Extended Streamflow Guidance
Issued by NWS

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ESGNV

ESGNV

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

...ELEVATED FLOOD THREAT DUE TO SPRING SNOWMELT ACROSS PORTIONS OF
NEVADA AND EASTERN CA...

THERE IS AN ELEVATED THREAT OF SPRING SNOWMELT FLOODING ALONG THE
HUMBOLDT RIVER AND ITS TRIBUTARIES DUE TO AN ABOVE AVERAGE SNOWPACK
AND SATURATED SOILS FROM WINTER PRECIPITATION.  THE LOWER HUMBOLDT
RIVER AT COMUS IS STILL RUNNING ABOVE FLOOD STAGE THIS WEEK DUE TO
HEAVY PRECIPITATION THAT FELL OVER THE PAST COUPLE OF WEEKS.  RUNOFF
EFFICIENCY WILL BE HIGH IN THE HUMBOLDT BASIN FROM ANY SPRING RAIN
OR MELTING SNOW AND COULD RESULT IN FLOODING, ESPECIALLY IN THE
LOWER PART OF THE BASIN.  THERE IS ALSO AN ELEVATED FLOOD THREAT FOR
THE EASTERN SIERRA DURING THE SPRING, ESPECIALLY THE WALKER AND
CARSON RIVERS WHERE SNOWPACK IS ALSO WELL ABOVE NORMAL TO EXTREME
CONDITIONS.

NOTE THAT FLOODING IN NEVADA COULD ALSO RESULT FROM HEAVY RAINFALL
ALONE, OR COMBINED WITH SNOWMELT ANYTIME DURING THE SPRING.

CURRENT BASIN CONDITIONS

SNOWPACK

THE CURRENT SNOWPACK IN THE HUMBOLDT AND EASTERN SIERRA IS WELL
ABOVE NORMAL TO EXTREME CONDITIONS.  THE MAJORITY OF THE SNOW
PILLOWS IN THESE REGIONS ARE REPORTING ABOVE 150% OF NORMAL, WITH
THE HIGHEST PERCENTAGES AT THE HIGHER ELEVATIONS.

SEASONAL PRECIPITATION

PRECIPITATION TOTALS FOR THE CURRENT WATER YEAR ARE MUCH ABOVE
NORMAL TO EXTREME FOR NORTHERN NEVADA AND THE EASTERN SIERRA IN CA.
SOUTHERN NEVADA IS ABOVE NORMAL TO MUCH ABOVE NORMAL.  NEAR NORMAL
CONDITIONS ARE EXPECTED OVER THE NEXT WEEK OR TWO.

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 HUMBOLDT BASIN
AND THE EASTERN SIERRA.

FLOOD EXCEEDANCE PROBABILITIES

FLOODING DURING THE SPRING SNOWMELT SEASON IS DEFINITELY MORE
PROBABLE THIS YEAR DUE TO THE MUCH ABOVE NORMAL SNOWPACK. FLOODING
COULD OCCUR FROM SNOWMELT, RAIN, OR A COMBINATION OF BOTH. 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 FLOODING DURING THE SPRING IS ELEVATED THIS YEAR FOR MUCH OF
THE EASTERN SIERRA AND HUMBOLDT BASIN DUE TO THE EXTREMELY LARGE
SNOWPACK. FLOODING COULD RESULT FROM SNOWMELT, HEAVY RAINFALL, OR
THE COMBINATION BOTH 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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