The Lone Star Fire burning 3 miles south of Old Faithful has continued to grow to just shy of 1,000 acres. Warmer temperatures and gusty winds associated with the approaching cold front led to increased activity Saturday, but that was moderated by a cold front that moved into the area Sunday night. Snow flurries were possible amid cooler, wet conditions on Monday, which was expected to slow the fire and, potentially, the work of the 49 people assigned to the wildfire.

“However,” Yellowstone National Park officials said, “the warming and drying trend predicted for the remainder of the week may cause smoldering areas to respond and pick up again in activity.”

Flames moved slowly into unburned pockets along the fire’s edge throughout Saturday. There were also a number of isolated heat sources outside its perimeter, park officials reported. An infrared flight confirmed the fire had grown to 960 acres.

A progression map shows the fire growing on the north edge, just south of the Lone Star Geyser near the Continental Divide.

A park resource team is focused on mapping sensitive riparian habitat and rare plants. The information will help the incident management team minimize impacts to important natural resources. Trails and campsites in the Shoshone Lake and Lone Star Geyser area are closed. However, the Grand Loop Road between Old Faithful and West Thumb Junction and day use areas reopened on Thursday.

The fire was first reported early evening on Saturday, Aug. 22. It more than doubled in size in the first 24 hours, from 256 acres to 660 acres, but slowed in the following week.

Two additional engines arrived Saturday to support firefighters around key Old Faithful infrastructure. Crews finished the first phase of chipping at the water treatment plant and continued cutting timber around the area’s cellular tower, the park reported.

Work continued Sunday near power lines, a substation, and park cabins. Warmer and drier conditions are expected to return midweek. While managing fires can be complicated and challenging, the basic principles of fire are relatively simple. Fire needs three elements to ignite and continue to burn: oxygen, heat, and fuel, said fire information officer Lori Iverson in a press release.

“Weather is perhaps the most variable factor in the fire behavior triangle, and it can quickly change,” Iverson said. “Fire teams closely monitor forecasts, noting the expected wind speeds and direction, humidity, temperatures, or possible precipitation and thunderstorms.”

Each morning, firefighters read a spot weather forecast for the area specific to where the fire is located, she said. Throughout the day, additional weather is gathered in the field and transmitted via radio to all personnel working on the incident. Crews reply to acknowledge they’ve heard the latest weather reading and are aware of how it may affect the fire’s behavior for the reminder of their day’s shift.