Smoke & Air Quality

Forest Fire Smoke Tracker: How to Track Wildfire Smoke Before It Reaches Your Lungs

📅 September 2026 ⏱ 52 min read ✍ US Wildfire Tracker team

A forest fire smoke tracker answers a different question than a fire map: not where the flames are, but where the particles are going. It combines NOAA satellite smoke analysis, HRRR-Smoke model forecasts and ground PM2.5 monitors so you can see haze arriving hours before you smell it.

What is a forest fire smoke tracker?

A forest fire smoke tracker is a map and data view that shows where wildfire smoke currently sits, where it is forecast to move, and what the air quality index reads on the ground beneath it. It answers a downwind question, not a flame-front question.

The distinction matters because smoke and fire live on different scales. A fire perimeter might cover 40,000 acres in one county. The plume from that same fire can shade a quarter of the continent, and the National Oceanic and Atmospheric Administration maps it as a polygon spanning multiple states.

Three independent data streams sit behind any credible forest fire smoke tracker. The first is satellite smoke analysis, in which a NOAA analyst outlines visible plumes in daytime imagery. The second is a numerical smoke forecast model. The third is a network of regulatory air monitors reporting particle concentrations hour by hour.

Each stream is honest about something the others hide. Satellite polygons show plume extent but say nothing about the concentration at your street corner. Ground monitors give you a real number in micrograms per cubic meter but only at their own location. The forecast model fills the gaps in space and time, at the cost of model error.

The plume is not the same thing as the air you breathe

A satellite sees the whole vertical column. NOAA's Hazard Mapping System smoke polygons are drawn from geostationary imagery looking down through the atmosphere, so a plume drawn over Ohio may be riding at 15,000 feet with clean air at street level.

This is the single most common misreading of a forest fire smoke tracker. Sky that looks milky and a sun that turns orange are column signals. Whether your lungs are affected depends on how much of that smoke has mixed down into the boundary layer, which is why the AQI number from a nearby monitor always outranks the polygon.

The reverse error also happens. Smoke can settle overnight into a valley under a temperature inversion when the satellite sees very little, because thin low-level haze against a bright background is hard to classify. The Environmental Protection Agency's guide for public health officials notes that strong inversions can allow smoke to accumulate in an area for days or weeks with little opportunity for clean air to improve conditions.

What a smoke tracker is used for in practice

Households use a forest fire smoke tracker to decide whether to open windows overnight, whether to run a portable air cleaner, and whether a child's soccer practice should move indoors. Those are small decisions that repeat daily through a smoke episode, and getting them right compounds.

Employers with outdoor crews use the same data to schedule work. Several states now require respiratory protection for outdoor workers above defined AQI thresholds, so the tracker becomes a compliance record as well as a planning tool.

Travelers use a forest fire smoke tracker to route around smoke rather than around fire. A closed highway is a fire problem; a highway with quarter-mile visibility in dense haze is a smoke problem, and the two rarely occur in the same county.

Our own live wildfire map approaches this from the fire side first, then layers smoke and air-quality context on top, so that a hotspot you see burning in Idaho and a haze forecast for Denver are visible in one place. If you are new to the underlying fire data, the complete fire tracker guide explains where every incident record comes from.

Why a smoke map differs from a forest fire tracker

A forest fire tracker plots heat: satellite thermal detections, official incident records and containment perimeters. A smoke map plots aerosol: plume polygons, modeled particle concentration and measured PM2.5. They share a cause but almost never share a footprint on any given day.

Consider the geometry. A fire detection from the Visible Infrared Imaging Radiometer Suite resolves to a 375-meter pixel. A smoke polygon from NOAA's Hazard Mapping System can span several degrees of latitude. Putting both layers of a forest fire smoke tracker on one screen at the same zoom is misleading unless you understand which layer you are looking at.

Why the fire and the smoke are usually in different states

Smoke rises on the heat of the fire and then travels with the wind at whatever altitude it reaches. The EPA guide describes this plainly: the intense heat generated by an active wildfire drives smoke high into the air where it remains until it cools and begins to descend.

That descent can happen hundreds of miles downwind. NOAA's Chemical Sciences Laboratory has described a single smoke plume stretching eastward more than 1,000 miles across the United States, which means the community with the worst air on a given day may be nowhere near an active incident.

So the practical workflow is two-sided. Use a wildfire tracker to know which fires are producing the emissions, and use a forest fire smoke tracker to know which of those emissions are heading toward you. Neither one substitutes for the other.

Same-day, same-county exceptions

Close to the fire, the two layers do converge. Carbon monoxide is the clearest example: the EPA notes it is rarely a concern for the general public unless people are in very close proximity to the wildfire, generally within three miles of the fire line and when smoldering fuels are present.

Inside that three-mile band you are dealing with fire behavior, ember cast, road closures and evacuation levels, not air-quality planning. That is a different decision tree, covered in our guide to finding fires near you and acting in the first hour.

Beyond roughly ten miles, almost everything that matters to a household is a particle problem. The particles are what travel, and PM2.5 is the pollutant that public health agencies track through an entire smoke season.

How does NOAA build the smoke map layer?

NOAA builds the smoke map layer inside every forest fire smoke tracker through the Hazard Mapping System, a human-in-the-loop product run by the Satellite Analysis Branch of NOAA's National Environmental Satellite, Data, and Information Service. Analysts inspect daytime imagery from geostationary satellites and hand-draw polygons around visible plumes.

The Hazard Mapping System was first implemented in 2002 in response to high demand for active fire and smoke information over North America, and it remains the reference smoke analysis that most public-facing products redraw. It covers the continent rather than a single state or agency footprint.

Timing is fixed and worth memorizing. Initial active fire detections are typically published by 8:00 AM Eastern Time and updated through the day. The first smoke classification is available between 11:00 AM and 12:00 PM Eastern Time, and a second classification is generally issued between 7:00 PM and 8:00 PM.

Light, medium and heavy: what the density classes mean

Every HMS smoke polygon carries a density attribute. Since a July 2022 update, the density field is expressed as light, medium or heavy, replacing an earlier numeric scale that used the values 5, 16 and 21. Both forms still appear in archived files, so date-check any historical download.

Read the classes as relative optical thickness in the column, not as a health threshold. A heavy polygon over a mountain range with an unmixed atmosphere may produce cleaner surface air than a light polygon sitting over a stagnant valley at dawn.

NOAA is explicit about the limits of the analysis. Smoke mapping can be greatly affected by observation conditions, most often as a result of cloud interference, which can lead to incomplete representation of smoke coverage. If a frontal cloud band is overhead, expect the polygon to be conservative.

Why the satellites underneath matter

The smoke analysis uses daytime imagery from GOES satellites, whose Advanced Baseline Imager scans the conterminous United States every five minutes and the full hemisphere every ten. That cadence is why a plume's growth through a burning afternoon is visible almost in motion.

Fire detections feeding the same system come from a wider sensor mix: GOES at about 2 kilometers, VIIRS aboard Suomi NPP and NOAA-20 at 375 meters, and MODIS on Terra and Aqua at 1 kilometer. NOAA notes that adding the 375-meter VIIRS and 2-kilometer GOES data caused a significant spike in the number of daily fire pixels the system reports.

Detection has a physical floor. NOAA states that traditional algorithms begin to respond to active fires occupying at least 0.01 percent of the pixel footprint, assuming an average fire temperature of at least 800 kelvin, so a fire must have an active area of roughly 100 square meters to be detected by a 1-kilometer pixel.

From column imagery to a public nowcast

Geostationary aerosol data has moved from research into daily warning practice. Shobha Kondragunta, air quality studies lead at NOAA's Center for Satellite Applications and Research, has said that NOAA's geostationary satellite data of fine particulate pollution increasingly are being used in nowcasting mode to provide warnings to the public.

For a reader, that means the smoke polygon shown by a forest fire smoke tracker at noon is not a curiosity. It is the same input that state air agencies use to write the afternoon advisory, and it usually leads the monitor network by several hours when a plume is approaching from upwind.

NOAA also cautions that its fire position information should be used as general guidance and for strategic planning, and that tactical decisions such as activating a firefighting response or evacuation should not be made without other corroborating information. The same caution applies to smoke polygons: they inform, they do not command.

Can a wildfire smoke tracker forecast tomorrow?

A wildfire smoke tracker can forecast roughly one to two days ahead using HRRR-Smoke, NOAA's High-Resolution Rapid Refresh Smoke model. It simulates emissions from detected fires and transports them through a full three-dimensional atmosphere, producing near-surface and column smoke fields.

HRRR-Smoke is a three-dimensional model that allows simulation of mesoscale flows and smoke dispersion over complex terrain, in the boundary layer and aloft, at high spatial resolution over the conterminous United States domain. That terrain sensitivity is the reason it outperforms a simple wind-trajectory guess in the mountain West.

Near-surface smoke versus vertically integrated smoke

HRRR-Smoke publishes two fields that people constantly confuse. Near-surface smoke is fire-emitted fine particulate matter concentration at approximately 8 meters above the ground, expressed in micrograms per cubic meter. That is the field to read for breathing.

Vertically integrated smoke is the simulated total PM2.5 mass within vertical columns over each model grid cell, with columns reaching roughly 25 kilometers above the ground, expressed in milligrams per square meter. That field explains hazy skies, dimmed sun and reduced solar output, and it will look alarming on days when surface air is fine.

A third product on a detailed forest fire smoke tracker, fire radiative power in megawatts, shows where the model believes the energy release is concentrated. It is processed at initialization from FRP detected during the previous 24 hours by VIIRS and MODIS.

How much to trust a smoke forecast

NOAA lists the error sources directly: uncertainties in satellite fire radiative power data and in biomass burning emission estimates affect concentration forecasts, and uncertainties in the weather forecast itself, such as wind speed and direction or mixing layer height, propagate into the smoke field.

Detections can also be missing entirely. NOAA notes that fire detections in the model could be absent due to cloud coverage or infrequent overpass times by polar-orbiting satellites, which means a real fire under a cloud deck contributes nothing to the run.

The National Weather Service office in Medford, Oregon, advises the practical interpretation in its HRRR-Smoke tutorial: no model is perfect, and it is usually best to use it to view trends where smoke is getting worse or better. Read the direction of change, then confirm the level against a monitor.

Ivanka Stajner, deputy director of the Environmental Modeling Center at the National Weather Service, has confirmed the loop closes in operations: NOAA's operational air quality forecast models use satellite observations as input to predict the impact of wildfires on air quality. The satellite view and the forecast view are not competitors.

What is PM2.5 and why does AQI smoke use it?

PM2.5 is fine inhalable particulate matter with diameters generally 2.5 micrometers and smaller, and it is the pollutant that AQI smoke reporting is built around during a fire episode. In wildfire smoke it is the principal air pollutant of concern for public health.

The scale is hard to picture, so the EPA anchors it: the average human hair is about 70 micrometers in diameter, making it 30 times larger than the largest fine particle. Particles that small are not filtered by the nose and throat.

Smoke particles cluster at the small end. The EPA's guide for public health officials states that approximately 90 percent of total particle mass emitted from wildfires consists of fine particles, and that smoke particles tend to be very small, with a size range near the wavelength of visible light at 0.4 to 0.7 micrometers.

That size range is also why smoke looks the way it does on a forest fire smoke tracker and to the naked eye. Particles near the wavelength of visible light efficiently scatter light and impact visibility, which can pose a serious safety risk when smoke crosses roads or affects airports.

What else is in the plume

Smoke from combustion of natural biomass is a complex mixture of particulate matter, carbon dioxide, water vapor, carbon monoxide, hydrocarbons and other organic chemicals, nitrogen oxides and trace minerals. The individual compounds present in smoke number in the thousands.

Two other regulated pollutants matter during smoke events. Carbon monoxide dilutes rapidly and is rarely a public concern beyond about three miles from the fire line. Ozone is not emitted directly but forms in the plume as smoke moves downwind, and can be enhanced when the plume mixes with urban nitrogen oxides.

Susan Anenberg, professor and chair of environmental and occupational health at George Washington University, summarized the risk for NOAA in one sentence: the smoke is a mixture of very small particles and gases that can cause a variety of heart and lung problems when breathed in.

Wildfires that burn into the wildland-urban interface add another variable. The EPA notes that wildfires may consume man-made materials in addition to natural fuels, and that more research is needed to understand potential health impacts of breathing that mixed emission.

Is smoke PM2.5 worse than city PM2.5?

The honest answer from the federal guide is that the scientific evidence does not indicate that particles generated from wildfire smoke are more, or less, toxic than particles emitted from other sources. The practical difference is dose and duration, not intrinsic toxicity.

Urban PM2.5 tends to run at moderate levels year-round. A smoke episode can push the same monitor from single digits to more than 200 micrograms per cubic meter within a day, then hold it there while an inversion caps the valley. That excursion is what drives emergency department visits.

Shantanu Jathar, an associate professor in mechanical engineering at Colorado State University, has framed the trend for NOAA: as more people move into wildland-urban interface regions, the probability of small and large fires increases, making it more likely that human-built structures will burn.

How do I read the AQI smoke scale?

The Air Quality Index converts a pollutant concentration into a single number from 0 upward, split into six color-coded categories. During a smoke episode, PM2.5 is almost always the driving pollutant, so the AQI smoke value you see is a PM2.5 sub-index.

The EPA anchors the scale to law rather than opinion. For each pollutant, an AQI value of 100 generally corresponds to an ambient air concentration that equals the level of the short-term national ambient air quality standard for protection of public health.

The PM2.5 numbers behind the colors

Colors are easy to remember on a forest fire smoke tracker, but the underlying micrograms per cubic meter are what a monitor actually reports. The EPA's technical assistance document for reporting daily air quality publishes the breakpoint table, revised alongside the 2024 particulate matter standards.

An AQI of 500 for PM2.5 corresponds to 325.4 micrograms per cubic meter, and the EPA specifies that values above 500 are calculated with the same equation extended past that concentration. Readings in that range have occurred in western valleys during severe episodes.

For context on the standards themselves, the primary annual PM2.5 standard is 9.0 micrograms per cubic meter as an annual mean averaged over three years, the secondary annual standard is 15.0, and the 24-hour standard is 35 as a 98th percentile averaged over three years.

Why the number changes every hour

Regulatory AQI categories are defined on 24-hour averages, but a smoke plume arrives in minutes. The EPA solves this with the NowCast, an algorithm that relates hourly readings from air quality monitors to the AQI for ozone and particle pollution.

The PM NowCast is a weighted average of the previous 12 hours. When air quality is stable, the hours are weighted more evenly, approaching a 12-hour average; when air quality is variable, the most recent hours are weighted more, approaching a 3-hour average. The weight factor is constrained between 0.5 and 1.

Two of the last three hours of data must be valid for a NowCast calculation. That rule is why a monitor sometimes goes blank on a smoke map: not because the air is clean, but because the instrument has not reported enough recent hours.

Where does a wildfire smoke map get its numbers?

A wildfire smoke map gets its numbers from three tiers of instruments: permanent regulatory monitors run by state, local and tribal agencies, temporary monitors deployed to fire incidents, and low-cost consumer sensors whose readings are mathematically corrected before publication.

The three tiers behind a forest fire smoke tracker differ in accuracy and in siting density. Regulatory monitors are sparse but authoritative. Temporary units appear where a fire is burning. Consumer sensors are dense in suburbs and absent in rangeland, which is why coverage looks patchy in exactly the places smoke often pools.

The correction step is not optional. The EPA states that before sensor data appears on the AirNow Fire and Smoke Map, an EPA scientific correction equation is applied so sensor data can be compared to data from permanent monitors. Raw sensor readings typically overstate smoke concentrations.

Air Resource Advisors and the gaps they fill

When a large fire threatens populated areas, an Air Resource Advisor may be assigned to the incident management team. These specialists produce smoke outlooks, place monitors and translate model output into plain community guidance.

Josh Hall, deputy director of the Air Resource Advisor program, has described the training pipeline: trainee deployments on wildfire incidents are critical steps in becoming an advisor, where trainees get one-on-one mentorship developing skills, producing forecasts, and working with incident management teams and partners.

Instrumentation at incidents has broadened beyond particles. Reports from recent deployments describe devices measuring particulate matter, carbon monoxide and black carbon simultaneously, along with roadway sensors placed to watch for super fog, the combination of smoke and water vapor that can drop visibility to zero.

Why two nearby readings disagree

The EPA acknowledges that monitors in the same area may show different NowCast AQI categories. Smoke is not evenly mixed, terrain channels it, and each instrument averages a slightly different history of hours.

Elevation is the most frequent explanation when a forest fire smoke tracker shows neighboring sites disagreeing. A monitor on a hilltop may sit above a nocturnal inversion while a valley-floor sensor two miles away reads three categories worse. On a forest fire smoke tracker, this looks like an error; it is usually real physics.

The EPA also advises against applying AQI colors to raw real-time sensor readings, especially one-minute values, because health studies do not tell us what a single minute of exposure to a pollutant may mean. Treat one-minute spikes as texture, not as a decision trigger.

Who is most at risk from wildfire smoke?

Federal guidance names a specific set of sensitive groups for particle pollution: people with heart or lung disease, older adults, and children including teenagers. The EPA adds that some minority groups, people with lower incomes and outdoor workers may experience higher exposure that can worsen underlying health conditions.

During a smoke event specifically, the EPA recommends including pregnant people as an at-risk group. The Centers for Disease Control and Prevention lists people with asthma, chronic obstructive pulmonary disease, diabetes, chronic kidney disease or heart disease, plus children, pregnant people and responders.

The CDC's framing is worth keeping in mind when a household argues about whether to cancel a run: wildfire smoke can make anyone sick, but some people have a higher risk of getting sick.

What the 2023 episode measured

The eastern smoke episode of June 2023 produced the clearest recent dataset. A CDC analysis of syndromic surveillance data from 4,317 emergency departments, representing 85 percent of participating facilities, found that asthma-associated emergency department visits were 17 percent higher than expected during the 19 days with wildfire smoke.

Regional detail sharpens the picture. The analysis reported 364 excess asthma visits in the New York and New Jersey region during June 6 to 8 alone, 179 excess visits in the mid-Atlantic region over the same days, and 172 in the Midwest region during June 27 to 29.

Maximum measured concentrations reached 204 micrograms per cubic meter in the New York and New Jersey region, 259 in the mid-Atlantic region and 216 in the Midwest region. Increases in visits occurred most commonly among people aged 18 to 64, followed by ages 5 to 17.

NOAA's own accounting of the same week estimated that more than 86 million people experienced fine particulate pollution above the federal health standard, and that more than 17 million people in cities including New York, Philadelphia and Washington were breathing air in the Very Unhealthy category.

Why smoke reaches beyond the lungs

Effects of particulate matter exposure range from eye and respiratory tract irritation to more serious disorders including reduced lung function, bronchitis, exacerbation of asthma, heart failure and premature death. Short-term exposures of days to weeks are associated with increased risk of premature mortality.

Carbon monoxide behaves differently. It enters the bloodstream through the lungs and reduces oxygen delivery to organs and tissues, and people with cardiovascular disease may experience chest pain or cardiac arrhythmias at lower levels than healthy people would.

Ozone formed downwind adds respiratory load of its own, causing reductions in lung function, airway inflammation, chest pain, coughing, wheezing and shortness of breath, even in healthy people. This is one reason a clear-looking day downwind of a fire can still feel hard to breathe.

Which symptoms signal air quality wildfire smoke harm?

The CDC describes the baseline effect directly: wildfire smoke irritates your eyes, nose, throat and lungs, it can make it hard to breathe, and it can make you cough or wheeze. Those symptoms are the body's early warning that exposure should stop.

Exposure to high concentrations of fine particles can cause persistent cough, phlegm, wheezing and difficulty breathing. Healthy people are not exempt: fine particle exposure can cause respiratory symptoms, transient reductions in lung function and pulmonary inflammation.

Three symptoms deserve separate treatment because federal cautionary language singles them out for people with heart disease. Palpitations, shortness of breath and unusual fatigue may indicate a serious problem, and the EPA advises contacting a health care provider if any of these occur.

A simple symptom-to-action ladder

1. Eyes and throat itch, mild cough: move activity indoors, close windows, reduce exertion, and check the forest fire smoke tracker for the trend over the next six hours.
2. Cough that persists after coming inside, or chest tightness: stop all exertion, use a clean-air room, and if you have asthma follow your asthma action plan and keep quick-relief medicine handy.
3. Wheezing or shortness of breath at rest: treat as an asthma or COPD exacerbation and seek medical advice rather than waiting for the AQI to fall.
4. Palpitations, unusual fatigue or chest pain in anyone with heart disease: contact a health care provider immediately, as federal guidance flags these as possible signs of a serious problem.
5. Any symptom that does not improve after moving to filtered indoor air: seek medical attention, which is the EPA's standing recommendation for everyone once AQI passes 200.

Children need active supervision rather than self-report, whatever a forest fire smoke tracker shows. The school activity guidance notes that even students who do not have asthma could experience coughing, wheezing, difficulty breathing and chest tightness during poor air quality, and that a symptomatic student may need a break, a less intense activity, or to go indoors.

How far can smoke travel on a smoke map?

Smoke on a wildfire smoke map routinely travels hundreds to thousands of miles from its source fire. NOAA's Chemical Sciences Laboratory notes that a major western fire can generate a plume that degrades air quality all the way to the Atlantic Ocean, with single plumes stretching more than 1,000 miles across the country.

Distance is governed by two mechanisms the EPA calls transport and dispersion. Vertical transport is controlled by the buoyancy of the smoke plume and the stability of the atmosphere, while horizontal transport is controlled by wind. The larger the volume of space smoke enters and the farther it travels, the more dispersed and less concentrated it becomes.

Dilution is why the worst air is not always near the fire. Winds can move smoke long distances into communities far from where the wildfire is burning, and smoke impacts close to the fire may actually be lessened when strong convection lofts the plume high above the surface.

The June 2023 case study every smoke reader should know

In early June 2023, smoke from fires in Quebec flowed south into the eastern United States and produced the worst measured smoke episode the region had seen in two decades. Amy Huff, an atmospheric scientist supporting NOAA's Center for Satellite Applications and Research, told NOAA that the last major smoke episode of a similar magnitude that impacted air quality in the eastern US occurred in July 2002, over 20 years ago.

The meteorology was a trap rather than a jet stream. NOAA meteorologist Brian Jackson described the setup as smoke caught "between a large low-pressure system swirling over Maine, an area of high pressure over the center of the U.S., and a stationary front spanning from Minnesota to North Carolina," a combination that was "literally fanning the flames and funneling the smoke southward" (NOAA NESDIS).

The measured outcome was extreme for a region with no nearby fire. NASA reported that the air quality index for PM2.5 in New York City surpassed 175 on June 6, topping the previous record of 167 from 2002, while more than 17 million people in the corridor were in Very Unhealthy air.

Upstate readings went further. AirNow monitors measured PM2.5 above 400 micrograms per cubic meter in Syracuse, New York, the highest on record for that city since routine measurements began in 1999. For comparison, the Hazardous category starts at 225.5 micrograms per cubic meter.

Diurnal cycles: why smoke gets worse at night

Terrain drives a daily rhythm that a forest fire smoke tracker will show as a repeating pattern. As the sun warms mountain slopes, air is heated and rises, carrying smoke and fire upslope with it; after sunlight passes, the terrain cools and the air descends, altering the smoke pattern seen during the day.

Evenings concentrate smoke. In mountain valleys and low-lying areas, temperature inversions in which air near the ground is cooler than air above are common, and the lid effect of an inversion coupled with a drop in wind speed can favor smoke accumulation in valleys close to the fire at night.

This is why many households in the interior West see their highest AQI between roughly 10 PM and 8 AM, then a partial clearing by mid-afternoon. Plan window opening, exercise and commuting around that cycle rather than around the daily headline.

Reading altitude on a smoke tracker

When the satellite polygon says heavy but the monitor says Moderate, the plume is aloft. When the polygon says light but the monitor reads Unhealthy, smoke has mixed to the surface or is being generated locally. The HRRR-Smoke near-surface field, valid at roughly 8 meters above the ground, is the tiebreaker.

Visibility is a useful manual check on any forest fire smoke tracker reading. Because smoke particles scatter light at 0.4 to 0.7 micrometers, a sharp drop in visible range at ground level is direct evidence that particles are near you rather than five kilometers overhead.

Sun color is a weaker check. A red sun can result from smoke in a layer far above the boundary layer, which is precisely the condition under which surface air can remain acceptable. Do not cancel an outdoor plan on sun color alone; check a number.

How do I use a forest fire smoke tracker daily?

A forest fire smoke tracker is most useful as a five-minute morning routine rather than an emergency reflex. The sequence is fixed: check the current index, check the trend, check upwind fires, then set the day's three decisions on windows, exercise and filtration.

Reading a forest fire smoke tracker in that order matters because each step constrains the next. A Moderate reading with a heavy plume approaching from the northwest calls for different choices than the same reading with a clearing trend behind a front.

1. Read the current AQI at the nearest monitor and note which category it falls in. Write down the actual micrograms per cubic meter if the tracker shows it, because category boundaries hide large ranges.
2. Compare with the same reading from the previous evening. A rise of more than one category overnight almost always means an inversion or a new plume arrival, not a data error.
3. Look at the smoke polygon and the near-surface smoke forecast for the next 12 hours. Note whether the plume edge is advancing toward you or retreating.
4. Open a live fire map and identify which upwind incidents are producing the smoke. Check acres, containment percentage and the last satellite heat timestamp for each one.
5. Set the day: decide whether windows stay closed, whether outdoor exercise happens and at what time, and whether the portable air cleaner runs continuously.
6. Re-check in the late afternoon. Mixing height collapses around sunset, which is when a stable day can turn into an unhealthy night.

The three decisions that actually change your exposure

Ventilation is the largest lever a forest fire smoke tracker can inform in most homes. In a lightly built house, outdoor particles infiltrate readily, so the difference between an open and closed window during a plume passage can be several tens of micrograms per cubic meter in the bedroom.

Exertion is the second lever. Breathing harder pulls more particles deeper, which is why federal guidance for every category above Good is written in terms of shortening and softening activity rather than simply avoiding the outdoors.

Filtration is the third. A portable air cleaner sized for the room, or a central system running on a high-efficiency filter with the fan set to On rather than Auto, can hold a bedroom well below outdoor levels through a multi-day episode.

Keeping the fire side and smoke side in one workflow

Smoke without a known source is hard to forecast informally, even with a good forest fire smoke tracker. If you can name the two or three fires upwind, you can reason about whether tomorrow is likely to be better: a fire at 60 percent containment with shrinking daily growth usually produces a declining plume.

Our extension and web map put the incident record, satellite heat timestamps and perimeter age next to each detection, so the source side of the question is answerable in seconds. The layer-by-layer fire tracker map guide walks through each of those symbols in detail.

For a national overview during a busy week, the roundup of current wildfires across the country is a faster way to see which regions are generating the season's emissions than scanning a map state by state.

How do I clean indoor air when AQI smoke spikes?

Cleaning indoor air during an AQI smoke spike comes down to four moves: stop outdoor air from entering, filter the air already inside, avoid adding indoor particles, and concentrate effort in one room. The EPA's indoor air guidance is specific about each one.

Sealing comes first, because filtration cannot outrun a wide-open window no matter what a forest fire smoke tracker shows. If your heating and cooling system has a fresh air intake, the EPA advises setting the system to recirculate mode or closing the outdoor intake damper during a smoke event.

Filtration then does the work. The EPA recommends choosing a high-efficiency HVAC filter, such as one with a Minimum Efficiency Reporting Value of MERV 13, or as high a rating as your system fan and filter slot can accommodate, and notes that the filter should fit snugly so air does not leak around it.

The table explains why MERV 13 is the recommended floor for smoke. Smoke particles sit at roughly 0.4 to 0.7 micrometers, inside the 0.3 to 1.0 micrometer band where MERV 9 to 12 filters remove as little as 20 percent and MERV 13 to 16 filters remove at least 50 percent.

Running the system correctly

A good filter in a fan that is off removes nothing. The EPA advises running the system's fan as often as possible by setting the fan to On instead of Auto, so air passes through the filter continuously rather than only during heating or cooling calls.

Most air conditioners are designed by default to recirculate indoor air, which is what you want during smoke. Window and portable units with a fresh air or vent control need that control set to recirculate; newer central systems with a fresh air intake need the damper closed.

Portable air cleaners supplement rather than replace this. The EPA advises choosing a unit sized for the room and ensuring it does not produce ozone, and notes that commercial air cleaners with a known clean air delivery rate are typically preferred over do-it-yourself designs.

What not to do while sheltering from smoke

Indoor sources stack on top of infiltrated smoke. The EPA's list of activities to avoid during a smoke event is short and specific, and most households violate at least one of them within a day.

1. Do not smoke or vape indoors, which adds fine particles directly to the room you are trying to protect.
2. Do not use gas, propane or wood-burning stoves, including a fireplace, during the episode.
3. Do not fry or broil food; choose cooking methods that do not aerosolize oil.
4. Do not burn candles or incense, a common comfort reflex during power outages that measurably raises indoor PM2.5.
5. Do not vacuum unless you use a vacuum with a HEPA filter, because ordinary vacuums resuspend settled particles.

Building a clean-air room

Concentration beats coverage once a forest fire smoke tracker shows a multi-day episode ahead. The CDC advises setting up a room you can close off from outside air and running a portable air cleaner or filter there to keep that room's air cleaner, and the EPA describes the same approach with windows and doors kept closed.

Choose a room with few windows, an interior wall if possible, and a door that closes tightly. Bedrooms usually win because occupancy is long and unbroken, which is when cumulative exposure is highest.

Size the cleaner to the room, not to the house. A unit rated for 200 square feet running in a 200-square-foot bedroom will hold a low concentration; the same unit in an open-plan living area will not.

Does a DIY box fan beat wildfire smoke indoors?

A do-it-yourself box fan air cleaner does work against wildfire smoke, and EPA laboratory testing has quantified how well. Researchers measured clean air delivery rates for several designs and found the best ones matched or exceeded small commercial units at a fraction of the price.

The EPA's measured results are the most useful numbers in this whole article for a household on a budget. Clean air delivery rate, measured in cubic feet per minute, is the volume of particle-free air a device effectively produces.

The cardboard shroud finding is the single best cost-to-benefit result in the study: EPA reports that a cardboard shroud increases the CADR by 40 percent without any cost change. It is a ring of cardboard taped over the fan's outlet face to reduce recirculation at the blade tips.

Safety rules that are not optional

Fan age is the critical safety variable. The EPA advises using only newer model box fans from 2012 or later, which carry UL or ETL safety markings and thermal cutoffs, and states that none of the scenarios tested posed any observable fire hazards, with the caveat that testing covered only five fan models.

Older fans are a different matter. The EPA's guidance is that if pre-2012 fans are used, they should not be used unattended or while sleeping. That restriction removes most of the benefit, since overnight is when a bedroom cleaner matters most.

Filter maintenance is the second safety and performance rule. EPA testing found DIY air cleaners were almost completely ineffective with dirty filters, highlighting the need for frequent filter replacement. During a heavy episode, inspect the filter every few days.

Choosing between DIY and commercial

EPA researchers found DIY units matched small commercial air cleaners for fine particle reduction but were louder and consumed more power, while lower upfront cost and cheaper replacement filters made them more economical overall.

The practical split is straightforward. Buy a commercial unit with a published clean air delivery rate for the bedroom where someone with asthma sleeps; build DIY units for the additional rooms you cannot afford to equip otherwise.

Build materials in the EPA description are a 20-by-20-inch box fan with a UL or ETL mark and a 20-by-20-inch filter, 1 inch or 4 inches thick, at a suggested MERV 13 rating. Designs using two to five filters are recommended for larger spaces.

Do N95 masks work against wildfire smoke?

A NIOSH-approved N95 respirator does work against wildfire smoke particles when it seals to the face. Cloth masks, surgical masks and single-strap dust masks do not, because they neither filter fine particles adequately nor seal against leakage.

The filtration numbers explain the naming. The EPA guide states that the numbers 95 and 100 on a respirator facepiece indicate the filter material captures 95 percent or 99.97 percent of particles passing through it when tested using 0.3-micron particles, which are the hardest to capture.

Sealing, not filtration, is the limiting factor for the public. The EPA notes that when used without individual fit testing, there is likely little difference in effectiveness between N95 and P100 respirators, as leakage around the face seal is a more significant factor than filtration efficiency.

How to wear one so it actually helps

Strap placement is the most common error. The EPA instructs positioning the facepiece over the nose and under the chin, with one strap at the back of the neck below the ears and the other at the crown or top of the head above the ears.

Facial hair defeats the seal. The EPA states that a good face seal is not possible if the user has a beard or other excess facial hair where the respirator seals to the face, and that users must be clean-shaven where the respirator touches the skin.

Look for the markings. Respirators must be certified by NIOSH, and the words NIOSH and either N95 or P100 will be printed on the facepiece by the manufacturer. Discard a disposable respirator when it becomes dirty, wet, deformed, or harder to breathe through.

Children, gases and the limits of a mask

The CDC states that children ages 2 years and older can wear respirators and masks, while noting that NIOSH-approved models typically lack suitable sizing for very young children. A poor fit reduces the intended benefit and increases the chance a child removes it.

Masks address only part of the plume. Disposable N95 or P100 respirators remove particles, not gases or vapors, so the smell of smoke through a properly fitted respirator is expected and does not mean the device has failed.

Treat a respirator as a bridge, not a strategy, and use a forest fire smoke tracker to judge when you need it. It covers the walk to the car, the trip to the store and the outdoor task that cannot wait. Filtered indoor air remains the primary protection for a multi-day episode.

What AQI smoke level should stop school sports?

Federal school guidance ties outdoor activity to the AQI category, not to a single number. At Unhealthy for Sensitive Groups, all outdoor activities should take more breaks and lower intensity; at Unhealthy, all activities move indoors or reschedule.

The guidance opens by protecting the default: regular physical activity, at least 60 minutes each day, promotes health and fitness, and the CDC recommends children get 60 or more minutes of physical activity daily. The goal is to modify activity, not to eliminate it.

Public health guidance layers additional steps above those. The EPA's smoke guide directs full implementation of school activity guidelines at Unhealthy, moving all school activities indoors and canceling physical education and athletic practice at Very Unhealthy, and considering school closures at the Hazardous level.

Why breaks and intensity matter more than a clock

There is no exact number of minutes a student can be outside in unhealthy air. The guidance is explicit that the worse the air quality, the more important it is to take breaks, do less intense activities and watch for symptoms.

The mechanism is respiratory. Students breathe harder when they are active for a longer period or when activity is more intense, and more pollution enters the lungs when a person is breathing harder. Rotating players frequently and walking instead of running are the two practical levers.

Indoor is not automatically clean. The guidance notes that if a building has a forced-air heating or cooling system that filters out particles, indoor particle pollution should be lower and it is fine to keep students moving, but only if the filtration system is properly installed and well maintained.

Students with asthma need a written plan

Every category above Good repeats the same instruction for asthma: follow your asthma action plan and keep quick-relief medicine handy. An asthma action plan is a written plan developed with a student's doctor covering medication, trigger control and how to recognize worsening symptoms.

Air pollution can make asthma symptoms worse and trigger attacks, with symptoms including coughing, wheezing, difficulty breathing and chest tightness. If symptoms do not improve after a break, the school activity guidance is to get medical help rather than to wait out the period.

School closure is a judgment call, not a formula. The EPA notes that indoor air quality in schools may be better than in local housing, making closure less beneficial from a public health perspective, and that newer schools with central air cleaning may be more protective than older, leakier buildings.

How do outdoor workers use a smoke map?

Outdoor workers use a smoke map as a scheduling instrument: check the forecast the night before, set the shift's start time to the cleanest window, stage respirators against a defined AQI threshold, and log the readings that justified each decision.

The exposure profile is unusual. Federal guidance explicitly lists outdoor workers among those who may experience higher exposure that can worsen underlying health conditions, because the workday coincides with heavy exertion and cannot be shortened at will.

Timing beats everything else on a smoke day, which is why crews read a forest fire smoke tracker the night before. In valleys, the overnight inversion often breaks between mid-morning and early afternoon, so shifting heavy labor later can move a crew from Very Unhealthy air into Moderate air without losing hours.

Driving and visibility hazards

Smoke is a road hazard before it is a health hazard for drivers. Because smoke particles scatter light efficiently, visibility loss can pose a serious safety risk when smoke crosses roads or affects airports.

Air Resource Advisor field reports describe super fog, the combination of smoke and water vapor that creates zero visibility, as a monitoring challenge requiring additional roadway sensors. It forms most often at night and near dawn over damp low ground.

If a route crosses a river bottom, a marsh or a burn scar at night during a smoke episode, treat the smoke map's near-surface field as a driving forecast and plan an alternative. Fire perimeters are not the only reason to change a route, which is why the live US wildfire map guide covers road and closure context alongside fire extent.

Pets, livestock and horses

Animals share the same particle physiology, so a forest fire smoke tracker guides their schedule too. Sensitive-group logic applies to older animals and to any animal with heart or lung disease, and exercise is the main controllable variable.

Working dogs and horses breathe far more air per kilogram of body mass during exertion than a person walking, so the practical rule is to reduce or cancel work during Unhealthy air rather than to rely on shortening it.

Livestock in open pasture cannot be filtered. Where possible, provide shade, avoid moving or transporting animals during peak concentrations, and check water frequently, since a smoke episode usually coincides with heat.

How to pair a forest fire tracker with a smoke map

Pairing a forest fire tracker with a smoke map turns two partial views into one causal chain: which fires are emitting, how much heat they are releasing, where the wind is carrying the plume, and what the nearest monitor now reads. Each link answers a question the next one depends on.

Start on the fire side of a forest fire smoke tracker, because emissions drive everything downstream. HRRR-Smoke itself is built this way, ingesting fire radiative power detected during the previous 24 hours by VIIRS and MODIS and using it to estimate biomass burning emissions and plume rise.

Then move to the plume, then to the ground. This ordering also protects you from the most common false alarm, which is a large smoke polygon with no meaningful surface impact.

What the fire side tells you about tomorrow's smoke

Containment percentage is a rough emissions forecast. A fire at low containment with fresh perimeter growth will keep emitting; a fire above 80 percent containment usually produces declining smoke unless interior fuels are still smoldering heavily.

Timestamps on a forest fire smoke tracker matter more than status labels. Our tracker exposes the last NIFC update, the last satellite heat detection and the last GOES heat detection separately for each fire, so you can tell whether an incident that looks quiet is genuinely quiet or simply not recently observed.

Because satellites can miss small or smoldering fires under cloud, a fire with old satellite heat and a recent official update is a different situation from one with fresh heat and a stale record. The guide to what real time means in wildfire data works through those latency cases in detail.

Where our tool fits in the chain

US Wildfire Tracker fuses official NIFC incident records and interagency perimeters, NASA MODIS and VIIRS thermal detections, NOAA Hazard Mapping System GOES heat detections and National Weather Service fire-weather alerts into a single free map, with smoke and air-quality overlays available alongside the fire layers.

Every detection carries a fire probability tier that fuses whether an official NIFC record is linked, how fresh that perimeter is and how recent the satellite heat is. Weak signals below 25 percent probability are hidden by default, and the app warns that hotspots can reflect prescribed burns or industrial heat.

That warning matters for smoke reasoning. NOAA makes the same point about its own feed, noting that some industrial heat sources such as gas flares and steel mills, and highly reflective surfaces such as solar panels, may generate signals similar to fires, though most are filtered during processing.

What can a forest fire smoke tracker not tell you?

A forest fire smoke tracker cannot tell you the exact concentration at your address, cannot see smoke reliably under cloud, cannot forecast a fire's behavior, and is not an emergency notification service. Knowing those four limits keeps the tool useful instead of misleading.

The address problem is a sampling problem. Regulatory monitors are separated by tens of miles in much of the country, and the EPA itself notes that monitors in the same area may show different NowCast AQI categories, so any single value is an estimate for your location.

The cloud problem is optical. NOAA states that smoke mapping can be greatly affected by observation conditions, most often cloud interference, leading to incomplete representation of smoke coverage, and that fire detections can be missing due to cloud cover or infrequent polar-orbiter overpasses.

The forecast horizon is short by design

HRRR-Smoke assumes persistence in forecasting biomass burning emissions and does not simulate fire behavior dependence on weather. A wind event that doubles a fire's size at 3 PM does not appear in a run initialized at noon.

Uncertainty compounds through the chain. NOAA lists uncertainty in satellite fire radiative power, in emission estimates, and in the underlying weather forecast, including wind speed, wind direction and mixing layer height, as all affecting smoke concentration forecasts.

Treat anything beyond 48 hours as climatology rather than forecast. If a large fire is burning upwind in August, the honest planning statement is that smoke is likely at some point this week, not that Thursday will be clear.

What no tracker measures at all

Indoor concentration is invisible to every public forest fire smoke tracker. Outdoor AQI is a poor proxy for a sealed, filtered room, and it is also a poor proxy for a leaky house with an open window. A low-cost indoor sensor is the only way to know.

Personal exposure is likewise unmeasured. Two people in the same neighborhood can differ by a factor of several depending on commute, occupation, exertion and hours spent in filtered air.

Long-term consequences remain an open scientific question. NOAA researchers have said plainly that until scientists unravel the full picture of smoke chemistry, millions of people remain at risk breathing smoke that is not fully understood.

Which wildfire smoke tracker terms should you know?

A wildfire smoke tracker uses vocabulary drawn from three agencies at once, and the same word can mean different things on the fire layer and the smoke layer. This glossary fixes the definitions used throughout this guide.

AQI

The Air Quality Index, EPA's tool for communicating air quality, divided into six color-coded categories from Good to Hazardous.

PM2.5

Fine inhalable particulate matter with diameters generally 2.5 micrometers and smaller; the principal pollutant of concern in wildfire smoke.

NowCast

EPA's algorithm relating hourly monitor readings to the AQI, using a weighted average of the previous 12 hours that shortens toward 3 hours when air quality changes rapidly.

HMS

NOAA's Hazard Mapping System, first implemented in 2002, which publishes analyst-drawn smoke polygons and satellite fire detections over North America.

Smoke density

The HMS polygon attribute expressed as light, medium or heavy, replacing an earlier numeric scale of 5, 16 and 21.

HRRR-Smoke

NOAA's High-Resolution Rapid Refresh Smoke model, run on a 3-kilometer grid with 50 vertical levels and initialized at 00, 06, 12 and 18 UTC.

Near-surface smoke

Modeled fire-emitted PM2.5 concentration at approximately 8 meters above ground, in micrograms per cubic meter.

Vertically integrated smoke

Modeled total PM2.5 mass in a column roughly 25 kilometers deep, in milligrams per square meter; explains haze, not breathing.

FRP

Fire radiative power, the radiant energy release rate of a fire pixel in megawatts; a fill value of -999 means the value is unavailable.

CADR

Clean air delivery rate, the volume of particle-free air an air cleaner effectively delivers, in cubic feet per minute.

MERV

Minimum Efficiency Reporting Value, a filter rating from 1 to 16; MERV 13 or higher is recommended for smoke.

Sensitive groups

For particle pollution: people with heart or lung disease, older adults, and children including teenagers, with pregnant people added during smoke events.

Air Resource Advisor

A specialist assigned to an incident management team to monitor, model and communicate smoke impacts.

Super fog

The combination of smoke and water vapor that can reduce roadway visibility to zero.

NAAQS

National Ambient Air Quality Standards; the primary annual PM2.5 standard is 9.0 micrograms per cubic meter and the 24-hour standard is 35.

Terms that mean different things on each layer

Heavy is the clearest example. On an HMS smoke polygon, heavy is an optical description of the whole column. On a monitor readout, a heavy smoke day means measured surface concentration in the Very Unhealthy range or above.

Active is the second. An active fire on the fire layer means a current incident record or a recent thermal detection. Active smoke on the smoke layer means a polygon drawn during today's analysis, which can outlive the fire that produced it by a day or more.

Clear is the third, and the most dangerous. A clear smoke map at 2 PM says nothing about 2 AM, because the mixing height that keeps daytime air breathable collapses after sunset.

Frequently Asked Questions About Forest Fire Smoke Tracker