Mount Hood area trail map (Not free but good)
Snow conditions for any given trail in the Oregon Cascade Mountains can vary significantly from one day to the next. This makes knowing the conditions difficult. Here are a few tips on checking the snow conditions:
Most years there is enough snow at most snowparks by mid-December, so you shouldn't have to worry about there being enough, just what the weather is that day and surface conditions.
Check the NOAA forecast for Government Camp. If the freezing level is 4,000 ft or lower it will likely be snowing at most of the snoparks. If the freezing level is above 5,500 ft, most snoparks will have rain. 4,500-5,500 ft is going to risk a rain/snow mix. Frog Lake snopark is slightly further east and often has a slightly better chance for snow than others if it's on the edge. Mirror Lake and Tamanawas Falls snoparks are lower elevation.
Another good way to check snow conditions at snoparks is to look at the nearest webcams on TripCheck (particularly helpful around Mount Hood).
Facebook groups can be helpful, such as Portland Hiker and various Nordic Club groups/pages (they are more geared toward cross-country skiing than snowshoeing but oftentimes the trails are in close proximity and share snoparks), downhill ski area sites are also good at posting conditions.