Atmospheric Rivers: What are they?

Maple Valley, near Seattle, was hit with rain and hail as an atmospheric river moved in. What are atmospheric rivers?

An atmospheric river moved into the Pacific Northwest over the weekend of Oct. 19-20, 2024. The Olympic Peninsula and the northern Cascades bore the brunt of this system. The video above shows rain, wind and hail pushing into Maple Valley, Wash. So, what is an atmospheric river?

Atmospheric rivers are narrow bands of concentrated moisture in the atmosphere that bring large amounts of moisture from tropical regions to higher latitudes. When these air streams encounter land, they release precipitation, ranging from light rain to intense downpours, depending on the conditions. You can see the atmospheric river from this weekend on the WeatherRadar.

The West Coast typically sees atmospheric rivers during the winter months. Atmospheric rivers play a vital role for this region of the U.S. They replenish mountain snow levels and fill reservoirs. However, atmospheric rivers sometimes lead to extreme weather events. For example, when they bring heavy rain to areas with already saturated soil, the result can be flooding and landslides.