Last year at this time, weather forecasters had a pretty good idea of what was in store as California headed into the rainy season. The Pacific Ocean surface was warming, and they were predicting one of the strongest El Niño weather patterns in recorded history.
El Niño ended up making an appearance, but it wasn’t the series of gully washers for which some had hoped. This year, the forecast is even less certain.
“It really is a crapshoot,” said Michelle Mead, a meteorologist with the Sacramento office of the National Weather Service. “We don’t know what exactly we’re going to get, and it’s going to be storm-by-storm dependent.”
In other words, there’s nearly as much chance that California experiences average precipitation or even flooding as there is for another dry winter akin to 2015 when Gov. Jerry Brown stood on a patch of bare grass where several feet of Sierra snow should have been and declared a statewide drought emergency.
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The uncertainty lies in what forecasters describe as neutral conditions in the vast area of the Pacific Ocean that creates El Niño or La Niña weather patterns. When the surface of the Pacific warms, it’s more likely to lead to the wet years typically associated with El Niño. Conversely, cooler ocean temperatures often produce drier La Niña conditions in California. This year, it’s neither warm enough nor cool enough to make a call.
The vague long-term forecast comes as a California hits a key benchmark that forecasters and water managers use to track the state’s hydrological conditions. The so-called “water year” ends Friday.
State officials say the data compiled during the 2016 water year shows that California remains mired in a five-year drought. The hottest summer on record certainly didn’t help ease the problems plaguing California including irrigation-water shortages, plummeting groundwater basins, elevated risk of wildfire and millions of dying Sierra trees.
While some heavy storms brought rain to parts of Northern California and snow to the Sierra, an unseasonably warm and dry February brought a hurried shrinking of the snowpack.
Arthur Hinojosa, the Department of Water Resources official overseeing the agency’s statewide drought response, said it wasn’t particularly surprising. Over the past few years, snow has begun to melt much earlier than normal. Historically, peak snowpack levels were measured in April. Lately, it’s mid-March or earlier.
“Although we did see some decent amounts of total (Northern California rainfall), the snowpack wasn’t on par with that percentage-wise,” Hinojosa said. “There was less snow proportionally than we’re used to seeing historically. This is in a large part due to the warm year it was.”
Should the trend persist into this rainy season, it doesn’t bode well for the state’s massive water-delivery system of reservoirs and canals operated by the state and federal governments. California’s rivers were dammed to take advantage of historic weather patterns, with a focus on regulating flows to prevent downstream flooding during heavy storms and capturing snowmelt to buoy the state through summer and fall.
The state’s approximately 1,500 reservoirs portion out water over the year to meet demand for farm and landscape irrigation, drinking water, and fish and wildlife habitat. The vast man-made conveyance network is capable of funneling Mount Shasta snowmelt 700 miles south to San Diego.
The Northern California rains brought some relief since the region is home to the largest reservoirs. The total statewide reservoir storage is around 82 percent of average, Hinojosa said. That’s a rosier picture at the end of September than last year at this time, when storage was 55 percent of average.
Southern California, meanwhile, remains especially dry. The Colorado River Basin, which provides a critical source of water used by Southern California cities and farms, is coming off the driest 16-year period in the historical record.
Forecasters say that, all told, it’s going to take a long time before anyone declares California’s drought over.
“Really, to fully erase the drought, you’d need multiple, consecutive wet winters and, ideally, cooler years in terms of getting a nice accumulation of mountain snowpack,” said Daniel Swain, a climate scientist at UCLA’s Institute of the Environment and Sustainability.
There is some good news in the short-term forecast, at least for Northern Californians tired of the summer heat.
National Weather Service forecasters say it’s about to get substantially cooler in the region. Sacramento temperatures should begin dipping into the mid-80s by Thursday, and on Sunday, there’s a slight chance of showers with a high near 69. It could snow that day in Truckee.
How this year compared
Water years start Oct. 1 and end Sept. 30. The 2016 water year ends Friday.
Sources: California Dept. of Water Resources, NOAA