Rialto, California Weather
Coastal fog thickens at dawn. Day 77 of spring. Read this microseason across nine climate regions →
Rialto weather forecast — hour by hour, 7-day outlook, NOAA radar
- TodayJun 4Clear——91°57°—
- FridayJun 5Foggy——90°58°-1°
- SaturdayJun 6Overcast——84°58°-6°
- SundayJun 7Clear——82°63°-2°
- MondayJun 8Overcast——81°62°-1°
- TuesdayJun 9Overcast——72°61°-9°
- WednesdayJun 10Overcast——79°57°+7°
Ozone at AQI 135 now. AQI flat over the last 6 hours (within ±3 points). With UV 10 peaking around 1 PM under clear skies, surface ozone likely climbs to AQI 183 by mid-afternoon.
CAUTION Sensitive groups (children, elderly, respiratory conditions) should limit prolonged outdoor exertion.
What's driving it
Ozone × UV × Sky
Ozone at AQI 135 now. With UV 10 peaking around 1 PM under clear skies, surface ozone likely climbs to AQI 183 by mid-afternoon.
- Present
- AQI 135
- UV peak
- 10.2 at 1 PM
- Sky at peak
- clear
- Projected peak
- AQI 183
PM × Wind × Precip
PM2.5 at 12.3 µg/m³, PM10 at 17.5 µg/m³ — typical background levels with no transport signature.
- PM2.5/PM10
- 0.70
- Wind
- light
- Recent rain
- 0h in last 6h
- Pattern
- background
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).
A summer fog for fair, a winter fog for rain.
- Moonrise
- 6:03 AM
- Moonset
- 4:12 PM
- In sign
- ♒︎ Aquarius
Coastal fog thickens at dawn
Rialto at a glance
- Today vs. normal: 4°F above the seasonal normal for this latitude
- Last frost: March 12 (climatological average for this latitude)
- Microseason: Jun 1–5
- Planting window: Harvest spring lettuce before it bolts. Sow heat-tolerant greens.
Right now in the garden
Peak growing season
As of June 4, the growing season is at its peak — frost is months away. Continue succession-planting beans and summer squash. Start fall brassicas (broccoli, cabbage, kale) from seed indoors for transplanting in late summer.
Planting calendar
| Month | Plant | Harvest |
|---|---|---|
| January | — | — |
| February | — | — |
| March | lettuce, peas, spinach, radishes | — |
| April | lettuce, peas, spinach, radishes, tomatoes, peppers, beans, squash | — |
| May | tomatoes, peppers, beans, squash | lettuce, peas, radishes |
| June | tomatoes, peppers, beans, squash | lettuce, peas, radishes |
| July | — | tomatoes, beans, summer squash |
| August | — | tomatoes, beans, summer squash |
| September | — | tomatoes, beans, summer squash |
| October | fall brassicas, garlic (overwinter), carrots | winter squash, tomatoes (last) |
| November | fall brassicas, garlic (overwinter), carrots | — |
| December | — | — |
A year in weather
Rialto's warmest month is August, with a mean temperature near 81°F, and its coldest is December at roughly 56°F. Rainfall peaks in February at 2.5 inches and drops to its lowest point in June at 0.1 inches.
| Month | Mean temp | Precip | Rainy days |
|---|---|---|---|
| January | 56° | 2.2″ | 4 |
| February | 57° | 2.5″ | 5 |
| March | 60° | 1.6″ | 3 |
| April | 64° | 0.6″ | 1 |
| May | 68° | 0.2″ | 1 |
| June | 74° | 0.1″ | 0 |
| July | 80° | 0.1″ | 0 |
| August | 81° | 0.1″ | 0 |
| September | 77° | 0.1″ | 0 |
| October | 69° | 0.4″ | 1 |
| November | 61° | 0.7″ | 2 |
| December | 56° | 1.4″ | 3 |
Regional context
Rialto belongs to a hot-summer Mediterranean climate region, a group that shares comparable temperature ranges, seasonal patterns, and growing conditions with neighboring cities.
Similar climates: Los Angeles, CA, San Francisco, CA, San Diego, CA, Riverside, CA, Sacramento, CA.
Naturalist notes
By late May, western fence lizards are emerging for longer periods on sun-warmed boulders and retaining walls across the inland basin, timing their activity to the days when afternoon soil surfaces reliably exceed 75°F.
Toland's night-blooming cereus, a native cactus of the inland foothills, opens its large white flowers for a single night in mid-to-late June, an event that typically coincides with the first sustained heat of summer.
Frequently asked
- When does it freeze in Rialto?
- Rialto's last spring frost typically falls around mid-March, and the first fall frost arrives around mid-December.
- What is the rainy season in Rialto?
- February is the wettest month with about 2.5 inches of rain on average; the city receives roughly 10 inches annually.
- What is the warmest month in Rialto?
- August is typically the warmest month, averaging about 81°F.
- What is the coldest month in Rialto?
- December is typically the coldest month, averaging about 56°F.
- When can I start a vegetable garden in Rialto?
- Cool-season crops like peas and lettuce can be sown around the last spring frost in mid-March; warm-season crops such as tomatoes and peppers should wait until 1–2 weeks after.
- How many rainy days does Rialto get?
- Rialto averages about 19 rainy days per year.
- What hardiness zone is Rialto?
- Rialto's USDA hardiness zone is based on the lowest average winter temperature; check the USDA's online lookup using the city ZIP code for the current zone designation.
Climate
Rialto, California has a hot-summer Mediterranean climate. Average January temperatures sit near 56°F while July averages 80°F — a 23°F swing between seasons.
Total precipitation comes to about 10 inches per year, spread across roughly 19 rainy days.
Latitude at 34.1°N, nearby water bodies, and local elevation all set the rhythm of the year. These factors shape the growing season, the likelihood of frost, and the daily weather pattern.