Today | Weather | Wednesday, March 18, 2026
Active Weather Warnings

Weather in San Marcos, California

07:41 AM
Now
Sunny Weather
66° F
Feels Like 66°
Precipitation 0 %
Wind 4 mph
UV Index (0 - 11+) 1
Humidity 50 %
Today
Cloudy Weather
Day 90°
Night 52°
Precipitation 0 %
Wind 6 mph
UV Index (0 - 11+) 6

San Marcos Weather Forecast Updated

3 minutes ago
Last updated on

Air Quality in San Marcos

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

Pollutant Concentrations:

PM2.5 28.58 µg/m³
PM10 37.68 µg/m³
O3 0.033 ppm
NO2 1.9 ppb
SO2 0.3 ppb
CO 0.20 ppm
NH3 0.08 µg/m³
NO 0.02 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)
PM2.528.58 µg/m³
PM1037.68 µg/m³
O363.9 µg/m³
NO23.57 µg/m³
SO20.87 µg/m³
CO234.11 µg/m³
NH30.08 µg/m³
NO0.02 µg/m³

Weather Alerts and Warnings for San Marcos

Severe Future Likely

Extreme Heat Watch

Extreme Heat Watch issued March 14 at 5:51AM PDT until March 20 at 8:00PM PDT by NWS San Diego CA
Mar 16, 10:00 AM Mar 20, 8:00 PM
WHAT: Dangerously hot conditions with temperatures 85 to 90 near
the coast, up to 105 inland.

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 Monday morning through Friday evening.

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

ADDITIONAL DETAILS: High temperatures next week will be 20 to
potentially 30 degrees above
normal for this time of year, where record breaking heat is likely.
+ 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: Mar 14, 12:05 PM Source: NWS Alert
Moderate Expected Likely

Heat Advisory

Heat Advisory issued March 18 at 2:49AM PDT until March 20 at 8:00PM PDT by NWS San Diego CA
Mar 18, 2:49 AM Mar 20, 8:00 PM
WHAT: High temperatures in the upper 90s to 104 expected.

WHERE: San Diego County Valleys.

WHEN: Until 8 PM PDT Friday.

IMPACTS: Hot temperatures may cause heat illnesses.
+ 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. Take extra precautions when outside. Wear lightweight and loose fitting clothing. Try to limit strenuous activities to early morning or evening. Take action when you see symptoms of heat exhaustion and heat stroke.
Updated: Mar 18, 7:37 AM Source: NWS Alert