Fire activity remained stable overnight on the Larch Creek Fire in Wasco County, allowing firefighters to secure the perimeter and expand mop-up activities.  Fire officials reported decreased winds overnight coupled with higher relative humidity provided good conditions for crews to make progress.  Estimated size of the fire went up by just about 200 acres to 18,684, with containment up slightly at 11%.  Firefighters today will continue to focus on structure protection and reinforcing fire line around the entire perimeter, while air resources continue to support crews moving deeper into burned areas.  Fire officials did note weather forecasts do show a potential for thunderstorms from Tuesday evening into Wednesday morning, which could bring gusty winds and additional ignitions in the region.  The Wasco County Sheriff’s Office has modified evacuation advisory levels on the east side of the fire, with Level 3 areas dropping to Level 2, and Level 2 to Level 1.  Evacuation advisories on the west side of the fire are unchanged.  Detailed evacuation advisory areas are available on the Wasco County Sheriff’s Facebook page.  There are 982 personnel assigned to the fire, including 27 hand crews, 71 engines, 20 water tenders, 13 dozers, and 11 helicopters.  The fire was human caused, but the exact cause has not been determined.