While atmospheric rivers can lead to dangerous conditions, NOAA notes that most of them are actually relatively mild affairs and provide critical precipitation for inland areas. When an atmospheric river rises to push its way over coastal mountains and meets the cooler air higher in the atmosphere, this is particularly likely to spawn precipitation. When the atmospheric rivers make landfall, they often release this water vapor in the form of rain or snow. These columns of vapor move with the weather, carrying an amount of water vapor roughly equivalent to the average flow of water at the mouth of the Mississippi River. What exactly is an atmospheric river? A National Oceanic and Atmospheric Administration blog from 2015 explains:Ītmospheric rivers are relatively long, narrow regions in the atmosphere-like rivers in the sky-that transport most of the water vapor outside of the tropics.

To a degree this is good news the state is short of its usual winter rainfall and snowpack in spite of a spate of notable storms since late last year.īut the oncoming downpour also comes with risks, as the forecast includes a note about the potential hazards of “localized flooding” (a risk to low-lying areas as the bay swells) and mudslides, which are a particular danger in the North Bay, where fire-scarred hillsides often cannot absorb heavy rain. Since then it seems that the degree of certainty has increased, as the current regional forecast calls for a 100 percent chance of heavy rain in San Francisco Friday, with an 80 percent chance that the downpour will start pummeling the city by Thursday. These areas are constantly cold, with average May temperatures between -6C. Stay tuned for additional forecast updates as the event approaches. 8-Precipitation (in) Actual: Historic Avg. Rainfall amounts and subsequent impacts will be heavily dependent on the where the AR makes landfall. While confidence continues to increase for wet weather to return, a great deal of uncertainty remains on exact details of timing, rainfall amounts, locations of greatest impacts, and winds.

In a notice posted Wednesday morning, NWS warns:Ī potent atmospheric river will bring moderate to heavy rain to the Bay Area Thursday through Saturday. The National Weather Service warns that a tremendous storm in the form of an “atmospheric river” is heading straight for Northern California and the Bay Area, bringing much-needed rain but also some risk of flooding and other hazards. There is also reporting of minor flooding on the 101 in North Marin. In San Francisco, Sixth Street “under 6 to 8 inches of water,” according to SFGate. Temperature 70° (1° below avg.[Update: A flood watch as been issued by the NSW, which will last until Saturday morning. A once robust surplus is now evaporating. September and October will bring temperatures close to normal and be a bit drier than usual.įree 2-Month Weather Forecast September 2022 Long Range Weather Forecast for Pacific Southwest Dates SAN FRANCISCO (KGO) - October's record daily and monthly Bay Area rains seem so long ago with our rain season turning sour after a vigorous beginning. The hottest periods will be in mid-June, mid- to late July, and mid- to late August. Summer temperatures will be hotter than normal, with generally above-normal rainfall. April and May will be slightly cooler than normal, with rainfall below normal in the north and above normal in the south. The stormiest period will be in late December. The coldest temperatures will occur from mid-December into mid-January, in mid-February, and in early March.

Winter will be warmer and drier than normal, with below-normal mountain snows. Enter Your Location Annual Weather Summary

Sf bay area precipitation totals