Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 290413
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
900 PM PDT SUN SEP 28 2014

.SYNOPSIS...A FRONT WILL BRING RAIN TO THE COAST MONDAY MORNING AND
TO THE INTERIOR OF WESTERN WASHINGTON BY THE AFTERNOON. SCATTERED
SHOWERS MONDAY NIGHT WILL TAPER OFF BY MIDWEEK. AN UPPER RIDGE OF
HIGH PRESSURE IS LIKELY TO BUILD OVER THE AREA LATE IN THE WEEK.

&&

.SHORT TERM...AN UPPER LOW PERSISTS OVER THE DESERT SOUTHWEST WHILE
A FRONTAL SYSTEM EXTENDS SOUTHWARD FROM THE QUEEN CHARLOTTE SOUND
THROUGH THE OFFSHORE WATERS JUST OUTSIDE OF 130W. THE WEAK RIDGE
OVER WESTERN WASHINGTON IS RAPIDLY ERODING AS THE FRONT TO THE WEST
OF THE AREA APPROACHES...AND STRATUS HAS STARTED TO FORM ALONG THE
CENTRAL COAST. IT IS STILL RATHER CLEAR IN THE INTERIOR AND GOOD
RADIATIONAL COOLING IS TAKING PLACE. TEMPERATURES ARE NEARING THE
DEWPOINT AND PATCHY FOG IS FORMING OVER THE NORTHERN INLAND WATERS
AND AROUND BELLINGHAM. EXPECT FOG PATCHES TO FORM THROUGH THE
INTERIOR LOWLANDS THIS EVENING BEFORE STRATUS MOVES IN FROM THE WEST
AFTER ABOUT MIDNIGHT.

SHORT TERM MODELS CONTINUE TO SHOW THE FRONT MOVING ONTO THE COAST
BY ABOUT NOON MONDAY THEN THROUGH THE INTERIOR AND INTO THE CASCADES
BY EVENING. MOST AREAS SHOULD SEE A TENTH TO A QUARTER OF AN INCH OF
RAIN JUST AHEAD OF AND WITH THE FRONT ON MONDAY.

UPPER FLOW TURNS TO THE WNW MON EVENING BEHIND THE FRONTAL PASSAGE
AND 850 MB TEMPERATURES FALL TO 2-4C. CONVERGENT WNW FLOW PROMISES
TO GIVE SCATTERED SHOWERS TO THE AREA LATE MON NIGHT INTO TUE
NIGHT...WITH SHOWERS MORE LIKELY IN THE CASCADES AND LIKELY WITH A
PUGET SOUND CONVERGENCE ZONE SOMEWHERE AROUND THE SEATTLE METRO
AREA. THE WNW FLOW ALOFT WILL GET RECHARGED WED...BRINGING YET
ANOTHER THREAT OF SHOWERS AND CONVERGENCE ZONE ACTIVITY...ALTHOUGH
THE GFS BUILDS UPPER LEVEL HEIGHTS A BIT MORE THAN THE ECMWF WITH
THE TROUGH A BIT FARTHER TO THE NE.

FORECASTS WERE UPDATED TO INCREASE CLOUDS OVERNIGHT THROUGHOUT THE
AREA AND TO ACCOUNT FOR THE DEVELOPMENT OF PATCHY FOG IN THE
INTERIOR AHEAD OF THE STRATUS DECK LATER TONIGHT. OTHERWISE
FORECASTS WERE LEFT ALONE FOR NOW. ALBRECHT

.LONG TERM...FROM THE AFTERNOON LONG TERM DISCUSSION...AN UPPER
RIDGE WILL BUILD OVER THE PACIFIC NORTHWEST THURSDAY AND FRI AND
WILL PROBABLY REMAIN IN PLACE FOR THE WEEKEND. THERE IS A SYSTEM
THAT MOVES INTO B.C. AND MOISTURE FROM THAT SYSTEM MAY WORK SOUTH
INTO WRN WA BY SAT. UPPER LEVEL HEIGHTS LOOK LIKE THEY OUGHT TO BE
HIGH ENOUGH FOR THE RIDGE TO BE ASSOCIATED WITH SUNNY WARM WEATHER
BUT THE MODELS HAVE OFTEN SHOWN A LITTLE RAIN DESPITE THE HIGH
HEIGHTS. WITH TROPICAL MOISTURE FROM A WESTPAC TYPHOON GETTING INTO
THE FLOW IT IS PROBABLY TOO EARLY TO SAY WHAT WILL HAPPEN YET BUT
NUDGED THE FORECAST TOWARD THE DRIPPY CLOUDY MODELS.

&&

.AVIATION...AN UPPER TROF AND ASSOCIATED CDFNT OVER THE NERN PACIFIC
WILL CONTINUE MOVING E OVERNIGHT. THE CDFNT WILL SWEEP ACROSS THE
AREA DURING THE DAY. LIGHT AND VARIABLE FLOW ALOFT WILL BECOME WLY
AND STRENGTHEN ON MON. WEAK LOW LEVEL ONSHORE FLOW WILL PREVAIL
OVERNIGHT.

THANKS TO LIGHT ONSHORE FLOW...STRATUS AND/OR FOG WERE DEVELOPING AT
THIS TIME. THUS ANTICIPATE AREAS OF VSBYS AOB 2SM AND CIGS AOB
500 FT THRU MUCH OF TONIGHT. CIGS/VSBYS WILL RAPIDLY LIFT EARLY MON
MORNING IN RESPONSE TO THE APPROACHING LOW PRESSURE SYSTEM. BY 1500
UTC...CIGS SHOULD BE MAINLY IN THE 1-2K FT RANGE BUT THERE WILL BE
AREAS OF 3-5SM -RA BR...ESPECIALLY ON THE COAST.

KSEA...CANNOT RULE OUT FOG /VSBYS AOB 2SM/ AND LOW CIGS /AOB 500 FT/
DEVELOPING OVERNIGHT. IF THIS HAPPENS...IT SHOULD NOT LAST MORE THAN
SIX HOURS OR SO. OTHERWISE...ANTICIPATE CIGS NEAR 1K FT TO DEVELOP
BY 1500 UTC.

&&

.MARINE...
HIGH PRES OVER WESTERN WASHINGTON WITH LOWER PRES E OF THE CASCADES
WILL RESULT IN WEAK ONSHORE FLOW OVERNIGHT. LOOK FOR A COLD FRONT TO
SWEEP ACROSS THE AREA DURING THE DAY MON. THERE IS A POSSIBILITY OF
GALE FORCE WINDS OVER THE STRAIT OF JUAN DE FUCA IN THE WAKE OF THIS
FRONT. ONSHORE OR WESTERLY FLOW WILL THEN PERSIST THROUGH TUE DUE TO
HIGH PRES OVER THE NE PACIFIC AND LOWER PRES E OF THE CASCADES.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...

WA...NONE.
PZ...GALE WATCH IN EFFECT MONDAY NIGHT FOR THE CENTRAL STRAIT OF
      JUAN DE FUCA AND EAST ENTRANCE TO THE STRAIT.

&&

$$

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