Atmospheric River

• These are the long, narrow regions in atmosphere that transport most of the water vapor outside the tropics. 
• These columns of vapor move with the weather, carrying an amount of water vapor roughly equivalent to the average flow of water at the mouth of the Mississippi River. When the atmospheric rivers make landfall, they often release this water vapor in the form of rain or snow.
• Although atmospheric rivers come in different shapes and sizes, for one to be a “true Pineapple Express,” location matters. The tail end, where the moisture is pulled into the atmosphere, must start near Hawaii. Then the river must stretch continuously through the atmosphere to the U.S. West Coast.
• Between 30% and 50% of the annual precipitation on the West Coast occurs from just a few atmospheric river events, according to the NOAA.

WHERE DO THEY OCCUR?

• They can occur anywhere across the world, but they are most dominant over West coast of Northern America taking up the moisture from Pacific ocean. 
• They also occur at eastern United States, where they often channel moisture from Caribbean.

CONSEQUENCES

• Positive: They bring much desired rainfall to the coastal areas which in turn is beneficial for economic activities like agriculture, transportation, fisheries and water supplies etc. 
• Negative: High intensity atmospheric rivers lead to torrential rainfalls, flash floods, landslides, snowfall, sheet erosion and strong winter storms.