An atmospheric river over the Pacific had been forecast, at least a week or so ago, to bring a lot of early December rain to California, but things have changed.
Seattle and the rest of the Pacific Northwest is bracing for some serious rain by early week, with 20 inches possible in the Olympic range and up to six inches falling in Portland and Seattle.
But here in the Bay Area, only the North Bay is likely to see some showers from the outer bands of this system, as National Weather Service meteorologist Matt Mehle tells Bay Area News Group today.
"Yeah, things have not been going as predicted," Mehle tells the news group. He goes on to explain that the weather system headed for the West Coast contains "cut-off lows, an area of low pressure that’s cut off from the main flow of the atmosphere." Because of that, the system is taking its own direction and defying earlier models, and the vast majority of the rain is going to miss California entirely.
Contributing to the system is also what's called a "Kona low," an area of low pressure around Hawaii that is leading to some heavy rainfall and even snow on the Big Island.
A very wet pattern, associated with multiple strong and warm #AtmosphericRivers, is taking aim at the Pacific Northwest. These are the storms that a week or so ago had been projected to head for California, but are now instead aimed farther north. #CAwx #CAwater https://t.co/pM5f93MNm1— Dr. Daniel Swain (@Weather_West) November 30, 2023
The incoming atmospheric river storms will soak some parts of the North Coast of California closer to the Oregon border, but that's about it, as Colin McCarthy with US Stormwatch says.
The Pacific Northwest is set to be hit by multiple significant atmospheric rivers over the next week, bringing widespread heavy rain and mountain snow.— Colin McCarthy (@US_Stormwatch) November 30, 2023
Seattle and Portland are projected to receive 3-6" of rain through early next week, with isolated amounts approaching 20" in… pic.twitter.com/BScgflP7hC
The Chronicle's meteorologist Gerry Diaz meanwhile has some longer-range forecasts, and he is predicting that, save for potential scattered showers, the Bay Area will stay mostly dry through about December 15. After that, Diaz says, "A ridge of high pressure that often blocks storm systems from arriving in California will begin to break down."
That means that our El Nino winter may not really arrive until the later part of December or January — and it remains possible that we won't end up with an especially wet winter after all.
Temperatures next week, meanwhile, will remain fairly average, in the mid-60s in the afternoon, and dropping into the 40s at night.