How to Read a Wildfire Smoke Map

The layers below are the ones behind the AirNow Fire and Smoke Map — a joint product of the EPA and the US Forest Service — plus the NOAA satellite analysis and the NOAA smoke model that most commercial smoke maps repackage. Once you can tell a monitor dot from a plume outline from a forecast frame, the confusing cases start to make sense: a gray sky over a green map, or a red map under a blue sky, is usually two layers describing two different altitudes.

Three kinds of dots on the Fire and Smoke Map

The Fire and Smoke Map plots its point data in 3 shapes. Circles are permanent regulatory monitors run by state, local, and tribal air agencies — the same instruments behind AirNow's everyday reporting, updating on a 1-hour cadence. Triangles are temporary monitors, trucked in near active fires for the season. Squares are low-cost sensors — largely PurpleAir units — displayed only after an EPA correction equation adjusts their raw output, which runs high in dense smoke.

All three shapes speak one color language: the fill is the EPA AQI category color, green through maroon. Shape tells you the pedigree of the measurement; color tells you the current reading. A square deserves a little more skepticism than a circle, but a corrected square an eighth of a mile away is often more useful than a regulatory circle across the county.

Smoke plume outlines: the NOAA HMS layer

The gray plume overlays on nearly every smoke map trace back to one source: NOAA's Hazard Mapping System. HMS analysts outline visible smoke by hand from GOES satellite imagery — the GOES-R satellites scan the continental US every 5 minutes — and grade each polygon into one of 3 density classes: light, medium, or heavy.

Because the analysis reads visible imagery, it carries two built-in limits. It sees the smoke column from above with no altitude information, and it can only be drawn where the analyst can see smoke in daylight. A plume outline means smoke is somewhere overhead — not that any of it has reached the ground.

Near-surface vs vertically integrated smoke

Forecast smoke layers mostly come from NOAA's HRRR-Smoke model, which runs on a 3-km grid and publishes two distinct smoke fields. Near-surface smoke estimates concentration about 8 meters above the ground — the air a monitor would actually sample. Vertically integrated smoke sums the entire column of atmosphere above each grid cell.

Those two fields explain the most common smoke-map confusion. A milky, dimmed sky over a Good AQI reading means the integrated field is loaded while the near-surface field stays clean — the plume is riding a few kilometers up. When sinking air or evening mixing brings that smoke down to the surface, the monitor dots catch up with what the sky already showed.

Reading a forecast loop

HRRR-Smoke starts a new run every hour, and a standard run looks 18 hours ahead; the 00, 06, 12, and 18 UTC cycles extend to 48 hours. A forecast loop animates those frames in sequence, so the first thing to check is the timestamp: frame one is the model's estimate of now, and each step is another hour into the future, usually stamped in UTC rather than local time.

The second thing to check is which field the loop is drawing. A dramatic vertically integrated animation can accompany a quiet surface forecast for the same hours. Watching the plume's leading edge against the frame clock — rather than judging by how dark the colors look — is the reliable way to read arrival timing for a given city.

Why the map covers Canada: long-range transport

Smoke maps run continental because plumes are continental. Big boreal fires loft smoke high into the free troposphere, where jet-stream winds carry it far downwind of the flames. During the June 2023 episode, HMS plume tracks stretched more than 1,000 miles from fires in Quebec and Ontario to the US Northeast, and New York City's monitors recorded index values in the 400s.

That geometry is why the Upper Midwest and Great Lakes can sit under thick smoke with no fire within hundreds of miles. On the map, the giveaway is a plume outline detached from any fire icon: the source is off-screen to the north, and the local question becomes whether the transported smoke stays aloft or mixes down.

The map versus your local monitor

When layers disagree, they are usually both right about different things. The plume outline says what a satellite saw overhead; the dots say what ground-level instruments measured in the last hour; the model says where the smoke should be next. For current conditions at street level, the nearest circle or triangle is the anchor, corrected squares fill the gaps between monitors, and the model's near-surface field is the tiebreaker for the hours ahead.

Disagreement itself is information. Outline-without-red-dots means smoke aloft; red-dots-without-outline usually means a local source, a night hour the analyst could not map, or smoke too thin to see against cloud. Reading the layers as one story — overhead, at the surface, and next — is the whole skill.

Check your local air quality

The worst modern AQI days east of the Rockies are wildfire-smoke days, and the transport corridor from the Canadian boreal fires runs across the Upper Midwest and Great Lakes. These metros sit in that path — check the current AQI for each, or look up any US city on the air quality hub:

• Minneapolis, MN air quality — Sits directly under the main transport corridor for Canadian boreal wildfire smoke.
• Milwaukee, WI air quality — Great Lakes geography puts it in the path of long-range smoke plumes riding the jet stream.
• Chicago, IL air quality — Smoke from Canadian fires regularly settles over the lakefront during summer episodes.
• Detroit, MI air quality — Downwind of both the boreal fire regions and Great Lakes smoke recirculation.
• Duluth, MN air quality — One of the first US metros a southbound Canadian smoke plume reaches.
• New York, NY air quality — Recorded AQI readings in the 400s when the June 2023 Canadian smoke plume arrived.

More air-quality guides

• The AQI Scale, Explained
• Air Quality Alerts, Decoded
• Why Wildfire Smoke Travels 1,000 Miles
• Air quality by city
• Live national forecast map