Today’s Image of the Day from NASA Earth Observatory captures a weather event that many people in the Pacific Northwest will not soon forget.

In early December 2025, rain fell hard and fast, soaking hillsides, swelling rivers, and pushing roads and neighborhoods to their limits.

The image shows just how much moisture was stacked in the atmosphere as the storm peaked, offering a clear look at why the impacts were so severe.

For residents on the ground, the storm meant flooded streets, mud sliding across highways, and rivers spilling beyond their banks.

For scientists, it was a powerful example of how far moisture can travel and how quickly conditions can unravel when it arrives all at once. This single snapshot helps explain days of chaos that unfolded across western Washington.

What fueled the December storm

The rainstorm that struck the region beginning around December 7 was driven by an atmospheric river, a concentrated corridor of moisture moving through the atmosphere.

Atmospheric river systems are common along the U.S. West Coast during fall and winter, but this one stood out for its reach.

Instead of drawing moisture only from the central Pacific, parts of this system traced back roughly 7,000 miles across the ocean, near the Philippines.

That long journey made a difference. The farther the moisture traveled, the more water vapor it carried into the storm.

By the time the system arrived over Washington, the atmosphere was loaded. When weather patterns forced that moisture upward, it condensed rapidly – releasing intense rainfall over a short period of time.

Seeing moisture from space

The image itself shows total precipitable water vapor at 11:30 p.m. Pacific Time on December 10.

The map was created using NASA’s Goddard Earth Observing System, which blends satellite observations with models that simulate how the atmosphere behaves. The green areas on the map highlight where moisture levels were highest at that moment.

Precipitable water vapor describes how much water is contained in a vertical column of air if all of it were squeezed out as liquid. It does not mean all that water will fall as rain, and it does not limit how much rain can occur.

Moisture can keep flowing into the same area, adding to the total. Still, high values are a strong signal that heavy rainfall is likely, especially when storms stall over one place.

Rainfall records and rising rivers

The impacts on the ground were swift. According to the National Weather Service, preliminary measurements showed that several locations in western Washington received more than 10 inches of rain over a 72-hour period ending on the morning of December 11.

At Seattle-Tacoma International Airport, December 10 set a daily rainfall record with 1.6 inches.

All that water had to go somewhere. By December 11, river flooding was ongoing across the region. The Skagit River and the Snohomish River both reached record or near-record flood levels that day.

Floodwater and mudslides forced the closure of numerous roadways, including the eastbound lanes of I-90 out of western Washington, cutting off key travel routes.

Atmospheric rivers and annual rainfall

Events like this help explain why atmospheric rivers draw so much attention from weather forecasters.

These systems can deliver a large share of a region’s yearly precipitation in just a few days. When they arrive one after another, or stall over mountainous terrain, the risks increase sharply.

Warm air holds more moisture than cool air, which means storms today often have more water to release than similar storms decades ago.

That does not guarantee flooding every time, but it raises the odds that heavy rain will overwhelm rivers, soil, and infrastructure, especially in areas already saturated from earlier storms.

Supporting response and recovery

As flooding continued, NASA’s Disasters Response Coordination System was activated to support response efforts led by the Washington State Emergency Operations Center.

The team provided maps and data products through an open-access mapping portal, updating information as conditions evolve.

These tools help emergency managers track flooded areas, assess damage, and plan next steps. They also show how satellite data and modeling now play a direct role in disaster response, not just long-term research.

In this case, a single image tells a much larger story about water, weather, and the growing challenges faced by communities in the path of powerful storms.

Image Credit: NASA Earth Observatory

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