May is one of the warmer months of the year in Ontario, with average highs near 26.5°C and lows around 10.8°C (mean 18.7°C). It is one of the drier months, averaging 8 mm of rainfall and 55% relative humidity across the period.
May is one of the warmer months of the year in Ontario. Across 45 years of records, the warmest May in Ontario was 1997 — when the month averaged 23.1°C — while the coldest was 1998 at 14.2°C. Typical May days reach 26.5°C with nights near 10.8°C. The long-term May temperature trend is broadly flat.
May is one of the drier months in Ontario, averaging 8 mm of rainfall. The wettest May on record was 1998 with 70 mm, while the driest were 2004 and 2007 at 0 mm.
Relative humidity in Ontario during May averages 55%. The most humid May was 1998 at 74%, and the least humid was 1984 at 35%.
May receives about 7.6 kWh/m²/day of solar energy in Ontario. The sunniest May was 2012 at 8.2 kWh/m²/day, and the cloudiest was 1984 at 6.7.
Average wind speed in Ontario during May is 1.9 m/s. The windiest May was 1990 at 2.3 m/s, while the calmest was 1992 at 1.6 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 19.0°C | 17.9°C | 19.6°C | 18.1°C | 18.8°C | -0.2°C |
| Avg High | 27.3°C | 25.5°C | 27.6°C | 25.6°C | 26.4°C | -0.9°C |
| Avg Low | 10.7°C | 10.3°C | 11.5°C | 10.5°C | 11.2°C | +0.5°C |
| Avg Rain | 4 mm | 12 mm | 5 mm | 10 mm | 5 mm | +1 mm |
May temperatures in Ontario have fallen by about 0.5°C between 1981–1985 and 2021–2025.
May has ranged from a record low of 2.3°C (1991) to a record high of 39.6°C (2003).
Rainfall in May is one of the drier months, averaging 8 mm, with a wettest year of 70 mm.
Daytime highs and overnight lows have shifted differently — highs fell about 0.2°C per decade while lows rose 0.1°C per decade, narrowing the gap between day and night.
One of the best times to visit Ontario
May is one of the best times to visit Ontario. Expect days averaging 26.5°C and nights around 10.8°C (mean 18.7°C) — close to Ontario's yearly average — with low rainfall (8 mm), so conditions are generally comfortable for sightseeing and outdoor plans.
| Year | Avg High | Avg Temp | Avg Low | Hottest Day | Coldest Day | Rainfall | Humidity | Wind | Solar |
|---|---|---|---|---|---|---|---|---|---|
| 2025 | 27.3°C | 19.9°C | 12.5°C | 36.7°C | 7.9°C | 10 mm | 59% | 1.9 m/s | 7.5 |
| 2024 | 24.9°C | 17.4°C | 10.0°C | 28.6°C | 4.6°C | 3 mm | 67% | 1.9 m/s | 7.9 |
| 2023 | 22.7°C | 16.8°C | 10.9°C | 30.6°C | 6.2°C | 16 mm | 71% | 1.9 m/s | 7.4 |
| 2022 | 28.0°C | 19.4°C | 10.8°C | 35.2°C | 4.9°C | 0 mm | 51% | 1.9 m/s | 8.1 |
| 2021 | 27.6°C | 19.2°C | 10.8°C | 33.1°C | 7.0°C | 1 mm | 54% | 2 m/s | 8.1 |
| 2020 | 28.0°C | 20.0°C | 11.9°C | 34.9°C | 8.1°C | 2 mm | 56% | 1.8 m/s | 8.1 |
| 2019 | 21.7°C | 15.6°C | 9.6°C | 27.0°C | 6.4°C | 31 mm | 73% | 2.1 m/s | 6.9 |
| 2018 | 25.6°C | 18.5°C | 11.4°C | 33.6°C | 7.9°C | 6 mm | 61% | 2.1 m/s | 7.6 |
| 2017 | 26.0°C | 18.5°C | 11.1°C | 34.7°C | 4.9°C | 10 mm | 56% | 1.9 m/s | 7.7 |
| 2016 | 25.1°C | 17.8°C | 10.6°C | 33.3°C | 7.8°C | 8 mm | 63% | 2 m/s | 7.6 |
| 2015 | 23.8°C | 17.2°C | 10.6°C | 31.7°C | 7.2°C | 21 mm | 62% | 2.2 m/s | 7.3 |
| 2014 | 28.9°C | 20.6°C | 12.2°C | 37.0°C | 7.7°C | 2 mm | 44% | 2.2 m/s | 8 |
| 2013 | 28.4°C | 19.8°C | 11.2°C | 37.3°C | 8.2°C | 8 mm | 50% | 2.1 m/s | 7.8 |
| 2012 | 28.9°C | 19.9°C | 10.9°C | 37.6°C | 6.5°C | 1 mm | 46% | 1.9 m/s | 8.2 |
| 2011 | 23.5°C | 16.1°C | 8.7°C | 32.6°C | 4.8°C | 10 mm | 58% | 2.2 m/s | 7.9 |
| 2010 | 24.4°C | 16.5°C | 8.5°C | 32.0°C | 4.1°C | 2 mm | 55% | 2 m/s | 8 |
| 2009 | 29.8°C | 21.2°C | 12.6°C | 36.1°C | 9.2°C | 0 mm | 50% | 1.7 m/s | 7.7 |
| 2008 | 25.5°C | 17.9°C | 10.3°C | 37.8°C | 5.1°C | 10 mm | 53% | 2 m/s | 7.6 |
| 2007 | 27.5°C | 19.1°C | 10.6°C | 34.2°C | 5.9°C | 0 mm | 46% | 1.9 m/s | 8.1 |
| 2006 | 27.8°C | 19.8°C | 11.9°C | 35.1°C | 6.8°C | 10 mm | 55% | 1.7 m/s | 7.7 |
| 2005 | 25.7°C | 18.6°C | 11.4°C | 33.4°C | 5.8°C | 8 mm | 65% | 1.8 m/s | 7.8 |
| 2004 | 28.4°C | 20.2°C | 12.1°C | 36.8°C | 7.0°C | 0 mm | 48% | 2 m/s | 8.1 |
| 2003 | 26.0°C | 18.5°C | 11.0°C | 39.6°C | 4.3°C | 15 mm | 55% | 1.9 m/s | 7.6 |
| 2002 | 27.0°C | 18.4°C | 9.8°C | 36.7°C | 5.4°C | 2 mm | 50% | 1.9 m/s | 8 |
| 2001 | 30.1°C | 21.7°C | 13.3°C | 37.1°C | 8.7°C | 2 mm | 50% | 1.7 m/s | 7.9 |
| 2000 | 28.4°C | 20.3°C | 12.1°C | 37.9°C | 5.5°C | 6 mm | 52% | 1.9 m/s | 8 |
| 1999 | 25.9°C | 17.5°C | 9.1°C | 30.7°C | 5.1°C | 3 mm | 56% | 1.9 m/s | 7.4 |
| 1998 ❄️ 🌧️ | 20.0°C | 14.2°C | 8.5°C | 24.5°C | 6.5°C | 70 mm | 74% | 2.1 m/s | 7.2 |
| 1997 🔥 | 31.5°C | 23.1°C | 14.7°C | 36.1°C | 9.9°C | 1 mm | 47% | 1.7 m/s | 7.7 |
| 1996 | 27.6°C | 19.4°C | 11.1°C | 33.3°C | 6.9°C | 1 mm | 52% | 2 m/s | 7.9 |
| 1995 | 21.3°C | 15.1°C | 8.9°C | 29.7°C | 5.2°C | 9 mm | 72% | 2.1 m/s | 6.9 |
| 1994 | 24.9°C | 17.4°C | 9.9°C | 31.2°C | 6.8°C | 8 mm | 61% | 1.9 m/s | 7 |
| 1993 | 25.4°C | 18.2°C | 10.9°C | 30.2°C | 7.2°C | 1 mm | 63% | 1.8 m/s | 7.7 |
| 1992 | 27.7°C | 20.0°C | 12.3°C | 32.0°C | 8.5°C | 7 mm | 62% | 1.6 m/s | 7.2 |
| 1991 | 24.5°C | 16.3°C | 8.1°C | 31.7°C | 2.3°C | 1 mm | 57% | 2.1 m/s | 7.3 |
| 1990 | 25.8°C | 17.5°C | 9.2°C | 35.5°C | 6.3°C | 19 mm | 54% | 2.3 m/s | 7.7 |
| 1989 | 27.2°C | 19.0°C | 10.8°C | 33.5°C | 6.0°C | 6 mm | 49% | 2.1 m/s | 7.1 |
| 1988 | 27.1°C | 18.8°C | 10.5°C | 35.6°C | 3.0°C | 4 mm | 45% | 2.1 m/s | 7.4 |
| 1987 | 27.6°C | 19.8°C | 12.0°C | 35.1°C | 6.9°C | 7 mm | 49% | 2 m/s | 7 |
| 1986 | 27.3°C | 18.8°C | 10.2°C | 34.8°C | 4.4°C | 0 mm | 48% | 1.9 m/s | 7.7 |
| 1985 | 26.5°C | 18.2°C | 9.9°C | 33.0°C | 6.1°C | 2 mm | 49% | 1.9 m/s | 7.5 |
| 1984 | 32.2°C | 22.7°C | 13.1°C | 38.9°C | 6.0°C | 1 mm | 35% | 2 m/s | 6.7 |
| 1983 | 25.5°C | 17.7°C | 9.8°C | 32.6°C | 3.8°C | 3 mm | 60% | 1.8 m/s | — |
| 1982 | 25.4°C | 17.7°C | 9.9°C | 32.7°C | 6.2°C | 9 mm | 60% | 1.8 m/s | — |
| 1981 | 27.1°C | 18.7°C | 10.2°C | 32.4°C | 6.1°C | 6 mm | 50% | 1.9 m/s | — |
Actual recorded May data for each year, 1981–2025 — sourced from NASA POWER.
The average high in May is around 26.5°C with lows near 10.8°C (mean 18.7°C), based on 45 years of NASA POWER data.
May averages 8 mm of rainfall in Ontario, one of the drier months. The wettest on record was 70 mm in 1998.
The hottest May reached 39.6°C in 2003. The coldest dipped to 2.3°C in 1991.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average May temperatures have fallen by about 0.5°C — but days and nights have moved in opposite directions. Overnight lows rose from 10.6°C to 11°C while daytime highs eased from 27.3°C to 26.1°C, narrowing the gap between day and night.
May is one of the warmer months of the year in Ontario and one of the drier months, so plan for around 26.5°C daytime highs and 10.8°C at night.
Not quite — May is the 7th coolest month in Ontario, averaging 18.7°C.
For May in Ontario, pack light layers you can adjust through the day, with typical highs of 26.5°C and lows of 10.8°C.
Relative humidity in May averages 55% — moderately humid.
Average wind speed in May is 1.9 m/s. The windiest May on record averaged 2.3 m/s (1990).
The wettest May on record was 1998 with 70 mm. On average, May sees 8 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 Ontario 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.
