Good morning! Here's a look at the simulated radar from the HRRR. Widespread rain will develop this afternoon and become heavy late this afternoon and evening. Gusty south winds will also develop making for extremely hazardous driving conditions during the PM commute. #CAwx pic.twitter.com/w7W12jgYW9
— NWS Bay Area (@NWSBayArea) January 16, 2019
Following a weaker storm that soaked the Bay Area on Tuesday, a powerful ‘atmospheric river’ is hours away from drenching the Bay Area with 1 to 2 inches of rain and will likely cause widespread roadway flooding during the Wednesday evening commute.
The storm is also expected to blanket the Sierra Nevada with a blizzard dumping 2 to 5 feet of snow.
San Jose could eclipse a record for rainfall on Jan. 16 (1.38 inches in 1973), based on weather records going back to 1893, according to the National Weather Service. In San Francisco, where weather records date back to 1850, the record for rain on Jan. 16 is 2.46 inches in 1862.
The heaviest rainfall rates should peak late Wednesday afternoon into the evening as a cold front approaches, according to the National Weather Service, bringing wind gusts of 50 to 70 mph in the hills, the risk of small streams flooding, downed trees and possible power outages.
“Compared to previous storms we’ve had this winter, this is definitely going to be one of the more notable storms,” said Matt Mehle, a forecaster with the National Weather Service in Monterey. “It is going to bring heavy rain, really strong winds and high surf.”
In a daily forecast issued Wednesday, the weather service said ‘the combination of heavy rain, areas of roadway flooding, strong winds, and tree/powerline damage will create very hazardous driving conditions Wednesday afternoon and evening.”
The weather service has issued a flash flood watch for streams and creeks from Big Sur to the North Bay during Wednesday afternoon and evening. “Urban and small stream flooding will become likely along with rapid rises on main-stem rivers,” the agency said in an alert. Forecasters said that major rivers are not expected to flood.
The weather service also issued a high hind warning from Wednesday afternoon through early Thursday morning for the coastal areas and higher terrain, where gusts of up to 60 mphare possible. The highest peaks will likely see even higher gusts. For the lower elevations away from the coast, a wind advisory is in effect Wednesday afternoon through early Thursday morning, where wind speeds of 25-35 and gusts up to 50 mph are expected.
Powerful storm system as seen by (preliminary, non-operational) GOES-17 satellite imagery this morning. Prepare for heavy rain, gusty winds, and scattered thunderstorms later today. #CAwx pic.twitter.com/sX0lCmQSPP
— NWS Bay Area (@NWSBayArea) January 16, 2019
The storm could bring 6 to 10 inches of rain in the Santa Cruz Mountains and Big Sur by Friday morning. Most Bay Area cities will see 1 to 3 inches, which will help boost winter rainfall totals back to near 100 percent.
The National Weather Service issued a blizzard warning for the Sierra Nevada on Wednesday and Thursday. The bulletin warned of “potentially life threatening conditions” above 7,000 feet in elevation, with winds up to 110 mph on ridge tops and high avalanche danger. It urged motorists to avoid mountain roads.
Atmospheric rivers are a particularly moisture-heavy, intense type of storm event. They can be 250 miles wide, 1,000 miles long and can carry 20 times as much water per second as the Mississippi River where it empties into the Gulf of Mexico.
A Blizzard Warning has been issued for the Sierra Wed PM-Thurs AM for elevations >7,000’. Dangerous & potentially life threatening conditions will be possible. Blizzard Warnings are saved for only the most serious situations at our office. Stay home, stay safe! #CAwx #NVwx pic.twitter.com/52nEAhq4LR
— NWS Reno (@NWSReno) January 15, 2019
Such storms are vital to the water supply of California and other Western states, with about a dozen significant ones providing between 25 and 50 percent of the annual water supply in most years.
“This is a very productive event. There are places in California that will get up to 10 inches of rain over the next week,” said Marty Ralph, director of the Center for Western Weather and Water Extremes at UC San Diego. “That could be 10 percent of the average annual precipitation for many parts of California.”
In years when there are more atmospheric rivers than average, serious flooding can occur. An atmospheric river storm last January caused major mudslides in Santa Barbara County over an area that had been burned the previous month in the Thomas Fire near Montecito. Those mudslides killed 21 people, injured 163 and destroyed 65 homes.
On the flip side, there can be droughts in years when there are fewer atmospheric rivers than normal, such as during the state’s 2011-2016 historic drought, when relentless ridges of high pressure air blocked many such storms from reaching California.
When the storms originate from Hawaii and tropical areas of the Pacific, they are called “Pineapple express” storms. The storm Wednesday is not a Pineapple express, said Mehle. It is coming from about 200 miles north of Hawaii.
A weaker storm Tuesday dropped one-quarter to half an inch of rain across much of the Bay Area, with some locations seeing nearly an inch. As of 6:30 a.m. Tuesday, 24-hour rainfall totals included .95 inches in San Francisco, .61 inches in Oakland, .39 inches in Hayward, .37 inches in Concord and .22 inches in San Jose. The wettest area was Ben Lomond in the Santa Cruz Mountains, which received 2.86 inches in the same 24-hour period, according to the weather service.
The rain is forecast to taper off by Friday. Following a chance of rain Sunday, the weather service is forecasting a “drying out” period next week.
The storm system is expected to bring snow levels in the Sierra Nevada up to 100 percent of the historic average for this time of year. On Tuesday morning, snow levels were 84 percent of normal, following a sub-par November and December.
After a slow start in November and December, a series of January storms has boosted rainfall totals across the Bay Area, though the region remains in a precipitation deficit for this time of year. Since the start of the rainfall season Oct. 1, San Francisco has received 7.76 inches of rain, or 71 percent of its historic average through Jan. 14. Oakland has received 6.74 inches, or 68 percent of normal; and San Jose has recorded 4.59 inches of rain, or 71 percent of normal.
But with soils saturated and creeks and rivers rising, reservoir levels should come up this week also, improving the summer water outlook.
“It’s definitely going to help,” said Mehle. “This week is going to be moving us in the right direction.”
Staff writer Jason Green contributed to this report.