The first arriving firefighters had trouble finding the Marshall Fire

Within hours it burned more than 6,000 acres and nearly 1,000 structures southeast of Boulder, Colorado

FEDEX truck blown over by wind -- Marshall Fire
FEDEX truck blown over by wind, with the Marshall Fire in the distance. Photo by Alyssa Lundgren, Dec. 30, 2021.

It seems hard to believe, but the the first firefighters and a sheriff’s deputy dispatched to the Marshall Fire southeast of Boulder, Colorado could not immediately find it. On December 30 they arrived four minutes after being dispatched at about 11 a.m. to a report of smoke and a downed power line, according to a time line compiled by Colorado Public Radio, but they did not see smoke or flames until 11 minutes after they were at the reported location.

They may have been distracted at first by what they thought was a downed power line on Marshall Road. They told the dispatcher the line is “hanging down low enough that it can touch a vehicle or trucks and people are attempting to go underneath it.” Later they found out that it was a telecommunications line that did not pose any fire danger, but apparently it was a physical hazard for motorists.

To see all articles on Wildfire Today about the Marshall Fire, including the most recent, click here,

It is possible that the 11-minute delay in finding the fire was due the reported location being incorrect. Or the fire was small and light fuel such as short grass was burning which did not produce a great deal of smoke and may have been kept low to the ground by the very strong wind. Later the blaze moved into heavier fuel, and in spite of the wind produced a convection column topped by condensation.

Fire south of Boulder, CO
Marshall Fire south of Boulder, CO. Posted Thursday at 12:26 p.m. MST by County Commissioner Claire Levy.

During the hour before it started, firefighters were sent to two other vegetation fires which were north of Boulder. Even with the very strong winds firefighters were able to stop both before they grew large.

These incidents may have reduced the number of fire resources that were available when the Marshall fire took off, spreading very rapidly pushed by winds gusting at 60 to more than 100 mph hour depending on the location.

Before the fires started a great deal of dust was being kicked up by the wind, then it became a mix of smoke and dust. Check out the dust blowing in this video with the fire in the background:

The wind was not predicted very far in advance for the Boulder area and there was no Red Flag Warning in effect. At 3 a.m. on December 30, about 8 hours before the Marshal Fire started, the forecasting data and models started to become clear — the wind would move from the mountains into the areas northwest of Denver. An existing wind warning was revised.


“It wasn’t a slam dunk high wind event,” said Jennifer Stark, meteorologist in charge at the Boulder office. “But ingredients were really coming together, and once we saw the latest model runs that forecaster on the midnight shift, put out that warning. And we were expecting wind gusts up around 90 miles an hour.”

Before the day was over winds would gust up to 115 mph at one location.

The warning, however, was not technically a “red flag” warning, which is specific to fire danger, and requires three elements: strong winds, cured fuels and relative humidities less than 15% for three hours or longer.

“So we had two of the ingredients,” said Stark. “We had the fuels that were cured and dry, and we had the very strong winds, but the relative humidities were actually a forecast to be in the lower 20 percents. So we did not go with the red flag warning.”

The lack of a red flag warning was a surprise to Philip Higuera, Professor of Fire Ecology at the University of Montana, Missoula, who is currently a visiting fellow at CU Boulder. He said there should be objective criteria for red flag warnings, but it should be revisited in an era of climate change.

“One of the things that we’re seeing broadly in the fire world is that the systems that we have in place are largely developed based on our past experiences,” said Higuera. “We’re increasingly seeing examples where those systems are either less applicable or no longer applicable under the conditions we’re experiencing now, in a world that’s changing rapidly.”

Still, the warning that was issued discussed the danger of a possible fire spreading rapidly, given months of drought in the region combined with the winds.

It is easy to say after the event, but wildland firefighters know that the three major factors that affect the spread of a fire are weather, fuels, and topography. Wildfires generally do not suddenly become rapidly spreading unless very strong winds are present, and they can make up for less than extreme fuel and topography.

The lengthy drought and much less than average precipitation on the Front Range of Colorado in October, November, and December helped set the stage. At 1:30 p.m. on Dec. 30 the relative humidity near Superior where much of the destruction occurred was low, 24 percent, and the temperature was 44 degrees. The extreme wind was able to overwhelm the factors of low but not extreme RH, a temperature generally not associated with fire storms, light to medium vegetation, and benign topography. The 991 structures that burned added a great deal to the fuel load. As buildings were consumed, radiant and convective heat ignited houses that in some places were only 10 to 20 feet apart, while burning embers blown by the wind lit spot fires far ahead in the home ignition zones, on structures, leaf-filled gutters, and vents, as well as bone dry lawns and mulch beds which in some cases spread to and ignited the homes.

The Boulder Office of Emergency Management declined to release to CPR a recording of the initial phone call reporting the fire.

Unlike most states, in Colorado county sheriffs have statutory responsibility to coordinate wildland fire response within their county. Sheriff Joe Pelle said his investigation had not found a power line near the point of origin. At least one search warrant has been served on a compound in that area where investigators have been seen.

The final determination of the cause is going to be huge. That, combined with snow covering the point of origin is part of the reason the investigators are taking their time, being careful and meticulous. Many of the nearly 1,000 structures destroyed are valued at $600,000 to $800,000 so regardless of what is found attorneys will no doubt file law suits.

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Author: Bill Gabbert

After working full time in wildland fire for 33 years, he continues to learn, and strives to be a Student of Fire.

10 thoughts on “The first arriving firefighters had trouble finding the Marshall Fire”

  1. Would it have made a difference if there had been a red flag warning? Probably not since it wasn’t “fire season” and they weren’t geared for fire. However, extreme wind can override relatively low temps and higher relative humidity. Case in point, the 2016 Rocky Top 2 fire in Tennessee in late November that burned 2000 homes in Gatlinburg and killed 14 people. Temps were around 60 degrees and RH was about 50% with hurricane force winds. In that case a Red Flag Warning was issued; there were numerous other large fires at the time. So Red Flags probably need different criteria for shoulder seasons versus traditional fire seasons, especially when extreme winds are forecast. Continual learning for us mere mortals!

  2. You mentioned in the article that there were two other fires before the Marshall fire just north of Boulder.
    What were the causes of those two fires?
    Secondly how were they able to extinguish them when they were dealing with the same conditions as with the Marshall fire?

  3. I do want to point out how important it is to build a good relationship, and communicate often, with one’s local National Weather Service office. I have had meteorologists reach out to me and/or my staff on those days when the official indices didn’t quite meet the Red Flag Warning or Fire Weather Watch criteria to have a discussion on what that all really meant for us firefighters. And we’ve reached out to them when things didn’t seem to “make sense” so we could have a discussion and decide what our next steps were. I would dare say that winds that high would negate the humidity being “only” in the low 20s. Regardless, a Special Fire Weather Statement is always an option.

  4. Contrary to what our intuition might tell us, fire spread rate is not very sensitive to air temperature. It IS very sensitive to the amount of moisture in the air, or more directly, the amount of moisture in the fuel. The fire spreads faster or slower depending on how much moisture must be heated and evaporated off in the fuel.

    As an example, I ran a standard fire spread model (BehavePlus which runs Rothermel’s spread model) comparing a warm day (80 F) and a cool day (44 F), with everything else being equal (RH 24%, short grass fuel, January 30th, time 13:30). On the warm day the fire is predicted to spread at 3.38 mph. On the cool day the fire spreads at 3.03 mph. So there is not much difference. It turns out that in both conditions, the amount of moisture in the fuel is about the same (6% moisture content on the warm day and 7% on the cool day).

    One last comment. Many of the news articles I’ve seen mention, and sometimes even focus on the point that this area is in an extreme drought and drought was one of the causal factors for this fire. I disagree. I believe the fire was spreading through mostly light grassy fuels (and then from house-to-house spread and spotting), and these light fuels are probably always dead and cured at this time of year. The dead fine fuels dry (and moisten) quickly with changes in weather. In fact, in fire behavior lingo they are called “1 hour” and “10 hour” fuels because these names indicate about how long it takes to dry them out given a change in the weather. So I would content it doesn’t matter that there is a months long drought or not in this case, what mattered was that the air at the time was dry, which meant the fine fuels were dry. So the combination of somewhat dry air, dead grass, and 100+ mph winds is all it takes for this event to occur. Extreme drought is not required. In other heavier fuel types that dry much slower (timber litter, large downed dead fuels, live fuels like shrubs), drought can be very important.

    1. Great points, and so important to get them into “common knowledge”. These conditions were set by the prior 2 weeks of December, not the driest ever recent 6 months. That is, it could happen again in a normal year, even a wet year, following a couple weeks of warm, dry, winter landscape.

      Does that mean building standards are wrong? Does sprawl need larger fire breaks? This fire skipped over the 6-lane US 36 like it wasn’t even there.

    2. I am curious about the classification of the structures. 1000 hour fuel? If this is operative a drought would have a profound affect on the propogation of the fire.

      Do structures behave and react to moisture and are they classed as fuel? They should be.

      1. Mike, that’s a great question, something I was also pondering. Here are a few of my thoughts:
        – From a wildland fire spread perspective, I don’t think we have much scientific information on fire spread through only “large fuel” beds. Most all of the fuel types that have been studied scientifically have had some fine fuels (really they are mostly or completely comprised of fine fuels). Moisture content is very important in fine fuel fire spread, but it’s not totally clear how important it would be in only-large-fuel fire spread. The Missoula Fire Sciences Laboratory actually just built a new test facility to examine burning effects of large fuels (energy release rate as a function of moisture, loading, packing, etc.) but, unfortunately this facility isn’t ideal for looking at spread rate in large fuels.
        – There is a really big difference in the intensity and duration of a burning house compared to a fire spreading through wildland fuels. Orders of magnitude when it come to duration. This would likely have big implications on how a nearby unburned house heats up, drives off existing moisture, and ignites. Possibly the moisture content would be insignificant. But it’s hard to say right now.
        – A good scientific investigation into house-to-house spread should be done. At least some work has been done in the past in the building fire research fields and for mass fire events such as dropping of nuclear bombs on cities. This could have implications for WUI and urban building codes.

  5. Hi Bill,

    You just reported: “The warning, however, was not technically a “red flag” warning, which is specific to fire danger, and requires three elements: strong winds, cured fuels and relative humidities less than 15% for three hours or longer.”

    I like to quote words of wisdom. Lewis Elxevair, the publisher of Galileo’s famous book wrote a preface to the reader of this 1638 book as translated by Crew and de Salvio (and published in 1914 and it seems seldom read) which was: “Intuitive knowledge keeps pace with accurate definition.” Another book for which I have evidence that has evidence, has been seldom read is ‘Louis Agassiz As A Teacher’ by Lane Cooper. If one reads this book it it not hard to see the one of the facts that a couple of his students learned from their assignment was: “The most obvious is most difficult to SEE!” (Jerry L Krause). I credit myself for this simple quote because you will not find it directly stated in Cooper’s book.

    Now, relatiive, to your report there are two terms (words maybe): HUMIDITY AND RELATIVE HUMIDITY. And relative to “relative humidities less than 15% for three hours or longer.” it is the HUMIDITY which is the critical issue and not the RELATIVE HUMIDIITY.

    A standard definition of HUMIDITY is: “A general term that refers to the air’s water vapor content.” and of RELATIVE HUMIDITY is: “The ratio of the amount of water vapor in the air compared the amount required for saturation (at a particular temperature and pressure).” (‘Meteorology Today’ 9th Ed. by C. Donald Ahrens)

    And I, a physical chemist, assure you that the HUMiDITY of the air in the summer-fall at 80F at 15% RELATIVE HUMIDITY is significantly GREATER than the HUMIDITY of the air in the winter at 32F and at a 24% RELATIVE HUMIDITY.

    Please point this comment out to Jennifer Stark!!!

    Have a good day, Jerry

  6. Doesn’t surprise me at all. The fire had lots of wind on it, smoke was laying on the ground, and the fire was already doing the weird things wind driven fires do such as sheeting, spotting far ahead, and making hard runs. Throw in terrain, dust, etc., and it can get hard to find the thing real fast. With this kind of event all that can be done is to get ahead of it and start getting folks out of the way. The plan to attack this thing went south before the engines even left the barns. Oakland Hills and Paradise are classic examples of wind driven fires and how to attack them – stay out of their way until the wind dies!!!!


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