El Niño finally arrived in Northern California on Monday, bringing rain, snow and hopes for relief from four years of drought.
After months of forecasts, the weather phenomenon caused by warming ocean temperatures began delivering on its promise. The light morning rain that greeted Sacramentans was expected to give way to heavier precipitation later in the day. The National Weather Service predicted “a stronger wave” after midnight and advised motorists to take extra care during the Tuesday morning commute.
Another series of storms was expected starting Wednesday and extending into Thursday.
Until now, the season’s storms have been the product of the northern polar jet stream, said Michelle Mead, warning coordination meteorologist with the weather service’s Sacramento office. This week’s storms, however, are being driven by southern subtropical weather patterns, as is common with El Niño, she said.
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The El Niño phenomenon is caused by warming of Pacific Ocean waters and generally brings a wet winter to much of California.
“The typical El Niño weather pattern has developed this week,” Mead said. “That will usher in a series of storms. It is happening quite textbook.”
She said the initial storm was forecast to bring significant rainfall Monday night and Tuesday, although the temperatures were expected to stay relatively warm and snowfall would probably be confined to higher elevations: 4,500 feet or above. The high temperature Monday was expected to hit 54 degrees in Sacramento.
“There’s definitely going to be some travel headaches for people heading over the Sierra,” she said.
A second storm, hitting Wednesday and Thursday, is expected to be accompanied by colder temperatures in the mountains. Snow could fall as low as 3,000 feet, Mead said.
State climatologist Michael Anderson said the back-to-back quality of the storms is another hallmark of El Niño.
“It follows that pattern of storm after storm lining up over several days,” he said.
For months, forecasters have said that El Niño would likely have its greatest impacts starting in January. Whether it delivers much more rain will depend on how it interacts with other atmospheric weather patterns across the globe, particularly in the Arctic and tropics, Anderson said.
“Will this pattern stick or is there anything going on with some of the other climate signatures?” Anderson asked, adding that it is too soon to answer the question. “For this week, it seems we are in a favorable pattern more consistent with El Niño.”
Kelly Redmond, deputy director and regional climatologist for the federal government’s Western Regional Climate Center in Reno, said warm water is concentrated off the coasts of the Pacific Northwest and Southern California, an atmospheric pattern that could increase the amount of rainfall associated with this El Niño.
“We do see that in the past, when we have El Niño, we do tend to see heavier precipitation over Northern California, even extending over to Oregon and Washington,” Redmond said.
El Niño appears to be losing some intensity, but is still strong, and will likely continue through winter and possibly into early spring, Redmond said. “It’s so strong that it has a long way to weaken,” he said.
El Niño often strikes hardest in Southern California, and authorities there were issuing warnings about mudslides and other problems. Officials in Azusa, for instance, offered sandbags because of potential floods, according to the Los Angeles Times.
In Northern California, things were less frantic. Caltrans reported no travel advisories, chain controls or road closures through much of the day. By midday, the rain had tapered off in much of the Sacramento region.
However, weather forecasters said travel conditions were expected to worsen much later in the day.
Forecasters have said this is likely to be one of the strongest El Niño winters ever. State officials are hoping for heavier-than-usual snowfall, which could be the key to breaking the drought. Despite some encouraging signs, the Sierra snowpack was just 97 percent of average heading into Monday’s storms. In a normal year, the snowpack can provide 30 percent of the state’s water supply, as melting snow in spring and summer helps replenish the state’s reservoirs.
For now, the key reservoirs remain depleted. Folsom Lake is just a quarter full, or about half as full as it should be this time of year, according to Department of Water Resources data.
Officials said they won’t know until April or May if El Niño has provided enough precipitation to bring meaningful drought relief.