Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 181601
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
859 AM PDT FRI APR 18 2014

.SYNOPSIS...WEAK HIGH PRESSURE WILL BUILD OVER THE AREA TODAY. THE
NEXT FRONTAL SYSTEM LOOKS TO ARRIVE SOONER THAN PREVIOUSLY FORECAST.
PRECIPITATION SHOULD REACH THE COAST SHORTLY AFTER SUNRISE SATURDAY
MORNING THEN SPREAD INLAND. WEAK HIGH PRESSURE RETURNS SATURDAY
NIGHT...AND THEN STRENGTHENS A BIT SUNDAY. WARMER SOUTHWEST FLOW
ALOFT SUNDAY WILL ALLOW INLAND DAYTIME TEMPERATURES TO BE A FEW
DEGREES ABOVE NORMAL. THE DRY PERIOD IS EXPECTED TO HOLD THROUGH
SUNDAY NIGHT...POSSIBLY AS LONG AS MONDAY MORNING...AS THE MAIN COLD
FRONT STALLS OFF THE COAST. THE FRONT FINALLY MOVES ONSHORE MONDAY
AFTERNOON INTO TUESDAY. THE PATTERN WILL THEN REMAIN FAIRLY UNSETTLED
THROUGH MUCH OF THE WEEK.
&&

.MORNING UPDATE...AS USUAL WHENEVER WE GET RAIN AND THEN CLEAR OUT
AND GET SOME WEAK SURFACE WINDS...WE GET SOME LOW STRATUS AND FOG
WHICH HAS BEEN LOCALLY DENSE ALONG THE WILLAMETTE IN THE SOUTH AND
CENTRAL VALLEY...AND ALONG MANY OTHER RIVER VALLEYS.  WEAK SURFACE
FLOW WILL CAUSE THE FOG AND STRATUS TO LINGER A BIT LONGER...BUT MID
APRIL SUN WILL CONTINUE ITS WORK TO ERODE FOG AND VISIBILITIES HAVE
BEEN IMPROVING. OTHERWISE TODAY SHOULD PLEASANT WITH PASSING HIGH
CLOUDS...THOUGH CLOUDS WILL REMAIN THICKER ALONG AND NORTH OF THE
COLUMBIA AS A DISTURBANCE SLIDES THROUGH IN NW FLOW AND EVEN
PRODUCES A SHOWER OR TWO. /KMD

&&

.SHORT TERM...FRIDAY THROUGH SUNDAY...THE SHARP UPPER TROUGH WAS NEAR
OR JUST EAST OF THE CASCADES AS OF 09Z. WATER VAPOR IMAGERY SHOWS AN
OBVIOUS DRY SLOT MOVING ACROSS THE FORECAST AREA. NWS DUAL-POL
DOPPLER RADAR SHOWING SCATTERED SHOWER ACTIVITY OVER THE HIGHER
TERRAIN...ESPECIALLY THE N OREGON COAST RANGE AND S WA CASCADES AND
FOOTHILLS. THIS ACTION WILL CONTINUE TO DIMINISH THE REST OF TONIGHT
AND FRI MORNING AS THE AIR MASS ALOFT GRADUALLY MODERATES...WHICH
WILL WEAKEN THE MID-LEVEL LAPSE RATES. NEED TO LEAVE SOME SLIGHT
CHANCE POPS FOR THE S WA CASCADES AND EXTREME N OREGON CASCADES THIS
MORNING WITH 10-15 KT WLY 850 MB OROGRAPHIC FLOW AND NW ONSHORE
LOW-LEVEL FLOW. LATEST NAM SHOWS THE SURFACE RIDGE AXIS SOUTH OF MT.
HOOD AT 18Z.

GFS AND ECMWF SHOW A VERY WEAK UPPER LEVEL WAVE MOVING THROUGH THE
500 MB RIDGE THIS AFTERNOON. THE FEATURE DAMPENS OUT AS IT MOVES
ONSHORE BUT STILL SHOULD PRODUCE SOME MID AND HIGH CLOUDS. THE DRY
PERIOD WILL BE SHORT-LIVED...AND EVEN SHORTER LIVED THAN EARLIER
FORECASTS INDICATED. MODELS CONTINUE TO SPEED UP THE TIMING OF THE
NEXT SYSTEM. MODELS LOOKING PRETTY CONSISTENT WITH THE OVERALL
DETAILS FOR THE SAT SYSTEM. PREVIOUS SHIFT BROUGHT RAIN TO THE COAST
IN THE 12Z-15Z SAT TIME FRAME AND THAT STILL LOOKS REASONABLE. RAIN
MAY EVEN PENETRATE A LITTLE FURTHER INLAND THAN THE CURRENT GRIDS
SHOW. THE FRONT MOVES THROUGH AT A DECENT PACE AND SHOULD BE EAST
OF THE CASCADES BY EARLY SATURDAY EVENING AS THE PARENT UPPER SHORT
WAVE IS ALREADY MOVING INTO CENTRAL OREGON BY 00Z SUNDAY.

SURFACE HIGH PRES STARTS TO BUILD AGAIN SAT NIGHT...WITH LINGERING
PRECIP GENERALLY N OF A MT. JEFFERSON TO KONP LINE. HIGHEST POPS WILL
BE IN THE S WA CASCADES AND FOOTHILLS...CLOSEST TO THE UPPER LEVEL
TROUGH AND COOL POOL ALOFT. ANY LEFT-OVER PRECIP 12Z SUN SHOULD BE
LIMITED TO THE SW WA. SUNDAY IS LOOKING NICER AS A TRANSITORY 500 MB
RIDGE MOVES OVER THE PAC NW. 850MB TEMPS WARM TO AROUND 5C IN THE FAR
N TO NEAR 10C IN THE FAR S. THIS TRANSLATES TO MAX TEMPS A FEW
DEGREES ABOVE NORMAL. WEISHAAR

.LONG TERM...SUNDAY NIGHT THROUGH THURSDAY...MADE SOME CHANGES TO THE
SUN NIGHT AND MONDAY TIME FRAME. A DEVELOPING GULF OF ALASKA UPPER
TROUGH WILL DEEPEN SUN NIGHT ALLOWING THE DOWNSTREAM UPPER RIDGE TO
AMPLIFY. AS A RESULT...WENT DRY SUN NIGHT EXCEPT FOR SLIGHT CHANCE
POPS NEAR THE S WA COAST. A STRENGTHENING COLD FRONT FROM NEAR
VANCOUVER ISLAND TO 40N 133W WILL PIVOT INTO A MORE NORTH-TO-SOUTH
ORIENTATION SUN NIGHT AND MON MORNING. THUS...DRY CONDITIONS MAY HOLD
THROUGH AT LEAST 18Z MON. THE FRONT FINALLY GETS FORCED INLAND MON
AFTERNOON AS THE DEEP GULF OF ALASKA UPPER TROUGH DIVES TO THE SE.
WILL NEED TO WATCH FOR THUNDERSTORM POTENTIAL MON AFTERNOON FOR THE
CASCADES WITH INCREASING S-SWLY FLOW...POSSIBLE SHORT-WAVES ROTATING
AROUND THE DEEP UPPER TROUGH AND STEEP AND MID-LEVEL LAPSE RATES.

LOOKS LIKE TUE AND WED WILL BE CHARACTERIZED BY COOL AND DAMP
CONDITIONS AS THE DEEP UPPER LOW MIGRATES ACROSS THE PAC NW AND INTO
THE NRN ROCKIES. LARGER MODEL DIFFERENCES CROP UP WED AND THU FOR
DIMINISHED FORECAST CONFIDENCE. THE ECMWF MAINTAINS A FAIRLY
PROGRESSIVE PATTERN THE LATTER HALF OF NEXT WEEK. WEISHAAR
&&

.AVIATION...VFR PREVAILING TODAY AND TONIGHT. HOWEVER...THERE IS
SOME PATCHES OF FOG ON THE COAST AND INLAND FROM KCVO TO KEUG THAT
SHOULD DISSIPATE AROUND 17Z. INCREASING CLOUDS AFT 06Z SAT AHEAD
OF NEXT FRONTAL SYSTEM. RAIN BEGINNING ON THE COAST ABOUT 12Z WITH
MVFR CIGS FOLLOWING AFTER 15Z. INLAND AREAS...INCREASING CHANCES
FOR MVFR CIGS AFTER 15Z SAT.

KPDX AND APPROACHES...VFR EXPECTED THROUGH EARLY SAT MORNING THEN
INCREASING CHANCES FOR MVFR CIGS AFTER 15Z SAT AS A FRONT
APPROACHES THE AREA.

&&

.MARINE...A RELATIVELY QUIET PERIOD TODAY WITH WEAK HIGH OVER THE
WATERS. THE HIGH PRES GIVES WAY TO A FRONT TONIGHT WHICH SHOULD
BRING SMALL CRAFT ADVISORY WINDS OVER ALL WATERS EARLY SAT THROUGH
SAT NIGHT. WINDS THEN DIMINISH FROM SOUTH TO NORTH SUN MORNING.

A LARGE SWELL TRAIN WILL FOLLOW THE FRONT SAT EVENING AND SUN.
SEAS APPEAR ON TRACK TO RAPIDLY BUILD TO 17 TO 20 FT AT 16
SECONDS FROM AROUND 11 PM SAT NIGHT...PEAKING BETWEEN MIDNIGHT
AND 5 AM SUN. SEAS WILL SLOWLY SUBSIDE SUN MORNING BUT REMAIN IN
THE 13 TO 16 FT RANGE THROUGH SUN NIGHT...AND TO 10 FT LATE MON. A
SMALL CRAFT ADVISORY FOR SEAS HAS BEEN ISSUED FOR THIS SWELL
TRAIN.

A HIGH SURF ADVISORY HAS BEEN ISSUED FOR LATER SAT NIGHT THROUGH
SUN MORNING FOR THE SOUTH WASHINGTON AND NORTH OREGON COASTS. THE
CENTRAL COAST WILL PROBABLY REMAIN JUST UNDER ADVISORY CRITERIA.

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...HIGH SURF ADVISORY FROM 10 PM SATURDAY TO 10 AM PDT SUNDAY FOR
     NORTH OREGON COAST.

WA...HIGH SURF ADVISORY FROM 10 PM SATURDAY TO 10 AM PDT SUNDAY FOR
     SOUTH WASHINGTON COAST.

PZ...SMALL CRAFT ADVISORY FOR WINDS FROM 2 AM TO 9 PM PDT SATURDAY
     FOR COASTAL WATERS FROM CAPE SHOALWATER WA TO CASCADE
     HEAD OR OUT 60 NM.

     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS FROM 4 PM SATURDAY TO 6
     AM PDT MONDAY FOR COASTAL WATERS FROM CAPE SHOALWATER WA TO
     FLORENCE OR OUT 60 NM.

     SMALL CRAFT ADVISORY FOR WINDS FROM 2 AM TO 4 PM PDT SATURDAY
     FOR COASTAL WATERS FROM CASCADE HEAD OR TO FLORENCE OR OUT 60
     NM.


&&

$$

MORE WEATHER INFORMATION ONLINE AT...
    HTTP://WEATHER.GOV/PORTLAND

INTERACT WITH US VIA SOCIAL MEDIA
    WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.PORTLAND.GOV
    WWW.TWITTER.COM/NWSPORTLAND

THIS DISCUSSION IS FOR NORTHWEST OREGON AND SOUTHWEST WASHINGTON FROM
THE CASCADE CREST TO 60 NAUTICAL MILES OFFSHORE. THE AREA IS COMMONLY
REFERRED TO AS THE FORECAST AREA..


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