Yosemite closes parts of park as warm weather raises flood threat

Most of Yosemite Valley – the tourist center of the famed national park – will close this weekend as rising temperatures threaten the region with a surge in snowmelt that’s expected to push the Merced River beyond its banks. Forecasters have warned that runoff from California’s historic snowpack, set high along the peaks of the Sierra Nevada range, could cause widespread flooding.

“Downslope there will be problems,” said the National Weather Service meteorologist David Spector, adding that the area around the Pohono Bridge just east of the park’s central entrance would reach flood stage by Friday. “Only parts of the valley are expected to be impacted for now,” he said. “But it may become worse by Sunday or Monday.”

The Merced is expected to reach 11.5ft (3.5 meters) at the Pohono Bridge by Sunday afternoon, according to forecasts issued by the California Nevada River Forecast Center. If it rises a foot higher, the main roads in Yosemite valley will be inundated.

Minor spring floods are not unusual and Spector said they typically affect the area every five or six years. But the park has also borne the brunt of more serious surges in snowmelt that left a damaging mark. The historic floods of 1997 – when the Merced rose above 23ft (7 meters) at Pohono – submerged roads and swept away infrastructure. Officials on scene at the time described picnic tables floating through the park alongside enormous boulders carried by the furious waterway, that left roughly $178m in damage.

Forecasts aren’t showing an indication that the river will close in on its record. The maximum level projected through the start of May is just over 15.6ft with higher probability that the Merced will stay below 12ft.

But this year has already been a standout – and there’s lots of snow still waiting to melt.

A grueling set of storms that peppered the park through the winter and into spring forced Yosemite to close for weeks and left behind a mess of scattered trees, tall berms of snow and inundated infrastructure that needed mending before visitors could return. The intense winter was just the latest in a series of extreme weather events to affect the park, which also spent stretches of the summer shrouded in smoke as wildfires threatened cherished landmarks. Officials have had to turn away hundreds of thousands of visitors, many of whom have waited years to score a scarce campsite or hotel reservation in the valley.

And this closure, which officials have extended through the weekend from Friday through next Wednesday, is probably not going to be the last this season. “It is very likely that the Merced River will reach flood stage off and on from late April through early July,” officials posted in an update on the park’s website, adding that when the Merced River surpasses 10ft at Pohono Bridge “roads and other critical infrastructure begin flooding, making it unsafe for visitors to be in Yosemite valley”.

It is still unclear how high the river will reach as the weather continues to warm. This week’s burst of heat, expected to push temperatures high enough to challenge records, will taper off as California is thrust into another cold system. Weather models are also showing the potential for a late-spring storm that could leave the Sierra with even more snow.

It won’t last long – and the threats posed by warming weather still loom large.

“This is going to last long term – well into the summer,” Spector said. “Parts of the park are going to be closed because of the flooding.”