BEND, Oregon.- Firefighters battling two of the largest fires in Oregon were preparing for windy and dry conditions that are forecast to reach some areas of the state on Friday and into Saturday.

Crews have been able to build some containment lines around the Akawa Butte Fire, which is burning near Sisters, a town about 22 miles (35 kilometers) northwest of Bend. The fire, started by lightning on July 16, burned 109 square kilometers (42 square miles) and destroyed two homes.

It has been designated the country’s top priority wildfire due to its proximity to people. The designation will allow officials to tap into resources from other states and other countries, Oregon Gov. Tina Kotek said Friday.

Strong winds and low humidity were expected later on Friday and Saturday and could lead to increased fire activity, officials warned. They urged residents to be prepared to evacuate if necessary.

The National Weather Service issued a red flag warning for central Oregon through Saturday, meaning conditions such as low humidity, warm temperatures and high winds can create an extreme wildfire risk.

The most critical period for Sisters, a city of 3,800 about 3 miles (5 kilometers) south of the fire, will be the next 24 to 48 hours, Sisters Mayor Jennifer Letz said. He said about half of the city’s population has been told to be ready to leave if necessary.

“If we can get through this weekend, we’ll probably be in a good position to move forward. But right now, we have the northern half of the city under orders to be prepared, to have a plan, to get their things in order,” he said.

There are more than 1,000 firefighters fighting the blaze and more are expected to join them to help strengthen and expand containment lines. The fire has shown extreme fire behavior, including flame heights of 200 feet (61 meters) and a pyrocumulus cloud that generated its own lightning, Kotek said.

“Here in Oregon it is necessary for everyone to be hands-on,” he said.

It’s not the only major wildfire in Oregon, making this an especially challenging period for emergency services, he said.

There are dozens more fires across the state, choking the air in Oregon and sending smoke across the country. Kotek said all available firefighters and firefighting resources are being used in the field.

The largest fire is the Rowe Creek Complex Fire, which has destroyed 300 square miles (777 square kilometers) since it was sparked by lightning on July 15. On Friday it was almost 30% contained.

Firefighters have made progress on the northern portion of the fire, where they have built containment lines, but strong winds fueled the fire and it expanded at its southern end after some fires jumped containment lines, said Thadd Niebel, chief of operations for the U.S. Forest Service.

Crews were being reassigned to the southern portion of the fire to strengthen containment lines and protect homes and other buildings ahead of winds of up to 20 mph (32 kph), Niebel said.

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Rodríguez reported from San Francisco.