Big storm is nearly here. Yosemite Valley will close, Fresno area girds for floods

Another atmospheric river — unusual for this time of year — is bearing down on California and the Valley, bringing an expectation for significant rain on the Valley floor and the prospect of flooding in the Sierra Nevada.

Yosemite Valley will be closed to all visitors by 5 p.m. Friday, and all visitors in Yosemite Valley will be asked to leave by that time. Jamie Richards, a spokeswoman for Yosemite National Park, said the road closures will be reassessed Saturday.

Forecasters with the National Weather Service predict that the storm will begin affecting the Valley about midday Friday and bring rain continuing through Saturday. Rangers in Yosemite National Park are bracing for the Merced River to rise above flood stage and flood some roads and campgrounds. Meanwhile, the prospects for localized street ponding are more modest in Fresno and adjoining communities.

A couple of weeks ago, another atmospheric river had crews in Fresno scrambling to deal with storm drains that were blocked by debris or overwhelmed by the volume of rain that fell during brief but intense spells. Brian Ochs, a meteorologist in the weather service's Hanford office, said Fresno streets could see some roadway ponding again this time, but likely not to the extent of the last big storm.

In the Valley, the heaviest rainfall should be in the north, with Merced getting as much as an inch and a half over the two-day storm, with most areas in the South Valley getting less than an inch, Ochs said. Fresno should receive a little more than half an inch of rain during the period of heaviest rain, Friday night into Saturday morning, Ochs added.

The Fresno Metropolitan Flood Control District's storm drain system can generally handle up to a half-inch of rain in an hour, city officials said. Occasionally, however, if storm-drain inlets are blocked by debris, or if the rainfall is particularly intense, localized street flooding can happen.

Even then, the storm drain systems "eventually catch up when the rain intensity drops off," said Mark Standriff, a spokesman for the city. "We will monitor where any heavy rains are occurring and will have on-call staff and supervisors available to respond as needed."

Most of the storm-drain basins in Fresno's system can handle about six inches of rainfall.

City street crews will be monitoring pumps at four underpasses where city streets go below railroad tracks and water is prone to accumulate.: Fresno Street in downtown under the Union Pacific Railroad; BNSF Railway underpasses on Wishon, Van Ness and Shaw/Marks avenues.

Heavy rains in Sierra

In the Sierra foothills, a flood watch is in effect from Fresno County to Mariposa County, and in the southern Sierra from Yosemite to Sequoia & Kings Canyon national parks.

In Yosemite Valley, the latest estimates for the Merced River above the Pohono Bridge put the river level as high as 15.1 feet, which is above the moderate flood stage, Ochs said.

Yosemite Valley could get between 3 and 4 inches of rain, and Mariposa around 3 inches.

All campgrounds and visitor lodging in Yosemite Valley will close Friday afternoon and reservations for Friday and Saturday evenings have been canceled.

Access to Yosemite Valley will be closed along the Big Oak Flat Road (Highway 120) at the Foresta Road Junction, along Wawona Road (Highway 41) at Chinquapin, and along Highway 140 at the park boundary in El Portal.

Visitor services and campgrounds remain open in Wawona, Hodgen Meadow, Crane Flat, and El Portal. The Big Trees Lodge, the El Portal Market, and the El Portal gas station are anticipated to remain open.

Roadways and park facilities may close at any time for safety concerns.

YARTS buses will be on their regular schedule on Friday, but service to Yosemite Valley will be suspended Saturday and Sunday.

This storm is a warm system, the result of an "atmospheric river" of precipitation originating near Hawaii and stretching across the Pacific to California. "Typically we don't get this amount of rainfall this late in the season," Ochs said.

As a result, the snow line is expected to stay high, between 10,000 and 11,000 feet, and drop between 8,000 and 9,000 feet on Saturday, Ochs said.

Rain totals in Fresno this year are just below normal. Fresno has received 5.68 inches of rain since Jan. 1. The average total during the same period is 6.42 inches, Ochs said.

Where streets can be affected

Markers on the map denote potential areas for street ponding during heavy rain. Click a marker on the map above to see details for that site. Red markers are intersections monitored by the city of Fresno during storms; yellow markers are sites affected in the March 22-23 storms, reported through the city's FresGo app or by Bee readers. Map by Tim Sheehan / The Fresno Bee

This story was originally published April 5, 2018 at 4:29 PM with the headline "Big storm is nearly here. Yosemite Valley will close, Fresno area girds for floods."