https://www.nwrfc.noaa.gov/rfc/

Stasop flows are going up vertical on the graph about 580 cfs rise so far and more to come. Hit the 240 forecast tab for percipitation and the ten day forecasted flows are going to be headed up no low water thing at all. Upper Chehalis is staying low until around the 27th then up we go. So no matter what we get from this storm on the Olympic tribs the Chehalis above Fuller Hill should be okay and if it gets some color it will not be much before the 27th.

Little edit: Updated forecast has the weather coming in at or around the 25th to be a substantial event. The 26th through 30th has the Olympics at 6.98 inches in four days with more coming.