Montana Wildfires: What Are the Odds?


Our wildfire season has begun in Western Montana.

On Monday, my nephew took a picture of the Scratch Gravel Hills fire from the driveway of his Helena home.

Do you want to see a wildfire up close and personal? Take your lawn-chair, haul it into the hills, pick a nice spot, sit down….and wait. What are the odds that a wildfire will chase you from your spot?

In attempting to predict when sub-atomic particles would be at given location, Einstein famously said “God doesn’t play dice with the universe.”

While it isn’t quantum physics, predicting when and where wildfires burn IS a daunting task. Scientists at the Missoula’s Fire Sciences Laboratory, have taken up the challenge.

To answer to our “Will it burn?” question, and to answer it for EVERY possible spot where you could set up a lawn-chair, you need to consider a dizzying array of variables. What are the fuels at and around your location? What is their moisture content? When, where, and in what type of terrain did the fire start? What was the weather before and during the fire? How fast will it spread? Will suppression efforts stop it before it reaches you and your lawn chair?

While he found it unsettling, even Einstein had to settle for a “roll of the dice” answer his particle location question. At best, he was only able to calculate the probability that it would be in a specific location.

The Fire Lab research team has embraced the “playing dice” approach to wildfire simulation. Using scientifically accepted “Monte Carlo” methods,

The result is this national map displaying relative burn probabilities across the nation. Zooming into western Montana gets us one step closer to the answer to our “burning” questions.they feed a computer model (called FSIM) a mix of random and defined variables to simulate 10,000 to 50,000 years of fire “seasons”.

Interestingly, if you pick up and haul your chair east into a yellow/green timbered spot in the Sapphire range, you could expect an average burn probability of 0.003 – 0.006 (3-6 chances in a 1000).For you and your lawn chair, let’s say you pick a grassy spot on the valley floor, south of Missoula with stunning views of the Bitterroots and Sapphire Mountains. By our map, the simulated burn probability of your spot would be between 0.01 and 0.03 (1-3 chances out of a 100).

Even though we generally associate wildfire with forests, by moving up into the timber you reduced the likelihood of burning. Fires in grass spread and grow large much faster than those in trees.

Regardless of where you sit, you’ll likely have plenty of time to pack up your lawnchair and leave. This is because around 3% of wildfires account for about 95% of all acres burned. Many wildfire ignitions peter out or are suppressed before the burning much area. Translated, the one that burns your cozy spot will very likely be a big one. Chances are you’ll have plenty of time to seeing it (or its smoke!) coming.

Alas, for with wildfire, as with life and dice, there are no guarantees. Even with low burn probabilities, it is possible that under just the right conditions, your favorite spot could burn the very day you unfold that chair!

Still, whether you are a land owner, land manager, fire fighter, or a member of the Montana general public, it’s good to know your odds.

The FSIM large fire simulator computer model was developed at the Missoula Fire Sciences Laboratory. It has seen wide spread use in nationwide wildfire risk assessment. For more information, download a PDF of the FSIM wildfire risk model.

Thanks to Mark Finney, Research Forester and Karen Short, Research Ecologist at the RMRS Fire Sciences Laboratory for your patient introductions to the FSIM computer model. 

Visit the WFAS website for the most recent fire danger rating rear you.

Photos courtesy of USFS.




Mark Vosburgh is a fourth-generation Montanan who has lived in Missoula for 26 years. He’s worked as chemical engineer, backcountry ski guide, and wildfire scientist. He started playing mandolin and attending bluegrass jams a few years and has just started performing with local bands: The Black Mountain Boys, Alley Cats Bluegrass Band, and The Flaming Wheelbarrows. He currently works for the US Forest Service as a scientist in the Fire Science Lab.