Firefighters on the Mt. Adams Complex are gearing up for a “subsidence inversion” forecast for tonight.  The inversion occurs when a widespread layer of air descends, usually at night, and compresses and heats due to increasing atmospheric pressure, leading to increased temperatures and decreased humidity that increases the potential for fire activity.  Firefighters have been preparing for the inversion by steadily mopping up the perimeters of the Riley and Horseshoe fires and extinguishing hot spots.  On the Riley Fire, firefighters continue to mop up and monitor activities with containment at 20 percent.  The Horseshoe Fire is at 90 percent containment, and fire officials say it has been “put to bed” but they are monitoring the area closely.