River Flood Warning 7, NWS Seattle, WA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
900 AM PDT SAT SEP 28 2013

.SYNOPSIS...A STRONG FRONTAL SYSTEM WILL MOVE THROUGH WESTERN
WASHINGTON THROUGH TONIGHT. ANOTHER STRONG FRONTAL SYSTEM WILL REACH
THE AREA SUNDAY AFTERNOON AND NIGHT AND THAT SYSTEM WILL HAVE A DEEP
LOW PRESSURE CENTER CROSS VANCOUVER ISLAND SUNDAY EVENING. COOL AND
SHOWERY WEATHER IS ON TAP MONDAY THROUGH WEDNESDAY.

&&

.SHORT TERM...THE STRONG WET FRONTAL SYSTEM MOVING OVER WESTERN WA
SHOWS AN AREA OF PRESSURE FALLS OF 5MB/3HR SOUTH OF VANCOUVER ISLAND
AT 8AM. PRESSURE GRADIENTS OVER WESTERN WA WILL INCREASE THIS
AFTERNOON AS THE STRONG PORTION OF THE SYSTEM MOVES OVER WRN WA. THE
CENTER OF THE LARGE LOW PRESSURE SYSTEM IS NEAR 130W AROUND 52N THIS
MORNING. THE FRONT IS STRONG AND BY LATE THIS AFTERNOON THE NAM
SHOWS WIND SPEEDS REACHING 70KT OVER NW OREGON AT 850MB WITH 60-70KT
WINDS DOWN TO 925MB ALONG THE NORTH AND CENTRAL OREGON COAST. THIS
SYSTEM HAS PLENTY OF MOISTURE AND WITH THE STRONG SW FLOW ALOFT
HEAVY RAIN WILL FALL IN THE MOUNTAINS.

THE SECOND SYSTEM IS CURRENTLY OUT AROUND THE ALEUTIAN ISLANDS.
THERE IS A GOOD CHANCE THAT FRONTAL WAVE WILL SPIN UP AND A DEEP LOW
WILL CROSS VANCOUVER ISLAND SUNDAY EVENING. THE 12Z NAM TAKES A
971MB LOW INTO THE TOFINO AREA SUNDAY EVENING. THE 12Z GFS HAS A
980MB LOW ABOUT 100 MILES WEST OF DESTRUCTION ISLAND LATE SUNDAY
AFTERNOON AND IT CROSSES VANCOUVER ISLAND AND IS SHOWN AT THE NRN
PORTION OF THE STRAIT OF GEORGIA AROUND 11PM SUNDAY. THE PDX-BLI
GRADIENT AT THAT TIME IS FORECAST BY THE 12Z GFS TO BE AROUND
11MB...SO A WINDY NIGHT IS ON TAP. AT SOME POINT TODAY IT IS LIKELY
THAT A HIGH WIND WATCH WILL BE ISSUED FOR THAT SYSTEM.

.LONG TERM...THE FIRST HALF OF THE WEEK WILL BE COOL AND SHOWERY
WITH A LOW SNOW LEVEL IN THE MOUNTAINS...PROBABLY GETTING DOWN
AROUND 4500FT. DRY WEATHER IS POSSIBLE THURSDAY AND FRIDAY AS HIGH
PRESSURE BUILDS INTO THE AREA.

&&

.HYDROLOGY...TWO FRONTAL SYSTEMS OUGHT TO BRING 3 TO 5 INCHES OF
RAIN TO THE MOUNTAINS EACH THIS WEEKEND. THE FIRST SYSTEM DRAGS
THROUGH WESTERN WA TODAY AND TONIGHT AND THE SECOND SYSTEM WILL
REACH THE AREA SUNDAY AFTERNOON AND NIGHT. RAINFALL IN THE MOUNTAINS
WILL FILL UP THE RIVERS AND THERE IS A CHANCE OF GETTING UP TO FLOOD
STAGE ON SOME RIVERS...THE SKOKOMISH RIVER IN MASON COUNTY THE MOST
LIKELY. THERE IS A FLOOD WATCH IN EFFECT.

&&

.AVIATION...A STRONG FRONTAL SYSTEM WILL AFFECT W WA THROUGH 06Z.
THE ASSOCIATED COLD FRONT WILL REACH THE N COAST AROUND 00Z AND
PUGET SOUND AROUND 03Z. CONTINUING RAIN AHEAD OF THE FRONT WILL
LOWER CIGS DOWN BELOW 3000 FEET WITH AREAS OF IFR CIGS DEVELOPING.
VISIBILITY WILL BE GENERALLY 3-7 MILES IN RAIN...BUT LOCAL VIS 2SM
RA BR IS POSSIBLE. STRONG SOUTHERLY LOW LEVEL WINDS WILL DEVELOP
WITH AREAS OF 35-50 KT S-SW WINDS AT FL025 EXPECTED. AREAS OF S-SE
SURFACE WINDS 15-30 KT GUSTING 45 KT ARE POSSIBLE ESPECIALLY ALONG
THE COAST AND OVER INTERIOR AREAS NORTH OF SEATTLE.

ANOTHER STRONG COLD FRONT WILL AFFECT THE AREA SUNDAY THROUGH SUNDAY
NIGHT.

KSEA...CIGS ARE CURRENTLY VFR BUT WITH RAIN CONTINUING SHOULD LOWER
TO BKN-OVC010-020 BY 21Z. COULD SEE SOME IFR CIGS BKN005-010 AS
WELL. SSW WINDS ALOFT AT 5000 FEET WILL BE AROUND 40 KT AT
15Z...RISING TO 60 KT 21Z-00Z. WINDS WILL WEAKEN AFTER FROPA AROUND
03Z. SURFACE WINDS WILL REMAIN SOUTHERLY 10-20 KT...WITH GUSTS 20-30
KT FROM 21Z THROUGH ABOUT 03Z. KAM

&&

.MARINE...A STRONG COLD FRONT WILL REACH THE N COAST LATE THIS
AFTERNOON AND SWEEP ACROSS PUGET SOUND EARLY THIS EVENING. EXPECT
S-SE GALES ALONG THE COAST AND N INTERIOR AHEAD OF THE FRONT. THERE
IS A SMALLER CHANCE OF S GALES OVER N PUGET SOUND THIS
AFTERNOON...BUT CONFIDENCE IS LOW.

ANOTHER STRONG COLD FRONT WILL REACH THE COAST LATE SUNDAY AFTERNOON
WITH THE ASSOCIATED 972 MB TO 980 MB LOW REACHING CENTRAL VANCOUVER
ISLAND EARLY SUNDAY EVENING. THIS WILL DEFINITELY BE A VIGOROUS
FRONTAL SYSTEM WITH ANOTHER ROUND OF SOLID GALES AND POSSIBLY STORM
FORCE WINDS...BUT MODEL DIFFERENCES IN TRACK AND STRENGTH ARE STILL
LOWERING CONFIDENCE IN SOME OF THE DETAILS.

TODAYS FRONT WILL GENERATE 14 TO 17 FT SEAS OFFSHORE THAT WILL
SPREAD INTO THE NEAR COASTAL WATERS THIS EVENING. SEAS WILL LIKELY
BUILD TO AROUND 25 FEET OVER THE COASTAL WATERS SUNDAY NIGHT. KAM

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...WIND ADVISORIES ARE IN EFFECT FOR THE COAST...NORTH
     INTERIOR...AND PARTS OF THE PUGET SOUND REGION TIL 7 PM
     PDT THIS EVENING.

     A FLOOD WATCH IS IN EFFECT FOR MUCH OF THE CWA FROM THIS
     EVENING THROUGH MONDAY MORNING.

PZ...GALE WARNING COASTAL WATERS...ENTRANCES TO THE STRAIT OF JUAN
      DE FUCA...ADMIRALTY INLET AND NORTHERN INLAND WATERS.

     SMALL CRAFT ADVISORY PUGET SOUND AND HOOD CANAL.

     SMALL CRAFT ADVISORY FOR ROUGH GRAYS HARBOR BAR.

     STORM WATCH COASTAL WATERS...NORTHERN INLAND WATERS...
      ADMIRALTY INLET AND EAST ENTRANCE TO THE STRAIT LATE SUNDAY
      AFTERNOON AND SUNDAY NIGHT.

     GALE WATCH PUGET SOUND AND HOOD CANAL...WEST ENTRANCE TO THE
      STRAIT OF JUAN DE FUCA...AND THE CENTRAL STRAIT OF JUAN DE
      FUCA SUNDAY AFTERNOON AND SUNDAY NIGHT.
&&

YOU CAN SEE AN ILLUSTRATED VERSION OF THE FORECAST DISCUSSION AT
WWW.WEATHER.GOV/SEATTLE/GAFD/LATEST_WEBAFD.HTML

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