Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 252221
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
220 PM PST SUN JAN 25 2015

.SYNOPSIS...HIGH PRESSURE ALOFT GRADUALLY SHIFT EAST TONIGHT AND
MONDAY. STRONG VALLEY INVERSIONS WILL CONTINUE TONIGHT...BUT START TO
WEAKEN MONDAY AFTERNOON. A VERY WEAK FRONTAL SYSTEM NEARS THE COAST
TUESDAY FOR A THREAT OF SOME LIGHT RAIN OR DRIZZLE. HOWEVER...HIGH
PRESSURE AND DRY WEATHER ARE EXPECTED TO RETURN AROUND MID-WEEK AND
LAST INTO NEXT WEEKEND.
&&

.SHORT TERM...TONIGHT THROUGH WEDNESDAY...VERY STRONG SUBSIDENCE
INVERSIONS ARE RESULTING IN PERSISTENT FOG THROUGHOUT THE WILLAMETTE
VALLEY AND CLARK COUNTY IN SW WA. HAD TO EXTEND THE DENSE FOG
ADVISORY THROUGH NOON...BUT AS OF 21Z AREAS OF DENSE FOG CONTINUE.
THE MAGNITUDE OF THE INVERSION IS QUITE IMPRESSIVE. ELEVATIONS ABOVE
2000 FT IN THE OREGON COAST RANGE WERE IN THE MID 60S TO MID 70S AT
21Z. MARYS PEAK...AT 4137 FT IN THE CENTRAL COAST RANGE...WAS 67 DEG
AT 2025Z. EQUALLY AS IMPRESSIVE WAS THE 21Z 63 DEG READING AT THE
6000-FOOT TIMBERLINE SENSOR WITH A HUMIDITY OF JUST 11 PERCENT.
SEVERAL CASCADE RAWS SITES BETWEEN 2500 AND 4500 FEET WERE IN THE 70S
AS OF 22Z.

PRIMARY FEATURES ON WATER VAPOR IMAGERY EARLY THIS AFTERNOON ARE THE
HIGH PRES CELL CENTERED OVER NE CALIFORNIA AND A CLOSED LOW JUST
SOUTH OF BAJA. 12Z MODEL FORECASTS SHOW 850 MB TEMPS PEAKING IN THE
16C TO 18C RANGE TONIGHT...WHICH WOULD BE CLOSE TO THE WARMEST 850 MB
TEMP RECORDED IN JANUARY IN NW OREGON SINCE RECORDS BECAME AVAILABLE
IN THE 1950S. THE UPPER RIDGE WILL START TO MOVE E TONIGHT AND
CONTINUE TO DO SO MON...RESULTING IN MODERATING TEMPS FOR THE HIGHER
TERRAIN. GFS HAS 850 MB TEMPS LOWERING TO 10 TO 13C BY 00Z TUE.
HIGHER PARTS OF THE COAST RANGE AND CASCADES COULD SEE MAX TEMPS MON
FAIRLY EARLY. VALLEYS ARE LIKELY TO SEE PERSISTENT LOW CLOUDS AND FOG
AS THE INVERSION WEAKENS DURING THE DAY MON.

MODELS ARE CONSISTENT IN DEPCITING A WEAK FRONT PUSHING  ONTO THE
COAST TUE AS THE UPPER FLOW FLATTENS OUT. MODEL CROSS SECTIONS
INDICATE MOISTURE WITH THIS DECAYING FRONT WILL BE RATHER
SHALLOW...GENERALLY BELOW 800 MB LATE MON NIGHT AND TUE. NOT LOOKING
AT MUCH PRECIP WITH THIS...WITH DRIZZLE MORE LIKELY THAN RAIN. THE
ECMWF HAS H5 RIDGING STARTING TO BUILD WED...BUT TIME-HEIGHT AND
MODEL CROSS-SECTIONS SHOW A FAIRLY DEEP MARINE LAYER IN PLACE.
THUS...HAVE LEFT LOW POPS IN THE FORECAST FOR WED. WEISHAAR

.LONG TERM...WEDNESDAY NIGHT THROUGH SUNDAY...A PASSING SHORTWAVE
LATE WED NIGHT MAY PROVIDE ENOUGH LIFT FOR A FEW SHOWERS...MOSTLY
ALONG THE NORTH COAST AND COAST RANGE AND INTO SW WASHINGTON. MODELS
REMAIN IN GOOD AGREEMENT THAT A RIDGE OF HIGH PRES ALOFT REBUILDS ON
THU AND PERSISTS THROUGH THE END OF THE WEEK. THIS WILL MAINTAIN DRY
CONDITIONS BUT BRING DAILY FOG AND LOW CLOUDS TO INTERIOR VALLEY
LOCATIONS. THE RIDGE WILL LIKELY BREAK DOWN AND SHIFT INLAND SOME
TIME NEXT WEEKEND...BUT STILL SOME UNCERTAINTY AS TO IF THIS WILL BE
SAT OR SUN. THE 12Z GFS IS A BIT MORE AGGRESSIVE IN BRINGING A MOIST
FRONTAL SYSTEM TO THE REGION BY LATE SAT NIGHT...WHILE THE ECMWF
WOULD KEEP THINGS DRY UNTIL SUN NIGHT. INCREASED POPS A BIT FOR NEXT
WEEKEND...PARTICULARLY FOR THE NW PORTION OF THE FORECAST
AREA...THOUGH RESTRICTED TO LOWER END CHANCE FOR SAT NIGHT THROUGH
SUN GIVEN THE SUPPORT FOR THE LATER TIMING FROM THE ECMWF AND
NUMEROUS GEFS MEMBERS. CULLEN
&&

.AVIATION...ASTORIA HAS CLEARED OUT...MEANING ALL COASTAL SITES
ARE NOW VFR. THEY SHOULD REMAIN VFR OVERNIGHT WITH A LIGHT
EASTERLY/SOUTHEASTERLY DOWNSLOPE WIND. FOG IS STILL LOWERING CIGS
AND VIS AT SOUTH VALLEY SITES TO LIFR/VLIFR. FOG OVER THE NORTHERN
WILLAMETTE VALLEY IS BURNING OFF AS EXPECTED...IMPROVING ALL BUT
KHIO TO VFR. KHIO SHOULD IMPROVE TO MVFR BY 23Z...AND POSSIBLY TO
VFR AFTER 00Z BEFORE FOG REDEVELOPS AROUND 02Z. KEUG MAY STILL
MAKE IT TO MVFR THIS AFTERNOON AROUND 23Z AS FOG SLOWLY BURNS OFF
IN THE SOUTH VALLEY. THERE MAY BE A BRIEF PERIOD OF VFR AFTER 00Z
BEFORE THE SUN GOES DOWN AND FOG STARTS TO RAPIDLY REDEVELOP. CIGS
AND VIS OVER THE SOUTH AND CENTRAL VALLEY WILL DROP TO LIFR/VLIFR
THIS EVENING AROUND 02-04Z...WHILE THE NORTH WILLAMETTE VALLEY
WILL DROP TO LIFR/VLIFR A BIT LATER AROUND 03-06Z. LIFR/VLIFR CIGS
AND VIS EXPECTED TO PERSIST AGAIN OVERNIGHT TONIGHT AS DENSE FOG
REDEVELOPS OVER THE INLAND TERMINALS. TIMING OF FOG BURN-OFF
SHOULD BE SIMILAR TO TODAY...WITH NORTH VALLEY SITES IMPROVING TO
VFR BY 20-22Z AND SOUTH VALLEY SITES STRUGGLING TO IMPROVE TO
MVFR/VFR BY 00Z.

KPDX AND APPROACHES...VFR CONDITIONS WILL START TO DROP AS FOG
BEGINS TO REDEVELOP AROUND 04Z. CIGS AND VIS DROP TO LIFR/VLIFR
AROUND 05Z AND WILL REMAIN WITH 1/4SM VIS FOG OVERNIGHT. TIMING OF
IMPROVEMENT MONDAY SHOULD BE SIMILAR TO TODAY...WITH FOG RAPIDLY
CLEARING TO VFR AROUND 21Z. -MCCOY

&&

.MARINE...SEAS CURRENTLY SITTING AROUND 9 TO 10 FT WITH LIGHT
WINDS OVER THE WATERS. SOUTHERLY WINDS WILL SURGE NORTHWARD ALONG
THE OUTER WATERS LATE THIS EVENING...WITH A BRIEF PERIOD OF GUSTS
AROUND 20 TO 25 KTS ALONG THE LEADING EDGE BEFORE STABILIZING
AROUND 15 TO 20 KTS. GUSTS ABOVE 20 KTS WILL NOT PERSIST LONG
ENOUGH TO WARRANT A SMALL CRAFT ADVISORY OVER THE OUTER WATERS.
SEAS SHOULD DROP TO AROUND 8 TO 9 FT LATER THIS EVENING...BUT
COULD COME BACK UP NEAR 10 FT OVER THE OUTER WATERS WITH GUSTY
SOUTHERLY WINDS MONDAY MORNING ALONG THE LEADING EDGE OF THE
SOUTHERLY SURGE. MONDAY EVENING SEAS WILL START TO SUBSIDE...
FALLING TO AROUND 5 FT BY TUESDAY NIGHT OR WEDNESDAY. -MCCOY


&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...NONE.
WA...NONE.
PZ...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL MIDNIGHT PST
     TONIGHT FOR COASTAL WATERS FROM CAPE SHOALWATER WA TO FLORENCE
     OR OUT 60 NM.

     SMALL CRAFT ADVISORY FOR ROUGH COLUMBIA RIVER BAR FROM 6 PM TO
     11 PM PST THIS EVENING.

&&

$$

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.


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