Atmospheric rivers
Long, narrow corridors of water vapour that can deliver both vital water supply and flooding rain.
This explanation is written conservatively from textbook-level science and has not yet been reviewed by a meteorologist. Treat it as a draft.
The mechanism
Follow the chain: each step causes the next.
01
Moisture is gathered
Warm oceans supply abundant water vapour to the lower atmosphere.
02
A storm funnels it
Strong low-level winds ahead of the cold front of a mid-latitude storm concentrate the vapour into a long, narrow band.
03
The air is lifted
When the band reaches a coast and meets mountains, the air is forced upward and cools.
04
Heavy rain or snow
Cooling condenses the vapour, producing heavy and sometimes prolonged rain or mountain snow.
Explore it
Step through the mechanism one stage at a time.
Step 1 of 4
Moisture is gathered
Warm oceans supply abundant water vapour to the lower atmosphere.
In short
Rivers in the sky
Atmospheric rivers are typically thousands of kilometres long but only a few hundred kilometres wide. They carry a large share of the water vapour moving from the tropics toward the poles and are an important source of precipitation on the west coasts of mid-latitude continents.
Deeper science
Open a section for more detail.
How they are identified
Scientists usually identify them with integrated water vapour transport (IVT): the total horizontal flux of water vapour through a column of the atmosphere. Detection methods apply a threshold to IVT together with shape criteria; different studies use different methods.
Beneficial and hazardous
Many atmospheric rivers are weak and replenish water supplies and snowpack. The strongest, or several arriving in quick succession, can cause flooding and landslides.
Related topics
Tropical cyclones
How warm oceans power the most intense storms on Earth.
5-step mechanismDraftRead topic