Flood Potential Outlook
Issued by NWS Seattle/Tacoma, WA

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PROBABILISTIC HYDROLOGIC OUTLOOK
NATIONAL WEATHER SERVICE SEATTLE WA
350 PM PDT MON JUN 20 2016

...WESTERN WASHINGTON Water SUPPLY AND SPRING SNOW MELT FLOOD
POTENTIAL...

OVERVIEW: THE FORECASTS OF WATER SUPPLY FOR THE SUMMER VARIED
GREATLY FROM MUCH BELOW NORMAL TO NEAR NORMAL FOR WESTERN
WASHINGTON RIVERS. MOST RIVERS HAD FORECASTS FOR BELOW TO MUCH BELOW
75 PERCENT OF NORMAL. THE SNOW PACK WILL HAVE LITTLE AFFECT ON THE
WATER SUPPLY FOR THE REMAINDER OF THIS SEASON AS THE LOCAL WEATHER
OVER THE NEXT SEVERAL MONTHS WILL DETERMINE ANY CHANGES IN THE WATER
SUPPLY AND DEMAND.

FLOODING IN WESTERN WASHINGTON IS UNLIKELY DURING THE PERIOD OF
MOUNTAIN SNOW PACK RUNOFF...WHICH PEAKS FROM APRIL THROUGH JUNE. WHAT
LITTLE THREAT THERE WAS HAS PASSED AS THE SNOW PACK IS LARGELY MELTED
DOWN.

PRECIPITATION SUMMARY
---------------------
MAY WAS VERY DRY FOR MOST OF WASHINGTON STATE...WITH MANY OF THE
REGIONS ON BOTH SIDES OF THE STATE RECEIVING MUCH BELOW TO BELOW
NORMAL PRECIPITATION.  ONLY THE CENTRAL BASIN AND NORTHEAST REGIONS
ON THE EASTERN SIDE RECEIVED NEAR NORMAL PRECIPITATION. AS FOR THE
WATER YEAR...ALL OF WASHINGTON REMAINS NEAR TO ABOVE NORMAL.

THE MONTHLY PERCENTAGE OF NORMAL FOR PRECIPITATION RANGED FROM 40
PERCENT IN THE PUGET SOUND LOWLANDS TO 57 PERCENT ON THE WESTERN
SLOPES OF THE CASCADES. THE GREATEST AMOUNT OF PRECIPITATION AT THE
CLIMATE STATIONS FOR THE MOUNTAINS...COAST AND INTERIOR LOWLANDS WAS
4.59 INCHES AT PALMER IN THE CASCADE FOOTHILLS...2.88 AT CLEARWATER,
AND 2.43 INCHES AT MAYFIELD IN THE SOUTHWEST INTERIOR.

                          MAY     WATER YEAR      PAST 3       PAST 12
                         2016       TO DATE       MONTHS        MONTHS
WESTERN WASHINGTON
  COAST                    42          114           95           111
  OLYMPICS                 48          115          110           112
  NORTHWEST INTERIOR       47          114           81           110
  PUGET SOUND LOWLANDS     40          128          101           123
  SOUTHWEST INTERIOR       47          117           92           111
  WEST FOOTHILLS CASCADES  52          118           86           112
  CASCADES WEST            57          121           88           115


SNOW PACK CONDITIONS
-------------------

THE SNOW PACK WAS WELL BELOW NORMAL FOR WESTERN WASHINGTON AS OF JUNE
19. MOST REPORTING SITES ARE ALREADY SNOW FREE WITH THE EXCEPTION
OF THE MOUNT RAINIER AREA. THE WATER CONTENT OF THE MOUNTAIN SNOW PACK
IN THE BASINS THAT FEED THE MAJOR RIVERS WEST OF THE CASCADES AND
OLYMPICS RANGED FROM 67 PERCENT OF NORMAL FOR THE SOUTH PUGET SOUND
REGION AND 0 TO 1 PERCENT OF NORMAL EVERYWHERE ELSE.


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

STREAMFLOWS FOR MANY OF WESTERN WASHINGTON RIVERS WERE RUNNING AT
MUCH BELOW NORMAL LEVELS AS OF JUNE 19. THERE WERE SOME
Exceptions...PARTICULARLY IN THE SOUTHERN PART OF WESTERN WASHINGTON
WHERE THERE HAS BEEN RECENT RAINS. LONGER TRENDS SHOW BELOW
NORMAL STREAMFLOW FOR MUCH OF THE AREA.

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

STORAGE FOR ROSS RESERVOIR FOR JUNE 1 WAS AT 90% OF AVERAGE. THE
COMBINED RESERVOIR STORAGE OF CHESTER MORSE LAKE...MASONRY
POOL...LAKE YOUNGS...AND SOUTH FORK TOLT WAS NEAR AVERAGE.


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

THE MONTHLY OUTLOOK FOR JUNE CALLS FOR GREATER CHANCES OF ABOVE
NORMAL TEMPERATURES AND EQUAL CHANCES OF ABOVE...BELOW OR NEAR
NORMAL PRECIPITATION.  THE THREE MONTH OUTLOOK FOR JULY THROUGH
SEPTEMBER CALLS FOR ABOVE NORMAL TEMPERATURES AND BELOW NORMAL
PRECIPITATION.


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

FORECASTS TRENDED SLIGHTLY DOWNWARD FROM A MONTH A GO FOR MOST
RIVERS. LONG RANGE HYDROLOGIC MODELS ARE FORECASTING A WIDE RANGE OF
AVAILABLE WATER FROM MUCH BELOW NORMAL TO NEAR NORMAL RIVER FLOWS
AND WATER SUPPLY FOR MOST RIVERS THROUGH THIS SPRING AND SUMMER.
WATER SUPPLY FORECASTS FOR WESTERN WASHINGTON RANGE FROM A LOW OF 52
PERCENT FOR THE CHEHALIS RIVER NEAR GRAND MOUND TO 90 PERCENT FOR
THE ELWHA RIVER AT MCDONALD BRIDGE.

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
JUNE 20.

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

RIVER AND GAUGING SITE            PERIOD   FORECAST   NORMAL  PERCENT

NOOKSACK RIVER
   AT NORTH CEDARVILLE            APR-SEP      808      1195      70

SKAGIT RIVER
   NEAR CONCRETE (REGULATED)      APR-SEP      5265     5934      89

BAKER RIVER
   UPPER BAKER RESERVOIR INFLOW   APR-SEP       693      806      86

SULTAN RIVER
   SPADA LAKE INFLOW              APR-SEP       136      189      72

TOLT RIVER
   TOLT RESERVOIR INFLOW          APR-SEP        35       46      76

CEDAR RIVER
   CHESTER MORSE LAKE INFLOW      APR-SEP       110      152      72

GREEN RIVER
   HOWARD HANSON DAM INFLOW       APR-SEP       177      260      68

NISQUALLY RIVER
   ALDER RESERVOIR INFLOW         APR-JUL       286      378      76

COWLITZ RIVER
   MAYFIELD RESERVOIR (REGULATED) APR-SEP      1409     1835      77

CHEHALIS RIVER
   NEAR GRAND MOUND               APR-SEP       204      390      52

ELWHA RIVER
   MCDONALD BRIDGE                APR-SEP       423      472      90

DUNGENESS RIVER
   NEAR SEQUIM                    APR-SEP       133      145      92

WYNOOCHEE RIVER
   WYNOOCHEE DAM INFLOW           APR-SEP        56       98      57

SKOKOMISH RIVER
   NF SKOKOMISH RIVER
   BELOW STAIRCASE RAPIDS         APR-SEP       108      135      80

SNOW MELT

WITH THE SNOW PACK LARGELY GONE IN MOST AREAS...THE CHANCE OF
SNOWMELT FLOODING IS OVER FOR THIS YEAR.

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:

HERE ARE THE LATEST SPRING AND SUMMER CREST FORECASTS FOR WESTERN
WASHINGTON RIVERS AS OF JUNE 20. STATISTICALLY THERE IS A 67 PERCENT
CHANCE THAT THE ACTUAL SPRING CREST WILL FALL WITHIN THE MOST LIKELY
RANGE.

RIVER AND SITE          FLOOD STAGE        MOST LIKELY RANGE OF
                                          THE SPRING/SUMMER CREST
SKAGIT RIVER
  NEAR MT. VERNON         28.0 FT          16.4 FT TO 18.1 FT

STILLAGUAMISH RIVER
  AT ARLINGTON            14.0 FT             3.1 FT TO 5.0 FT

SNOQUALMIE RIVER
  NEAR SNOQUALMIE        20000 CFS          2565 CFS TO 5875 CFS

COWLITZ RIVER
  AT RANDLE               18.0 FT               6.1 TO 6.9 FT

SF SKOKOMISH RIVER
  NEAR UNION                                 213 CFS TO  570 CFS


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/ESPNATURAL (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 AND SPRING FLOOD OUTLOOK FOR WESTERN
WASHINGTON WILL BE ISSUED AROUND THE WEEK OF JULY 4.

$$

WEATHER.GOV/SEATTLE
JBB



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