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 for different locations.

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, ratings can be given to each criteria (“red,” “yellow,” and “green”), 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 aggregate numerical 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.

Land agencies

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

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. CalTopo is also my go-to mapping platform, so I can see both fire activity and my route plan on the same screen.

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 related offering is the Fire & Smoke Map, which integrates multiple sources of data.

A third 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, and
  • Wind direction.

An excellent wind-focused resource is Windy. It also has air quality and fire layers, and forecasting options.

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.

Posted in , on September 16, 2020
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10 Comments

  1. Steve on September 17, 2020 at 3:23 am

    Cal Fire and the USFS have broken their containment efforts for The Creek Fire into two operational zones (north and south), each with its own management team. The Sierra National Forest Facebook page is posting the daily operational briefings from both. Very helpful.

    https://www.facebook.com/watch/SierraNF/

    Unfortunately, the SW winds and a consistently horrible AQI level a have killed my plans for the Ansel Adams Wilderness in coming weeks. Even if Inyo’s closure is lifted, it just isnt happening. I hope your program isn’t similarly derailed.

  2. seano on September 17, 2020 at 1:06 pm

    Between the horrible AQI and all of the California National Forests being closed for some indeterminate time, I’ve pretty much given up on the Sierra for this season, or at least until October. I still periodically check NOAA’s GOES-W satellite imagery (available in CalTopo) and HRRR smoke forecasts, but without much optimism. The Creek and SQF fires are positioned to dump smoke into most of the High Sierra with typical prevailing winds, and firefighters are too busy saving lives to put much effort into containing wildland fires.

    • Andrew Skurka on September 17, 2020 at 1:45 pm

      Sadly, I think your expectation is realistic.

  3. Jamie Compos on September 18, 2020 at 8:22 pm

    Hi Andrew, this was a great idea for a post. I’m familiar with Caltopo and Inciweb (love Caltopo) but everything under your Air Quality subhead is new to me, thanks!

    These resources will be increasingly vital to those of us that want to continue recreating in the West. Maybe all the forests will burn until new life zones take hold?

    (Un)fortunately I think you’ll be able to update and recycle this one for several years to come. 🙂

  4. James Johnston on September 19, 2020 at 4:03 pm

    For checking air quality, I also routinely the Purple Air maps directly: https://www.purpleair.com/map — these offer many additional data points not seen on AirNow. It looks like the fire.airnow.gov map you found has a pilot project to integrate PurpleAir sensor data, but it also looks like they are omitting some of the PurpleAir sensors – airnow.gov shows only 3 Purple Air sensors in my neighborhood, but there are many more on the Purple Air map.

    The AQI values reported by Purple Air on their map are also supposedly more immediate (i.e. real-time); the AirNow values are less so, but are also supposedly more accurate. More discussion here, found via quick 10 second Google: https://www.sfgate.com/news/editorspicks/article/Why-PurpleAir-and-AirNow-show-different-AQI-15514576.php

    AQ-SPEC evaluates low-cost air sensors against the expensive regulatory sensors; you can see which ones are worth trusting http://www.aqmd.gov/aq-spec/evaluations/summary-pm — the outdoor Purple Air sensors appear to be some of the best; I suspect this may be because they are the only one (AFAIK) that have dual sensors.

  5. Jeremy Howard on September 22, 2020 at 10:01 am

    After dancing around from Dusy Basin to Yosemite to Mt Ranier since the 6th, pivot was the name of the game. I’ve been dismissive of smoke in the past but one day on the trails on Sep 9 in Yosemite in 250 ft of visibility and my lungs truly hurt the next morning. Ranier wasn’t much better but the smoke did tend to settle into the valleys at night leaving the higher elevation somewhat clear. Even more shocking was returning to the East Coast and waking up the same orange glow in the morning only to find it traveled clear across the skies. Wishing you some escape in Utah!

  6. bcap on September 23, 2020 at 6:57 am

    Another resource I like is https://worldview.earthdata.nasa.gov/

    The actual data source is the same as many other mapping sites, but the interface is very easy to use and I like how easy it is to step through time. I found it the day the Cameron fire blew up and Boulder got super-smoky. (I wanted to know which fire was causing our AQI problems.) The only downside of the resource is that I spent time looking at Oregon’s fires over the past month and it was depressing to see how much has burned. On one hand, I’m glad I already hiked the PCT and saw much of the terrain. On the other it is sad to think that much of the terrain is now altered for decades.

  7. Ed C. on September 24, 2020 at 1:58 pm

    This rings true to home. A friend and I were scheduled to have a 4 day trip out of Saddlebag lake, up and over the pass into Yosemite to get to Young Lakes.

    Sadly, our permits were cancelled as all national forests in the state were closed. I have a trip planned for Columbus day weekend out of Bridgeport area and I’m hopeful that the forests will open and they will allow cooking. Right now, no open flames (even from stoves) are allowed.

    I’m sure yours were as well. At least many airlines are offering free cancellations now that their business is hurting due to low travel volume. Hopefully your clients were able to get refunds.

    Up until the closures, I was regularly reviewing the CalFires, AirNow, and Forestry websites. That’s in addition to watching local news as we had a pretty large fire in eastern San Diego that was affecting many coworkers and friends.

    As sad as it was to miss a trip, safety is always more important. Assuming this isn’t “THE End” there will be more time for trips.

    Stay safe all.

  8. Sean on September 24, 2020 at 6:10 pm

    I tend to use valleyair.org since I live in Fresno. I also prefer RAAN to AQI since it’s more concrete, showing PM2.5 in ug/m^3 which is a definitive measurement compared to AQI which is an index.

    It only covers the valley but it’s pretty easy to tell generally speaking what the higher elevations are going to be like. We spent 3 weeks with the RAAN at a stage 5 alert, the maximum, with PM 2.5 usually around 150 micrograms (75 is stage 5 alert for *everyone* to stay indoors and minimize physical activity) and frequently as high as 450micrograms per cubic meter. Basically, you’re looking at maybe half a mile visibility, and you will smell like a campfire after being outside for 10 minutes. You will cough and your lungs will hurt.

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