In what could be Northern California’s last dose of heavy rain this season, a system moving in from the Pacific Ocean began pelting Lake County on Thursday. Another 2.5 inches or more will soak the area by the time the clouds clear on Sunday, according to Accuweather forecasts.
“Statistically speaking, this should be the last big storm of the season,” said Brian Mejia, a forecaster with the National Weather Service. “But we do see another chance of rain by mid-week next week.”
Although it had not yet rained this month until yesterday’s bout, most area cities receive an average of 1 to 2 inches of wet stuff in April, according to the weather service. Some monthly April averages include Lakeport 1.7 inches, Santa Rosa 2.0 inches, San Francisco 1.5 inches, Oakland 1.35 inches and San Jose 1.06 inches.
A second system is expected Friday night into Saturday morning and will bring another round of rain and heavy winds. Drier weather is expected Sunday and Monday.
A few weaker systems could produce showery conditions early next week, and again after midweek.
Sunday will be much warmer, according to Mejia. The highs are expected to reach the low to mid-60s, Mejia said, kicking off a warming trend that could last into part of next week.
But a dry start to April and a modest March that brought 2.95 inches of rain to Accuweather’s weather station in Lakeport — almost 2 inches below normal — knocked the 2016-17 season out of the record books.
California’s current water season can no longer lay claim to being No. 1. Instead, it now ranks as the second wettest in 122 years of record-keeping, according to data released Thursday by federal scientists.
Between October 2016 and March 2017, California averaged 30.75 inches of precipitation, the second-highest average since such records began being kept in 1895, according to the National Centers for Environmental Information, part of the National Oceanic and Atmospheric Administration.
This current water season was outpaced by 1982-83 (34.38 inches average), when a series of powerful and deadly El Nino storms brought high wind, heavy rain, and heavy snowfall across all of California. The storms resulted in widespread flooding and mudslides to coastal mountain ranges, causing 36 deaths, according to the Western Regional Climate Center.
The statewide precipitation values given by NCEI “represent area weighted average of values observed at weather stations across the state,” according to Nina Oakley, a California Climate Specialist with the Western Regional Climate Center, part of NOAA.
This current water season had ranked No. 1 through the end of February, fueled largely by a conveyor belt of “Pineapple Express” storms that inundated much of the state with rain and snow. The water year (October through September) record for California is 1982-83, which totaled an average of 40.41 inches, according to the NCEI data.
Jan Null, a meteorologist with Golden Gate Weather Services, places little value in the statewide rankings because they take into account “a lot of areas that do not contribute to our water supply.”
Instead, Null said the most important factor for California rainfall are three watersheds along the Sierra Nevada that account for three-quarters of the state’s water supply. The eight-station Northern Sierra Nevada index, a mix of rain gauges near major Northern California reservoirs, currently stands at 83.48 inches of rain, about 5 inches shy of the all-time record set in 1982-32.
The five-station Central Sierra index and the six-station Southern Sierra index have also received more than 150 percent of their normal averages, and all three could finish this season with record numbers, Null said.
“This is certainly a significantly wet year,” Null said. “In terms of snow pack, it’s only the sixth highest. There are so many different metrics to look at. I think the best ones are the Sierra multi-station indexes. That’s what ends up in the reservoirs.”
Driving California’s precipitation totals this year was a parade of “Pineapple Express” storms, a type of “atmospheric river” that gets its name from the plume of moisture coming from Hawaii into California. Pineapple Express storms can be 250 miles wide, 1,000 miles long and carry 20 times as much water as the Mississippi River at its terminus with the Gulf of Mexico.
The record precipitation has allowed California to pull out of a five-year drought. In March 2016, just 5 percent of California was classified as free from drought. As of April 4, 2017, 91 percent of the state was no longer in drought condition, according to federal scientists.
For years, the National Weather Service reported data for the rainfall season, which runs from July through September. A few years ago, at the request of the state’s Department of Water Resources, the weather service began reporting data for the water year, which runs from October through September, according to Bob Benjamin, a meteorologist with the weather service.
Meteorologist Anna Schneider of the National Weather Service agreed the upcoming storms could be the last big rain events of the season in the Bay Area.
‘It would be unusual to see any more potential rainfall,” Schneider said.
However, Accuweather’s long term forecast for the month anticipates small amounts of rain possible each day from April 11 to April 18.
Dave Faries of the Lake County Record-Bee contributed to this report
