For finding out the flow/water levels of many rivers in the US check out the sight run by the USGS, at http://water.usgs.gov/realtime.html . For the Au Sable, near Au Sable, MI the web site is http://water.usgs.gov/mi/nwis/uv/?site_no=04137500&PARAmeter_cd=00065,00060 current #'s are height 8.93 ft, flow 995 CFS which is slightly beow the median flow for this date of 1,150 cfs. There are several other sights on the Au Sable. I am unfamilar with Michigans geography and just picked one at random.
Unfortunately, I can't help you with the current fishing conditions. Good luck.
Added data; I loked at the website for a couple of the Au Sable river locations and Michigan has better data than I'm used to seeing. The temperature near Red Oak (closest station I saw to Grayling) is 60-63 degrees F, so the water temp is reasonable for trout.