They describe different quantities
HRRR-Smoke estimates primary fire-emitted fine-particle mass. AirNow AQI is an index based on ambient pollutant observations and official category breakpoints. The reported primary pollutant may be PM2.5, PM10, or ozone, and the NowCast uses multiple recent hours to describe changing conditions.
Smoke Window never converts one into the other. The model panel uses micrograms per cubic meter and a product-defined planning scale; the AirNow panel uses official AQI values, colors, categories, reporting area, observation time, agency, and pollutant.
Location and time rarely match exactly
The model value comes from the approximately 3 kilometer cell containing the selected point. The AirNow reading comes from a nearby reporting area that can be up to 50 miles away in this app. Terrain, wind, and local emissions can differ between those positions.
The forecast frame is valid at one future or current model time, while the preliminary NowCast summarizes multiple recent observations. Compare their timestamps and distance labels before interpreting a difference.
Disagreement can be useful
A higher AQI with low modeled smoke may indicate another pollutant, another PM source, model error, or monitor-location differences. Higher modeled smoke with lower AQI may reflect a forecast plume that has not arrived, elevated smoke, an edge displaced from the monitor, or model overprediction.
Use the two views as complementary evidence. AirNow and official agencies should guide health decisions; the model can help compare possible timing over the next 48 hours.
How a NowCast differs from one monitor hour
AirNow’s NowCast is designed for conditions that can change quickly. It uses multiple recent hours with weighting that responds to variability, so the displayed AQI is not simply the latest instantaneous concentration. Smoke Window shows the reporting time but does not reconstruct the calculation. HRRR, by contrast, supplies a model value valid at one forecast time. A lag between the two products can reflect their time definitions rather than a data error.
Primary pollutant changes the interpretation
A high nearby AQI driven by ozone tells a different story from a high AQI driven by PM2.5. Smoke Window displays the AirNow primary pollutant so users do not automatically blame a fire plume. PM10 can also drive a reporting area. Even PM2.5 is not source-specific: urban emissions, dust chemistry, secondary aerosol, and other combustion can contribute. The smoke model isolates a narrower primary fire-emission quantity.
Distance and terrain between the two points
The selected forecast point and the AirNow reporting-area coordinate can be separated by many miles, elevation changes, or a plume boundary. The interface reports that distance because “nearby” is not “co-located.” A valley monitor may remain smoky while an upland model cell improves, or a coastal station may sit outside an inland plume. Search a closer location when possible and consult local networks if agencies provide more detailed observations.
Four disagreement scenarios
Low model and high AQI can arise from another pollutant, missed emissions, local sources, or spatial error. High model and low AQI can arise before plume arrival, from elevated smoke, monitor placement, or model overprediction. Both high can support a broad smoke concern without proving source. Both low can be reassuring context but still cannot guarantee a person’s exposure. The timestamp, pollutant, distance, and surrounding map help distinguish these scenarios.
Which value should guide which decision
Use the forecast to compare when modeled smoke at the cell may rise or fall. Use AirNow and official local forecasts for category and health guidance. If current observations conflict with an older model during an immediate decision, do not dismiss the observation. If planning tomorrow, the model may reveal a change before a monitor can observe it, but the plan should be checked again near departure. The products are complementary precisely because neither does the other’s job.
Bottom line: modeled smoke vs observed AQI
When the two panels disagree, first assume the comparison needs context—not that one source has failed. Check pollutant, distance, valid time, model lead, and plume position. The model may be early, late, displaced, elevated, or missing emissions; the observation may reflect another pollutant or another place. Their separation is a trust feature: users can see both pieces of evidence and choose official observed guidance for immediate health decisions.
A careful reading of modeled smoke vs observed AQI
Modeled smoke predicts smoke-specific mass at a grid cell and future time. Observed AQI summarizes recent monitored pollutant conditions for a reporting area. Keep that immediate answer attached to the valid time, selected geography, model run, and product limits described above. Those details are part of the result, not fine print, and they should travel with any shared interpretation of this guide.