A blue-sky forecast can still be a bad-air weekend. In late summer across the West, smoke decides more trips than rain does — and the forecast app that tells you about sunshine says nothing about what you'll be breathing.
At a glance
Check the Air Quality Index (AQI) at your exact destination, not your home town, using FireSmoke.gov or AirNow.gov before you leave. Under 50, go. From 51 to 100, most healthy adults are fine but expect hazy views. From 101 to 150, cut hard effort and keep kids and pets moving slowly. Above 150, reschedule — especially with children, asthma, or heart conditions in your group.
Best for: anyone camping, hiking, or paddling west of the Rockies from July through October.
Key takeaway: AQI is a live number that changes fast. Check it again the night before and the morning of your trip, not just when you plan.
What the AQI numbers actually mean
The AQI runs from 0 to 500, but almost everything you'll see sits under 200. The scale is color-coded, and each band has a real-world meaning:
| AQI | Color | What it means outside |
|---|---|---|
| 0–50 | Green | Clean air. Go. |
| 51–100 | Yellow | Acceptable. Haze possible. Sensitive people watch symptoms. |
| 101–150 | Orange | Unhealthy for sensitive groups. Skip the summit push. |
| 151–200 | Red | Unhealthy for everyone. Easy movement only. |
| 201–300 | Purple | Very unhealthy. Stay inside if you can. |
| 301+ | Maroon | Hazardous. Leave the area. |
The number that matters is PM2.5 — tiny particles from smoke that slip deep into your lungs. That's the pollutant driving nearly every smoke-season reading you'll see on a trailhead sign or weather app.
Where to check before you go
Three free sources cover everything you need:
- AirNow.gov — the EPA's official map. Search any town near your destination and read the current number plus today's forecast.
- FireSmoke.gov — Canadian and US smoke forecasts on one map. Best for seeing where smoke is headed, which matters for multi-day trips.
- NPS and Forest Service alerts — your specific forest or park page lists closures tied to active fires. A green AQI means nothing if the trailhead is evacuated.
Check all three the night before you pack. Smoke can drift hundreds of miles overnight, and a "moderate" reading can turn orange by morning.
How to adjust your plans by band
You rarely have to cancel — most of the time you change what you do.
Green or yellow: normal plans. Pack a N95 mask if fire season is active around you; it costs nothing until you need it.
Orange (101–150): swap the 4,000-foot climb for a flat lakeside loop. Hard breathing pulls particles deeper into your lungs, so effort — not distance — is what to cut. Paddling beats running. Fishing beats scrambling.
Red (151–200): make it a basecamp trip, not a mileage trip. Swim, wade, read in the shade, cook good food. If anyone starts coughing, wheezing, or complaining of a scratchy chest, drive out of the smoke rather than sleeping in it another night.
Purple or worse: go home. No trip is worth a week of recovery.
Special cases
Kids and pets breathe faster, which pulls in more particles per pound of body weight. With young kids in the group, treat orange like red: easy mornings, naps indoors or in the car with recirculated air, and no games that involve sprinting.
Asthma? Bring the inhaler even if you haven't used it in months, and know where the nearest urgent care is before you lose cell signal.
Multi-day routes need an exit plan. Smoke shifts with wind, so before committing to day two, check tomorrow's smoke trajectory map, not just today's dot.
Sources Checked
- AirNow.gov (EPA) — AQI bands and health guidance.
- FireSmoke.ca / FireSmoke.gov — smoke trajectory forecasting.
- US Forest Service and NPS alert pages — fire closures and advisories.