Flood Potential Outlook
Issued by NWS Seattle/Tacoma, WA

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WATER SUPPLY OUTLOOK
NATIONAL WEATHER SERVICE SEATTLE WA
734 PM PDT TUE AUG 20 2014

...WESTERN WASHINGTON WATER SUPPLY...

OVERVIEW: THE OUTLOOK FORECASTS OF WATER SUPPLY FOR THE SUMMER IN
WESTERN WASHINGTON ARE FOR NEAR TO BELOW NORMAL NORMAL VOLUMES FOR
WESTERN WASHINGTON RIVERS.

PRECIPITATION SUMMARY
---------------------

FOR JULY...MOST OF WESTERN WASHINGTON SAW NEAR TO ABOVE NORMAL
RAINFALL...WHILE MOST OF EASTERN WASHINGTON RECEIVED BELOW NORMAL
PRECIPITATION FOR THE MONTH. AS FOR THE WATER YEAR...MOST OF THE
WESTERN HALF OF THE STATE CONTINUES TO BE NEAR NORMAL FOR
PRECIPITATION WHILE THE EASTERN HALF CONTINUES TO BE MOSTLY BELOW
NORMAL.

IN WESTERN WASHINGTON...THE MONTHLY PERCENTAGE OF NORMAL FOR
PRECIPITATION RANGED FROM 31 PERCENT IN THE OLYMPIC MOUNTAINS TO 116
PERCENT IN THE WESTERN SLOPES OF THE CASCADES. THE GREATEST AMOUNT
OF PRECIPITATION AT THE CLIMATE STATIONS FOR THE
MOUNTAINS...COAST... AND INTERIOR LOWLANDS WAS 2.66 INCHES AT
PARADISE ON THE WESTERN SLOPES OF THE CASCADES...0.92 INCHES AT
CLEARWATER...AND 1.81 INCHES AT CLEARBROOK IN THE NORTHWEST INTERIOR.


SNOWPACK CONDITIONS
-------------------

THE SNOWPACK WAS ABOVE NORMAL FOR THE SOUTH AND NORTH PUGET SOUND
BASINS AND BELOW NORMAL FOR THE CENTRAL PUGET SOUND AND OLYMPIC
BASINS AS OF JUNE 11. THE WATER CONTENT OF THE MOUNTAIN SNOWPACK IN
THE BASINS THAT FEED THE MAJOR RIVERS WEST OF THE CASCADES RANGED
FROM 48 PERCENT OF NORMAL FOR THE OLYMPICS TO 161 PERCENT OF NORMAL
FOR THE NORTH PUGET SOUND.

STREAMFLOWS SUMMARY
-------------------

WESTERN WASHINGTON RIVERS WERE NORMAL TO BELOW NORMAL FOR JUL.


RESERVOIR STORAGE SUMMARY
-------------------------

THERE WAS JUST ONE REPORT OF STORAGE FOR MAJOR RESERVOIRS AROUND THE
WESTERN WASHINGTON FOR THE END OF MAY. ON THE SKAGIT RIVER...ROSS
STORAGE WAS 75 PERCENT OF AVERAGE.


WEATHER OUTLOOK
---------------

THE OUTLOOK FOR AUGUST AND BEYOND...FOR THE NEXT TWO WEEKS THE
OUTLOOK IS FOR BELOW NORMAL PRECIPITATION FOR ALL OF WASHINGTON. THE
MONTHLY OUTLOOK FOR AUGUST IS CALLING FOR EQUAL CHANCES OF
NORMAL...ABOVE...OR BELOW NORMAL PRECIPITATION FOR THE ENTIRE STATE.
THE THREE MONTH OUTLOOK FROM AUGUST TO OCTOBER ALSO CALLS FOR EQUAL
CHANCES OF NORMAL...ABOVE...OR BELOW NORMAL PRECIPITATION FOR THE
ENTIRE STATE.

WATER SUPPLY OUTLOOK
--------------------

LONG RANGE HYDROLOGIC MODELS ARE FORECASTING NEAR TO BELOW NORMAL
RIVER FLOWS AND WATER SUPPLY FOR MOST RIVERS THROUGH THIS SUMMER.
WATER SUPPLY FORECASTS FOR WESTERN WASHINGTON RANGE FROM A LOW OF 43
PERCENT FOR THE ELWHA RIVER TO 113 PERCENT OF NORMAL FOR THE COWLITZ
RIVER. WATER SUPPLY FORECASTS THAT INCLUDE REGULATION ARE USED FOR
LOCATIONS WHERE FORECASTS ARE LISTED BELOW AS REGULATED...FOR ALL
OTHER LOCATIONS FORECASTS ARE FOR NATURAL VOLUMES.

HERE ARE THE STREAM FLOW VOLUME FORECASTS FOR SPECIFIC RIVERS AND
SITES AS OF AUG 19.

                           WATER SUPPLY FORECASTS
                  NATURAL FLOW UNLESS OTHERWISE SPECIFIED
                        (IN THOUSANDS OF ACRE FEET)

RIVER AND GAUGING SITE            PERIOD   FORECAST   NORMAL  PERCENT

SKAGIT RIVER
   NEAR CONCRETE (REGULATED)      AUG-SEP       684      790      87

BAKER RIVER
   UPPER BAKER RESERVOIR INFLOW   AUG-SEP       106      122      87

SULTAN RIVER
   SPADA LAKE INFLOW              AUG-SEP        15       28      55

TOLT RIVER
   TOLT RESERVOIR INFLOW          AUG-SEP         4        6      65

CEDAR RIVER
   CHESTER MORSE LAKE INFLOW      AUG-SEP         6        8      71

NISQUALLY RIVER
   ALDER RESERVOIR INFLOW         AUG-SEP        39       48      82

COWLITZ RIVER
   MAYFIELD RESERVOIR (REGULATED) AUG-SEP       165      146     113

ELWHA RIVER
   MCDONALD BRIDGE                AUG-SEP        28       66      43

DUNGENESS RIVER
   NEAR SEQUIM                    APR-SEP       127      144      88

WYNOOCHEE RIVER
   WYNOOCHEE DAM INFLOW           AUG-SEP         9       13      67

N.F. SKOKOMISH RIVER
   CUSHMAN DAM INFLOW             AUG-SEP        15       26      59


SNOW MELT CLIMATOLOGY:

RIVERS WEST OF THE CASCADES CREST USUALLY REACH THEIR HIGHEST PEAK
FLOWS DURING THE WINTER SEASON. THE VAST MAJORITY OF RIVER FLOODING
IN WESTERN WASHINGTON...AND ALMOST ALL MAJOR FLOODS...OCCUR BETWEEN
OCTOBER AND MARCH. HEAVY RAINFALL...RATHER THAN SNOW MELT...IS THE
PRIMARY CAUSE OF THESE EVENTS.

THE HISTORICAL RECORD DOES NOT SHOW MAJOR FLOODING IN WESTERN
WASHINGTON DURING THE PERIOD WHEN THE MOUNTAIN SNOWPACK RUNS OFF.
THE RUNOFF FROM SNOW MELT...EVEN DURING UNUSUALLY HOT WEATHER...IS
SMALL COMPARED TO THE RUNOFF DURING HEAVY WINTER RAINS. THIS IS TRUE
REGARDLESS OF THE SIZE OF THE MOUNTAIN SNOWPACK. RARELY...UNDER JUST
THE RIGHT CONDITIONS OF GREATER THAN NORMAL SNOW PACK...GREATER
COVERAGE TO LOWER ELEVATIONS...AND NEAR RECORD WARM TEMPERATURES...
RIVER FLOWS MIGHT RISE TO NEAR MINOR FLOOD STAGE.

WHILE FLOOD PRODUCING RAINFALL IS RARE AFTER MARCH...MODERATE TO
HEAVY RAIN IN SPRING OR SUMMER...WHILE RIVERS ARE SWOLLEN WITH SNOW
MELT RUNOFF...OCCASIONALLY DRIVE THE MOST FLOOD PRONE RIVERS ABOVE
FLOOD STAGE. TYPICALLY THESE ARE RIVERS SUCH AS THE SKOKOMISH AND
SNOQUALMIE. HEAVY RAIN IN THE SPRING OR SUMMER...WHEN ROSS LAKE IS
FULL...CAN ALSO CAUSE THE SKAGIT RIVER TO FLOOD. WHILE THESE FLOODS
ARE TYPICALLY MINOR COMPARED TO THE WINTER EVENTS...THEY SOMETIMES
CAUSE SUBSTANTIAL DAMAGE TO FARM CROPS.


SPRING AND SUMMER SNOW MELT PEAK FLOW FORECASTS:

SNOW MELT CRESTS OCCURRED FOR MOST RIVERS IN WASHINGTON.

FORECASTS ARE SELECTED FROM THOSE PREPARED BY THE NWRFC.
FOR FURTHER DETAILS...GRAPHICS...AND STATISTICS REGARDING THE WATER
SUPPLY FORECASTS VISIT:
HTTP://WWW.NWRFC.NOAA.GOV/WS (LOWER CASE)
HTTP://WWW.NWRFC.NOAA.GOV/OUTLOOK (LOWER CASE)

FOR FURTHER DETAILS...GRAPHICS...AND STATISTICS REGARDING THE PEAK
FLOW FORECASTS VISIT:
HTTP://WWW.NWRFC.NOAA.GOV/PEAK (LOWER CASE)

THE NEXT WATER SUPPLY OUTLOOK FOR WESTERN WASHINGTON WILL BE ISSUED
AROUND THE WEEK OF SEP 1.

$$

WEATHER.GOV/SEATTLE
























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