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.

A strong storm system fueled by a moderate atmospheric river is on a direct path to bring soaking rain to Oregon and Southwest Washington this week.

An atmospheric river will push multiple low pressure systems into the Pacific Northwest, leading to an active pattern across the entire U.S. though this week and weekend.

The next storm is expected to approach the Pacific Northwest Tuesday night, unleashing showers and thunderstorms along the coast and portions of the Coastal Ranges that have the potential to trigger flooding. As the storm moves east, it could bring more snow to the Cascades.

A pair of back-to-back storms were forecast to dump heavy snow and rain over parts of the Pacific Northwest, northern California and the Rockies this week, triggering winter storm and flood warnings.