Tutorial: Smoke forecasting in Yosemite & the High Sierra

For five of the past eight years, we’ve guided trips in Yosemite or Sequoia-Kings Canyon National Parks in September. Wildfires have occasionally affected us — like with trail closures and hazy air — but we’ve typically found ideal conditions: comfortable days and crisp nights, no bugs, and low backcountry traffic.

September 2020 has presented us with conditions that I’d always feared but that had never materialized. Across the state, multiple large wildfires are burning unconstrained and generating LOTS of smoke, and fall-like weather has not yet arrived with cooler temperatures and meaningful moisture.

How have I determined if we can (or should) run our Yosemite trips this month as scheduled? In this tutorial, I’ll explain my process; the framework can be replicated for your own trip and a different location.

So far, we were able to run two intro-level courses September 11-13, but I cancelled two seven-day trips that were to start on September 14. The fate of upcoming five-day trips on September 21 has not yet been decided.

An obvious decision: When we pulled into Yosemite and saw these conditions, cancelling was undoubtedly the right call.



Decision-making criteria

What are the primary considerations in making a go/no-go decision? I’m looking at:

Land access: Is Yosemite open and is backcountry use permitted? What roads or trails have been closed? What is the status of adjacent lands?Wildfire activity: Do wildfires within or near Yosemite present a safety risk to our groups, like if they grew or jumped a containment line?Air quality: What are current and forecasted particulate levels? How will the smoke be affected by forecasted weather?Trip quality: Can we achieve our trip goals under the current conditions?

If it’s helpful, you can apply “red,” “yellow,” and “green” ratings to these criteria, as I did with Covid conditions. For example, unrestricted use of Yosemite would be “green”; partial road or trail closures in or near Yosemite would be “yellow”; and closure of Yosemite would be “red.”

I make my decision based on my overall assessment, not on some type of number scale. “Red” lights are often deal-breakers, but not always.

A helicopter drops water on a fire in the Middle Fork of the Kings River.



Resources

The media sensationalizes wildfires, like many other things, and it will not provide the information that I need and want. Instead, I rely on:

Land agencies

The National Park Service and US Forest Service websites will have official and updated information about what’s happening within their bounaries.

Yosemite National ParkSequoia-Kings Canyon National ParkInyo National ForestSierra National ForestSequoia National Forest

The National Forests in California are part of the Pacific Southwest Region, which manages eighteen separate units.

Wildfires

For official fire information, use Inciweb, which is an interagency all-risk incident information management system.

To view wildfire locations and their size, I use CalTopo and I turn on the “Fire activity” layer.

Air quality

AirNow.gov provides point-specific air quality ratings and a more helpful interactive map with current and forecasted air quality levels.

What defines an “acceptable” air quality level? It varies by the person, but I’d generally be weary of recreating for any extended period of time when levels are above 150, which is defined as “unhealthy” for all groups.

A second resource is the NOAA HRRR-Smoke map.

Weather

The smoke forecasts are only for the next 24-36 hours. So it’s necessary to look at the weather to predict beyond this.

I rely mostly on the National Weather Service, specifically their point forecasts (like for Tuolumne Meadows at 8,500 feet and for southern Yosemite at 11,600 feet) and also their “Forecast Discussion,” which is a narrative that explains the larger weather patterns at play.

In the weather forecast, I’m paying most attention to:

Temperatures,Precipitation amounts,Wind speed, andWind direction.

Right now, southerly winds are catastrophic for Yosemite, since they will blow smoke from the large Creek Fire directly into the park. North winds are best, but rare; east and west winds are okay.

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