Similar to down-scaled models of precipitation (like PRISM), I am looking for down-scaled models of snow pack for northern California and southern Oregon. Any help is truly appreciated.
I would try your first suggestion to start. You might find this by contacting any popular ski areas such as mount Ashland near Medford Oregon. Also besides the states and county and community raingauges with snow accumulation dara, the national forests and parks such as Oregon Caves might locally keep these records. Contact with local meteorologists and hydrologists with the various agencies may help if you are not finding success. More attention to snow is probably going to be evident in rain recording stations where elevations exceed 5000 feet.