Flood Potential Outlook
Issued by NWS Sacramento, CA

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Hydrologic Outlook
National Weather Service Sacramento CA
127 PM PST Wed Mar 1 2017

Elevated Spring Flood Threat Across Portions of California

The potential for flooding due to spring snowmelt in California
Nevada River Forecast Center`s domain is elevated due to much
above normal snowpack. In California, this elevated risk is for
many locations in the mountainous areas of the Cascades and the
Sierra Nevada. Some of the lower elevation regulated systems, like
the San Joaquin River and its tributaries, will likely be under
additional stress throughout the spring due to higher than normal
releases from the large reservoirs as they manage inflows from the
above normal snowmelt volumes. In many cases, above normal flow
conditions are already being experienced due to flood control
requirements to make space for the expected snowmelt. Flows are
expected to remain above normal in the San Joaquin system well
into the snowmelt season, putting continuous stress on the flood
conveyance system. Note that flooding in California could also
result from heavy rainfall alone, or combined with snowmelt
anytime during the spring.

Current Basin Conditions

Snowpack
Everywhere from the northern portions of the Klamath basin down
to the Tulare basin in the southern Sierra Nevada is experiencing
above average snowpack. Percent of normal numbers tend to increase
from North to South within the Sierra Nevada.

Seasonal Precipitation
Precipitation totals for the current water year are much above
normal to extreme for the entire state of California. The Northern
Sierra 8-Station Index is on pace to break an all-time record
assuming climatology for the rest of the water year.

Seasonal (April-July) Runoff Forecasts
The seasonal runoff forecasts are very similar to the snowpack
conditions. Much above normal to extreme runoff volumes can be
expected during the April-July period throughout the Cascades and
Sierra Nevada.

Flood Exceedance Probabilities
Flooding during the spring snowmelt season is definitely more
probable this year due to the much above normal snowpack. Consult
the AHPS Long Range Flood Risk Map for the latest point exceedance
probabilities at http://water.weather.gov/ahps/long_range.php.

Summary
Risk of California flooding during the snowmelt season is elevated
this year for much of the Cascades and Sierra Nevada. Flood
conveyance systems below major reservoirs in the San Joaquin basin
will be under additional stress throughout the spring. Flooding
anywhere in the state could also result from heavy rainfall, or
the combination of rain and snowmelt at any time during the
spring. Refer to the long range outlook product for flood
exceedance probabilities at particular locations for the March
through May period. For short term hydrologic forecasts and
general water resources information, please see the CNRFC homepage
at http://www.cnrfc.noaa.gov.


$$

CNRFC/BW
WFO STO/CM



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