Soggy, snow-covered California faces another month of wet weather, but what remains uncertain is whether this late winter precipitation will add to weeks of record-breaking snow, or cause it to dissipate as warmer rains arrive.
Last week, an icy storm transformed parts of the state into a white landscape as trees toppled, caused power outages, spurred water rescues and left some residents stranded by heavy snow.
Now, with forecasts calling for more rain and snow in March — including the potential for at least one more atmospheric river system — California is girding itself for what comes next.
“If we got heavy rain with a warm system and a lot of tropical moisture in it, it would melt all the snow that just fell in the mountains,” said David Sweet, a meteorologist with the National Weather Service in Oxnard. .
Typically, California’s snowpack provides about one-third of the state’s water supply and has long been relied upon for its steady, slow melting during the hot, dry months of summer. However, a deluge of warm rain can cause melting snow to fill rivers too quickly and cause widespread flooding.
“We have to keep that in mind and think, ‘Boy, I really hope that doesn’t happen,'” Sweet said.
The National Oceanic and Atmospheric Administration’s outlook shows above normal chances of precipitation throughout California through March.
(NOAA)
Forecasters say it’s too early to say exactly how the rest of the winter will play out, but the latest 30-day outlook from the National Oceanic and Atmospheric Administration’s Climate Prediction Center, published on Tuesday, shows above-normal chance of precipitation throughout California through March, as well as a higher chance of cold temperatures. That could bode well for the state’s ample snow pack.
“We are confident that the next two weeks will likely see wet weather and that an active pattern (of wet weather) may very well continue for the remainder of the month,” said Jon Gottschalck, head of the operational forecasting arm of the company. climate center. an e-mail.
In the coming days, the western United States is expected to be “dominated by upper-level low pressure,” Gottschalck said, likely bringing more low temperatures and low-lying snow to California. That means “much of the precipitation, at least over the next week, will add to the snow pack.”
But the arrival of more precipitation in the weeks that follow may be cause for concern.
UCLA climate scientist Daniel Swain said about 20% of forecast models currently show a very strong and warm atmospheric river storm in California around mid-March. In early January, California was pummeled by a series of nine atmospheric river storms, breaking levees and contributing to nearly two dozen deaths.
Should such an event occur in the wake of extensive snow, “that could indeed pose (a) significant flood threat”, Swain said on Twitter. However, he said this is “early speculation” because the current chance of such a warm storm is about 1 in 5.
The recent winter storm has already dropped a lot of cold rain and snow in parts of California. Many Southland peaks received more than 50 inches of fresh powder, with the Mountain High ski resort in Wrightwood recording 93 inches, according to the National Weather Service. Daily rainfall records were set at Los Angeles International Airport and in Burbank, downtown Los Angeles and several other parts of the region.
If similar conditions continue, the season has a chance to become one of California’s snowiest on record, Swain said.
Across the state, snowpack remains incredibly healthy — 186% of normal for the date as of Tuesday, according to state data. In the southern Sierra it is 224% of normal. Reservoirs are also remarkably healthier, with Lake Shasta’s volume nearly doubling from two months ago.
The immediate forecast in the Sierra is continued icy conditions, including “a very cold pattern with several feet of snow this weekend,” said Wendell Hohmann, a meteorologist with the National Weather Service in Reno.
“The atmospheric river signals are quite far out there, so the predictability is quite low and confidence is therefore quite low,” Hohmann said, “but it kind of opens the door for us to keep an eye on it at this point.” , see how it evolves.”
In addition to flooding, a warm rain-on-snow event can pose challenges from a water supply perspective. Earlier-than-usual snowmelt, especially in the Sierra, could make it harder for state water managers to plan ahead and could have negative impacts on hydropower and ecology, experts say.
Sweet, from the weather service, said he focuses mainly on short-term forecasts, but also keeps an eye on longer-term models, which are “starting to hint” at the possibility of such a system.
As it stands, the forecast for more precipitation of any kind comes amid a winter that has already defied expectations in California. In October, the seasonal outlook pointed to a drier-than-normal season, driven by a rare third La Niña rise. The fact that conditions have gotten so wet speaks to the challenges of long-term forecasting, Sweet said.
“We still don’t have absolute razor sharp focus, or a way to look at the extended forecast, and really be sure,” he said.
Despite the dangers, the wet weather has had many benefits in California.
Improved snowpack and reservoir levels have enabled state water managers to tentatively increase State Water Project allocations to 35%. In December, they said they would only be able to give about 5% to 29 agencies, which collectively serve about 27 million Californians.
The U.S. Drought Monitor also removed nearly all of California from its worst two categories this year for the first time since 2020: exceptional and extreme drought.
As of this week, about 33% of the state remains in severe drought, the third worst category, This is reported by the Drought Monitor. About 52% of the state is categorized as moderately dry and 15% as “abnormally dry”.
A small county — Del Norte, in the far northwestern corner of the state — has completely emerged from the drought.
