A conveyor belt of atmospheric rivers that filled reservoirs across Northern California and blanketed the Sierra Nevada with snow last year have been replaced in 2018 by a recurring ridge of high pressure that is bouncing storm systems north to the Pacific Northwest.
A ridge of high pressure building about 900 miles west of Los Angeles is expected to keep California dry for the next several days, according to the National Weather Service. Not only is there no rain in the extended February forecast, meteorologists with the weather service say the Bay Area could experience record-high temperatures this weekend, with daytime highs soaring into the mid-70s.
“That high pressure is going to allow for continued warmth through the first week of February, with virtually no rain chances through at least Feb. 11,” said Scott Rowe, a meteorologist with the weather service. “Until we see the ridge break down, virtually no rain chances are expected.”
The warm-up began Thursday. Between Friday and Sunday, many cities in the Bay Area could experience record high-temperatures for this time of year.
According to Accuweather, daytime highs will remain in the low 70s for communities in Lake County at lower elevations through Feb. 9. The forecast for today calls for a peak of 73 in Lakeport, with temperatures reaching 76 on Saturday.
The average for this time of year is for highs in the mid-50s.
One of the driest Decembers on record in California put the entire state in an early rainfall deficit for this water year, which began Oct. 1. Despite a wetter than average January, rainfall totals throughout California remain below average for this time of year.
Those percentages will continue to fall during this extended stretch of dry weather of February, which is typically one of the three wettest months of the year.
Accuweather’s monitoring station in Lakeport records 5.93 inches of rain in a typical year. But long range forecasts do not see any precipitation in Lake County until Feb. 21.
“The dry start, the December deficit really added up,” Rowe said. “We definitely did not dig ourselves out of that.”
The weather service said some models suggest signs of a strong jet energy eventually breaking down the ridge of high pressure, but that could be a few weeks away.
“It appears a high probability we will essentially lose the first two weeks of February for any rain potential,” the weather service wrote in its daily forecast.
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.”
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.”
Rainfall across the state has varied dramatically this winter — and is far below levels seen a year ago.
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.”
