Cities like Boston and Chicago celebrate the day with parades, river dyeing, and cultural events, attracting millions of people each year.

"A Pacific storm and atmospheric river will impact the Pacific Northwest states and northern Rockies this weekend," the NWS said.

When plotted on a map or looked down upon from a satellite in space they looked just like rivers. For a long time, they were colloquially and scientifically referred to as things like the ...