Today | Weather | Sunday, October 4, 2026
Active Weather Warnings

Weather in Fullerton, California

09:26 AM
Now
Sunny Weather
84° F
Feels Like 84°
Precipitation 0 %
Wind 7 mph
UV Index (0 - 11+) 2
Humidity 34 %
Today
Hot Day
Day 104°
Night 73°
Precipitation 0 %
Wind 7 mph
UV Index (0 - 11+) 5

Fullerton Weather Forecast Updated

Last updated on
Weather Forecast History
Last Year's Weather on This Day (October 4, 2025)
Night

Day

73°

Night

57°

Wind

5 mph

Precipitation

0 %

Air Quality in Fullerton

NOW
69 AQI
Moderate air quality Dominant pollutant: PM2.5

Pollutant Concentrations:

PM2.5 21.09 µg/m³
PM10 35.35 µg/m³
O3 0.039 ppm
NO2 1 ppb
SO2 0.3 ppb
CO 0.18 ppm
NH3 0.08 µg/m³
NO 0.17 µg/m³
PM2.5 – 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)
PM2.5 – 21.09 µg/m³
PM10 – 35.35 µg/m³
O3 – 76.5 µg/m³
NO2 – 1.95 µg/m³
SO2 – 0.88 µg/m³
CO – 204.09 µg/m³
NH3 – 0.08 µg/m³
NO – 0.17 µg/m³

Weather Alerts and Warnings for Fullerton

Severe Future Likely

Extreme Heat Watch

Extreme Heat Watch issued September 30 at 8:47PM PDT until October 7 at 9:00PM PDT by NWS San Diego CA
Oct 2, 10:00 AM → Oct 7, 9:00 PM
WHAT: Dangerously hot conditions with high temperatures on the
hottest days ranging from around 90 near the coast to the upper 90s
to around 105 for the valleys possible. Low temperatures for
coastal areas into the western valleys will warm into the lower to
mid 70s during the weekend with those warm overnight temperatures
continuing for next week.

WHERE: Orange County Coastal Areas, Orange County Inland Areas,
San Bernardino and Riverside County Valleys-The Inland Empire, San
Diego County Coastal Areas, San Diego County Valleys, and Santa Ana
Mountains and Foothills.

WHEN: From Friday morning through Wednesday evening.

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

ADDITIONAL DETAILS: A long-duration heat wave is expected to
develop late this week and continue through much of next week into
the following weekend with Moderate or greater HeatRisk for the
coast and valleys and Major to Extreme HeatRisk for inland coastal
areas into the western valleys.
+ Read More
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 30, 11:16 PM Source: NWS Alert
Severe Expected Likely

Extreme Heat Warning

Extreme Heat Warning issued October 4 at 4:28AM PDT until October 8 at 8:00PM PDT by NWS San Diego CA
Oct 4, 4:28 AM → Oct 8, 8:00 PM
WHAT: Dangerously hot conditions with high temperatures in the mid
90s to 103 and warm nights with low temperatures in the 70s
expected.

WHERE: Orange County Inland Areas.

WHEN: Until 8 PM PDT Thursday.

IMPACTS: Heat related illnesses increase significantly during
extreme heat events.
+ Read More
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: Oct 4, 7:59 AM Source: NWS Alert