Two more atmospheric rivers heading toward California
By Mark Gomez
PUBLISHED: February 16, 2017 at 5:54 am | UPDATED: February 16, 2017 at 8:08 pm
Two more atmospheric rivers are barreling toward California, including one early next week that will bring a new torrent to Lake Oroville.
The wettest winter in 20 years, courtesy of a never-ending conveyor belt of storms, has washed away the drought in 75 percent of the state. But it has also caused tens of millions of dollars in damage, leading Gov. Jerry Brown to declare a state of emergency last month.
Friday, the first atmospheric river is expected to deluge Southern California with as much as 6 inches of rain. It will also soak the Bay Area.
The second atmospheric river will arrive Monday, and its heaviest rainfall is forecast to occur in Northern California.
“The heaviest rain could go right into the Oroville area,” said Bob Benjamin, a National Weather Service forecaster. Nearly 190,000 people were evacuated from the area Sunday amid concerns about a crumbling emergency spillway at an overflowing Lake Oroville.
The new storms have also stoked concerns about additional flooding, mudslides and road closures potentially affecting Highway 17, streams including Coyote Creek in Santa Clara County and travelers heading to and from the Sierra Nevada.
In just one week, the percentage of California considered to be in a drought dropped by 22 percent, according to the U.S. Drought Monitor, a weekly report issued by the National Oceanic and Atmospheric Administration, the U.S. Department of Agriculture and the University of Nebraska. A year ago, just 5 percent of the state was out of drought.
The largest percentage of the state that remains in a drought is in Southern California, which on Friday could see its strongest storm in the past six years, according to the National Weather Service Los Angeles office. The weekly drought report, published on Thursdays, did not take into consideration any precipitation that will fall through Tuesday. “I wouldn’t be surprised at all if there’s more widespread improvement across California,” said Jessica Blunden, a climatologist with NOAA who wrote Thursday’s drought report. “I would expect more big improvements.”
While the brunt of Friday’s atmospheric river will be felt by Southern California, the Bay Area will see its share of rain, Benjamin said. Monterey Bay will likely see rain early in the morning as the storm moves south to north, delivering rainfall totals ranging from 1 to 2 inches in the hills and a quarter-inch to 1 inch in urban locations.
The storm could impact efforts to clear a mudslide from a stretch of Highway 17 in Scotts Valley and repair the auxiliary spillway of the Oroville Dam.
Of greater concern is another atmospheric river that could soak Northern California on Monday, with the heaviest rainfall north of the Golden Gate and in the Sierra Nevada, Benjamin said.
He added that the Santa Cruz Mountains could also see heavy rainfall, which might result in more mudslides and blocked roadways. Thursday, a stretch of northbound Highway 17 near Scotts Valley remained closed as Caltrans crews continued to clear a mudslide from last week.
On Friday, Anderson Dam in southern Santa Clara County could reach 100 percent capacity for the first time since 2006, resulting in water releases that could cause flooding along Coyote Creek. Anderson Reservoir cannot be more than 68 percent full, a mandate issued in 2009 by the state’s Division of Safety of Dams in Sacramento because of concerns that the dam could fail in a major earthquake.
That order allows for the reservoir to fill up during heavy rains, as long as waters are drained as quickly as possible. Anderson’s outlet has been 100 percent open since Jan. 9, releasing water into Coyote Creek at a rate of more than 400 cubic feet per second, according to the Santa Clara Valley Water District. But the amount of rain and runoff flowing into the reservoir has at times exceeded the rate of water being released.
The storm Friday is the second in a series of four. It follows a quick-moving system Thursday that delivered modest rainfall totals, ranging from nearly 2 inches in Venado in Sonoma County, 1.33 inches in the Santa Cruz Mountains and less than a half-inch in most cities.
Drier weather is in the forecast for the weekend. A fourth system is set to follow Monday’s atmospheric river, arriving late Tuesday night, according to the weather service.
Rainfall totals throughout the Bay Area are all running above average for the season, which began on Oct. 1, including Santa Rosa, which has received a staggering 47.41 inches (195 percent of normal). Others include San Francisco at 22.22 inches (139 percent), Oakland at 19.47 inches (146 percent) and San Jose at 11.90 inches (120 percent).
========
'Biggest storm of winter' to unleash flooding rain in California at week’s end
By Alex Sosnowski, AccuWeather senior meteorologist
February 16, 2017, 7:04:05 PM EST
A new train of storms has arrived along the Pacific coast, and a potent one is set to hit California hard with heavy rain, mountain snow and strong winds to end this week.
The first storm will focused on areas from Northern California to Washington during Wednesday and Thursday.
The second storm in the series will focus most of its moisture on Central and Southern California from Thursday night to Saturday.
"The late-week storm has the potential to be the biggest of the winter in terms of rainfall and impact to much of Southern California," according to AccuWeather Meteorologist Jim Andrews.
The storm will bring enough rain and excess runoff to cause flash flooding, which can cause major delays for motorists. Along with the heavy rain will be the potential for mudslides in some neighborhoods, especially in recent burn scar locations.
"We expect 3 to 6 inches of rain to fall in the lowlands along the coast and over the Los Angeles basin," according to AccuWeather Senior Meteorologist Ken Clark. "From 6 to 12 inches of rain is likely below snow levels in the mountains, especially along the south-facing slopes."
In the Los Angeles and Santa Barbara, California areas, much of this rain may fall in 24 hours from early Friday morning through Friday night. In San Diego, the heaviest rain will fall Friday evening into Saturday morning.
Pedestrians cross a rainy street in downtown Los Angeles on Monday, Feb. 6, 2017. From Dec. 1, 2016, through Feb. 14, 2017, nearly 15 inches of rain has fallen on Los Angeles, which is about twice that of average for the period. (AP Photo/Nick Ut)
That much rain in such a short period of time could lead to some roads becoming impassable for a while.
"From Los Angeles to Santa Barbara County, this storm will bring a widespread and significant flood threat," Clark said.
The combination of heavy rain, a low cloud ceiling and gusty winds will also lead to airline delays.
As the ground becomes soggy again, gusty winds will raise the risk of fallen trees and sporadic power outages.
In addition to strong winds, there can also be locally severe thunderstorms on Friday. It is possible a couple of the strongest storms produce a brief tornado.
Snow levels will remain well above the passes in Southern California. However, those venturing over Donner Pass are likely to encounter slippery conditions. The ski resorts in the Sierra Nevada will likely receive 1 to 3 feet of snow from the storm later this week.
In the wake of the big rain through Friday night, spottier showers will continue to dampen the region on Saturday and Saturday night.
However, locally heavy rain will hit parts of the Desert Southwest and northwestern Mexico this weekend.
The rain will fall in a hurry over the deserts. Normally dry stream beds can quickly fill with water. Motorists should be prepared for flash flooding in cities such as Palm Springs, California, Las Vegas and Yuma, Arizona.
No rain is projected to fall on Southern California during the period from Sunday through next week. The break in the rain will allow crews and property owners to clean up after the storm.
Another storm will roll ashore from the Pacific during Sunday. Most effects from the storm, including the potential for significant flooding will be focused over Northern California during the first part of next week.
As a result of the ongoing storms, more challenges are ahead for crews, officials and residents in the Oroville, California, area. Damage to the spillway at the Oroville Dam forced evacuations earlier this week.
Rainfall from the storms through Friday have the potential to aggravate the situation around Oroville and other reservoirs filled to capacity in Northern California. Additional rainfall will force officials to release more water downstream. Some of these rivers are already at flood stage.
The rainfall to end this week will take another big chunk out of the drought over Southern California.
Total rainfall since Dec. 1 over much of Southern California has ranged from 1.5 to 2.5 times that of average.
While less than 1 percent of the state remained in extreme drought as of last week, much of the region remained in moderate to severe long-term drought, according to the United States Drought Monitor.