Colfax, California Air Quality

An Air Quality Alert is issued by the National Weather Service on behalf of a state or local agency when pollution is expected to reach a level that harms health. An Air Stagnation Advisory means the air will not move enough to clear what is already in it.

None are in force near Colfax right now. All California warnings.

Moderate

Nearest monitor

Colfax, under a mile away (site 060610004)

Index measured

52 · Moderate

Measured at

Mon, 2:00 PM PDT

Fine particles

10 µg/m³

Ozone

47 ppb

Reporting area

Colfax, CA, under a mile away

Reported by

Placer County APCD

Area index

48 · Good

Measured, not modeled. AirNow observations are preliminary until the operating agency certifies them, which happens months later.

Placer County APCD's own forecast for Colfax, written by a forecaster rather than read off a model.

Written by Placer County APCD for Colfax and filed with AirNow.

NOAA’s National Air Quality Forecast Capability, bias-corrected against monitors, for this town’s own coordinate. The worst hour ahead is an index of 60, Moderate, around Tue, 2:00 AM PDT, from the run issued Mon, 5:00 AM PDT. This is a model, not a measurement.

Fine particles in micrograms per cubic meter, ozone in parts per billion as an 8-hour average. The index for each hour is EPA’s: the ozone figure is already the 8-hour average the ozone index is defined on, and the particle figure is run through EPA’s NowCast, which is how an hourly PM2.5 concentration becomes an index.

NOAA’s Hazard Mapping System analysts drew light smoke over Colfax in satellite imagery today (Mon, 5:00 AM PDT to Mon, 8:00 AM PDT). That is smoke seen from above; it is not always smoke at ground level.

NOAA’s model forecasts near-surface smoke peaking at 2.9 µg/m³ around Mon, 6:00 AM PDT.

Smoke on the radar over Colfax

Moderate

Air quality is acceptable. There may be a risk for some people, particularly those who are unusually sensitive to air pollution.

Who is affected

People who are unusually sensitive to ozone or fine particles.

What to do

If you are unusually sensitive, consider making long or intense outdoor activity shorter or easier.

Index range

51 to 100

Category descriptions are the Environmental Protection Agency’s own.

What these numbers are. An index beside a monitor’s name is a measurement, published hourly by AirNow and preliminary until the operating agency certifies it. A category for today or tomorrow is a state or local agency forecaster’s own forecast for a reporting area. An hourly index is NOAA’s air quality model on a five-kilometer grid, not a reading from any instrument. Where a town has no monitor within reach, only the model figures appear, and the page says so.

The nearest towns with a page of their own, closest first.

• Alta Sierra, CA6 miles
• Lake of the Pines, CA7 miles
• Meadow Vista, CA8 miles
• Foresthill, CA9 miles
• Grass Valley, CA10 miles
• Nevada City, CA12 miles
• Auburn Lake Trails, CA13 miles
• North Auburn, CA14 miles

Observations and daily forecasts from AirNow, the US Environmental Protection Agency’s program with NOAA, the National Park Service, NASA, tribal, state and local agencies. Hourly forecasts from NOAA’s National Air Quality Forecast Capability. Smoke analysis from NOAA’s Hazard Mapping System. Alerts from the National Weather Service. Index categories and breakpoints are EPA’s, as revised in 2024.