Colorado experienced a winter city fire storm that was blown up by a hurricane

On December 30, 2021, strong winds roared from the west and descended along the front slope of the Rocky Mountains. In the northwest of Denver, peak gusts reach 115 mph (185 km/h)-equivalent to Category 3 hurricanes. These winds created violent grass and bush fires and blew them east along small valleys and highways towards the towns of Superior and Louisville. By the time the fire ended, nearly 1,100 houses were destroyed or damaged, and two others were reported missing.

Unlike many fires that have usually occurred in forests and wastelands in recent years, the Marshall Fire quickly entered densely populated communities and transitioned from wildfires to urban fires.

Tens of thousands of residents were evacuated as flames were blown onto the streets and through the alleys. The fire was called an “amber storm” by climate scientist and Boulder resident Daniel Swain. Under the blow of the hurricane, embers jumped from house to house, burning many houses from the inside out. At the same time, they also burned down trees, lit commercial buildings and jumped onto a highway.

The above natural-color image was acquired by the Moderate Resolution Imaging Spectrometer (MODIS) on the NASA Aqua satellite a few hours after the fire started on December 30. At that time, the plume still visible on the radar extended about 60 miles (100 kilometers) across the eastern plains of Colorado. In addition, the fire also produced its own weather: the rising heat created an area of ​​low pressure that led the surface wind to the fire from all directions.

The next day brought much needed water, because the arrival of the cold front dropped more than 10 inches of snow, which reduced the fire but also complicated the countermeasures. As of January 2, 2022, nearly 75% of the area surrounding the 6,200-acre fire has been controlled.

Strong winds and wildfires are not uncommon in frontline areas, but they are true for December wildfires; the normal fire season lasts from May to September. A recent study found that the increase in extreme fire weather is driven by a decrease in atmospheric humidity and an increase in temperature. In 2021, Colorado experienced an unusually warm summer and autumn, coupled with record dryness. After the warm and dry spell, it was an unusually humid spring, which reduced wildfires throughout the summer but encouraged the growth of vegetation and dried it out, which provided ample fire for the December fire.

At the time of the fire, the eastern part of Boulder County was in an extremely dry state. Nearby Denver usually has 30 inches of snow at this time of the year, but the first winter snowfall was not recorded until December 10, the latest on record.