Hampered by hot weather and a stubborn high-pressure ridge that has blocked winter storms, California’s Sierra Nevada snowpack — a key source of the state’s water supply — on Tuesday was a paltry 30 percent of normal.
The last time there was so little Sierra snow at the end of January was in 2015, when it was 25 percent of its historic average.
By April 1 that year — after the snowpack had shrunk to an all-time low of 5 percent of average — Gov. Jerry Brown stood in a barren, rocky field in the mountains near Lake Tahoe and declared a drought emergency that included mandatory statewide water restrictions for the first time in California history.
“This historic drought demands unprecedented action,” Brown said then, urging Californians to cut water use 25 percent and to “pull together and save water in every way possible.”
They did. The drought ended last April after relentless winter storms that brought flooding to San Jose and wrecked Oroville Dam’s spillway also filled reservoirs across California.
But now, as the state Department of Water Resources prepares on Thursday to do its monthly manual snow reading at Echo Summit, with TV cameras in tow, the continued hot, dry winter weather is raising concerns.
“February is the peak season for snow accumulation,” said Daniel Swain, a climate scientist at UCLA who studies Western weather patterns. “Every week that we don’t reverse this trend from here forward, it’s going to be that much harder to get to where we want to be by the end of the season.”
Nearly all of California’s rain and snow falls between Nov. 1 and March 31. So time is running short.
“The figures don’t lie,” said Doug Carlson, a spokesman for the state Department of Water Resources. “We’re at 30 percent snowpack right now, and last year at this time we were at 182 percent.”
Ominously, the forecast for the next two weeks calls for more hot weather across the state, with almost no chance of rain or snow.
The reason: A ridge of high-pressure air, which is nearly 4 miles high and stretches from the Gulf of Alaska to the California-Mexico border, has been strengthening in recent days. Such ridges, which were the main cause of the state’s 2012-2017 drought, block storms that normally bring California moisture during the winter months.
“It’s like a giant boulder sitting in the stream and preventing the stream from reaching the state,” Swain said. “The stream is the jet stream, and it’s sending storms into Alaska and British Columbia.”
What’s particularly vexing is that precipitation levels haven’t been terrible in Northern California this winter. In the Northern Sierra, after a few big storms earlier this month, total precipitation since Oct. 1 has been about 70 percent of average. It’s about 50 percent of average in the Central Sierra and about 30 percent in the Southern Sierra.
But the snowpack overall is less than a third of its historic average because it’s been much warmer than normal this winter, Swain said. Over the past 90 days, the average temperature in the Sierra has been about five degrees hotter than average, he noted.
“That’s a big deal — especially when you are in a place where it sometimes snows and sometimes rains,” he said. “And if you add 5 degrees to your temperature when it is close to freezing, you aren’t close to snow any more.”
Scientists and meteorologists don’t know exactly what is causing this year’s temperature spikes and the return of the strong ridges. Some of it is random bad luck, they say.
Some of the problem is related to La Niña, the cooling of the sea surface in the eastern Pacific Ocean near the equator — a phenomenon that has been linked to dry weather in California in years past. But climate change is also to blame. The 10 hottest years on Earth since 1880, when modern temperature records began, have all occurred since 1998, according to NASA.
And the last three years have been the three hottest.
“Short term, we’re talking weather,” said Jan Null, a meteorologist with Golden Gate Weather Services in Saratoga. “When we look at enough of a history to see a pattern, decade by decade, then we are talking about climate. Everything going on is affected by the fact we have warmer oceans and a warmer atmosphere than we did years ago. We still have cold periods, but if we extend the trend line in the direction it is going now, it is certainly going to be warmer and probably drier in California in the coming decades.”
The average January high temperature in Los Angeles from 1981 to 2010 was 58 degrees. On Tuesday it reached 83 degrees, according to the National Weather Service. The day before, heat records fell across Southern California as wildfire officials issued red-flag warnings. On Monday it was 91 at Long Beach Airport, breaking the previous record of 83.
Rainfall across the state has varied dramatically this winter — and is far below levels seen a year ago.
Since Oct. 1, San Francisco has been at 65 percent of normal rainfall, with 8.5 inches. Last year at the end of January, it was at 142 percent of normal after a series of drenching “Pineapple Express” storms delivered 18.45 inches.
Similarly, San Jose is now at 60 percent of its historic average, with 4.77 inches since Oct. 1. Oakland is at 70 percent, having received 7.81 inches.
But Southern California is in a much more dire situation. Los Angeles has had only 27 percent of its average rainfall at this point in the winter season, with a meager 1.89 inches. Last year at this time, the city had more than seven times as much rain, with 14.33 inches — 207 percent of normal. Some areas are even drier. Fullerton had had 18 percent normal rainfall, Irvine 6 percent.
Only two winter seasons that have been this dry through January in San Francisco have ended in a year with normal or above rainfall, according to Null’s calculations, and none in San Jose or Los Angeles have occurred when January rain totals are this low.
But there have been wet March months in the past — particularly the “March Miracle” of 1991 that brought triple the average March precipitation, boosted the Sierra snowpack from 15 percent to 75 percent in 30 days and signaled the beginning of the end of the 1987-1992 drought.
And reservoirs around California are in good shape. Most are nearly full after last year’s storms, reducing the chance of summer water restrictions.
“It is a reason to be somewhat concerned, but we still have a ways to go,” Carlson said. “It’s a good time to remember the lessons we learned in 2015 and 2016. We can save water and make conservation a way of life. That should never be out of mind.”
