When will we get a break from the storms?
Blue skies eventually will return, but more rain is in the forecast
We needed the rain, but now we need to know: When will we get a break?
The powerful train of Pacific storms battering California with record rainfall and major flooding will slow, perhaps even stop, meteorologists say — but not until the second half of January.
In the meantime, expect the weather drama to continue. At least three more storms — ranging from moderate to significant — were predicted this week, flooding more landscapes that already are saturated with rainwater.
On the distant horizon is a ridge of high-pressure air that may help block incoming storms and weaken those that do get through, according to state climatologist Michael Anderson. High-pressure ridges deflect storms north toward British Columbia, away from California.
“After January 19th, the storms die down and we see that high pressure resuming its `blocking stance' of shunting storms back to the north,” said Anderson, although there's uncertainty in such a long-term forecast.
Monday's storm was a continuation of atmospheric rivers , which are plumes of tropical moisture that are responsible for much of California's precipitation.
Another storm was expected Tuesday, with at least two others likely to follow this week.
Tuesday's cloudburst is likely to produce brief spiraling bands of strong coastal thunderstorms from the Bay Area to Los Angeles County, with brief and intense rain, wind gusts over 60 mph and potential waterspouts or weak coastal tornadoes.
These are the kinds of conditions that set the stage for significant flash flooding and debris flows, especially along the Big Sur coast and the steep transverse ranges of Santa Barbara, Ventura, and other Southern California counties.
After that, the incoming sequence is likely to be cooler, with accumulations of dryer mountain snowfall, according to UCLA climate scientist Daniel Swain. This is good news because it reduces the amount of runoff coming from the mountains, where California's frozen reservoir of snowpack accounts for about one-third of the state's water supply.
While no single storm in this sequence has proven catastrophic, the relentless pattern has left little time for drainage, recovery and drying out.
Flooding concerns will likely persist all week, although they do not appear as threatening as Monday's and Tuesday's events, Swain said.
Then “we will start to get a break,” he said. “It will give the rivers in Northern California and in central California a chance to come down.
“We still do have significant events to get through between now and then, but there is some `cool down' of this active pattern on the horizon.”
The steady downpours are unsettling to Californians because we've become accustomed to dry conditions, climate scientists say. Over the past decade, our winters haven't felt much like winter.
The late 1990s were the last times that the state had a sustained wet period and regionally devastating events, with many storm cycles like the current one, Swain said.
Those storms were associated with strong El Niño events. But, interestingly, El Niño — when ocean waters warm, often causing wet winters to California — isn't behind the current pattern. We are in our third year of La Niña — and it is weakening, exerting a waning influence..
“We really can't attribute this current cycle either to La Niña or El Niño because neither of them are particularly strong right now,” Swain said. “So there's something else going on this year. It could just be random luck, or it could be something that's a little more traceable that we'll find out about later. It's almost impossible to see in the moment.”
Delving back further into the historical and geophysical record shows that the Golden State is a landscape that has long experienced swings in precipitation.
“California is intrinsically a place that has a lot of variability … with extreme swings between extreme dry and extreme wet conditions,” Sain said.
Climate scientists call that “precipitation whiplash.”
Extraordinary megaflood events are rare. The most recent occurred in 1861-1862 when a multiweek super-soaker storm sequence dubbed The Great Flood of 1862 inundated vast swaths of California, including a 300-mile long stretch of the Central Valley, large portions of the modern-day Los Angeles metro area and virtually every narrow river valley throughout the state, according to Swain.
That storm started on Christmas Eve and continued until early February.
When UC Berkeley geologist B. Lynn Ingram looked back even further into the historic record — using sediment cores from flood plains, bays or the ocean coasts — she found thick flood layers produced by other big storms, with an 1861-type flood, or larger, occurring about every 200 years.
With climate change, California will face more profound floods, according to models. It will experience overall drying, but also larger and more frequent atmospheric river storms fueled by increasing evaporation in the tropics.
Last year, Swain's Arkstorm scenario modeled the impacts of an 1861-type storm and calculated potential losses of more than $700 billion.
“We strongly believe that someday — and perhaps sooner rather than later, although we don't know when — we will see a truly catastrophic storm sequence in California,” Swain said. “We should get used to storms cycles like this one.”