Fire officials say overnight, three small, targeted burn operations were completed along the northwestern border of the fire.
Firefighters are about halfway through securing control lines along the northern section of the fire.
The fire is burning mainly within the burn scar of the 2002 Biscuit Fire. Now, its also grown into the burn scar of the Klondike Fire.
A Red Flag Warning remains in effect for Southwestern Oregon due to hot, dry, and windy conditions. The Rogue River-Siskiyou National Forest issued a closure for trails, roads, and portion of the Illinois River impacted by the fire.
The cause of the Flat Fire is still under investigation.
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