Still need to clear out gutters or haul a Christmas tree home?
Sunday may be the last chance to stay dry while tackling last-minute errands or holiday to-do lists, because a week of rain is on its way to the Bay Area — good news after a slow start to the winter rain season.
Between now and Thursday, the National Weather Service forecasts that two to three inches of rain will most likely drench large swaths of Alameda, Contra Costa and San Mateo counties.
Coastal communities from Santa Cruz to Half Moon Bay will bear the brunt of the storm system with up to four inches of rain, while residents further inland — near San Jose, Livermore and Antioch — may barely see one inch.
However, the bulk of the region will likely stay dry until dusk Sunday, as the main front of the incoming “weather maker” system continues to lurk over the Pacific Ocean.
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The weather service forecasts that the first bands of light precipitation will reach the Santa Cruz Mountains by Sunday afternoon and linger into the evening.
Bay Area residents should plan for a wet Monday morning commute, when forecasters are anticipating the most significant round of steady, moderate rain showers and gusty winds to make landfall.
Once precipitation chances increase by Monday, NWS meteorologist Rachel Kennedy said all of those inches of rain totals are going to arrive in a couple of waves — rather than a weeklong misting or intense deluge.
“I would say you should keep an umbrella with you,” Kennedy said. “It’s coming in along the cold front, which should help to keep it more steady and more consistent.”
Temperatures this week are forecast to dip into the low 50s, with highs topping out at 65 degrees.
Despite the incoming storm, 2023 has been much drier than last year when heavy rains and record snowpack helped end the state’s latest drought.
In December 2022, the Bay Area had logged about double the average rainfall by this time in the water year, which starts in October. Additionally, the atmospheric river storms that followed in January brought rainfall five times the month’s average in much of the Bay Area.
So far this year, Kennedy said that most stations in the Bay Area are either at 100% of average rainfall, or are very close to it. But California as a whole is at about 45% of normal for rainfall for this time of year, according California Water Watch.
She said it’s unclear just how much that stat will change this week, even though Sunday evening’s rain — including a slight chance for thunderstorms, particularly in the North Bay — is expected to remain in the area for more than four days.
The state’s snowpack — the frozen reservoir that provides about 30% of California’s water needs — is also off to a slow start: As of Friday, the statewide average for the Sierra snowpack was 28% of normal for this time of year. The Northern Sierra, where many of the state’s largest reservoirs are located, was at 38%.
Last year, the statewide snowpack average was 201% of normal, with the Northern Sierra at 180%.
According to current projections, meteorologists anticipate about an inch of rain to fall in the hills by Monday afternoon, while rain-shadowed communities in the valley may experience up to three-quarters of an inch.
The NWS said wind gusts may reach between 30-40 mph as the front moves through the region Monday morning, but light, scattered precipitation is expected to settle in tomorrow afternoon.
After this onset of rain was delayed earlier this week, the NWS’ Saturday forecast acknowledged that, “the whole system is literally a disorganized mess.”
The weather service said uncertainty also plagues the forecast after Tuesday, when the low pressure “drifts aimlessly towards Southern California later in the week.”
Notably, forecasters say only light showers are expected by Thursday, and dry weather will likely return through next weekend, before another stretch of rain may arrive just in time for the Christmas holiday and New Year’s celebrations.
