The Gage was discontinued this year. You can go to the NW River forcast page and manually click on the Sol Duc tab and you will get a current real time water level. I have not yet figured out how to compare hight with what the Flow used to be. I am keeping a log every time i am out there of what the height says and how many boards it is at Maxfield. Good luck and let us know if you find something better.
Following the adjacent watershed gauges will also be helpful, the Calawah and Bogachiele rivers are intimately associated to the Sol Duc. Ie; Once the Bogachiele starts doing what it is doing today you can expect high water, dirty water, on the Sol Duc too.
Another useful tool is the webcam at www.theferngallery.com, which is near Whitcomb Dimmel ramp on the so Duc at Hwy 101 just outside of Forks. (Note that the time stamp on the webcam picture of the Sol Duc is not accurate, but the picture is real-time)
Check that along with the other local gauges and you will have a general sense of it. And counting the ramp "boards" above water as often as you can is also very helpful, if not the most helpful "local knowledge". This time of year the Olympic Mountain weather, altitude of freezing levels, snow levels etc., will really count towards forecasting too. Just reading a river gauge will never be enough information.