How the forecast is made

1 · Where the numbers come from

Every number on this site starts at NOAA — the US National Oceanic and Atmospheric Administration, the agency behind the National Weather Service. NOAA runs a smoke forecast for the whole country and publishes it free, every hour.

Smoke — National Digital Guidance Database (NDGD). Two fields: smoke near the ground, and total smoke in the air column above you.
Wind — High-Resolution Rapid Refresh (HRRR), 10 metres above ground. This is the blue flow on the map.
Terrain — the contour lines are GFS surface geopotential height, which is the ground the smoke model itself runs on. Not a separate elevation dataset: using a sharper one would draw ridges the forecast does not know about.
Fire locations — National Interagency Fire Center (NIFC). An app feature; not shown on this website.

NOAA GFS 0.25deg HGT:surface, cycle 20260809 18Z, via the NOMADS GRIB filter

2 · How a value is read for one place

The forecast is a grid. Your town almost never sits exactly on a grid point, so the value is interpolated — blended from the four surrounding points, in proportion to how close each one is.

That sounds like a detail and is not. Snapping to the nearest grid point instead can be several kilometres off, and on a smoke map several kilometres is the difference between the edge of a plume and the middle of it. On one measured case during development, snapping read 67.7 against a true value of 53.2; interpolating read 52.4.

3 · How smoke becomes an air quality number

Ground-level smoke is reported as PM2.5 — the mass of fine particles in a cubic metre of air, in micrograms. That unit means nothing to most people, so it is converted to the US Air Quality Index, the 0–500 scale you already see in weather apps, using the EPA's published breakpoint table.

What the number means
AQI	Category	In practice
0–50	Good	Clean air. Nothing to think about.
51–100	Moderate	Fine for most people. Unusually sensitive people may notice it.
101–150	Unhealthy for Sensitive Groups	Children, older adults, and people with asthma or heart conditions should ease off outdoors.
151–200	Unhealthy	Everyone starts to feel it. Limit time outside.
201–300	Very Unhealthy	Stay indoors if you can.
301+	Hazardous	Emergency conditions.

The sky-smoke layer has no AQI, deliberately. There is no health index for smoke high above your head, so inventing one would be misleading. That layer is reported in its own unit and described in plain words — clear, light haze, heavy aloft.

4 · How it is drawn

Colour is amount: dark is clear air, bright orange is heavy smoke, on a single continuous ramp. Because colour alone is unreliable — roughly one man in twelve has some colour vision deficiency — every value on this site is also written out in words and numbers, in the table under each chart.

Blue flow lines are the wind. Contour lines are terrain. Both sit under the smoke, so nothing ever covers the thing you came to look at.

5 · What it cannot do

This is a forecast, in the same sense as a rain forecast. It is good at what is coming and roughly when, and less exact about a precise number at a precise hour. Confidence falls the further ahead you look.

It is not a measurement, and it is not official guidance. For measured readings from monitoring stations and for health advice, use AirNow, which is run by the EPA.

6 · Credits and terms

Forecast data on this site is produced by the National Weather Service and other parts of NOAA, and by the US Environmental Protection Agency. That material is in the public domain and is not subject to copyright. Smaze claims no copyright over it.

Smaze is not affiliated with, and is not endorsed by, NOAA, the National Weather Service, the EPA, NIFC, or any government agency. The forecast is presented here in a reformatted, interpolated and unit-converted form; it is not official government material and should not be treated as such.