AUSTIN (KXAN) – Atmospheric rivers have been stealing the headlines over the past several months as California has experienced a relentless amount of rain and snow. An atmospheric river is a narrow corridor of concentrated moisture or water vapor in the atmosphere. They can stretch hundreds to even thousands of miles in length while usually being much narrower in width (less than 500 miles or so). As this water vapor gets pushed up the mountains along the West Coast, this moisture is forced upwards creating cooling, condensation and a continuous torrential train of falling heavy precipitation. The faster the atmospheric river, the more intense these precipitation rates can be.

The Sierra Nevada mountains supply nearly a third of California’s water supply. Our partners over at Climate Central plotted the annual snow water equivalent (the amount of water that forms after the melting of snow) for snowpack of the west coast over the last 50 years. Years with more atmospheric river events had a healthier snowpack.

However, over the long term Western snowpack has been shrinking and peaking earlier. Unfortunately, five of the last 10 years had snowpack levels less than 50% of the historic average. Furthering the discussion of droughts becoming more intense in a warming world.

2023’s historic Western Snowpack – a major outlier

Western snowpack since 1981

This 2022/2023 winter season, however, has been a complete outlier from the trends we are seeing from past decades. The reason? Increased amount of atmospheric river events.

Major winter snowpack notables

-California’s (2023) snowpack is now more than double their statewide average.

-The Southern Sierra Mountain’s have hit record April 1 snowpack levels.

-Average snowpack across the western U.S. has exceeded levels not seen on April 1 for 40 years.

Snowpack in the West is crucial for reservoirs

This historic snowfall is great news! Atmospheric rivers and a healthy snowpack is vital to the west and its local community and economy. In California, up to 50% of total annual precipitation and streamflow can come from a few intense atmospheric rivers during fall and winter.  

Water uses

Western mountain ranges act as natures water towers holding snow each winter that later melts to recharge reservoirs and meet the majority of the region’s water demands including the ecosystems and farms.

A full reservoir is important to help get through the tough, drought-stricken years where they don’t experience any atmospheric river events.

Climate change is playing a major role

Warmer air holds more moisture

Winter is the fastest warming season for much of the United States. Warmer air holds more moisture, which can fall as snow when temperatures are below freezing. For every 1 degree F of increasing temperate, you can expect 4% more water vapor.

Overall, in a warming world you can expect less snow. But on average, single snow storm events will bring heavier and more intense amounts of snow. Warmer temperatures combined with more frequent atmospheric rivers, could certainly be playing a role in this years historic snowfall in the west.