A "bomb cyclone" is forecast to intensify an atmospheric river and bring snow to the northern Sierra Nevada starting on Tuesday, with heavy rain expected along the West Coast. Hector Crespo,

Forecasters said a final round of rain, snow and high winds were targeting the Pacific Northwest and Northern California regions on Friday.

In the northern hemisphere, atmospheric rivers typically occur during winter and are often cited for strong storms in the West. According to NASA, they are the largest transport mechanisms of fresh water on Earth.