Another atmospheric river hits San Francisco Bay Area

Another atmospheric river event has made its way to Northern California, with a flood watch in effect through Sunday morning.

Why it matters: This will be a milder storm than the series of blizzards that have hit the Golden State in recent weeks, delivering rain on top of snow even at mid-to-high elevations. But with a near-record snowpack, there are flood risks, Axios' Andrew Freedman and Sareen Habeshian report.

State of play: Dubbed the "Pineapple Express," the storm is drawing moist air from the subtropics near Hawaii.

• Atmospheric rivers are long, narrow highways of moisture that can travel thousands of miles and are responsible for 30%-50% of the wet season precipitation along the West Coast of the U.S., according to the National Oceanic and Atmospheric Administration.
• They have been unusually persistent and powerful this winter, with no signs of an impending weather pattern shift to drier conditions.
• South Lake Tahoe on Thursday issued a local emergency ahead of the storm, and officials have warned all Tahoe residents to prepare for potential roof collapses and flooding, SFGATE reports.

Be smart: San Francisco's public works department is providing residents with up to 10 free sandbags per address Monday through Saturday from 8am-2pm.

Between the lines: While a recent analysis by the nonpartisan Climate Central found many areas across the country have experienced warmer winters since 1970, San Francisco has seen the opposite — average temperatures have dipped to 52.5 degrees this winter, compared to 53.6 in 1970.

The bottom line: The astonishingly thick snowpack in California has raised hopes of more abundant water supplies and a less active early fire season across the state.

• But so much snow sitting at lower elevations in particular is also a concern this week.
• The dramatic swing from historically dry to very wet conditions in parts of California is consistent with what climate studies show will occur more frequently and sharply in coming decades.