Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 171023
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
325 AM PDT FRI OCT 17 2014

.SYNOPSIS...A WARM FRONT WILL LIFT NORTHEAST ACROSS THE AREA THIS
MORNING GIVING LIGHT RAIN. RAIN AND LOCALLY WINDY CONDITIONS WILL
SPREAD FROM THE COAST INTO THE INTERIOR THIS AFTERNOON AND THIS
EVENING AS A COLD FRONT MOVES ACROSS THE AREA. PRECIPITATION WILL
TAPER TO SHOWERS LATE TONIGHT THEN COME TO AN END SATURDAY MORNING
AS HIGH PRESSURE BUILDS OVER THE AREA. AN UPPER LEVEL RIDGE AND
OFFSHORE FLOW WILL BRING PARTLY SUNNY AND WARMER WEATHER ON SUNDAY.
A SERIES OF FRONTS WILL GIVE PERIODS OF RAIN AND WINDY CONDITIONS AT
TIMES NEXT WEEK.

&&

.SHORT TERM...RADARS SHOW RAIN ALONG THE COAST SPREADING RAPIDLY
INLAND EARLY THIS MORNING. THIS PRECIPITATION IS DEVELOPING NE OF A
WARM FRONT THAT SITS FROM A LOW NEAR 50N 132W SOUTHEASTWARD INTO
NORTHWESTERN OREGON. AFTER A BRIEF LULL IN PRECIPITATION LATER THIS
MORNING OVER SOUTHERN PORTIONS OF THE INTERIOR...RAIN ASSOCIATED
WITH AN INCOMING N-S ORIENTED FRONT OVER THE COASTAL WATERS WILL
SPREAD EASTWARD. THE RAIN WILL TAPER TO SHOWERS BEHIND THE FRONT
THAT WILL MOVE ONTO THE COAST AROUND 7 PM THIS EVENING AND THROUGH
THE INTERIOR LOWLANDS BY 11 PM. HEAVY RAIN AT TIMES CAN BE EXPECTED
THIS AFTERNOON AND EVENING OVER THE COASTAL ZONES AND ALONG THE WEST
SLOPES OF THE OLYMPICS.

CONCERNING WIND...PRESSURE GRADIENTS ARE RATHER EASTERLY THIS
MORNING. WINDY CONDITIONS CAN BE EXPECTED ON THE COASTAL
BEACHES...MAINLY THIS AFTERNOON AND EARLY THIS EVENING AS THE FRONT
PUSHES INLAND. WIND OVER AREAS OF THE NORTH INTERIOR THAT ARE
TYPICALLY SUSCEPTIBLE TO SOUTHEASTERLIES WILL LIKELY BE DELAYED
UNTIL LATER THIS AFTERNOON AND EVENING AHEAD OF AND WITH THE COLD
FRONT. THE AREAS MOST LIKELY TO SEEING WINDS STRONG ENOUGH TO SNAP
SMALL BRANCHES AND CAUSE LOCAL POWER OUTAGES WILL BE OVER THE SAN
JUANS...LUMMI ISLAND...POINT ROBERTS...AND COASTAL SECTIONS OF
WHATCOM COUNTY. SINCE PRES GRADIENTS ARE SO EASTERLY THIS MORNING
AHEAD OF THE WARM FRONT...THE WIND ADVISORY THAT IS IN EFFECT FOR
COASTAL WHATCOM AND SAN JUAN COUNTIES IS BEING PUSHED BACK TO START
AT 11 AM. THE FRONT WILL BE WEAKENING AS IT MOVES INLAND THIS
EVENING...SO THE ADVISORY WILL BE ENDED AT 11 PM THIS EVENING.

POST FRONTAL SHOWERS WILL TAPER OFF LATE TONIGHT INTO SATURDAY
MORNING. CLOUDS WILL DECREASE DURING THE AFTERNOON HOURS ON
SATURDAY...AND THERE MAY BE A FEW SUN BREAKS THAT WILL ALLOW
TEMPERATURES TO WARM INTO THE MID 60S.

THE NEXT SYSTEM...REMNANTS OF TYPHOON VONGFONG THAT HIT JAPAN A FEW
DAYS AGO...IS WINDING UP AT 50N 160W. THIS LOW WILL SPIN NORTHWARD
THEN FLOUNDER ABOUT OVER THE GULF OF ALASKA. DOWNSTREAM OF THIS
LOW...EXPECT STRONG RIDGING AT THE SURFACE AND ALOFT TO DEVELOP OVER
EASTERN WASHINGTON SATURDAY NIGHT AND SUNDAY. THE END RESULT FOR THE
INTERIOR WILL BE PARTLY SUNNY SKIES AND TEMPERATURES REACHING A VERY
NICE 70 DEGREES. THE FRONT ASSOCIATED WITH THE OFFSHORE LOW WILL
STRETCH AND WEAKEN AS IT BECOMES N-S ORIENTED ON SUN. IT APPEARS
THAT THE FRONT WILL START GIVING SOME RAIN TO THE COAST LATE SUN
AFTERNOON THEN WILL PUSH INLAND AND SLOWLY DIE OVER THE INTERIOR SUN
NIGHT. ALBRECHT

.LONG TERM...MONDAY AND TUESDAY WILL BE SHOWERY AS THE UPPER TROUGH
ASSOCIATED WITH SUNDAY NIGHTS FRONT MOVES ACROSS THE AREA.

A BIG CHANGE TO A VERY RAINY AND WINDY PATTERN WILL TAKE PLACE
TUESDAY NIGHT AND WILL CONTINUE THROUGH MUCH OF NEXT WEEK. THE
SYSTEM CAUSING THE CHANGE IS CURRENTLY IN THE WEST PACIFIC OFF OF
KAMCHATKA. ALL GLOBAL MODELS SHOW THIS STRONG SYSTEM ENTRAINING
MOISTURE FROM THE REMNANTS OF TROPICAL STORM/HURRICANE ANA NOW
APPROACHING THE HAWAIIAN ISLANDS. GIVEN THE SOURCE OF THE AIR
MASS...TEMPERATURES AND DEWPOINT TEMPERATURES IN THE EXTENDED
FORECAST PERIOD FROM TUESDAY NIGHT THROUGH THURSDAY WERE RAISED
SEVERAL DEGREES. POPS WILL BE HIGH THROUGH THE PERIOD...AND IT WILL
LIKELY BE WINDY AT TIMES...ESPECIALLY ALONG THE COAST AND IN THE
NORTH INTERIOR. SNOW LEVELS ARE EXPECTED TO BE RATHER HIGH...8000
FEET OR HIGHER...WEDNESDAY AND THURSDAY. ALBRECHT

&&

.HYDROLOGY...LOCALLY HEAVY RAINFALL ALONG THE COAST AND ON THE WEST
SLOPES OF THE OLYMPICS THIS AFTERNOON AND EVENING WILL RESULT IN
RISES ON COASTAL RIVERS. BUT FLOODING IS NOT EXPECTED.

AFTER A PERIOD OF RELATIVELY DRY WEATHER...ANOTHER ROUND OF RAINFALL
IS EXPECTED SUNDAY NIGHT THROUGH TUESDAY. THIS RAINFALL IS NOT
EXPECTED TO BE HYDROLOGICALLY SIGNIFICANT.

GLOBAL MODELS AND THEIR ENSEMBLES ARE STRONGLY SUGGESTING THAT AN
ATMOSPHERIC RIVER EVENT WILL SET UP SOMEWHERE BETWEEN NW WASHINGTON
(CANADIAN AND ECMWF MODELS) AND CENTRAL OREGON (GFS) WEDNESDAY
THROUGH FRIDAY OF NEXT WEEK...AND SEVERAL INCHES OF RAIN CAN BE
EXPECTED IN A 24 HOUR PERIOD WHEREVER THE PATTERN SETS UP. THE FIRE
HOSE MAY (GFS) OR MAY NOT (CANADIAN AND ECMWF) WAVE SOUTH AND NORTH
ACROSS THE AREA DURING THIS PERIOD. THERE IS A GOOD DEAL OF
UNCERTAINTY AT THIS RANGE...BUT FLOODING IS POSSIBLE ON SOME RIVERS
ACROSS WESTERN WASHINGTON TOWARD THE MIDDLE OR END OF NEXT WEEK IF
THE CANADIAN OR ECMWF SOLUTIONS VERIFY. ALBRECHT

&&

.AVIATION...A WARM FRONT WILL LIFT NWD ACROSS THE REGION THIS
MORNING. THE COLD FRONT WILL REACH THE COAST LATE THIS AFTERNOON AND
PUSH ACROSS INTERIOR WRN WA EARLY THIS EVENING. STRONG SLY FLOW WILL
SHIFT TO SWLY BEHIND THE FRONT. STABLE AND MOIST ATMOSPHERE WITH
RAIN AT TIMES. WEAKLY UNSTABLE TONIGHT WITH SHOWERS. VFR CIGS THIS
MORNING...THEN AREAS OF MVFR CIGS DEVELOP JUST AHEAD OF THE FRONT
THIS AFTERNOON.

KSEA...RAIN DEVELOPING EARLY THIS MORNING WITH CIGS ABOVE 4K FT.
MVFR CIGS LIKELY AFTER 21Z AS RAIN INCREASES AS A COLD FRONT
APPROACHES. E-SE WINDS 8 TO 12 KT...THEN S-SW WINDS 8-13 KT W/ GUSTS
TO 20 KT AFTER 02Z. DTM

&&

.MARINE...GALE FORCE WINDS OVER THE COASTAL WATERS WILL SPREAD TO
THE NORTHERN INLAND WATERS AND ENTRANCES TO THE STRAIT OF JUAN DE
FUCA THIS MORNING. THE CENTRAL STRAIT AND ADMIRALTY INLET SHOULD
HAVE SMALL CRAFT UNTIL THE FRONT PASSES EARLY THIS EVENING. SLY
WINDS SHOULD INCREASE IN PUGET SOUND BEHIND THE FRONT THIS EVENING
WITH BORDERLINE SMALL CRAFT WINDS EXPECTED. COMBINED SEAS OF 12 TO
14 FT OVER THE COASTAL WATERS WILL BUILD TO OVER 15 FT BY MIDDAY.

SURFACE HIGH PRESSURE BUILDS OVER THE WATERS ON SAT AS THE LOW
PRESSURE SYSTEM EXITS THE REGION. THE NEXT FRONT WILL ENTER THE
COASTAL WATERS SUN AFTERNOON AND AFFECT THE AREA THROUGH MON.
ADDITIONAL FRONTS WILL AFFECT THE WATERS THE REMAINDER OF NEXT WEEK.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...WIND ADVISORY NORTH AND CENTRAL COAST THROUGH 11 PM PDT THIS
      EVENING.
     WIND ADVISORY WESTERN WHATCOM COUNTY AND THE SAN JUAN ISLANDS
      NOON TODAY THROUGH 11 PM THIS EVENING.

PZ...GALE WARNING COAST...ENTRANCES...AND NORTHERN INLAND WATERS.
     SMALL CRAFT ADVISORY CENTRAL STRAIT AND ADMIRALTY INLET.
     SMALL CRAFT ADVISORY FOR ROUGH GRAYS HARBOR BAR.

&&

$$

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