Atmospheric Rivers (AR) - GFS Water Vapor Forecast

Data NOAA Earth System Research Laboratory

Atmospheric Rivers (AR)

Atmospheric Rivers (AR) are relatively narrow regions in the atmosphere that are responsible for most of the horizontal transport of water vapor outside of the tropics. While ARs come in many shapes and sizes, those that contain the largest amounts of water vapor, the strongest winds, and stall over watersheds vulnerable to flooding, can create extreme rainfall and floods. These events can disrupt travel, induce mud slides, and cause catastrophic damage to life and property. However, not all ARs cause damage – most are weak, and simply provide beneficial rain or snow that is crucial to water supply.

On average, about 30-50% of annual precipitation in the west coast states occurs in just a few AR events, thus contributing to water supply. A strong AR transports an amount of water vapor roughly equivalent to 7.5–15 times the average flow of liquid water at the mouth of the Mississippi River.

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North America - 24 hour Integrated Water Vapor (IWV)




North America - 48 Hour Integrated Water Vapor (IWV)




Northeast Pacific - Integrated Vapor Transport (IVT)




North America - Integrated Vapor Transport (IVT)




Northeast Pacific - 48 Hour Forecast




North Pacific - 48 Hour Forecast