Rancho Cucamonga, California Weather
Coastal fog thickens at dawn. Day 77 of spring. Read this microseason across nine climate regions →
Rancho Cucamonga weather forecast — hour by hour, 7-day outlook, NOAA radar
- TodayJun 4Overcast——89°56°—
- FridayJun 5Foggy——89°58°0°
- SaturdayJun 6Foggy——83°56°-6°
- SundayJun 7Clear——82°61°-1°
- MondayJun 8Partly Cloudy——81°61°-1°
- TuesdayJun 9Overcast——71°59°-10°
- WednesdayJun 10Partly Cloudy——78°56°+7°
Ozone at AQI 142 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 195 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 142 now. With UV 10 peaking around 1 PM under clear skies, surface ozone likely climbs to AQI 195 by mid-afternoon.
- Present
- AQI 142
- UV peak
- 10.3 at 1 PM
- Sky at peak
- clear
- Projected peak
- AQI 195
PM × Wind × Precip
PM2.5 at 20.3 µg/m³, PM10 at 28.7 µg/m³ — typical background levels with no transport signature.
- PM2.5/PM10
- 0.71
- Wind
- breezy
- 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
- 6:04 AM
- Moonset
- 4:13 PM
- In sign
- ♒︎ Aquarius
Coastal fog thickens at dawn
Rancho Cucamonga at a glance
- Today vs. normal: 6°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
August brings Rancho Cucamonga's peak warmth with mean temperatures around 81°F, while December delivers the year's coldest conditions at 56°F. Precipitation follows a Mediterranean pattern, with February receiving the most rainfall at 2.5 inches and June seeing just 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
As part of the broader hot-summer Mediterranean climate region, Rancho Cucamonga shares temperature ranges, seasonal patterns, and growing conditions with surrounding cities in this climate zone.
Similar climates: Los Angeles, CA, San Francisco, CA, San Diego, CA, Riverside, CA, Sacramento, CA.
Naturalist notes
California poppies typically begin their spring bloom in late March as soil temperatures warm.
Allen's hummingbirds start their northward migration through the region during April and May.
Frequently asked
- When does it freeze in Rancho Cucamonga?
- Spring's final frost usually occurs around mid-March in Rancho Cucamonga, while the first fall frost returns around mid-December.
- What is the rainy season in Rancho Cucamonga?
- February brings the heaviest rainfall, averaging 2.5 inches, while the city's total annual precipitation reaches roughly 10 inches.
- What is the warmest month in Rancho Cucamonga?
- August typically records the year's highest temperatures, with averages near 81°F.
- What is the coldest month in Rancho Cucamonga?
- December marks the coldest period, with temperatures averaging around 56°F.
- When can I start a vegetable garden in Rancho Cucamonga?
- Plant cool-season crops like peas and lettuce around the last spring frost in mid-March, but wait 1–2 weeks later for warm-season varieties such as tomatoes and peppers.
- How many rainy days does Rancho Cucamonga get?
- The city experiences approximately 19 rainy days each year.
- What hardiness zone is Rancho Cucamonga?
- For Rancho Cucamonga's current USDA hardiness zone, use the USDA's online lookup tool with the city's ZIP code, as the zone reflects the area's lowest average winter temperatures.
Climate
Rancho Cucamonga, California experiences a hot-summer Mediterranean climate. Winter temperatures in January hover near 56°F, while July brings averages of 80°F — creating a 23°F seasonal swing.
Annual precipitation totals about 10 inches, falling across roughly 19 rainy days throughout the year.
Geography shapes the local weather patterns through three key factors: latitude (34.1°N), proximity to large water bodies, and elevation. These elements determine plant growth cycles, frost timing, and daily weather conditions.