Yosemite Valley National Park is shaping up to be a dangerous place to venture in the coming months.

The National Park Service has indicated the partial closure of Yosemite Valley starting Friday at 10 a.m. — just before the Merced River is forecast to reach flood stage at 10 feet — is a precursor of things to come.

The earliest the entire valley may reopen is Wednesday, May 3.

The Merced River — due to a Central Sierra snowpack that reached 270 percent of normal this year — is expected to subject Yosemite Valley to more closures due to flooding possibly into early July.

That’s because periods of heat and rain puncturing the usual temperatures can accelerate snowpack melt that can repeatedly return to a more normal pace of melting.

California’s state climatologist Michael Anderson warned this week that rising temperatures will speed up the snowmelt and double the amount of water flowing into some of the state’s reservoirs.

The temperatures on the floor of Yosemite Valley are expected to be in the mid-70s — above average — for four days starting Thursday.

The highs will return to the low 50s accompanied by rain on Tuesday and Wednesday.

But it is the temperatures in the mountains above the valley that has an elevation that varies from 3,000 to 3,500 feet that will accelerate snow melt,

The high country around Tioga Pass at 9,943 feet forecast to have temperatures reach an unseasonably warm 55 degrees over the weekend.

The National Weather Service now expects three days of 90 degree plus temperatures in Manteca, Lathrop, and Ripon starting Thursday.

In January 1997 when failed levees flooded 70 square miles between Manteca and Tracy, the Merced River in  spots rose as high as 10 feet above its banks cutting a wide swath of damage through Yosemite Valley.

Water managers have been making steady releases on the Stanislaus, Merced and Tuolumne rivers — the three tributaries to the San Joaquín that pose the main threat to levees protecting Manteca, Lathrop and rural Tracy.

Reservoirs on all three rives have adequate space to handle a surge in snowmelt in the coming days.

As a result residential communities on the Lower San Joaquin River  are not expected to see immediate flooding due to the warming trend.

To contact Dennis Wyatt, email dwyatt@mantecabulletin.com