If the predictions are correct, Northern California is going to see some impressive amounts of rain this weekend. As much as 5-9 inches is being forecasted in the Central valley and 20+ inches is a possibility in the Sierras.
Unfortunately, this is a warm storm, with snow levels assumed to be somewhere around 10,000 feet. All that rain on top of the good snow that just fell earlier in the week will certainly cause major flooding.
To read all about the storm, go to Weatherwest