Baby goats, bunny rabbits and other furry petting zoo animals seemed like such a good idea for Amanda Sills' joint son-daughter birthday party this month.

Toddler attendees could play with the potbellied pigs Saturday and splash in the Sills family's Moraga pool to cool down.

And then the spring of 2011 hit.

As rain pelted the pool, the petting zoo company canceled because the weather would spook the animals.

Like many other East Bay residents, the Sills family had to improvise this wet weekend. They hired James the Entertainer off Craigslist to make balloon animals inside their dry house for 4-year-old Lucas and 1-year-old Ava's 70 party guests.

"My son was crying but now he's smiling and screaming around the house," Sills said.

Records broke as raindrops fell Saturday, with some long-standing rainfall measurements blown away before noon as a deep low-pressure weather system swept in from the Gulf of Alaska. The resulting precipitation came at a time when outdoor festivals, graduations and pool parties were a part of many people's weekend plans.

By 11 a.m., rainfall levels in downtown Oakland and San Francisco, which are measured each hour, had shattered records. More than 1 inch of rain fell in Oakland, beating the previous high of 0.10 inches, according to Bob Benjamin, a National Weather Service forecaster.

Measurements for other cities are tracked over a 24-hour period so Benjamin said those amounts would not be available until Sunday. But he said the records don't stand a chance.

"All will come toppling down," Benjamin said.

Art patrons in Oakland splashed through the puddles to attend the East Bay Open Studios event, where more than 400 artists in 14 East Bay cities opened their studios to the public.

Attendance was definitely down Saturday, according to program coordinator Jackie Im, but as the clouds began to break up by the afternoon she said the art lovers began to return.

Vendors at the Art and Wine Festival at Walnut Creek's Heather Farm Park who chose to pitch their tents and sell their wares had their pick of spots on the park's fields because many decided to skip the event.

Customers, on the other hand, were hard to come by.

Evone Wilson, co-owner of Hats 'n' More, drove from Oroville to work at the festival but had yet to recoup her costs. She said people tend to buy hats when the sun is shining. When it's raining, they stick to umbrellas.

"We've hardly made any money at all, not today. But maybe tomorrow," Wilson said.

The weather is expected to normalize in the coming days with less rain and higher temperatures, according to forecasts. Saturday's brunt of moisture is expected to move south into Monterey County by Sunday and farther south by Monday, according to Benjamin.

Scientists are poring over data, trying to explain the odd weather.

"It's what I call global weirding," said Bill Patzert, a climatologist at NASA's Jet Propulsion Laboratory in Pasadena. "This has been a very strange year all over the planet."

What's going on?

First of all, this spring's weather is not unprecedented, just uncommon. California has had wet, cold spring weather before, notably in 1983, a year that produced record Sierra snows.

This year, the blame falls on a complex interaction between La Niña and another phenomenon called a negative Arctic oscillation, Patzert and others said.

La Niña is marked by a cooling of equatorial waters in the Pacific Ocean -- the opposite of El Niño. In the past, this pattern means an equal chance of wet or dry weather.

What made this year so wet was the negative Arctic oscillation.

Typical conditions make the Arctic colder than the mid-latitudes, which include the United States and Europe. This is a positive oscillation.

Negative conditions flip this around, making the Arctic warmer than usual and pushing cold air and a vigorous jet stream down into the United States and Europe.

One theory gaining traction is that climate change, in fact, might be to blame.

The theory was developed in several published papers by Judah Cohen, an atmospheric scientist in Massachusetts.

Colder and snowier winters caused by global warming? It may be one of the counterintuitive consequences of climate change, he said.

"We don't understand everything, and we don't understand how the different feedbacks affect different parts of the climate system," said Cohen, director of seasonal forecasting at Atmospheric and Environmental Research, a private firm in Lexington, Mass. "It's very complicated. So we should expect the unexpected."

Just ask Amanda Sills: "As soon as the last party guest left, the sun came out."

Staff writer Matthias Gafni and the Sacramento Bee contributed to this report.