MARSHALL FIRE: What factors contributed to the fatal Colorado fire? | Weather blog

On December 30, 2021, the Marshall Fire ravaged suburban neighborhoods on the west side of the Denver-Boulder metro area. Spread by high winds and fueled by dry conditions, the wildfire killed two people, burned more than 6,000 acres and destroyed more than 1,000 homes, according to news reports.

High winds, even with occasional hurricane-force gusts, are not unusual in this region of the “foothills”, where the eastern prairies meet the Rockies. On the day of the windstorm, air pressure dropped sharply east of the Rockies and strong downdraft winds followed. At the foot of the foothills west of Denver, wind gusts reached 100 miles per hour.

But the winds alone did not explain the destruction. In the months leading up to the forest fire, climatic conditions set the stage for disaster. Spring 2021 brought exceptionally humid conditions, encouraging vigorous plant growth. From June, however, precipitation levels fell below average and remained well below average for the remainder of the year.

Monthly precipitation in 2021 at the weather station in Boulder, Colorado (blue bars) compared to average (white line). Spring is generally wetter than summer and fall in the Rocky Mountain foothills, but last spring was unusually wet and summer and fall were unusually dry. Background photo shows the foothills area as of September 2014. NOAA image, based on data from the NWS Denver-Boulder Forecast Office and photo by Flickr user MikeB, used under a Creative Commons license.

Although snow fell in the Rocky Mountains to the west, the Denver-Boulder area remained dry. Denver recorded its first measurable snowfall of the season – just 0.3 inches – on December 10, 2021. It was the last first snowfall date on record, and after this light snowstorm, dry conditions resumed.

While humidity remained elusive, temperatures remained unusually warm, reaching over 20 degrees Fahrenheit above average in early December 2021 and reaching 10 degrees or more above average on several days during the month. .

Average daily temperatures at the weather station in Boulder, Colorado in 2021 compared to average. December 2021 was not only a little warmer than average. Temperatures were 10 degrees Fahrenheit or warmer than average for half the days of the month. NOAA image, based on data from the NWS Boulder Weather Forecast Office.

Where the wildfire struck – in the southeast corner of Boulder County, Colorado – unusually dry conditions set in in September. By the beginning of October, the dry conditions had turned to drought. At the end of December, the drought conditions were extreme.

This map shows the evolution of the NOAA Evaporation Demand Drought Index (EDDI for short) for two overlapping 6-month periods: July 5 to December 30 versus April 6 to October 3 . the Marshall fire area was at record highs at the end of December 2021 due to the extreme heat and drought of the fall. Image by Mike Hobbins, NOAA / ESRL Physical Sciences Laboratory.

As of January 4, 2022, the cause of the fire was still under investigation, but its origin had been located in an area west of Marshall Lake. Once ignited, the fire spread at a ferocious speed, charging north and east. The hot, dry conditions of the months leading up to the outbreak of the Marshall fire provided the fire with abundant fuel. The winds carried embers through the paved areas, dropping those embers onto parched vegetation that was ready to burn, as well as buildings and vehicles.

Unable to fight the flames amid the hurricane gusts, first responders focused on the evacuation. Residents, diners and buyers were caught off guard, some forced to flee at any time. In addition to seeing and smelling the smoke and flames, residents of the area heard several bangs, potentially resulting from the fire reaching the propane tanks. It wasn’t until the winds slowed late on the evening of December 30 that firefighters were able to begin to put out the flames.

A few days after the fire, two people are still missing and are presumed dead. The tally of damaged houses stood at 149. The tally of burnt houses stood at 1,084. Dozens of businesses were also damaged or destroyed.

In terms of area burned, the Marshall Fire has been eclipsed by many other fires, including the state’s three largest wildfires, all of which struck within weeks of each other in 2020: Cameron Peak, East Troublesome and Pine Gulch. But in terms of lost homes, the Marshall Fire was the most destructive in Colorado history. The Marshall fire did not strike a sparsely populated mountainous region. The fire burned down a densely populated suburban area where most residents had not previously viewed wildfires as a threat.

Beginning on the afternoon of December 31, a day after the fire, heavy snow finally fell in the Denver-Boulder metro area.

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The references

9NEWS. (2021, December 30). Evacuation of Costco due to the Marshall fire. Accessed January 4, 2021.

Colorado Fire Prevention and Control Division. Historical information on forest fires. Accessed January 4, 2022.

Denver7 News. (2021, December 30). Better weather conditions are expected on Friday. [December 31, 2021]. Accessed January 4, 2022.

Denver7 News. (2021, December 10). Denver is celebrating 0.3 inches of snow – its first measurable snowfall of the season. Accessed January 4, 2022.

Fish, S., Paul, J. (2022, January 1). MAP: These are the 991 structures destroyed and 127 damaged in the Marshall fire. Colorado sun. Accessed January 4, 2022.

Flynn, C. (2022, January 6). Nearly 1,100 homes destroyed in the Marshall fire, valued at over $ 500 million. KDVR. Accessed January 6, 2022.

Heberton, B. (2022, January 1). Colorado’s most destructive fire is the result of extreme winds, an expanding forest-urban interface, and a stressed climate. Weather 5280. Accessed January 4, 2022.

National Interagency Fire Center. Map of the area burned by Marshall Fire. Accessed January 4, 2022.

National Meteorological Service. High Winds and Marshall Fire December 30, 2021. Accessed January 4, 2022.

United States Drought Monitor. Accessed January 4, 2022.