I've generally relied on snowfall incidence and percents of terrain open. Northeast resorts do close terrain after rain/freeze events, precipitously after the big rain event before Christmas. Trail counts drifted down some during the fairly dry first half of February but recovered with the ~15 inches of snow that fell just before President's Weekend. With little snow since then the trail counts remain high but I'm sure surfaces have degraded. That scenario is still a B in the chart linked above because I know trails do get closed when it's really bad.