Firefighters battling California’s largest wildfire of the year are preparing for treacherous conditions entering the weekend when thunderstorms could unleash fire-starting lightning and erratic winds that could erode progress made over the past week.
And in Colorado, a wildfire burning in the heavily populated Front Range region has burned dozens of homes and outbuildings, while a second fire crept within a quarter-mile of evacuated homes near Denver.
Dry and hot conditions posed threats across the fire-stricken west, with firefighting crews battling more than a hundred large blazes. Warm temperatures and difficult firefighting conditions have challenged responders across the region.
Acres burned
US wildfires are measured in terms of acres. While the size of a wildfire doesn’t necessarily correlate to its destructive impact, acreage provides a way to understand a fire’s footprint and how quickly it has grown.
There are 2.47 acres in a hectare, and 640 acres in a square mile, but this can be hard to visualise. Here are some easy comparisons: one acre equates to roughly the size of an American football field. London’s Heathrow airport is about 3,000 acres. Manhattan covers roughly 14,600 acres, while Chicago is roughly 150,000 acres, and Los Angeles is roughly 320,000 acres.
Megafire
A megafire is defined by the National Interagency Fire Center as a wildfire that has burned more than 100,000 acres (40,000 hectares). That’s an area about the size of Rhode Island.
Containment level
A wildfire’s containment level indicates how much progress firefighters have made in controlling the fire. Containment is achieved by creating perimeters the fire can’t move across. This is done through methods such as putting fire retardants on the ground, digging trenches, or removing brush and other flammable fuels.
Containment is measured in terms of the percentage of the fire that has been surrounded by these control lines. A wildfire with a low containment level, such as 0% or 5%, is essentially burning out of control. A fire with a high level of containment, such as 90%, isn’t necessarily extinguished but rather has a large protective perimeter and a rate of growth that is under control.
Evacuation orders and warnings
Evacuation warnings and orders are issued by officials when a wildfire is causing imminent danger to people’s life and property. According to the California office of emergency services, an evacuation warning means that it's a good idea to leave an area or get ready to leave soon. An evacuation order means that you should leave the area immediately.
Red flag warning
A red flag warning is a type of forecast issued by the National Weather Service that indicates when weather conditions are likely to spark or spread wildfires. These conditions typically include dryness, low humidity, high winds and heat.
Prescribed burn
A prescribed burn, or a controlled burn, is a fire that is intentionally set under carefully managed conditions in order to improve the health of a landscape. Prescribed burns are carried out by trained experts such as members of the US forest service and indigenous fire practitioners. Prescribed burns help remove flammable vegetation and reduce the risk of larger, more catastrophic blazes, among other benefits.
Prescribed burning was once a common tool among Native American tribes who used “good fire” to improve the land, but was limited for much of the last century by a US government approach based on fire suppression. In recent years, US land managers have returned to embracing the benefits of prescribed burns, and now conduct thousands across the country every year.
In northern California, weather, fuels and terrain are posing growing challenges for the 6,000 firefighters battling the Park fire, which has spread over more than 390,000 acres in the Sierra Nevada foothills.
The fire’s push northward has brought it toward the rugged lava rock landscape surrounding Lassen Volcanic national park, which has been closed due to the threat.
“Lava rocks make for hard and slow work for hand crews,” Cal Fire, the state’s fire agency, said in situation report. “Crews are being flown into access areas that have been hard to reach because of long drive times and steep, rugged terrain.”
After days of benign weather, increasing winds and a surge of monsoonal moisture were expected to increase fire activity and bring a chance of thunderstorms Friday night into Saturday, said Ryan Walbrun, incident meteorologist with the National Weather Service (NWS).
“The concern with thunderstorms is any gusty outflow winds that would push the fire itself or create some new fire ignitions within the vicinity of the Park fire,” Walbrun said.
Collapse of thunderstorm clouds can blow wind in any and all directions, said Jonathan Pangburn, a fire behavior analyst with Cal fire.
“Even if there’s not lightning per se, it is very much a safety-watch-out environment for our firefighters out there,” Pangburn said.
Walbrun said there was little prospect of beneficial rains from the storms and the forecast for next week calls for continued warming and drying.
“As we look forward in time, we’re really just entering the peak of fire season in California,” he said.
In Colorado, a wildfire on the edge of metro Denver crept within a quarter-mile of evacuated homes, but authorities said Thursday they were hopeful that hundreds of threatened residences could be saved despite sweltering temperatures and firefighters suffering heat exhaustion.
The Quarry fire south-west of the Denver suburb of Littleton encroached on several large subdivisions. Neighborhoods with nearly 600 homes were ordered to evacuate after the fire spread quickly Tuesday afternoon and overnight when relatively few firefighters were yet on the scene.
Jim and Meg Lutes watched from an overlook near their house north-east of the fire as smoke plumed up from the ridges. Their community west of Littleton was not yet under evacuation orders, but the couple had been ready to start packing a day earlier when flames could be seen blanketing the mountains.
“It can come over that hill pretty quick if the wind changes,” said Jim Lutes, 64, pointing to a nearby ridge.
Five firefighters were injured Wednesday, including four who had heat exhaustion, said Mark Techmeyer, a spokesperson with the Jefferson county sheriff’s office.
Miles to the north near the city of Lyons, officials lifted some evacuations and reported making progress on the Stone Canyon fire. That blaze has killed one person and destroyed five houses. The cause was under investigation.
New, large fires were reported in Idaho, south-eastern Montana and north Texas.
Scientists say extreme wildfires are becoming more common and destructive in the US West and others parts of the world as climate change warms the planet and droughts become more severe.
Weeks of intense heat have parched the landscape, leaving it vulnerable to sudden ignitions. Scientists have also pointed at the heat as among the reasons why fires like the Park fire have spread so quickly.
“We’ve got a south wind that’s carrying this and hot dry conditions combined with the amount of fuels [the area] accumulated,” said Don Hankins, a pyrogeographer and Plains Miwok fire expert at California State University, Chico.
“A lot of those areas started to dry out early in the season. It’s just a recipe for once you have an ignition, a human caused-ignition, things aligned to create this situation.”
