The National Weather Service is forecasting a major storm for Yosemite and the Sierra Nevada beginning Monday night and continuing through Tuesday night. The Sierra foothills could get two to three inches of rain and higher elevations could get three to five inches, or two or more feet of snow above 9000 feet. Here a link to the NWS forecast for Yosemite, and their Special Weather Statement.
It’s likely that Tioga Pass will close, possibly for several days or more. It’s difficult to know what the effect will be on fall color. The good news is that this storm will be warm, so shouldn’t cause leaves to freeze, wither, and turn brown. But high winds could strip some trees that have already turned. During or just after the storm the rain will enrich the color in moss and leaves. I took advantage of such wet conditions when photographing the oak trees above in Yosemite Valley several years ago.