Ontario, CA weather in August
Ontario is hot and dry in August: highs average 95°F and nights drop to about 65°F. Rain is rare. This is the peak of the warm season in Ontario. Midday heat is the main thing to plan around.
- Normal high
- 95°F
- Normal low
- 65°F
- Wet days
- 0
- 0.03 in total
- Muggy days
- 0
- dew point 65°F+
How August changes from start to finish
| August 1 | August 31 | |
|---|---|---|
| Normal high | 95°F | 95°F |
| Normal low | 65°F | 65°F |
| Chance of a wet day | 2% | 2% |
| Sunrise / sunset | 6:02 am / 7:51 pm | 6:23 am / 7:18 pm |
| Daylight | 13.8 h | 12.9 h |
Chance of a wet day: average for the first and last 7 days of the month. Times are local clock time (Pacific Time).
A typical August day
- 6 am65°Fdew point 56°F
- 9 am81°Fdew point 55°F
- Noon92°Fdew point 52°F
- 3 pm93°Fdew point 53°F
- 6 pm84°Fdew point 53°F
- 9 pm73°Fdew point 55°F
NOAA hourly normals (local standard time) from March AFB (26 mi away); average wind 6 mph; clear or few clouds in 85% of daytime hours, mostly cloudy or overcast in 8%.
What kind of days to expect
- Comfortable dayshigh 65-80°F and dew point under 60°F0 of 31
- Hot dayshigh 90°F or more24 of 31
- Muggy daysdaily mean dew point 65°F or more0 of 31
- Wet daysat least 0.01 in of rain or melted snow0 of 31
- Notable rainat least 0.10 in0 of 31
- Freezing nightslow 32°F or below0 of 31
Average days per August, counted from daily records for each year 1991-2020.
Rain in August
Normal precipitation is 0.03 in; a dry August brings about 0.0 in and a wet one about 0.0 in (25th and 75th percentiles). Days with half an inch or more are rare.
How August varies from year to year
- Warmest August, 1991-20202020: average high 98°F
- Coolest August2002: average high 90°F
- Wettest August2005: 0.3 in
- Driest August1999: no measurable precipitation
- Highest reading112°F (August 31, 2017)
- Lowest reading56°F (August 8, 2011)
From the station's daily records with NOAA quality flags removed; most recent date shown when a reading repeats.
August compared with July and September
| July | August | September | |
|---|---|---|---|
| Normal high | 94°F | 95°F | 91°F |
| Normal low | 65°F | 65°F | 64°F |
| Wet days | 1 | 0 | 1 |
| Comfortable days | 1 | 0 | 4 |
| Daylight | 14.2 h | 13.4 h | 12.4 h |
Highs change by +1°F from July and -4°F into September.
Nearby alternatives in August
- Warmer: Palm Springs, CA65 mi · high 108°F · 1 wet day
- Cooler: West Covina, CA16 mi · high 84°F · 0 wet days
How Ontario ranks in August
- Normal high52nd warmest of 378 cities; 14th of 60 in California
- Wet days32nd driest of 378
- Comfortable days223rd most of 341
What to pack for Ontario in August
- Light, breathable clothing – highs near 95°F
- Layers – afternoons near 95°F but nights near 65°F
Heating and cooling
August has 0 heating degree days and 467 cooling degree days (base 65°F), 14% of the year's total heating and cooling demand.
Questions
How hot is Ontario in August?
The normal high is 95°F and the normal low is 65°F. From 1991 to 2020 the hottest August reading was 112°F (August 31, 2017).
Does it rain a lot in Ontario in August?
About 0 days in August have at least 0.01 in of precipitation, and the normal total is 0.03 in. The wettest August in 1991-2020 was in 2005 (0.3 in); the driest was in 1999, with no measurable precipitation.
Is August a good time to visit Ontario?
August ranks 12th of 12 months on our comfort score for Ontario (41 out of 100). It has almost no comfortable days and about 24 days at 90°F or hotter. The best months are March, April and May.
Where the numbers come from
- Temperature, rain and frost dates: Ontario Intl Airport (USW00003102), 2.9 mi E of the city center, 949 ft (52 ft lower than the city). NOAA normals and daily records, 1991-2020.
- Snowfall and snow depth: San Gabriel Canyon PH (USC00047776), 16 mi WNW of the city center, 744 ft (257 ft lower than the city). NOAA normals and daily records, 1991-2020.
- Humidity and wind by hour and cloud cover: March AFB (USW00023119), 26 mi ESE of the city center, 1,516 ft (515 ft higher than the city). NOAA normals and daily records, 1991-2020.
- Daily humidity and wind: March Air Reserve Base (722860-23119), 26 mi ESE of the city center, 1,536 ft (535 ft higher than the city). Hourly observations, 1991-2020.