Flood Potential Outlook
Issued by NWS San Francisco Bay Area, CA

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HYDROLOGIC OUTLOOK
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA
141 PM PST Wed Feb 15 2017

...Series of storms to impact Bay Area and Central Coast...

It was only 2 days ago (Monday) that real-time soil moisture
sensors in the Bay Area indicated dissipation of the infiltrated
rainwater from last week`s multiple storms. The sunny weather
throughout California over the last 5 days or so has allowed
creeks to drop back down to safe flow levels in coastal locations,
but watersheds remain quite saturated just beneath the surface.

So again, California will experience another round of storms this
week in a condition that favors rapid conversion of rain into
runoff and a high likelihood of additional landslides and debris
flows in mountainous terrain. The first storm in the series is
forecast to impact the greater Bay Area as well as the Central
Coast, first sweeping through the North Bay later tonight
(Wednesday) and quickly progressing southwards through the Central
Coast tomorrow (Thursday). This event will not likely lead to much
flooding, except in isolated locations where drainage is poor and
rainfall rates are high. Debris flows and shallow landslides are
entirely possible even with this first system, as there are many
slopes poised to respond or that are actively deforming as we
speak, even in dry weather. Notable examples are in the Santa Cruz
Mountains. The second system is expected to focus more on the
Central Coast Friday, with several additional inches expected in
the Santa Lucias and Santa Cruz Mountains of Monterey and Santa
Cruz Counties, respectively. Rainfall accumulation in the Santa
Lucias especially could be quite high (4 additional inches or
more). Of note here is that this second system has a southern to
southeastern source, and constitutes an Atmospheric River (AR)
aimed at San Luis Obispo County. The upper Salinas River watershed
is right in the cross hairs, and storm origination will prevent
the typical rainshadowing of the Salinas Valley that we often see
in Monterey County. The expected result is minor to moderate
flooding in many locations along the Salinas River, a situation we
have not seen in many, many years. The middle portions of the
Salinas River Valley, south of King City, will likely see bankfull
conditions reached without much flooding, but areas near Soledad
and northwards could experience periods of flooding Sunday into
Monday where channel capacity is restricted and floodplain
elevations are low relative to the channel. The Salinas River near
Spreckels, for example, is expected to flood low lying areas.
Other smaller watersheds will appreciably respond in Monterey and
Santa Cruz Counties. Notably, the Arroyo Seco, Big Sur River,
Cachagua Creek are examples of systems that may also experience
flooding given the magnitude and trajectory of the storm system.

Continued unsettled weather is expected through the weekend and
into next week, with a third system set to impact California on
Monday. Rainfall totals for this third system and any subsequent
wet weather next week will be clarified in coming days as refined
weather simulations are completed. So please stay tuned to
bulletins from NWS, NWS social media (NWSBayArea), or other
sources of local weather information.

$$

MWS



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