USA –– Researchers striving to understand the ways wildfires make some of their own weather are looking at clouds from both sides now.
Colorado scientists work to predict ground conditions by learning how heat and smoke radiating from big fires like the more than 52,000-acre High Park fire can affect wind and cloud formation.
With more accurate forecasts, fire managers could better predict fire behavior, deploy assets and protect firefighters, residents and property, said Sher Schranz, research coordinator with Colorado State University’s Cooperative Institute for Research in the Atmosphere.
“It’s been difficult to predict the behavior of the High Park Fire,” Schranz said. “It jumped over the (Poudre) river and the road. That was unexpected early on. This fire has sometimes baffled incident managers.”
The behavior of winds in the complex terrain and conditions of the High Park fire has also at times stumped researchers by not conforming to their models, Schranz said.
Numerical weather prediction models forecasting wind speed, direction, temperature, humidity and visibility for fire managers have greatly improved in the last 10 years, she said, but they still aren’t good enough.
“We need greater resolution in real time,” she, referring to the institute and other collaborators at the NOAA Earth System Research Lab in Boulder. “We need more detailed observations of the atmosphere from the ground up to several thousand feet.”
Fires are fought on the ground a few feet at a time, she said, so knowing what’s generally expected over a few square miles isn’t adequate.
To take the next leap forward, Schranz said, more instrumentation is needed to obtain more data. Several hundred thousand dollars for purchase of mobile atmospheric surface observing systems ( ASOS) and unmanned aircraft would yield better forecasts.
“It’s chump change compared with some projects,” Schranz said. “Right now we don’t have any funding to be at the fire to be in the field.”
The High Park fire is complicated because topography and elevation are highly varied, fire managers have said. The fuels are especially volatile because of dry conditions and beetle-killed trees. And the fire is in the wildland-urban interface. Houses burn differently than trees.
The High Park fire is also a crown fire jumping through the air, throwing firebrands at treetops and rooftops.
“We don’t know how to predict the effects of all these factors,” Schranz said. “We don’t know why one house is left standing with the forest burned all around it. We don’t know why another house burns down but the trees around it are spared.”
National Weather Service meteorologist Kyle Fredin said when scientists talk of wildfires creating their own weather, they mean weather on a very small scale.
“A fire can create stronger winds in the immediate vicinity slightly stronger than the prevailing winds, and more erratic,” he said. “Fires can drive themselves. If they have fuel and space they can run faster than the prevailing wind. But it’s predominantly directed and influenced by general weather patterns.”
Yet research has just begun on how large smoke plumes affect clouds hundreds of miles from the flames that made them, Schranz said.
“We have satellite pictures from the California fires that show that no high clouds formed above the smoke plume. We don’t know why not,” Schranz said. “But when there’s a large fire with smoke plume that hangs about in the atmosphere you get some shading of the surface or something else that inhibits natural cloud formation.”
Another cloud phenomenon associated with forest fires and volcanic eruptions is the pyrocumulus cloud. Intense heating of air from the surface induces convection, which causes an air mass to rise above the fire and, in the presence of moisture, can induce formation of this cloud.
A pyrocumulus can contain severe turbulence, which can result in strong gusts at the surface. The cloud can produce lightning and even rain, but Fredin said it’s rare to get a thunderstorm out of it.
“(Pyrocumuli) are something else we’d like to figure out,” Schranz said. “We don’t know all the triggers for those. We don’t know now, but might know retrospectively, whether the High Park fire produced a pyrocumulus cloud.”