 4.8 |
| 1988 | 11.6°C | 9.6°C | 7.7°C | 18.3°C | 2.6°C | 96 mm | 89% | 2.8 m/s | 4.9 |
| 1987 | 11.4°C | 9.1°C | 6.9°C | 20.7°C | 3.7°C | 72 mm | 86% | 2.7 m/s | 5.4 |
| 1986 | 11.6°C | 9.6°C | 7.7°C | 18.5°C | 2.3°C | 71 mm | 87% | 2.9 m/s | 5.2 |
| 1985 | 11.5°C | 9.2°C | 6.9°C | 18.7°C | 1.9°C | 65 mm | 85% | 2.9 m/s | 5.4 |
| 1984 🌧️ | 11.4°C | 9.5°C | 7.5°C | 15.5°C | 4.1°C | 250 mm | 88% | 2.9 m/s | 4.2 |
| 1983 | 11.5°C | 9.6°C | 7.7°C | 14.9°C | 4.3°C | 147 mm | 89% | 3.3 m/s | — |
| 1982 | 12.2°C | 10.1°C | 8.1°C | 16.7°C | 5.4°C | 56 mm | 87% | 2.4 m/s | — |
| 1981 | 12.2°C | 9.9°C | 7.7°C | 17.3°C | 4.1°C | 60 mm | 86% | 2.9 m/s | — |
Actual recorded May data for each year, 1981–2025 — sourced from NASA POWER.
The average high in May is around 12°C with lows near 8°C (mean 10°C), based on 45 years of NASA POWER data.
May averages 98 mm of rainfall in Portland, about average for rainfall. The wettest on record was 250 mm in 1984.
The hottest May reached 23.2°C in 2010. The coldest dipped to 1.9°C in 1985.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average May temperatures have risen by about 1.4°C. Daytime highs moved from 11.8°C to 12.9°C and overnight lows from 7.6°C to 9.2°C over the same span.
May is one of the warmer months of the year in Portland and about average for rainfall, so plan for around 12°C daytime highs and 8°C at night.
Not quite — May is the 7th coolest month in Portland, averaging 10°C.
For May in Portland, pack light layers you can adjust through the day, with typical highs of 12°C and lows of 8°C. Bring an umbrella or light rain jacket too.
Relative humidity in May averages 86% — quite humid.
Average wind speed in May is 2.9 m/s. The windiest May on record averaged 3.5 m/s (2020).
The wettest May on record was 1984 with 250 mm. On average, May sees 98 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 Portland 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.
