Popular River in Yosemite Witnesses the Highest Flow Ever Recorded in 52 Years— and Experts Know Why

The rugged slopes of the Sierra Nevada mountains guard the Yosemite Valley. But sometimes, their towering shapes provoke the dormant corridors of water in the atmosphere. Called “atmospheric rivers” or “rivers in the sky,” the clusters of water molecules in these corridors start shaking loose, and as they fall, they release heavy torrents of precipitation, also casting a “rain shadow” around the mountains. In a recent episode, an atmospheric river slammed into Sierra, triggering a deluge of heavy rain. This unforeseen collision proved to be a blessing in disguise for the rivers in the Yosemite Valley. Merced River, for instance. Storm chaser Colin McCarthy (@US_Stormwatch) shared footage of the Merced River, exclaiming, It’s absolutely gushing today!”

According to an explanation by CBS News, atmospheric rivers are formed when molecules of water suspended in the atmosphere are forced to lift upwards and cool down. As they cool, they form clusters of water molecules, like tunnels or clouds of water hanging out. When the pressure exerted by these molecules turns extreme, the cloud bursts, sending down barrages of precipitation upon the mountain slopes. Combined with erratic winds, the heavy rains can trigger heavy snowpack, mudslides, flooding, and even power outages. Episodes like these are common on the West Coast, but this is the first time, perhaps, that people are witnessing it happening in the Merced River.

For the past few decades, the Merced River had been living under a curse of drought, from a bubbling and rippling dance of flow, it had turned into a meagre stream coursing along the San Joaquin Valley. But as this newcomer atmospheric river exploded into the mouth of California, the river leaped by 4 feet over the weekend, mainly at the Happy Isles Bridge gauge in the valley. At the gauge, the river level jumped from roughly 1.4 feet on Friday to 5.39 feet on Saturday. McCarthy says, This is the highest flow in the past 52 years, the 'highest November river flow since 1973.”

"The Merced River at Happy Isles just hit its 3rd-highest November peak flow ever recorded, dating all the way back to 1915," he described. "The November 14th flow of 1,280 CFS was also the 8th-highest November day on record." And although the dramatic burst of showers has proved to be a resurrection for Merced, an uncontrolled flow could pose a risk to the surrounding population. National Weather Service warns that “excessive runoff could result in flooding of rivers, creeks, streams, and low-lying areas. Low-water crossings may be flooded,” per Newsweek.

On X, a viewer @Packers92821 shared a photo of the Merced River to paint the right perspective and scale of how the concentrated water in the atmospheric river reshaped its whole geology. They had taken this photo in August this year while standing in the river behind Ahwahnee, the historic hotel tucked in the Yosemite Valley. Remarkably, the photo shows a river shrunken to a bland landmass glistening with no rolling waves, but just a scanty sheet of water splattered with muddy rocks.

On the flip side, the footage shared by McCarthy tells a tale of dramatic transformation. Foamy spouts of sparkling waters are gushing through the trails of meandering rocks. Outpours of swift, whirling rapids can be seen snaking through the pine groves leading towards the half dome in Yosemite Valley. Meanwhile, the leafy branches dangling from the rugged mountain cliffs appear to be quivering with the monstrous currents. Funnelling surges of water look like schools of pearly white dolphins playing, tumbling, chasing, rushing along the granite rocks. Where? Only the river itself knows its fate.