A very moist air mass associated with an atmospheric river will bring periods of rain to Southwest California through tonight. The heaviest rainfall is expected to occur this morning into early this afternoon.
Peak rainfall rates during this period are expected to range between 0.50 and 1.00 inches per hour, with the highest rates focused across south and southwest facing slopes of the Santa Monicas and San Gabriels.
Shallow mud and debris flows will be likely in the first year burn areas, with the potential for more significant and damaging debris flows. In addition, roadway flooding is likely, especially in low lying areas, along with rock and mudslides on
canyon roads and below steep terrain.
For the Los Angeles county mountains and adjacent foothills, especially in the San Gabriel range, there will be the potential for flash flooding as well as significant risk for
mudslide/rockslides activity due to the extended period of heavy rain expected this morning through early this afternoon. Therefore, in the San Gabriel Mountains, the flash flood watch is also in effect for locations outside of the recent burn areas