Green River/Howard Hanson Dam Monitoring

FXUS66 KSEW 240529
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
930 PM PST MON NOV 23 2009

.HYDROLOGY...THE SKOKOMISH RIVER IN MASON COUNTY HAS RECEDED BELOW 
FLOOD STAGE SO THE FLOOD WARNING HAS ENDED. 

PREVIOUS DISCUSSION...THE FRONT TONIGHT MAY BRING UP TO AN INCH OF 
RAIN TO THE OLYMPICS WITH LESSER AMOUNTS ELSEWHERE. THIS SHOULD NOT 
BE ENOUGH TO BRING RIVERS TO FLOOD...INCLUDING THE SKOKOMISH. 
HOWEVER...THE SKOKOMISH WILL CONTINUE TO RUN HIGH...POSSIBLY JUST 
BELOW FLOOD STAGE THROUGH TUESDAY GIVEN THE RENEWED RAINFALL TONIGHT.

THE 12Z/18Z MODEL RUNS HAVE MOSTLY ALL TRENDED TOWARD A WETTER 
SOLUTION FOR THE LATE WEDNESDAY THROUGH THANKSGIVING DAY SYSTEM. 
PREVIOUS GFS SOLUTIONS HAD SHOWN A MORE PROGRESSIVE AND SPLIT TROUGH 
TO MOVE THROUGH WHICH WOULD NOT HAVE LED TO FLOOD CONCERNS. THE NEW 
NAM AND GFS NOW SHOW THIS ELONGATED TROUGH TO REMAIN INTACT WITH A 
RATHER VIGOROUS FRONTAL BAND TO STALL ACROSS THE OLYMPIC PENINSULA 
AND N CASCADES FROM WEDNESDAY AFTERNOON THROUGH THANKSGIVING DAY. 
THE 24 HOUR QPF AMOUNTS VARY FROM 3-4 INCHES FROM THE NAM TO 2 OR 
MAYBE 3 INCHES ON THE GFS. THESE AMOUNTS COULD CONCEIVABLY PUSH SOME 
RIVERS CLOSE TO FLOOD STAGE...ESPECIALLY THE SKOKOMISH RIVER. 
HOWEVER...THERE ARE A LOT OF THINGS GOING AGAINST FLOODING. FIRST 
OFF...THE ECMWF KEEPS THE FRONTAL BAND HUNG UP ALONG THE FAR N WA 
COAST AND S VANCOUVER ISLAND...BYPASSING THE N CASCADES AND POSSIBLY 
THE OLYMPICS WITH THE HEAVIEST RAIN. ALSO...THE FLOW ALOFT IS WEAK 
WITH ALMOST NO OROGRAPHIC CONTRIBUTION TO RAINFALL. SIMPLE DYNAMICS 
WOULD HAVE TO DO THE TRICK. PW VALUES ARE NOT TOO IMPRESSIVE 
EITHER...1.5 INCHES MAX IN THE PLUME. WITH ALL THIS SAID...I WILL 
HOLD OFF ON ISSUING AN ESF BASES ON JUST THE MORNING RUNS. MAY NEED 
TO ISSUE SOMETHING ON TUE IF MODELS CONTINUE TO TREND WET...STAY 
TUNED TO THE LATEST FORECAST. IF FLOODING DOES DEVELOP IT WOULD NOT 
OCCUR UNTIL LATER THANKSGIVING DAY INTO FRIDAY.

NO FLOODING IS EXPECTED ON THE GREEN RIVER AT ANY TIME DURING THE 
FORECAST PERIOD.

• Entire Text Forecast Discussion
• Graphical Forecast Discussion
• NWS Seattle Hydrology Page

• Washington Atmospheric River Observatories
  Includes Westport, Spanaway, and Ravensdale

• Water Vapor Trails
• Global Precipitable Water Loop
• Weather Briefing Package (under construction)

• 10-Day Precipitation and Temperature Forecasts
• 3-Day Precipitation Forecasts

• Why all this New Concern for Flooding in the Green River Valley?
• Western Washington Flooding 101 (.pdf file)
• Flood Preparation & Response - Emergency Phone Numbers & Resources (.pdf file)

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