Ontario, California Weather
Ceanothus blooms again. Day 93 of summer. Read this microseason across nine climate regions →
Ontario weather forecast — hour by hour, 7-day outlook, NOAA radar
Conditions updated 7:25 AM PDT · Open-Meteo
- TodaySep 21Clear later——81°65°—
- TuesdaySep 22Overcast——83°64°+2°
- WednesdaySep 23Clear——91°61°+8°
- ThursdaySep 24Clear——91°73°0°
- FridaySep 25Overcast——93°74°+2°
- SaturdaySep 26Overcast——93°76°0°
- SundaySep 27Partly Cloudy——90°75°-3°
Air quality now AQI 61 · Moderate
AQI 61 (Moderate), driven by PM2.5. AQI flat over the last 6 hours (within ±3 points). PM2.5 at 25.3 µg/m³ (AQI 81) with a 0.86 fine-to-coarse ratio and 3 mph wind — combustion smoke trapped in stagnant air, not road dust.
OK No precautions needed for the general population; unusually sensitive individuals may consider limiting prolonged outdoor exertion during the projected peak around 8 PM.
What's driving it
PM × Wind × Precip
PM2.5 at 25.3 µg/m³ (AQI 81) with a 0.86 fine-to-coarse ratio and 3 mph wind — combustion smoke trapped in stagnant air, not road dust.
- PM2.5/PM10
- 0.86
- Wind
- calm
- Recent rain
- 0h in last 6h
- Pattern
- stagnant smoke
Trends
Seven days of AQI and PM2.5.
Hourly air-quality data from the Copernicus Atmosphere Monitoring Service, charted across the past and next several days. Dashed lines mark the AQI breakpoints at 50 (Good → Moderate) and 100 (Moderate → Unhealthy for Sensitive Groups).
September dries up ditches or breaks down bridges.
- Moonrise
- 4:09 PM
- Moonset
- 1:34 AM
- In sign
- ♑︎ Capricorn
Ceanothus blooms again
Read this microseason across nine climate regions →
All 72 microseasons on the year wheel →
Ontario at a glance
- Today vs. normal: Today averages 73°F (high 81°F, low 65°F), 2°F below the 75°F normal for Sep 21
- Last frost: None in most years — 32°F in 41% of 1991–2020 years (NOAA station 2 km away)
- Microseason: Sep 21–25
- Planting calendar: September — plant lettuce, peas, spinach, radishes, beans, squash; harvest lettuce, peas, spinach, radishes, tomatoes, peppers, beans, summer squash, winter squash
16-Day Forecast — Ontario
- Mon81°65°0%
- Tue83°64°1%
- Wed91°61°0%
- Thu91°73°1%
- Fri93°74°2%
- Sat93°76°1%
- Sun90°75°2%
- Mon94°74°4%
- Tue99°79°5%
- Wed101°82°7%
- Thu104°86°5%
- Fri103°88°11%
- Sat101°85°13%
- Sun100°86°12%
- Mon99°85°10%
- Tue95°82°6%
Forecast data from Open-Meteo (CC BY 4.0).
Live wind & temperature near Ontario
Interactive wind and temperature map centered on Ontario — it loads in your browser. Open the full weather map.
Right now in the garden
Year-round growing
As of September 21, sowing here runs through the year. Freezes are uncommon, so there is no frost date to plan around; heat and rainfall set the calendar instead. This city's planting calendar for September: plant lettuce, peas, spinach, radishes, beans, and squash; harvest lettuce, peas, spinach, radishes, tomatoes, peppers, beans, summer squash, and winter squash.
Sun & seasons in Ontario
Ontario sits in San Bernardino County, where the year’s longest day runs 14h 25m of daylight and its shortest just 9h 53m — a swing of +4h 33m between the June and December solstices. Clocks spring forward on Sunday, March 8, 2026 and fall back on Sunday, November 1, 2026.
Los Angeles, the state’s largest city, lies about 46 miles to the W. The nearest town Ontario tracks is Rancho Cucamonga, roughly 6 miles to the NNE.
Air quality in Ontario
Air quality in Ontario’s county has trended cleaner since 2020; its cleanest year on record was 2023 (median AQI 71). See the full air-quality history for Ontario.
Planting calendar
| Month | Plant | Harvest |
|---|---|---|
| January | lettuce, peas, spinach, radishes | lettuce, peas, spinach, radishes |
| February | lettuce, peas, spinach, radishes | lettuce, peas, spinach, radishes |
| March | lettuce, peas, spinach, radishes | lettuce, peas, spinach, radishes |
| April | lettuce, peas, spinach, radishes, tomatoes, peppers, beans, squash | lettuce, peas, spinach, radishes |
| May | spinach, radishes, tomatoes, peppers, beans, squash | lettuce, peas, spinach, radishes, summer squash |
| June | tomatoes, peppers, beans, squash | lettuce, peas, spinach, radishes, tomatoes, peppers, beans, summer squash |
| July | lettuce, peas, tomatoes, peppers, beans, squash | tomatoes, peppers, beans, summer squash, winter squash |
| August | lettuce, peas, spinach, radishes, tomatoes, peppers, beans, squash | tomatoes, peppers, beans, summer squash, winter squash |
| September | lettuce, peas, spinach, radishes, beans, squash | lettuce, peas, spinach, radishes, tomatoes, peppers, beans, summer squash, winter squash |
| October | lettuce, peas, spinach, radishes | lettuce, peas, spinach, radishes, tomatoes, peppers, beans, summer squash, winter squash |
| November | lettuce, peas, spinach, radishes | lettuce, peas, spinach, radishes, tomatoes, peppers, beans, summer squash, winter squash |
| December | lettuce, peas, spinach, radishes | lettuce, peas, spinach, radishes |
A year in weather
Ontario's warmest month is August (~80°F mean) and its coldest is January (~52°F). Rainfall peaks in February (3.4 inches) and bottoms out in August (0.0 inches).
| Month | Mean temp | Precip |
|---|---|---|
| January | 52° | 3.3″ |
| February | 54° | 3.4″ |
| March | 57° | 3.0″ |
| April | 62° | 1.5″ |
| May | 67° | 0.5″ |
| June | 73° | 0.1″ |
| July | 79° | 0.1″ |
| August | 80° | 0.0″ |
| September | 76° | 0.1″ |
| October | 69° | 0.5″ |
| November | 59° | 1.6″ |
| December | 53° | 2.6″ |
Regional context
Similar climates Chino, CA, Eastvale, CA, Montclair, CA
Per modelled 1991-2020 normals (EC_Earth3P_HR model via Open-Meteo), Ontario runs from a 52°F January mean to 79°F in July, a 27°F seasonal spread, with near 16.7 inches of precipitation.
Cool-season fronts carry Ontario's rain: February logs 3.4 inches, against August's 0.0 inches — winter does the heavy lifting in Ontario. That groups Ontario with places like Chino, CA, Eastvale, CA and Montclair, CA on the same cool-season storm track.
Hard freezes are rare in Ontario: the coldest month averages 52°F, so Ontario's growing window runs most of the year. August is the hottest stretch near 80°F, pushing cool-season crops to the milder shoulder months. Ontario's rare cold nights chill open ground first.
Similar climates: Chino, CA, Eastvale, CA, Montclair, CA, Upland, CA, Rancho Cucamonga, CA.
Naturalist notes
Coastal live oaks begin dropping their acorns in September as temperatures start their gradual decline.
Frequently asked
- When does it freeze in Ontario?
- Most years Ontario doesn't freeze: the nearest NOAA station reached 32°F in 41% of 1991–2020 years, so Ontario has no reliable frost date.
- What is the rainy season in Ontario?
- Rainfall in Ontario peaks in February near 3.4 inches, out of about 17 inches annually.
- What is the warmest month in Ontario?
- August is Ontario's warmest month, averaging about 80°F.
- What is the coldest month in Ontario?
- Ontario bottoms out in January, with a mean near 52°F.
- When can I start a vegetable garden in Ontario?
- Any season works in Ontario: without a reliable freeze, Ontario's heat, not frost, decides when greens and tomatoes do best.
- What hardiness zone is Ontario?
- Ontario sits in the USDA zone set by January lows near 52°F; the USDA ZIP tool gives the band.
- What is the 10-day forecast for Ontario?
- Ontario's extended outlook — daily high and low temperatures and precipitation chances for each upcoming day — is in the daily forecast above.
- Will it rain this week in Ontario?
- See this week's day-by-day rain chances for Ontario in the daily forecast above, and the next 24 hours in the hourly chart.
- What is the weather like right now in Ontario?
- Current conditions for Ontario and the next 24 hours — temperature, precipitation chance, and wind by the hour — are in the hourly forecast chart above.
- How often is the Ontario forecast updated?
- The Ontario forecast on this page is built from Open-Meteo weather-model data and refreshes regularly through the day.
- When are sunrise and sunset in Ontario?
- Today's sunrise and sunset times for Ontario are in the Almanac section above, along with civil dawn, civil dusk, and day length. Day length is longest near the summer solstice and shortest near the winter solstice.
- How accurate is the weather forecast for Ontario?
- The next few days in Ontario's forecast are the most reliable; accuracy declines beyond about a week as weather-model uncertainty grows.
Ontario sits at 34.0°N; its climate zone is hot-summer Mediterranean (Köppen approximation).
ZIP codes in Ontario
- 91743
- 91758
- 91761
- 91762
- 91764