An atmospheric river with a moisture tap originating near the Hawaiian Islands turned parts of the Bay Area into a soggy mess over the weekend.

The wet storm started delivering rain Saturday morning and showers are continuing into Monday and possibly Tuesday.

Depending on location, rain rates have varied greatly, with downpours in the mountains and light showers in the valleys.

While some locations in the Santa Cruz Mountains recorded more than 7 inches of rainfall, San Jose saw a mere .17 inch in 48 hours, running Saturday morning through Monday morning.

National Weather Service forecaster Rick Canepa explains this pattern is typical when southerly winds accompany a storm.

“The term we use to explain this weather behavior is ‘rain shadowing,'” Canepa explains. “It can rain cats and dogs in the Santa Cruz Mountains and, when the air gets to the other side over the valley, all the precipitation has already fallen out in the mountains.”

In the mountains of Sonoma County, the unincorporated town of  Venado holds the record for the storm, measuring 11 inches. Venado, 10 miles west of Healdsburg, usually sees the highest rainfall in storms.

A few locations in the hills of Marin County measured more than 7 inches. Meanwhile, downtown San Francisco recorded .36 inch and on the Peninsula, Redwood City got .36 inch.

Just south of the Bay Area, Monterey County saw the brunt of the storm with one location in the southwest area of the county recorded more than 156 inches.

The Bay Area saw a slow start to the rainy season this year with weeks of dry weather marking October and most of November. The storm door finally opened Thanksgiving week, and while the series of storms have helped, they haven’t delivered enough precipitation to put rainfall totals at normal.

Downtown San Francisco has recorded 1.55 inches since Oct. 1, with the rainfall total being 35 percent of normal. Normally through Dec. 1, the city would expect to see 4.41  inches.

The Santa Rosa Airport has measured 4.32 inches, or 63 percent of normal. The average value for this time of year is 6.85. San Jose has recorded 1.04 compared to the seasonal average of 2.73 inches, or 38 percent of normal.

“We are below average,” says Duane Dykema. “Even though we got some rain at the end of the month we weren’t able to make up for deficits. That said, California doesn’t really have ‘typical’ winter weather. We tend to get periods of wet weather followed by periods of dry weather and because of that I guess you would say pretty much anything is typical except the really extreme events.”

Rains are expected to continue Monday with the heaviest showers just south of the Bay Area.

“The same system that has been bringing rain this weekend is retreating offshore in the next day or so and then will move back inland on Tuesday, but it will be focused further to the south in Central California near Point Conception. We may see some rain in the Bay Area Tuesday,” says Dykema.

Later in the week, another system is forecast to drop down from the Northwest and sweep into the Bay Area as early as late Thursday night. With a wind pattern that’s different from this last storm, the system is expected to deliver more widespread rain that will reach both mountains and valleys.

The current forecast shows the heaviest rains on Friday and continuing into Saturday.

Amy Graff is a digital editor for SFGATE. Email her at [email protected]