Today | Weather | Wednesday, September 9, 2026

Active Weather Warnings

Weather in Rancho Cucamonga, California

05:49 PM

Now

99° F

Feels Like 97°

Precipitation 7 %

Wind 9 mph

UV Index (0 - 11+) 1

Humidity 29 %

Today

Day 106°

Night 79°

Precipitation 25 %

Wind 5 mph

UV Index (0 - 11+) 8

Warning: High UV Index Today: 8

High risk of harm from unprotected sun exposure. Take precautions: wear a hat, sunglasses, and apply sunscreen regularly if you’ll be outdoors for extended periods.

Rancho Cucamonga Weather Forecast Updated

37 minutes ago

Last updated on September 09, 2026 at 5:12 PM

Weather Forecast History

Last Year's Weather on This Day (September 9, 2025)

Day

82°

Night

61°

Wind

7 mph

Precipitation

25 %

Air Quality in Rancho Cucamonga

NOW

88 AQI

Moderate air quality Dominant pollutant: O₃

Pollutant Concentrations:

PM_2.5 14.43 µg/m³

PM₁₀ 23.75 µg/m³

O₃ 0.066 ppm

NO₂ 1.2 ppb

SO₂ 0.4 ppb

CO 0.15 ppm

NH₃ 0.04 µg/m³

NO 0.14 µg/m³

PM_2.5 – Fine particles <2.5μm

PM₁₀ – Inhalable particles <10μm

O₃ – Ozone

NO₂ – Nitrogen dioxide

SO₂ – Sulfur dioxide

CO – Carbon monoxide

NH₃ – Ammonia

NO – Nitric oxide

Health Recommendations:

Air quality is acceptable; however, for some pollutants, there may be a moderate health concern for a very small number of people who are unusually sensitive to air pollution.

Show raw pollutant concentrations (µg/m³)

PM_2.5 – 14.43 µg/m³

PM₁₀ – 23.75 µg/m³

O₃ – 130.12 µg/m³

NO₂ – 2.18 µg/m³

SO₂ – 1.14 µg/m³

CO – 171.98 µg/m³

NH₃ – 0.04 µg/m³

NO – 0.14 µg/m³

View Hourly Air Quality Forecast

Weather Alerts and Warnings for Rancho Cucamonga

Severe Expected Likely

Extreme Heat Warning

Extreme Heat Warning issued September 9 at 2:25PM PDT until September 10 at 8:00PM PDT by NWS San Diego CA

Sep 9, 2:25 PM → Sep 10, 8:00 PM

WHAT: For the Extreme Heat Warning, dangerously hot conditions
with high temperatures in the upper 90s to 106 on Thursday with
morning low temperatures in the 70s and lower 80s expected.

WHERE: San Bernardino and Riverside County Valleys-The Inland
Empire.

WHEN: Until 8 PM PDT Thursday.

IMPACTS: Heat related illnesses increase significantly during
extreme heat events.

ADDITIONAL DETAILS: Major HeatRisk through today. Moderate to
major HeatRisk on Thursday. Warm overnight temperatures will limit
relief from the heat.

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Drink plenty of fluids, stay in an air-conditioned room, stay out of the sun, and check up on relatives and neighbors. Do not leave young children and pets in unattended vehicles. Car interiors will reach lethal temperatures in a matter of minutes.

Updated: Sep 9, 5:12 PM Source: NWS Alert

Moderate Expected Likely

Heat Advisory

Heat Advisory issued September 9 at 2:58AM PDT until September 10 at 8:00PM PDT by NWS San Diego CA

Sep 9, 8:00 PM → Sep 10, 8:00 PM

WHAT: For the Extreme Heat Warning, dangerously hot conditions
with high temperatures of 104 to 110 with low temperatures in the
70s and lower 80s expected. For the Heat Advisory, high
temperatures in the upper 90s to 105 expected.

WHERE: San Bernardino and Riverside County Valleys-The Inland
Empire.

WHEN: For the Extreme Heat Warning, until 8 PM PDT this evening.
For the Heat Advisory, from 8 PM this evening to 8 PM PDT Thursday.

IMPACTS: Heat related illnesses increase significantly during
extreme heat events.

ADDITIONAL DETAILS: Major HeatRisk through today. Warm overnight
temperatures will limit relief from the heat.