Colorado faces an urban winter firestorm – whipped up by hurricane winds

Hurricane winds whipped fires over drought-dried grasslands and suburban neighborhoods.

On December 30, 2021, strong winds roared from the west and down the front slopes of the Rocky Mountains. Northwest of Denver peak gusts reached 115 miles (185 kilometers) per hour – the equivalent of a Category 3 hurricane. These winds whipped up intense grass and bushfires and blew them east through a small valley and a road to the cities of Superior and Louisville . By the end, almost 1,100 houses had been destroyed or damaged, and two people were reported missing.

Unlike many of the mega-fires of recent years – which typically occur in forests and wilderness areas – the Marshall Fire quickly spread in densely populated neighborhoods, evolving from wildfire to urban conflagration.

Tens of thousands of residents were evacuated when flames hit streets and cul-de-sacs. The fire was carried by what climate scientist and resident of Boulder Daniel Swain called “an embers storm”. Blown by hurricane winds, the embers leapt from house to house, burning many inside out, setting trees on fire, igniting commercial buildings, and jumping over a highway.

This natural-colored image was obtained by the Moderate Resolution Imaging Spectroradiometer (MODIS) just hours after the fire started on December 30th. recorded ">NASA‘s Aqua satellite. The plume of smoke, that too visible on the radar, at that time stretched about 100 kilometers over the eastern plains of Colorado. The fire also created its own weather: the rising heat created a depression that drew surface winds from all directions in the direction of the fire.

The next day brought in much-needed moisture when a cold front pulled in and dropped more than 10 inches of snow – which dampened the fire but also made it difficult to respond. On January 2, 2022, nearly 75 percent of the 6,200-acre fire was contained.

Strong winds and wildfires are not uncommon in the Front Range, but a wildfire in December is; the normal fire season lasts from May to September. A recent study found that the increase in extreme fire weather is being driven by decreases in humidity and rising temperatures. In 2021, Colorado saw one unusually warm summer and autumn, along with Record dryness. The warm, dry phase followed unusually wet springwhich reduced forest fires in the summer but fueled vegetation growth, which dried up and provided plenty of tinder for the December fire.

At the time of the fire, eastern Boulder County was extremely dry. Nearby Denver, which usually has 30 inches of snow at this time of year, didn’t see its first winter snowfall until December 10, the newest on record.

NASA Earth Observatory image by Joshua Stevens, using MODIS data from NASA EOSDIS LANCE and GIBS / Worldview.