The Natural Resources Conservation Service folks, among other things, maintain and monitor the SNOTEL system that projects moisture received by river drainage (e.g., Boise 59%, Salmon 67%).
They have some remarkable photos:
For the latest map of the percentage of average snow-water in NW river drainages: http://www.wcc.nrcs.usda.gov/ftpref/data/water/wcs/gis/maps/west_swepctnormal_update.pdf
Richardson's rummage 