WINTHROP, Wash. — Cooler temperatures and lighter winds are forecast to descend on a wildfire-stricken Washington state, helping firefighters battle flames that have been growing unfettered for a week and have covered hundreds of square miles.

While Sunday’s weather was a slight improvements on the hot temperatures and gusty winds that have fueled the wildfires, the forecast for Monday and Tuesday calls for lighter winds and temperatures, said Spokane-based National Weather Service meteorologist Greg Koch.

“Overall, it looks like the weather scenario is improving,” Koch said.

Then on Wednesday a “vigorous” front is expected to cover Washington, bringing rain to much of the state. But it will also bring lightning, he said.

“The benefits of the system are still up in the air,” Koch said. “We may get some rain where we need it, but we may also experience some lightning that could cause some new ignitions.”

Sunday’s official estimate put the wildfire burning in north-central Washington at more than 370 square miles. It measured 260 square miles Friday.

Okanogan County Sheriff Frank Rogers estimated that 150 homes have been destroyed, but that number could be higher. His deputies haven’t been able to search parts of the county where homes are spread miles apart. No serious injuries have been reported, he said.

There are nearly 1,400 firefighters battling the flames, assisted by more than 100 fire engines, helicopters dropping water and planes spreading flame retardant.

On Sunday, Rogers was driving to the town of Twisp to survey the damage.

“It’s the first time in four days I’ve seen blue sky,” he said. “Every day, when you got up, it was nothing but smoke. All we’ve seen of the sun is a red ball.”

Although the weather is improving, towns in the scenic Methow Valley remain without power and have limited landline and cellphone service. Okanogan County Public Utility District officials told KREM that fully restoring power to the area could take weeks.

Gov. Jay Inslee said Friday about 50 fires were burning in Washington, which has been wracked by hot, dry weather, gusting winds and lightning. About 2,000 firefighters were working in the eastern part of the state, with helicopters from the Department of Natural Resources and the National Guard, along with a Washington State Patrol spotter plane.