Atmospheric rivers are 250 to 400 miles wide and split off like a tributary from larger band of moisture from the tropics. 30%-50% of annual precipitation on the west coast occurs in atmospheric events. They cause major flooding when they make landfall and stall over a particular that the bay area is bracing itself for. The highest elevations of northern California are expected to get 10 inches of rain. SF is believed to possibly see 4 inches in city and 8 inches in the hills.
The SFUSD superintendent said, "I did not arrive at this lightly. First and foremost, we don't want to risk having our students injured or seriously delayed transporting to and from school. In addition to student absences, the storm could result in large numbers of staff absences, which could then lead to inadequate supervision of our students. Furthermore, power outages could affect the district's ability to feed students' school meals, among many other operational challenges."
Oakland school officials cited “ an extreme and potentially dangerous weather system” as a reason for closing.” Rain is much more common if along the gulf or Atlantic coasts, but for parched California, which researchers at the university of Nebraska say is most drought stricken state in the country. Bay area on Tuesday, public works crews got ready for downpour. “This is not the most glamorous work here is, even with equipment like this. This is still really hard work. Hard and dirty work but something that has to be done to make sure the system functions properly when we do have a big storm," Caltrans spokesman Bob Haus.
Bay Area power crews cut pine tree limbs hanging over power lines ahead of winds of 30-40 mph with gusts up to 70 mph. howling winders will drive up and down the west coast.