Ontario weather in September: Ontario, California: normal highs, lows, rain and records for September
Ontario in September has a normal high of 91°F and a normal low of 64°F, a daily mean of 78°F, falling from 95°F on the 1st to 87°F by the 30th. Measurable precipitation falls on 1 days in a normal September, 0.10 inches in all. (NOAA 1991-2020 normals)
In metric: a normal high of 33°C and low of 18°C, 3 mm of precipitation in September.
- NOAA stationOntario International Airport
- Station IDUSW00003102
- Location34.06°N 117.60°W
- Elevation949 ft (289 m)
- From the center1 miles
- Population185,285
- Jan 68° 45°
- Feb 68° 46°
- Mar 72° 49°
- Apr 76° 51°
- May 80° 56°
- Jun 86° 60°
- Jul 94° 65°
- Aug 95° 65°
- Sep 91° 64°
- Oct 83° 57°
- Nov 75° 49°
- Dec 67° 44°
Each month: normal high (large) and low, °F. Fill: the month's normal mean, colder blue to hotter red.
How warm is Ontario in September?
The normal high is 91°F and the normal low 64°F, for a daily mean of 77.6°F. September is 2.5°F cooler than August and 7.8°F warmer than October. September is the 3rd warmest month of the year in Ontario and the 9th wettest. Across the month the normal high falls 8°F, from 95°F on September 1 to 87°F on September 30. From one year to the next September's mean temperature typically moves about 2.2°F either way (NOAA's standard deviation), so roughly two Septembers in three average between 75°F and 80°F.
Bars above: each day's normal high to low. Columns below: the chance of 0.01 inch or more of precipitation that day, on a scale of 0 to 100% (highest 4%).
| Day | High | Low | Chance of 0.01 in | Chance of 0.10 in |
|---|---|---|---|---|
| September 1 | 95°F | 65°F | 2% | 1% |
| September 8 | 94°F | 65°F | 2% | 1% |
| September 15 | 92°F | 64°F | 2% | 1% |
| September 22 | 90°F | 63°F | 3% | 1% |
| September 30 | 87°F | 61°F | 4% | 2% |
Every day of September: normal high, low and chance of precipitation (warmest afternoon September 1, coldest night September 30)
| Day | High | Low | Chance of 0.01 in | Chance of 0.10 in | Daylight |
|---|---|---|---|---|---|
| September 1 | 95°F | 65°F | 2% | 1% | 12 h 50 min |
| September 2 | 95°F | 65°F | 2% | 1% | 12 h 50 min |
| September 3 | 94°F | 65°F | 2% | 1% | 12 h 50 min |
| September 4 | 94°F | 65°F | 2% | 1% | 12 h 50 min |
| September 5 | 94°F | 65°F | 2% | 1% | 12 h 50 min |
| September 6 | 94°F | 65°F | 2% | 1% | 12 h 40 min |
| September 7 | 94°F | 65°F | 2% | 1% | 12 h 40 min |
| September 8 | 94°F | 65°F | 2% | 1% | 12 h 40 min |
| September 9 | 93°F | 65°F | 2% | 1% | 12 h 40 min |
| September 10 | 93°F | 65°F | 2% | 1% | 12 h 40 min |
| September 11 | 93°F | 65°F | 2% | 1% | 12 h 30 min |
| September 12 | 93°F | 65°F | 2% | 1% | 12 h 30 min |
| September 13 | 92°F | 65°F | 2% | 1% | 12 h 30 min |
| September 14 | 92°F | 64°F | 2% | 1% | 12 h 30 min |
| September 15 | 92°F | 64°F | 2% | 1% | 12 h 30 min |
| September 16 | 92°F | 64°F | 2% | 1% | 12 h 20 min |
| September 17 | 91°F | 64°F | 2% | 1% | 12 h 20 min |
| September 18 | 91°F | 64°F | 2% | 1% | 12 h 20 min |
| September 19 | 91°F | 64°F | 3% | 1% | 12 h 20 min |
| September 20 | 90°F | 63°F | 3% | 1% | 12 h 20 min |
| September 21 | 90°F | 63°F | 3% | 1% | 12 h 10 min |
| September 22 | 90°F | 63°F | 3% | 1% | 12 h 10 min |
| September 23 | 89°F | 63°F | 3% | 1% | 12 h 10 min |
| September 24 | 89°F | 63°F | 3% | 1% | 12 h 10 min |
| September 25 | 89°F | 62°F | 3% | 1% | 12 h 10 min |
| September 26 | 88°F | 62°F | 3% | 1% | 12 h |
| September 27 | 88°F | 62°F | 3% | 1% | 12 h |
| September 28 | 87°F | 62°F | 3% | 2% | 12 h |
| September 29 | 87°F | 61°F | 3% | 2% | 12 h |
| September 30 | 87°F | 61°F | 4% | 2% | 11 h 50 min |
- Normal high
- 91°FSeptember average
- Normal low
- 64°FSeptember average
- Precipitation
- 0.10 inmonth total
- Days with precipitation
- 10.01 inch or more
- Days at 90°F or more
- 18
- Daylight
- 12 h 50 min to 11 h 50 minSeptember 1 to September 30
- Days at 70°F or more
- 30
- Days at 80°F or more
- 26
- Sunshine
- 95%of clear-sky sunlight (NASA)
Source: NOAA NCEI 1991-2020 daily normals, station USW00003102; monthly normals. Daylight is computed from the place's latitude with NOAA's solar equations.
Does it rain in Ontario in September?
On a given September day the chance of 0.01 inch or more is 2% on average, highest around September 30 (4%). In all, 0.10 in falls on 1 days of a normal September.
In a normal September in Ontario, 18 days reach 90°F.
Source: NOAA NCEI 1991-2020 daily and monthly normals, station USW00003102.
What are the records for September in Ontario?
The warmest September temperature on this station's record (since 1998) is 118°F, on September 5, 2020; the coldest is 51°F, on September 27, 2013. The wettest September brought 1.72 in (2015).
The September mean against the 1991-2020 normal of 77.6°F: 2021 78.8°F (+1.2), 2022 81.3°F (+3.7), 2023 73.5°F (−4.1), 2024 77.6°F (at normal), 2025 78.0°F (+0.4), 2026 78.3°F (+0.7). 4 of 6 ran warmer than normal.
| September | Mean | Against normal | Precip. |
|---|---|---|---|
| 2021 | 78.8°F | +1.2°F | 0.00 in |
| 2022 | 81.3°F | +3.7°F | 0.27 in |
| 2023 | 73.5°F | −4.1°F | 0.24 in |
| 2024 | 77.6°F | at normal | 0.00 in |
| 2025 | 78.0°F | +0.4°F | 0.12 in |
| 2026 | 78.3°F | +0.7°F | 0.56 in |
Source: records: ACIS, station USW00003102; recent months: ACIS, station USW00003102. Records and recent months use complete months only.
How does September in Ontario compare across California?
Across the 219 places PlainClimate covers in California, September normal highs run from 64°F in Eureka to 104°F in Brawley; Ontario's is 91°F.
Source: NOAA NCEI 1991-2020 monthly normals for every station in the state.