More rain, fog expected for Central Valley next week

A Pacific storm spread needed rain to much of California on Friday, causing traffic snarls but no immediate trouble for communities near slopes left barren by wildfires.

Northern and central sections of the state felt the brunt of the storm’s impacts, but the threat of heavy rain rapidly diminished as it moved south and flash-flood watches in local mountains were canceled.

Merced County saw about 0.6 inches of rain in the latest storm front, but more storms are expected through next week followed by Central Valley fog.

“With the hot pressure moving in after the storms, usually fog begins to form,” William Peterson, meteorologist technician for the National Weather Service, said Friday. “That’s the main nemesis.”

The storm system that hit Merced County on Thursday and Friday left 0.57 inches of rain at Merced Regional Airport. A gauge northwest of Merced read 0.64 inches, Peterson said Friday afternoon.

The West Side registered similar rainfall totals. About 0.6 inches fell in Los Banos, and 0.58 inches fell in Gustine.

The storm system dropped more than an inch in the foothills on the West Side, Peterson said. The Los Banos dam registered 1.94 inches.

An urban and small stream flood advisory was issued for parts of the Valley on Friday because of heavy rain.

Two more storm fronts are expected to hit the Central Valley through Wednesday, Peterson said.

The first one is forecast to arrive Saturday night from the northwest continuing through Sunday, Peterson said. That will be a colder system precipitating more in the mountains, from 6 to 17 inches of snow, and less in the Valley.

The National Weather Service is still determining what will happen with a second system that could hit the Central Valley on Tuesday and Wednesday, Peterson said.

But following that, a high-pressure system could mix with the moisture left behind to form fog, Peterson said.

A year ago, almost the entire state was in severe, extreme or exceptional drought – from the Oregon state line to the Mexico border. But since then, enough rain has fallen that a chunk of northwestern California is now back to normal and the worst levels of drought designation have retreated somewhat to the central and southern regions, according to the U.S. Drought Monitor.

Other storms are expected to follow during the weekend, with potential for significant snow in sections of the Sierra Nevada, which normally stores a huge amount of the state’s water supply in the form of a winter snowpack that eventually runs off into major reservoirs.

After five years of drought, it’s uncertain how much snow to expect in the current water year.

When the 2016 water year ended Sept. 30, the California Department of Water Resources summarized it as a “snow drought,” with “meager precipitation that fell more often as rain than snow” even though parts of the north had average or above-average precipitation.

That occurred during a strong El Niño, the periodic warming of the equatorial Pacific that sometimes brings heavy precipitation to California. Now, federal forecasters see a nascent La Niña, an ocean-cooling phenomenon linked to drier-than-normal conditions in California.

According to the state Department of Water Resources, in 18 La Niña winters since 1950-51, above-average precipitation occurred 11 times in the northern Sierra and eight times in the central and southern Sierra.

In Southern California, La Niña winters brought below-average precipitation to the coastal region 16 times and 15 times in the region’s interior.

This story was originally published October 28, 2016 at 5:11 PM with the headline "More rain, fog expected for Central Valley next week."