• Hydrologic Outlook for San Francisco Bay Shoreline County, California
  • Hydrologic Outlook issued April 04 at 11:30AM PDT by NWS
  • Effective: Friday, April 6, 2018 at 11 p.m.
  • Expires: Thursday, April 5, 2018 at 11:30 a.m.
  • ...Potential flooding later this week in the North Bay and Santa
    Cruz Mountains due to Atmospheric River Event...
    A late season storm system with unseasonably high moisture
    content will bring periods of rain, possibly heavy at times, to
    the San Francisco Bay Area and Monterey Bay Area later this week.
    Light rain is forecast to develop in the North Bay by Thursday
    afternoon. Rainfall is then expected to spread south across the
    rest of the San Francisco Bay Area and into the Monterey Bay Area
    late Thursday and Thursday night. Rainfall intensity through
    Thursday night is expected to be light to moderate.
    Rainfall intensity is forecast to increase on Friday and rain
    rates could be heavy at times by Friday afternoon. Periods of
    heavy rain are then possible through Friday night and into early
    Saturday morning. Rainfall is expected to taper off by midday
    Saturday. Rainfall totals from late Thursday through midday
    Saturday are forecast to range from 2 to 4 inches across the North
    Bay, except 4 to 6 inches in the North Bay Mountains. Rainfall
    totals forecast for the Santa Cruz Mountains are also in the 4 to
    6 inch range. Local amounts of more than 6 inches are possible in
    the wettest locations of the North Bay Mountains and Santa Cruz
    Based on current rainfall projections, mainstem rivers such as the
    Russian River and Napa River are forecast to see significant
    rises late this week and into the weekend, but remain well within
    their banks. However, smaller rivers and streams could flood,
    especially if heavy rain rates persist across a watershed longer
    than anticipated. Flooding would be most likely in low lying and
    flood prone areas. In addition, heavy rain rates across the North
    Bay burn scars could trigger flash flooding or mudslide/debris
    flows across and downstream from the burn scars. Outside of the
    burn scars, widespread landslides are not expected from this
    event. This is because there has been a sufficiently long period
    of time since the last rain event for drying to occur. However,
    localized landslides or rockslides may still be possible outside
    of burn scar areas, especially in areas of steep terrain.
    Persons living near rivers and streams or other flood prone areas
    should be alert for the possibility of flooding during this
    Atmospheric River event late in the week. Flood watches may be
    issued once forecast confidence concerning rainfall amounts
    increases, especially if subsequent forecast models indicate
    higher rainfall totals or more intense rain rates. Please stay
    tuned to bulletins from NWS, NWS social media (NWSBayArea), or
    from other sources of local weather information.

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