A massive plume of moisture from the Pacific called an atmospheric river will hit the West Coast on Tuesday afternoon and last into Friday.
The storm is expected to become a bomb cyclone -- which means the pressure in the center of the storm will drop 24 millibars within 24 hours.
The storm could be so strong that it even drops close to double that rate -- meaning more than 40 millibars in 24 hours.
MORE: Rain on the way could spell relief for crews battling rash of Northeast wildfiresNumerous alerts for snow, flooding, high wind and high surf have been issued along the West Coast, from the San Francisco Bay area to Oregon to Washington.
Rain totals could surpass 1 foot in Northern California and southern Oregon. More than 3 feet of snow is possible in the higher elevations.
Wind gusts could reach 85 mph along the coast and waves could climb to 34 feet.
By the weekend, some of the rain from this system will make its way to Southern California.