Weather radar observations of smoke and ash from the most destructive wildfire in Colorado’s history

Wildfire at Cameron Peak, CO, USA by Starry Eyed Creative
Weather & Environment

The Cameron Peak wildfire started on August 13, 2020, in Larimer County west of Fort Collins, Colorado. On December 2, 2020, the United States Forest Service declared the fire 100% contained. In the 112 days it burned, the fire became the largest wildfire in Colorado history, burning a total of 208,913 acres while damaging or destroying 468 structures. According to a Larimer County assessor’s report published in January 2021, the monetary loss due to the fire was estimated to be just over USD 6.3 million. 

Even relatively small amounts of smoke and ash produced by wildfires can be detected by weather radars

The nature and operating characteristics of dual-polarization radars make them especially capable of detecting smoke and ash in a variety of conditions, from clear to cloudy skies, calm to windy conditions, dry to wet, and during the day or at night.

Data collected of the Cameron Peak wildfire and surrounding precipitation from August 14 through August 15, 2020, by a Vaisala WRM200 C-band dual-polarization weather radar. The left panel shows reflectivity, the center panel shows the cross-correlation ratio (or correlation coefficient) between the horizontally and vertically polarized signals, and the right panel shows the classification of the hydrometeors using Vaisala’s HydroClass.

The data presented show the benefit of a weather radar with dual-polarization capability. Although the reflectivity values created by the wildfire smoke and ash are similar to those produced by precipitation, the correlation coefficient provides clear differentiation between the two types of particles. Reflectivity measures the density of particles in the atmosphere. This directly translates to the strength of precipitation and also the thickness of smoke and ash. Correlation coefficient measures the uniformity of the shape of particles in the atmosphere. Falling raindrops are oblate in shape and much more uniform than smoke and ash, which are random in shape and orientation as they fall or drift through the atmosphere. This difference is clearly seen in the correlation coefficient data, where the correlation coefficient values of smoke and ash are systematically lower than those of precipitation. This allows for reliable type discrimination between wildfire smoke and ash and precipitation. Vaisala’s HydroClass uses the correlation coefficient when determining the type of hydrometeor being observed.

These radar observations of wildfire smoke and ash also show the potential for emergency managers, firefighters, pilots of firefighting planes, and residents in nearby areas to have new information about wildfire initiation and behavior, possibly also resulting in improved firefighting and evacuation actions. More specifically, these data could possibly be used in the following ways:

  • Detecting smoke and ash emission to assist in precisely locating a wildfire shortly after it has started.
  • Forecasting evolution of the wildfire, including prevailing wind direction, speed, and impacts of projected growth.
  • Forecasting the depth and location of the smoke and ash to create alerts for air traffic and/or degraded air quality.
  • Forecasting weather conditions above and around the fire for more effective and safer firefighting on the ground and in the air.
  • Improved environmental modeling of fine particulate matter and black carbon for the impacted surrounding areas through better initial state estimation of the current location and concentration levels.

Future studies can be applied to other locations and weather radars, and eventually radar-assisted monitoring of wildfire smoke and ash could potentially save lives and property during future wildfires around the world.

Read more about the topic in the article by Evan Ruzanski in the spring 2021 issue of the Meteorology Technology International magazine.


Image: Cameron Peak wildfire from Lake Loveland, CO, USA by Starry Eyed Creative / Shutterstock.

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