La Nina, the periodic cooling of the central Pacific Ocean that affects weather around the world, has arrived and may last until February.
This usually means wetter winters for the Rockies, Pacific Northwest and Ohio Valley, while the South will see warmer, drier conditions.
There's a 55 percent chance it will last all winter, which could continue Southern California's lengthy drought. Three-quarters of the state is still in drought; it lost $2.7 billion to the drought in 2015 alone.
The Smithsonian breaks it down in graphic form.
The Associated Press contributed to this report.