Ontario, CA weather in September
In September, Ontario sees highs around 91°F and lows around 64°F: hot and dry. Rain falls on about 1 day.
- Normal high
- 91°F
- Normal low
- 64°F
- Wet days
- 1
- 0.1 in total
- Muggy days
- 1
- dew point 65°F+
How September changes from start to finish
| September 1 | September 30 | |
|---|---|---|
| Normal high | 95°F | 87°F |
| Normal low | 65°F | 61°F |
| Chance of a wet day | 2% | 3% |
| Sunrise / sunset | 6:24 am / 7:16 pm | 6:44 am / 6:36 pm |
| Daylight | 12.9 h | 11.9 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 September day
- 6 am61°Fdew point 52°F
- 9 am77°Fdew point 52°F
- Noon88°Fdew point 48°F
- 3 pm89°Fdew point 50°F
- 6 pm79°Fdew point 52°F
- 9 pm69°Fdew point 54°F
NOAA hourly normals (local standard time) from March AFB (26 mi away); average wind 5 mph; clear or few clouds in 82% of daytime hours, mostly cloudy or overcast in 12%.
What kind of days to expect
- Comfortable dayshigh 65-80°F and dew point under 60°F4 of 30
- Hot dayshigh 90°F or more18 of 30
- Muggy daysdaily mean dew point 65°F or more1 of 30
- Wet daysat least 0.01 in of rain or melted snow1 of 30
- Notable rainat least 0.10 in0 of 30
- Freezing nightslow 32°F or below0 of 30
Average days per September, counted from daily records for each year 1991-2020.
Rain in September
Normal precipitation is 0.1 in; a dry September brings about 0.0 in and a wet one about 0.04 in (25th and 75th percentiles). Days with half an inch or more are rare.
How September varies from year to year
- Warmest September, 1991-20202020: average high 97°F
- Coolest September1998: average high 84°F
- Wettest September2015: 1.7 in
- Driest September1999: no measurable precipitation
- Highest reading118°F (September 5, 2020)
- Lowest reading51°F (September 27, 2013)
From the station's daily records with NOAA quality flags removed; most recent date shown when a reading repeats.
September compared with August and October
| August | September | October | |
|---|---|---|---|
| Normal high | 95°F | 91°F | 83°F |
| Normal low | 65°F | 64°F | 57°F |
| Wet days | 0 | 1 | 2 |
| Comfortable days | 0 | 4 | 12 |
| Daylight | 13.4 h | 12.4 h | 11.3 h |
Highs change by -4°F from August and -8°F into October.
Nearby alternatives in September
- Warmer: Palm Springs, CA65 mi · high 102°F · 1 wet day
- Cooler: West Covina, CA16 mi · high 83°F · 1 wet day
How Ontario ranks in September
- Normal high30th warmest of 378 cities; 12th of 60 in California
- Wet days28th driest of 378
- Comfortable days215th most of 342
What to pack for Ontario in September
- Light, breathable clothing – highs near 91°F
- Layers – afternoons near 91°F but nights near 64°F
Heating and cooling
September has 1 heating degree days and 378 cooling degree days (base 65°F), 12% of the year's total heating and cooling demand.
Questions
How hot is Ontario in September?
The normal high is 91°F and the normal low is 64°F. From 1991 to 2020 the hottest September reading was 118°F (September 5, 2020).
Does it rain a lot in Ontario in September?
About 1 days in September have at least 0.01 in of precipitation, and the normal total is 0.1 in. The wettest September in 1991-2020 was in 2015 (1.7 in); the driest was in 1999, with no measurable precipitation.
Is September a good time to visit Ontario?
September ranks 10th of 12 months on our comfort score for Ontario (47 out of 100). It has about 4 comfortable days and about 18 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.