Yes, you can absolutely see Old Faithful erupt in the rain, and for many visitors, the rain actually enhances the drama of the experience. The geyser's schedule is determined by the internal thermodynamics of the Upper Geyser Basin, not by surface weather conditions. During a rainstorm, the contrast between the boiling water/steam and the cool, damp air often makes the eruption appear larger and more voluminous, as the steam condenses more rapidly into thick white clouds. The primary drawback of seeing it in the rain is visibility; if the rain is accompanied by heavy wind, the spray and steam may be blown toward the viewing boardwalks, potentially obscuring the view or getting spectators wet. However, the crowds at Yellowstone National Park often thin out during bad weather, meaning you might get a "front-row seat" without the usual thousands of other tourists. If it's a cold rain, you'll also see more "ghostly" steam rising from the surrounding thermal pools. As long as there is no lightning (which would make standing on the open boardwalk dangerous), Old Faithful remains a reliable and spectacular show, rain or shine.