Extended Streamflow Guidance
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SPRING FLOOD POTENTIAL OUTLOOK
NATIONAL WEATHER SERVICE
CALIFORNIA-NEVADA RIVER FORECAST CENTER SACRAMENTO CA
1250 PM PST WED MAR 1 2017

ELEVATED SPRING FLOOD THREAT ACROSS PORTIONS OF CALIFORNIA

THE POTENTIAL FOR FLOODING DUE TO SPRING SNOWMELT IN THE CALIFORNIA
NEVADA RIVER FORECAST CENTERS 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 IN 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: 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
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
RESOURCE INFORMATION, PLEASE SEE THE CNRFC HOMEPAGE AT:
HTTP://WWW.CNRFC.NOAA.GOV.


CNRFC/BW



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