May is close to Portland's year-round average, with average highs near 15.5°C and lows around 12.4°C (mean 14°C). It is about average for rainfall, averaging 67 mm of rainfall and 77% relative humidity across the period.
May is close to Portland's year-round average. Across 45 years of records, the warmest May in Portland was 2007 — when the month averaged 15.5°C — while the coldest was 1995 at 12.8°C. Typical May days reach 15.5°C with nights near 12.4°C. The long-term May temperature trend is broadly flat.
May is about average for rainfall in Portland, averaging 67 mm of rainfall. The wettest May on record was 1987 with 152 mm, while the driest was 1996 at 17 mm.
Relative humidity in Portland during May averages 77%. The most humid May was 1983 at 83%, and the least humid was 2025 at 71%.
May receives about 2.2 kWh/m²/day of solar energy in Portland. The sunniest Mays were 2003, 2024 and 2025, among others at 2.4 kWh/m²/day, and the cloudiest were 1997 and 1998 at 1.9.
Average wind speed in Portland during May is 5.3 m/s. The windiest May was 1994 at 6.9 m/s, while the calmest was 1991 at 4.1 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 13.9°C | 13.6°C | 14.1°C | 14.2°C | 14.1°C | +0.2°C |
| Avg High | 15.6°C | 15.2°C | 15.6°C | 15.7°C | 15.6°C | 0°C |
| Avg Low | 12.3°C | 12.1°C | 12.6°C | 12.7°C | 12.5°C | +0.2°C |
| Avg Rain | 86 mm | 56 mm | 66 mm | 74 mm | 47 mm | -39 mm |
May temperatures in Portland have risen by about 0.6°C between 1981–1985 and 2021–2025.
May has ranged from a record low of 8.7°C (2000) to a record high of 22.7°C (2002).
Rainfall in May is about average for rainfall, averaging 67 mm, with a wettest year of 152 mm.
A good time to visit Portland
May is a good time to visit Portland, with days averaging 15.5°C and nights around 12.4°C (mean 14°C, close to Portland's yearly average) and moderate rainfall. February and January 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 | 16.8°C | 15.0°C | 13.3°C | 22.6°C | 10.6°C | 26 mm | 71% | 4.8 m/s | 2.4 |
| 2024 | 15.5°C | 14.1°C | 12.6°C | 18.6°C | 10.3°C | 17 mm | 78% | 4.5 m/s | 2.4 |
| 2023 | 15.4°C | 14.1°C | 12.8°C | 19.2°C | 11.1°C | 57 mm | 76% | 5.9 m/s | 2.2 |
| 2022 | 15.6°C | 14.2°C | 12.8°C | 20.0°C | 10.1°C | 53 mm | 77% | 5.3 m/s | 2.3 |
| 2021 | 15.6°C | 13.9°C | 12.2°C | 19.5°C | 9.5°C | 47 mm | 75% | 6 m/s | 2.3 |
| 2020 | 14.9°C | 13.2°C | 11.6°C | 18.6°C | 9.9°C | 81 mm | 77% | 5.9 m/s | 2.2 |
| 2019 | 16.0°C | 14.5°C | 13.0°C | 21.2°C | 10.9°C | 78 mm | 77% | 6 m/s | 2.2 |
| 2018 | 15.9°C | 14.6°C | 13.2°C | 20.6°C | 11.4°C | 81 mm | 75% | 6.4 m/s | 2 |
| 2017 | 15.2°C | 13.8°C | 12.4°C | 19.2°C | 10.8°C | 47 mm | 77% | 5 m/s | 2.1 |
| 2016 | 16.3°C | 14.7°C | 13.1°C | 19.7°C | 9.8°C | 65 mm | 76% | 6.8 m/s | 2.1 |
| 2015 | 15.3°C | 13.6°C | 12.0°C | 20.4°C | 9.7°C | 66 mm | 77% | 6.7 m/s | 2.2 |
| 2014 | 16.3°C | 14.8°C | 13.2°C | 20.2°C | 10.6°C | 67 mm | 80% | 4.9 m/s | 2.1 |
| 2013 | 16.3°C | 14.7°C | 13.0°C | 22.7°C | 11.2°C | 114 mm | 74% | 5.4 m/s | 2.1 |
| 2012 | 15.4°C | 14.1°C | 12.8°C | 20.4°C | 10.6°C | 88 mm | 77% | 5.8 m/s | 2.2 |
| 2011 | 14.2°C | 13.0°C | 11.9°C | 17.7°C | 10.3°C | 74 mm | 76% | 4.8 m/s | 2 |
| 2010 | 15.6°C | 14.0°C | 12.4°C | 20.2°C | 9.6°C | 60 mm | 78% | 4.7 m/s | 2.3 |
| 2009 | 15.5°C | 14.2°C | 13.0°C | 19.0°C | 10.7°C | 46 mm | 80% | 4.8 m/s | 2.2 |
| 2008 | 15.7°C | 14.2°C | 12.6°C | 19.4°C | 10.9°C | 59 mm | 78% | 4.7 m/s | 2.3 |
| 2007 🔥 | 17.3°C | 15.5°C | 13.7°C | 21.0°C | 11.3°C | 139 mm | 79% | 6.5 m/s | 2 |
| 2006 | 14.3°C | 13.0°C | 11.8°C | 16.8°C | 9.3°C | 65 mm | 78% | 5.1 m/s | 2.1 |
| 2005 | 15.6°C | 14.1°C | 12.6°C | 22.3°C | 10.8°C | 25 mm | 77% | 4.9 m/s | 2.2 |
| 2004 | 15.0°C | 13.5°C | 12.0°C | 18.0°C | 10.3°C | 63 mm | 78% | 5.9 m/s | 2.2 |
| 2003 | 15.6°C | 13.9°C | 12.2°C | 18.5°C | 9.8°C | 29 mm | 79% | 4.3 m/s | 2.4 |
| 2002 | 16.4°C | 14.7°C | 13.0°C | 22.7°C | 10.5°C | 62 mm | 75% | 4.8 m/s | 2.4 |
| 2001 | 15.5°C | 14.1°C | 12.7°C | 20.8°C | 10.9°C | 47 mm | 79% | 4.5 m/s | 2.3 |
| 2000 | 15.5°C | 14.0°C | 12.5°C | 19.3°C | 8.7°C | 121 mm | 78% | 6.4 m/s | 2.1 |
| 1999 | 16.4°C | 14.5°C | 12.6°C | 20.6°C | 10.1°C | 66 mm | 77% | 5.9 m/s | 2 |
| 1998 | 14.9°C | 13.5°C | 12.0°C | 20.0°C | 9.8°C | 42 mm | 78% | 4.8 m/s | 1.9 |
| 1997 | 14.6°C | 13.4°C | 12.3°C | 19.9°C | 10.1°C | 109 mm | 80% | 4.5 m/s | 1.9 |
| 1996 | 15.4°C | 13.7°C | 12.0°C | 20.3°C | 9.8°C | 17 mm | 78% | 4.5 m/s | 2.1 |
| 1995 ❄️ | 14.3°C | 12.8°C | 11.4°C | 18.4°C | 9.9°C | 47 mm | 81% | 4.9 m/s | 2.2 |
| 1994 | 15.3°C | 13.8°C | 12.2°C | 20.0°C | 9.9°C | 96 mm | 75% | 6.9 m/s | 2.1 |
| 1993 | 15.4°C | 13.8°C | 12.1°C | 18.4°C | 10.6°C | 43 mm | 77% | 4.7 m/s | 2.2 |
| 1992 | 14.5°C | 13.2°C | 11.8°C | 19.6°C | 9.2°C | 82 mm | 80% | 4.5 m/s | 2.1 |
| 1991 | 15.2°C | 13.7°C | 12.2°C | 18.2°C | 10.4°C | 25 mm | 79% | 4.1 m/s | 2.1 |
| 1990 | 15.6°C | 14.0°C | 12.4°C | 21.4°C | 9.8°C | 27 mm | 75% | 5.3 m/s | 2.3 |
| 1989 | 15.9°C | 14.5°C | 13.0°C | 19.4°C | 10.5°C | 73 mm | 80% | 5.1 m/s | 2.1 |
| 1988 | 16.7°C | 15.0°C | 13.4°C | 21.9°C | 11.0°C | 71 mm | 81% | 4.4 m/s | 2 |
| 1987 🌧️ | 15.3°C | 13.7°C | 12.1°C | 19.5°C | 9.0°C | 152 mm | 79% | 5.6 m/s | 2.1 |
| 1986 | 15.1°C | 13.6°C | 12.2°C | 17.7°C | 10.7°C | 95 mm | 80% | 4.8 m/s | 2 |
| 1985 | 15.6°C | 13.9°C | 12.3°C | 21.3°C | 10.4°C | 71 mm | 76% | 5 m/s | 2.3 |
| 1984 | 15.9°C | 13.8°C | 11.8°C | 19.0°C | 10.1°C | 56 mm | 77% | 5.1 m/s | 2.4 |
| 1983 | 15.0°C | 13.3°C | 11.6°C | 17.0°C | 8.9°C | 106 mm | 83% | 5.4 m/s | — |
| 1982 | 15.2°C | 13.5°C | 11.8°C | 19.1°C | 9.3°C | 75 mm | 74% | 6.1 m/s | — |
| 1981 | 15.9°C | 14.0°C | 12.1°C | 20.7°C | 9.7°C | 74 mm | 75% | 5.5 m/s | — |
Actual recorded May data for each year, 1981–2025 — sourced from NASA POWER.
The average high in May is around 15.5°C with lows near 12.4°C (mean 14°C), based on 45 years of NASA POWER data.
May averages 67 mm of rainfall in Portland, about average for rainfall. The wettest on record was 152 mm in 1987.
The hottest May reached 22.7°C in 2002. The coldest dipped to 8.7°C in 2000.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average May temperatures have risen by about 0.6°C. Daytime highs moved from 15.5°C to 15.8°C and overnight lows from 11.9°C to 12.7°C over the same span.
May is close to Portland's year-round average and about average for rainfall, so plan for around 15.5°C daytime highs and 12.4°C at night.
Not quite — May is the 6th coolest month in Portland, averaging 14°C.
For May in Portland, pack light layers you can adjust through the day, with typical highs of 15.5°C and lows of 12.4°C. Bring an umbrella or light rain jacket too.
Relative humidity in May averages 77% — quite humid.
Average wind speed in May is 5.3 m/s. The windiest May on record averaged 6.9 m/s (1994).
The wettest May on record was 1987 with 152 mm. On average, May sees 67 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.
