Atmospheric River to Drench Pacific Northwest with Heavy Rain

The Northwestern United States is once again under the influence of a powerful atmospheric river, delivering intense moisture, heavy rainfall, and a heightened risk of flooding and landslides.

Drawing on decades of research and recent insights from Alex Tardy, Project Policy Analyst and Meteorologist at UC San Diego’s Scripps Institution of Oceanography, this article explains what atmospheric rivers are, why this event matters, and how science and policy must work together to protect communities and infrastructure.

Table of Contents

What Is an Atmospheric River?

Atmospheric rivers are not ordinary storm systems. They are long, narrow bands of concentrated water vapor that transport enormous amounts of moisture from ocean to land.

While invisible to the naked eye, their impact becomes obvious when that moisture condenses and falls as heavy rain or snow.

How Atmospheric Rivers Form and Behave

An atmospheric river forms when strong winds in the lower atmosphere tap into warm, moisture-rich air over the ocean and channel it toward land.

When this corridor of moisture encounters mountains or colder air, the water vapor condenses and falls out as precipitation—sometimes at astonishing rates.

Key characteristics of atmospheric rivers include:

Intensity of moisture: A single atmospheric river can transport as much water vapor as the average flow at the mouth of the Mississippi River—only in the sky instead of the channel.

Duration: Events can last from several hours to a few days, leading to prolonged heavy rainfall over the same areas.

Geographic focus: Because they are narrow, they can focus rainfall over specific regions, dramatically increasing local flood risk.

The Current Atmospheric River Impacting the Northwest

The system now affecting the Northwestern U.S. is a textbook example of a high-impact atmospheric river.

According to Tardy, the corridor of moisture is delivering intense rainfall capable of overwhelming local rivers, urban drainage systems, and vulnerable hillsides.

Flooding, Landslides, and Infrastructure Risk

The volume of water being delivered in a short period raises multiple hazards:

Widespread flooding: Rivers and streams can rise rapidly, and low-lying areas may flood even far from the coast.

Landslides and mudflows: Steep, saturated hillsides are prone to failure, particularly in areas with recent wildfire scars or destabilized soils.

Infrastructure impacts: Roads, bridges, stormwater systems, and power infrastructure can be damaged or disrupted by high flows, erosion, and debris.

Authorities are urging residents to stay informed, heed evacuation notices where issued, and avoid driving through flooded roadways.

In events like this, a few inches of water can conceal severe road damage or powerful currents.

Atmospheric Rivers: Both Beneficial and Hazardous

Despite their destructive potential, atmospheric rivers are also a vital part of the Western water cycle.

They provide a substantial share of the annual precipitation that refills reservoirs, recharges groundwater, and sustains ecosystems.

The Double-Edged Nature of These Storms

The same processes that replenish water supplies can, under the wrong conditions, cause serious damage.

Some key contrasts include:

Benefits: Recharging snowpack, refilling reservoirs, supporting agriculture and hydropower, and reducing drought severity.

Risks: Overwhelming rivers and levees, saturating soils to the point of failure, and damaging homes, transportation networks, and utilities.

Rising Need for Preparedness and Policy Integration

The Northwestern U.S. has experienced multiple impactful atmospheric rivers in recent years, a trend that aligns with broader concerns about climate variability and changing extremes.

As the climate system warms, the atmosphere can hold more moisture, increasing the potential intensity of such events.

Science, Policy, and Community Resilience

The current storm highlights the importance of close collaboration between scientists, emergency managers, and policymakers.

Effective strategies include:

Advanced monitoring and forecasting: Using satellites, radar, and numerical models to track atmospheric rivers days in advance.

Risk-informed infrastructure: Designing and upgrading roads, bridges, levees, and drainage systems to withstand more intense downpours and higher flows.

Public communication and education: Providing clear, timely warnings and practical guidance so communities can prepare and respond effectively.

Here is the source article for this story: Powerful atmospheric river headed for the Northwest U.S. | Latest Weather Clips