Since Christmas, no fewer than eight atmospheric rivers — narrow but intense filaments of deep tropical moisture stretching thousands of miles across the Pacific — have bombarded California. The atmospheric rivers were aimed at the coast like a series of meteorological fire hoses, and at least 17 deaths have been attributed to the onslaught, which has brought damaging floods, landslides, downed trees and power outages.
Prolific rain totals of 10 to 20 inches, up to 200 inches of mountain snow, winds approaching hurricane force and even a handful of tornado warnings have accompanied the promenade of storms. At long last, there is a possible pause in sight — probably in about 7 to 10 days — but not before several more episodes of heavy precipitation. And, if there is a pause, it’s too soon to know whether it will be sustained or short-lived.
The latest wave of rain was soaking areas near and north of the Bay Area on Wednesday morning. That will taper into downpours mainly affecting Northern California near the Oregon border into Friday morning, before the possibility of more soaking rain for the Bay Area and Central Valley, and eventually areas farther south, into the weekend.
That will then be followed by yet another gut punch to the beleaguered region on Monday into Tuesday.
Flood watches and wind advisories blanket the northern two-thirds of California, with winter weather advisories in the mountains. Gusty winds at times mean an ongoing threat for downed trees and power outages. For now, the National Weather Service office serving the Bay Area writes that the “storm door remains open,” though there’s finally a glimmer of hope for sunnier days ahead.
Storminess targets areas of Northern California through Friday
On Wednesday, a large cyclone, or low-pressure system, was located about 1,000 miles offshore of the Pacific Northwest. Its counterclockwise spin was swirling ashore waves of moisture along a warm front, with widespread light to occasionally moderate rain.
Rainfall will be steady on Wednesday, but not overly intense. The bulk of the precipitation will fall north of the Bay Area. A half-inch to an inch of rain is probable in San Francisco, with up to 1 to 2 inches north of the city through Wednesday night.
On Thursday, rainfall ahead of an approaching cold front will be mainly confined in a north to south strip over northern coastal California. Most computer models suggest this will skirt north of the Bay Area, at least until Thursday night. Some models bring heavy rain back toward San Francisco on Thursday night into Friday, which could also push eastward into northern areas of the Central Valley.
Areas along the Northern California coast could see 2 to 4 inches of rain through Friday, with 3 to 6 inches in the higher terrain of the Coastal Range. Closer to an inch is probable around San Francisco and Sacramento.
The Weather Service office serving the Bay Area cautioned, “additional accumulating precip will be problematic given saturated soils and full creeks/streams.”
“Storm drains and ditches may become clogged with debris,” wrote the National Weather Service in Sacramento. “Area creeks and streams are running high and could flood with more heavy rain.”
Significant atmospheric river on Saturday
A more significant atmospheric river will surge into California over the weekend. That will come as the aforementioned low-pressure system over the northeast Pacific shifts to the north and east, tugging a jet of moisture into much of the state, progressing from north to south.
Coastal areas over almost the entire state as well as the Central Valley could see another 1 to 3 inches of rain, including around the Bay Area, Sacramento, Santa Barbara and Los Angeles. At least 2 to 4 inches are probable in the higher terrain in places where it’s too warm to snow. In the high elevations of the Sierra Nevada, a few more feet of snow are probable.
Grand finale early next week?
Yet another atmospheric river will affect California late Sunday into Monday or Tuesday.
While it’s too early to pinpoint rainfall or snow totals, a general inch or two of rain can be expected in Northern California, with amounts probably waning as one heads farther south.
It’s not out of the question that one more atmospheric river will come ashore in the middle of next week, but it’s uncertain where it could hit and its intensity.
Pattern change possible in 7 to 10 days
Some time late next week, there are signs that high pressure will become established over the eastern Pacific, moving into a position that will deflect the eastward-moving atmospheric rivers toward the Pacific Northwest.
This prediction is far enough into the future that it’s not a guarantee, and there’s no telling exactly how long this less stormy pattern might persist.