Climate averages 1991–2020
Ontario weather
in May.
A warm, very dry month: the 6th warmest and the 5th driest of the year. Meets the pleasant-weather rule
Long-term climate patterns, not a forecast for a particular trip.
May is a warm month in Ontario: daytime highs average 24.6°C and nights cool to about 12.4°C. By daytime temperature it is the 6th warmest of the 12 months.
Expect about 11 mm of rain on roughly 2 days, which makes May a very dry month (the 5th driest of the 12 months). Daylight, from sunrise to sunset, lasts about 13 h 55 min on an average May day.
The nearest other city in this atlas is Chino (7 km away). In May its highs average 24.0°C, 0.6°C cooler than Ontario, with 11 mm of rain.
Among the 498 cities listed in the United States, Ontario ranks joint 213th of 498 for the warmest May highs and joint 56th of 498 for the driest May (rainfall, lowest first). The mean May high of those 498 cities is 23.8°C; Ontario is 0.8°C warmer than that mean.
From May to June, average highs rise by 3.8°C to 28.4°C, and monthly rainfall falls from 11 mm to 2.4 mm.
The annual picture
May in context
Monthly rainfall
Average total · mmAverages from hourly ERA5 reanalysis data. Actual weather varies from year to year. How these numbers are calculated
Every month, side by side
Ontario climate table
| Month | Average highHigh / low | Average low | Rainfall mm/month | Rain days ≥1 mm/day | Daylight hours/dayDaylight h/day |
|---|---|---|---|---|---|
| January | 17.5°C6.4°C | 6.4°C | 93 | 5.9 | 10.210 h |
| February | 17.8°C6.7°C | 6.7°C | 102 | 6.6 | 10.911 h |
| March | 19.7°C8.2°C | 8.2°C | 62 | 6.2 | 12.012 h |
| April | 22.1°C9.8°C | 9.8°C | 25 | 3.7 | 13.013 h |
| May, selected | 24.6°C12.4°C | 12.4°C | 11 | 2.2 | 13.914 h |
| June | 28.4°C15.3°C | 15.3°C | 2.4 | 0.3 | 14.414 h |
| July | 31.8°C18.6°C | 18.6°C | 1.7 | 0.5 | 14.214 h |
| August | 32.8°C19.3°C | 19.3°C | 0.9 | 0.2 | 13.413 h |
| September | 31.1°C17.7°C | 17.7°C | 4.3 | 0.9 | 12.412 h |
| October | 26.5°C13.8°C | 13.8°C | 19 | 2.6 | 11.411 h |
| November | 21.6°C9.5°C | 9.5°C | 25 | 2.8 | 10.410 h |
| December | 17.2°C6.1°C | 6.1°C | 62 | 5.3 | 9.910 h |
Rainfall is the average of the 30 separate monthly totals. A rain day is a local calendar day with at least 1 mm of precipitation. Daylight is the calculated sunrise-to-sunset length, not measured sunshine.
Compare places
May in nearby cities
- Chino in MayUnited States · 7 kmHigh 24.0°C · Low 12.5°C · 11 mm rain
- Rancho Cucamonga in MayUnited States · 7 kmHigh 24.8°C · Low 12.2°C · 15 mm rain
- Pomona in MayUnited States · 9 kmHigh 24.1°C · Low 12.1°C · 11 mm rain
- Chino Hills in MayUnited States · 13 kmHigh 23.5°C · Low 12.3°C · 11 mm rain
- Fontana in MayUnited States · 20 kmHigh 24.8°C · Low 11.7°C · 15 mm rain
- Corona in MayUnited States · 22 kmHigh 25.1°C · Low 13.1°C · 15 mm rain
- Riverside in MayUnited States · 26 kmHigh 25.2°C · Low 12.3°C · 15 mm rain
- West Covina in MayUnited States · 27 kmHigh 24.9°C · Low 12.7°C · 9.6 mm rain
Read the numbers correctly
Climate, not a promise.
These patterns help compare months. They cannot tell you the weather on a specific day of your trip.
Sources, method and limitsHow these numbers are made (what the highs, lows and rain days mean, the sources and the model cell used for Ontario) is explained once on the Ontario year overview and on the Sources, method and limits page.
Pomona, Chino and Chino Hills lie in the same rainfall cell, so their rainfall figures are identical to these; temperatures differ because they come from smaller 0.1° cells.