Forecasters are confident that weak El Nino atmospheric conditions will set in as the winter progresses, and in California, that can mean anything.
While El Nino conditions are known for producing wet, warm storms from the south, state and National Weather Service forecasters say there’s an equal chance of below-normal, normal or above-normal precipitation in California this winter.
The Golden State has a good chance of seeing warmer-than-average temperatures, but that doesn’t mean there won’t be any cold storms or freezes, says Cindy Matthews, a NWS forecaster in Sacramento.
“California winters are determined storm by storm, and the seasonal outlooks will not capture these storms,” Matthews says in an email. “We, as operational forecasters, can see the storms and their potential impact about seven to 10 days out.”
Matthews’ words of caution came amid a winter outlook report she prepared with NWS warning coordinator Michelle Mead, the California Nevada River Forecast Center’s Pete Fickenscher and California State Climatologist Mike Anderson.
The state’s water year started Oct. 1. It looked promising in some areas, as some decent showers moved through Northern California and some remnant tropical storm moisture appeared over southeastern California and the Southern Sierra Nevada range, Matthews notes.
But no storms have come through since then, getting most areas of the state off to a slow start in terms of season precipitation. For instance, Fresno usually accumulates over an inch of rainfall by mid-November, but it had only recorded 0.1 inches as of Nov. 13, according to the weather service. Likewise, Sacramento had only accumulated 0.04 inches, well below its average 1.65 inches.
As such, most of the state is shown as being abnormally dry or in moderate drought, according to the U.S. Drought Monitor. More severe drought conditions exist along the Southern California coast, the border with Mexico, and the California-Oregon state line.
Many key reservoirs are dipping below their historical averages, according to the state Department of Water Resources. Shasta Lake, the centerpiece of the federal Central Valley Project, was at 47 percent of capacity and 80 percent of its seasonal average as of Nov. 12. Lake Oroville, the State Water Project’s chief reservoir, was at only 31 percent of capacity as the DWR was still keeping surface levels low to accommodate crews finishing up their work on the dam. A year ago in November, most reservoirs were comfortably above their seasonal averages.
El Nino is marked by warmer-than-average sea surface temperatures in the equatorial Pacific Ocean and can produce robust southern storms. The last El Nino in 2015-16 helped California start to emerge from a five-year drought, but equatorial temperatures were considerably warmer than they are now, forecasters say.
As it is, meteorologists say a wetter-than-normal winter is likeliest from Arizona into Texas and the U.S. Southeast, with northern Idaho, Montana and Wyoming likely to be relatively dry. As for temperature, all of the Western U.S. – and particularly the Pacific Northwest – are likely to be warmer than normal, according to the federal Climate Prediction Center.
“Even though we’re experiencing a slow start to our water year, you need to keep California’s water story in mind,” Matthews says. “Recall, our wettest months are still to come – December, January, February and March. We typically receive the bulk of our precipitation and snow during those months. It’s still early.”