A team of researchers with Pyregence have developed a system for predicting when strong upper-air winds will descend to the surface 8 to 10 hours in advance. Strong wind is the environmental factor that is virtually always present during catastrophic wildfire events that destroy hundreds of structures and put thousands of residents at great risk. Fuel conditions, humidity, and topography are also important factors, but few fires become fire storms without strong winds. Predicting the onset of a wind event can affect the deployment of firefighters, the tactics they employ on existing fires, and allow better decisions about preemptive power shutoffs, community warnings, and evacuations.
A device called sodar blasts a very loud 91-decibel pulsing beep into the sky which is then scattered by atmospheric turbulence back to the sodar, allowing profile calculations of wind speed, direction, and height.
Below is an excerpt from an article at Pyregence.org:
Profilers offer distinct advantages over other data collection methods. Most upper-atmosphere weather data is collected using radiosondes, instruments carried aloft, generally by balloon, two times a day. Profilers, by contrast, gather data two or three times every hour, and they also collect more detailed information throughout the lowest levels of the atmosphere—factors that allow for more accurate forecasts.
In 2003, for example, a profiler in New Mexico detected intensifying upper-air winds that had been missed by nearby radiosonde observations. The profiler helped forecasters accurately predict a midnight wind surge, giving fire crews the information they needed to rapidly contain the spread of the fire.
“Sodars have the ability to provide information that you can’t get from other instruments, and that are not available in the surface meteorological network,” says Kenneth Craig, a Senior Atmospheric Scientist and Meteorologist with Sonoma Technology, an environmental consulting firm that conducted the study for Pyregence.
For the Pyregence pilot test, the sodar system collected data from July 25 through October 26, 2020 [north of Santa Rosa in Northern California.]
Although a number of high-wind events occurred at the site during the pilot study period, a Diablo event that developed in late September proved particularly revealing.
Between 3 and 4 p.m. on September 25, strong winds developed 300–600 meters above ground level. Then, just after 1 a.m. that night, surface wind gusts of about 35 mph were recorded. The next day saw a similar pattern: strong winds developed aloft in the mid-afternoon and then gradually descended to the surface around midnight.
Both days, that is, saw high winds develop first in the upper atmosphere and then, about 8–10 hours later, descend to the surface. That time gap offers a window of opportunity to improve wildfire preparedness, especially during active fire situations.
[…]
The Extreme Weather Team concluded that a statewide network of strategically placed upper-air profilers could improve short-term forecasts of surface winds and help scientists who model fire behavior better understand the complex interactions of the atmosphere and wildfire.
How many sodars are needed? Although the scientists who led the study cautioned that they had not conducted a detailed analysis of this issue, they indicated that a relatively small number—perhaps in the range of 10–15 sodars carefully positioned across California—could dramatically improve the ability to predict strong winds.
“You don’t have to blanket every geographic area with instruments—there’s always a balance between the cost and the benefit,” Craig says. “But a handful of strategically placed sodars would fill gaps in our observing network and provide valuable information to support situational awareness and forecasting efforts.”
