Wetter, cooler weather has helped firefighters make progress in their efforts to get the largest wildfire in Washington state's history under control.
With more rain in the forecast, crews worry that moisture could lead to flash floods after so much ground vegetation has been burned away.
The Carlton Complex of fires, which has burned nearly 400 square miles in the north-central part of the state and destroyed 150 homes, was 16 percent contained as of Tuesday, fire spokeswoman Jessica Payne said.
The National Weather Service issued a flash flood watch from Wednesday morning through evening because of expected heavy rainfall.
"It takes as little as 10 minutes of heavy rain to cause flash flooding and debris flows in and below areas affected by wildfires," the advisory said. "Rain runs off almost instantly from burned soils ... causing creeks and drainages to flood at a much faster rate than normal."
Still, the shift in weather was a positive development.
"The cooler weather and the moisture has cooled aspects of the fire down," fire spokeswoman Susan Peterson said Tuesday evening. "In some instances, firefighters were able to do a direct attack.
"We had additional crews come in, and they were able to put lines in closer to the fire itself."
"A lot of it has to do with drought, a lot of it has to do with changing precipitation patterns, and a lot of that has to do with climate change," the president said.
Obama signed an emergency declaration Wednesday because of wildfires burning the past two weeks in the state. The declaration authorizes the Federal Emergency Management Agency and the Department of Homeland Security to coordinate disaster relief and help state and local agencies with equipment and resources.
At more than 250,000 acres, the Carlton Complex is larger than the 1902 Yacolt Burn, which consumed 238,920 acres in southwestern Washington and was the state's largest recorded forest fire, according to HistoryLink.org, an online resource of Washington state history.
The fire is being blamed for one death. Rob Koczewski, 67, died of an apparent heart attack Saturday while he and his wife were hauling water and digging fire lines near their home. Gov. Jay Inslee said Obama called Koczewski's wife to express his condolences.
More than 2,100 firefighters and support crew are involved with fighting the fire, Payne said. She said firefighters have had success with fire lines on the east side of state Highway 153 between Carlton and Twisp.
Karina Shagren, spokeswoman for the state's Military Department, said the National Guard has already been offering aerial support, but 100 National Guard troops were now being used on the ground for firefighting, and additional troops were receiving firefighting training for potential future use.
Inslee briefed Obama on the fire situation after the president arrived in Seattle on Tuesday afternoon at the start of a three-day West Coast trip.
"We have real significant challenges," Inslee said. "To have the president here today is actually a stroke of luck."
Patty Murray and Maria Cantwell were among a dozen U.S. senators who sent a letter to Senate leaders Tuesday asking for passage of emergency legislation to allocate $615 million to fight wildfires.
Fires are burning in Oregon, Washington, Idaho, Utah, Arizona and California, and both Oregon and Washington have declared states of emergency.