With neither team sporting indoor facilities both were forced to change locations in order to practice.
The Niners also moved their practice to a separate facility in advance of their showdown with the Seattle Seahawks, per the team.
The storm, which includes torrential downpours and reported winds between 71-90 mph in certain areas, is the strongest in years for the California region, according to Weather.com. A flash flood warning has been issued and some major highways are flooded. Thousands in Northern California are also without power.
To all those in the eye of the storm: Be safe and stay dry.
The latest Around The NFL Podcast reacts to the fallout of Cam Newton's car accident and debates how the Browns will look with Johnny Manziel at QB. Find more Around The NFL content on NFL NOW.