Possible broken forearm? Not sure, but does seem very swollen. Can I wait until tomorrow when the doctor is open?

Yes but ice &elevate. As long as you're not having too much pain, numbness, tingling or loss of circulation, you should be ok to wait until tomorrow. However, if any of these symptoms occur or worsen, go the the emergency department immediately. Once you have had an x-ray, you'll know for sure if you have a fracture or not. For now, ice and elevate the extremity. Try to avoid using the extremity and take an nsaid.