Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 202129
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
228 PM PDT SAT SEP 20 2014

.SYNOPSIS...THERMAL LOW PRESSURE REMAINS DOMINANT ACROSS WESTERN
OREGON WITH HIGHER PRESSURE EAST OF THE CASCADES. THIS IS CAUSING
MODERATE OFFSHORE FLOW WHICH IS RESULTING IN WARMER TEMPERATURES THIS
AFTERNOON. A SURGE OF MARINE AIR IS RAPIDLY PUSHING NORTH ALONG THE
OREGON COAST...AND SHOULD APPROACH ASTORIA BY SUN MORNING. THE
TENDENCY WILL BE FOR THIS TO BRING ONSHORE FLOW BACK FOR COOLER
TEMPERATURES SUNDAY AND MONDAY. A WEAK FRONT WILL ALSO BRUSH BY
MONDAY...POTENTIALLY BRINGING A COUPLE SHOWERS TO THE COAST AND
CASCADES. A STRONGER FRONT WILL BRING A BETTER CHANCE FOR RAIN
THROUGHOUT THE DISTRICT LATE TUESDAY OR WEDNESDAY...FOLLOWED BY A
COOL SHOWERY PATTERN FOR THE REST OF THE WEEK.

&&

.SHORT TERM...TONIGHT THROUGH TUESDAY...TEMPERATURES HAVE WARMED UP
QUICKLY TODAY...WITH NOT A CLOUD IN THE SKY ACCORDING TO VISIBLE
SATELLITE IMAGERY THIS AFTERNOON. THE ONE OBSCURATION WHICH IS
BECOMING INCREASINGLY VISIBLE AS THE AFTERNOON PROGRESSES IS SMOKE
FROM THE 36 PIT FIRE...WHICH IS A BIT MORE ACTIVE THAN IT HAS BEEN
DURING OUR RELATIVELY COOL DAMP WEATHER THE PAST COUPLE DAYS. THIS
SHOULD RESULT IN MORE SMOKE PRODUCTION TO SETTLE DOWN INTO THE LOWER
CLACKAMAS AND WILLAMETTE VALLEYS OVERNIGHT...LINGERING INTO SUNDAY
MORNING.

MEANWHILE PRESSURE GRADIENTS HAVE SWITCHED FROM DECIDEDLY NORTHERLY
TO SOMEWHAT SOUTHERLY ALONG THE CENTRAL AND SOUTHERN OREGON COAST.
THE KACV-KOTH GRADIENT WAS -4.5 MB YESTERDAY EVENING...INDICATING A
NORTHERLY COMPONENT TO THE FLOW. THIS HAS SINCE SWITCHED TO +1.3 MB
AND APPEARS TO BE INCREASING FAIRLY RAPIDLY...A DECENT SIGN THAT A
SOUTHERLY SURGE OF MARINE AIR IS POISED TO MOVE NORTHWARD ALONG THE
OREGON COAST TONIGHT. THIS WILL ENHANCE ONSHORE FLOW FOR THE COAST
AND COASTAL VALLEYS SUNDAY...AND SHOULD EVEN CAUSE A BIT OF COOLING
INLAND AS WELL. THE REAL COOLING OCCURS INLAND ON MONDAY AS THE
THERMAL TROUGH PRESENTLY LINGERING WEST OF THE CASCADES SHIFTS OVER
TO THE EAST SIDE. THIS WILL ALLOW MORE PROLIFIC ONSHORE FLOW...
PERHAPS EVEN SOME LOW CLOUDS INTO THE WILLAMETTE VALLEY MON MORNING.

AT THE SAME TIME...A FRONTAL SYSTEM ALONG 145W WILL BE APPROACHING
THE PAC NW COAST. THERE IS GOOD AGREEMENT THAT THIS SYSTEM WILL
STRETCH APART WHILE APPROACHING THE COAST...WITH THE BULK OF LEFTOVER
ENERGY HEADED TOWARD BRITISH COLUMBIA. THE FRONT MAY HOLD TOGETHER
LONG ENOUGH FOR A COUPLE SHOWERS ALONG THE NORTH COAST OR IN THE
CASCADES MONDAY...BUT THAT IS ABOUT ALL. INCREASED CLOUD COVER AND
FALLING 500 MB HEIGHTS/850 MB TEMPS SHOULD HOLD TEMPS IN THE 70S FOR
MOST INLAND AREAS MON AFTERNOON.

THE MONDAY SYSTEM LIKELY LEAVES A DISORGANIZED BAROCLINIC ZONE DRAPED
ACROSS WESTERN WA/OR MON NIGHT/EARLY TUE. THIS COULD PROVIDE A
CONDUIT FOR A MORE ORGANIZED SYSTEM TO PUSH ONSHORE LATE TUE/WED. 12Z
GFS/ECMWF SEEM TO SHOW FAIRLY GOOD AGREEMENT THAT THERE WILL AT LEAST
BE A PERIOD OF RAIN THROUGHOUT OUR DISTRICT SOMEWHERE AROUND MIDWEEK
AS THIS OCCURS. RIGHT NOW LATE TUE/WED APPEARS TO BE MOST LIKELY.
DEPENDING ON HOW THIS SYSTEM SETS UP...IT COULD ALSO BE OUR FIRST
BREEZY SOUTH WIND EVENT OF THE SEASON ALONG THE COAST.WEAGLE

.LONG TERM...MODELS CONTINUE TO SHOW A STRONG COLD FRONT MOVING IN
FROM THE NORTHEAST PACIFIC OCEAN ON TUESDAY BRINGING WIDESPREAD RAIN
TO THE REGION ON WEDNESDAY. AS THE SYSTEM MOVES ONSHORE WE COULD SEE
PRECIPITABLE WATER VALUES CONTINUING TO APPROACH 1.5 INCHES. WITH
DECENT UPPER LEVEL SUPPORT...PROVIDED BY A STRONG JET STEAK...SOME
AREAS MY RECEIVE OVER AN INCH OF RAIN. SEVERAL SHORTWAVES EMBEDDED
WITHIN THE MEAN LONGWAVE FLOW WILL LIKELY CONTINUE TO BRING
UNSETTLED WEATHER TO THE REGION...AT LEAST INTO FRIDAY. DECREASED
POPS AND SKY COVER SLIGHTLY NEXT WEEKEND DUE TO SLIGHT DIFFERENCES
AND A DOWNWARD TREND SHOWN BY THE VARIOUS MODELS. TEMPERATURES IN
THE EXTENDED WILL GENERALLY BE NEAR SEASONAL NORMALS. TJ/64

&&

.AVIATION...VFR CONDITIONS PERSIST THROUGH TONIGHT UNDER OFFSHORE
FLOW. THIS IS SHORT LIVED AS OFFSHORE FLOW QUICKLY EASES TONIGHT
THEN EXPECT ONSHORE FLOW TO DEVELOP SUNDAY AFTERNOON. SOUTHERLY
MARINE SURGE IS CURRENTLY WORKING ITS WAY NORTH ALONG THE OREGON
COAST THIS AFTERNOON. EXPECT IFR AND LIFR CONDITIONS ALONG THE
COAST AFTER 04Z SUNDAY.

KPDX AND APPROACHES...VFR CONDITIONS NEXT 24 HRS. EAST WINDS WITH
GUSTS NEAR 25 KT WILL CONTINUE THROUGH 02-04Z SUNDAY...BEFORE
EASING. /27

&&

.MARINE...NORTH WINDS CONTINUE TO EASE EARLY THIS AFTERNOON AS THE
THERMAL TROUGH EXPANDS OVER THE WATERS. SOUTHERLY WINDS WILL
SPREADS ACROSS THE WATERS BY THIS EVENING...BUT WILL REMAIN LIGHT
TONIGHT. AS THE WEAK LOW PRES CENTER MOVES UP OFFSHORE...GUSTS
WILL LIKELY REACH 20 KT MIDDAY SUNDAY. SHALLOW STRATUS AND FOG
WILL COME WITH THE WIND REVERSAL.

WESTERLY SWELL 8 TO 9 FT WILL PREVAIL TONIGHT...SEAS THEN SLOWLY
SUBSIDE OVER THE NEXT FEW DAYS. A MORE ACTIVE PATTERN WILL ARRIVE
MID WEEK WITH SMALL CRAFT OR HIGHER WINDS AND SEAS BUILDING TO
OVER 10 FT.

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...NONE.
WA...NONE.
PZ...SMALL CRAFT ADVISORY FOR ROUGH COLUMBIA RIVER BAR UNTIL 5 PM
     PDT THIS AFTERNOON.

&&

$$

INTERACT WITH US VIA SOCIAL MEDIA
WWW.FACEBOOK.COM/NWSPORTLAND
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 AS THE FORECAST AREA.


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