The first in a series of storms that will make the pleasant weather of the past week seem a distant memory left the ground wet, the air cold and the tree leaves rippling through most of the region early Wednesday.
By Wednesday night, it was expected to be even wetter, colder and gustier, according to the National Weather Service — all of it from a pattern that the weather service said carries atmospheric river characteristics.
A couple of such patterns thrashed the Bay Area over the winter. This pattern won’t be quite so intense, but it won’t pass through quietly, either.
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“This is probably going to be one of the weaker ones we’ve seen,” NWS meteorologist Brayden Murdock said Wednesday.
The Center for Western Weather and Water Extremes at UC San Diego forecast the atmospheric river to be weak, saying it rated as a 1 on a scale of 1 to 5.
The rain that fell before sunrise Wednesday came from what Murdock called “frontal showers” that preceded the main system. That left about eight-hundredths of an inch of rain in Mill Valley, .06 inches in San Rafael, .05 inches in San Francisco and .03 inches in Richmond and Orinda by 7 a.m.
Those totals are expected to go up significantly by the time all three storm systems from the pattern roll through the region. The weather service said the first storm is expected to be gone by late Wednesday; the second one is forecast to arrive late Thursday going into Friday; and the final one is expected early Sunday and likely to last into Monday.
In all, the weather service said the storms will bring a half-inch to two inches of rain to the region and as much as four inches could fall in the coastal ranges.
The initial system also will bring with it intense winds, according to the weather service. Gusts as high as 55 mph are expected in the higher elevations, and 20-30 mph gusts are expected to blow steadily in the lower ones. The weather service issued a wind advisory from 8 a.m.-8 p.m. Wednesday.
Also expected on tap will be thunder and lightning. The weather service said Wednesday’s storm could light up the sky as far north as Santa Rosa and as far south as King City.
“The big thing with these thunderstorm chances is that they’re going to develop out over the (ocean),” Murdock said. “They’re gonna start there and move inland, so we’ll be able to see them coming.”
Temperatures are expected to be cold as the storms move through. Daytime highs are not expected to exceed the high 50s until Saturday. Overnight lows are expected to dip into the low 40s in most of the region and into the high 30s in the most inland places.
“These subsequent systems are really not looking as strong as the first one,” Murdock said.