Yes masks can stop it. But if people are not wearing masks and getting infected and then breathing in concentrated areas of high density then a "swarm" develops where invisible armies of the virus descend on WHOLE AREAS. So if you are in that area and come out of your home then you have the possibility of walking into the swarm generated by hundreds and hundreds if not thousands of infected people just breathing. Now lets take areas with pollution or stagnant air. Then the swarm hovers and is not dissipated and I would expect infections to soar.
The swarm falls apart when people mask up and there is less virus in the air. Wind comes along and scatters the swarm and it loses potency and falls to earth and basically moves on. Then another state like say Florida or Texas becomes the next incubator for a swarm as people become infected. Once the swarm develops it becomes a hotspot where people are literally walking into a fog of virus.
So I am not a doctor. But this would explain the way the virus takes hold over an area and everyone seems to be getting it until they arent' and like New York City the virus moves on to greener pastures and descends again. Just like locusts.