Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 250104 AAA
AFDPQR

AREA FORECAST DISCUSSION...UPDATE
NATIONAL WEATHER SERVICE PORTLAND OR
604 PM PDT FRI OCT 24 2014

.SYNOPSIS...A DEEPENING LOW PRESSURE AREA WELL OFF THE NORTHERN
CALIFORNIA WATERS THIS AFTERNOON WILL MOVE NORTH TO NORTHEAST TONIGHT
AND SATURDAY. EXPECT A BRIEF PERIOD OF STRONG WIND BEHIND THE LOW
PRESSURE AREA LATE SATURDAY AFTERNOON THROUGH MID-EVENING
...PRIMARILY ALONG THE CENTRAL OREGON COAST AND IN THE INTERIOR
VALLEYS. AN UPPER LEVEL TROUGH OVER THE REGION SUNDAY WILL CONTINUE
SHOWER ACTIVITY. THERE WILL BE A SHORT DRYING PERIOD MONDAY...
FOLLOWED BY ANOTHER SYSTEM TUESDAY. THE TUESDAY SYSTEM COULD BRING
ANOTHER ROUND OF SIGNIFICANT RAINFALL TO THE FORECAST AREA.

&&
.UPDATE...DID A QUICK UPDATE TO THE FORECAST FOR THIS EVENING AS THE
FRONT IS LIFTING NORTH SLIGHTLY QUICKER THAN WHAT MODELS INDICATED.
ALSO UPDATED QPF AND TO REFLECT THE RAINFALL THAT WAS OBSERVED WITH
THE FRONT EARLIER AS IT WAS ACROSS LANE COUNTY. SATELLITE IMAGERY
AND SURFACE OBSERVATIONS SUGGESTS THAT THE FRONT JUST LIFTED NORTH
OF SALEM. LOW CLOUDS ARE FILLING IN THE INLAND VALLEYS BEHIND THE
FRONT. THERE IS WIDESPREAD RAIN NORTH OF SALEM. TJ

PREVIOUS DISCUSSION FOLLOWS...TONIGHT THROUGH MONDAY...INFRA-RED
SATELLITE IMAGERY AND KRTX DOPPLER RADAR SHOW A WARM FRONT EXTENDING
FROM THE CENTRAL OREGON COAST TO NORTH-CENTRAL OREGON. LIGHT RAIN
HAS REACHED A KMMV-KONP LINE AS OF 20Z. RAINFALL AMOUNTS OVER THE
CENTRAL OREGON COAST AND COAST RANGE THROUGH 20Z HAVE BEEN RATHER
LIGHT..GENERALLY ONE-TENTH OF AN INCH OR LESS. OFFSHORE LOW-LEVEL
FLOW HAS STRENGTHENED A BIT SINCE THIS MORNING. 20Z KTTD-KDLS
GRADIENT AT -3.3 MB...STILL SLIGHTLY MORE THAN THE 6-HR NAM
FORECAST. HAVE HAD GUSTS TO 25 MPH AT CORBETT AND 35-40 MPH AT CROWN
POINT. GRADIENT SHOULD HOLD AROUND -3.5 MB THROUGH THIS
EVENING...THEN INCREASE TO -5 TO -6 MB BY 12Z SAT.

BIGGEST SHORT-TERM FORECAST CHALLENGE REMAINS THE DEVELOPING LOW NEAR
39N 132W. LATEST NAM INDICATED A 997 MB CENTER AT 18Z. WATER VAPOR
IMAGERY SHOWS GOOD DRY AIR INTRUSION ON THE EAST FLANK OF THE LOW. IT
IS ALSO STARTING TO SHOW SIGNS OF ELONGATION...SIMILAR TO THE NAM
SOLUTION. MODELS HAVE STARTED TO COME INTO BETTER AGREEMENT WITH THE
DEPTH AND TRACK. BY 12Z SAT THE NAM...GFS AND ECMWF SHOW AN
ELONGATED LOW...WITH THE PRIMARY LOW CENTER AT 41N 129W. THE
NAM...AND TO SOME EXTENT THE ECMWF...SUGGEST A SECOND WEAKER LOW
CIRCULATION DEVELOPING OFF THE S WA OR FAR N OREGON COAST 12Z SAT.
THE PRESENCE OF TWO LOW CENTERS COULD RESULT IN AN OVERALL WEAKER
SYSTEM. AT 18Z SAT THE GFS MAINTAINS MORE OF A CONSOLIDATE LOW PRES
CENTER JUST W OF KOTH. THE NAM HOLDS ON TO TWO SEPARATE LOW CENTERS
WHILE THE ECMWF SEEMS TO BE THE WEAKEST OF ALL MODELS WITH THE
TIGHTEST SURFACE GRADIENT ALONG THE N CALIFORNIA AND FAR S OREGON
COAST. THE 12Z WRF-GFS IS A BIT STRONGER THAN ITS 00Z RUN...
INDICATING A 3-HR PERIOD OF 55-60 KT WIND GUSTS ALONG THE CENTRAL
OREGON COAST STARTING AT 21Z SAT. THE 18Z NAM SHOWS 45 KT 975 MB WIND
SPEEDS ALONG THE CENTRAL COAST FOR 21Z SAT. BASED ON ALL OF THE
ABOVE...AM STILL NOT CONVINCED THE COAST WILL REACH WIDESPREAD
HIGH-WIND CRITERIA. WOULD NOT RULE OUT SPOTTY 55-60 MPH WIND GUSTS
ON THE CENTRAL OREGON COAST HEADLANDS BETWEEN 18Z SAT AND 00Z
SUN...BUT DO NOT BELIEVE THE FREQUENCY AND COVERAGE WARRANT A
HIGHLIGHT. HAVE A HIGHER DEGREE OF CONFIDENCE FOR BLUSTERY CONDITIONS
IN THE WILLAMETTE VALLEY. EXPECT A BRIEF PERIOD (2-4 HOURS) OF WINDY
CONDITIONS AS THE SURFACE LOW MOVES N-NE INTO SW WA LATE SAT
AFTERNOON AND EARLY EVENING. 12Z GFS SHOWS A +13 MB 6-HR PRES CHANGE
BULLSEYE NEAR KONP 06Z SUN...WHICH IS PRETTY CLOSE TO BENCHMARK
THRESHOLDS TO GET WINDY CONDITIONS IN THE VALLEY. WOULD LIKE TO SEE
THIS ISOBARIC CHANGE IN A MORE SOUTH-TO-NORTH ORIENTATION. IN ANY
EVENT...CURRENT FORECAST OF 35-45 MPH GUSTS IN THE WILLAMETTE VALLEY
LATE SAT AFTERNOON THROUGH EARLY EVENING LOOKS GOOD. STRONGEST GUSTS
SHOULD BE S OF KSLE. ALSO CANNOT RULE OUT ISOLATED THUNDERSTORMS SAT
EVENING...MAINLY ALONG THE COAST...AS THE COLD UPPER TROUGH MOVES
ASHORE.

THIS BROAD UPPER TROUGH...SIMILAR TO WHAT WAS OVER THE AREA
THURSDAY...SETTLES OVER THE REGION SUNDAY. THIS WILL BRING ADDITIONAL
SHORT-WAVES THROUGH THE FORECAST AREA FOR CONTINUED PRECIPITATION. AS
USUAL...THE COAST RANGE...SW WA WILLAPA HILLS AND THE CASCADES WILL
HAVE THE MOST NUMEROUS SHOWERS DUE TO 15-25 KT WLY 850 MB FLOW. SNOW
LEVELS FALL TO NEAR CASCADE PASS LEVELS AS WELL SUNDAY. WEAK RIDGING
MOVES OVER THE AREA SUNDAY NIGHT AND INTO MONDAY. CUT BACK ON POPS A
BIT FOR MON...AND FUTURE SHIFTS MAY NEED TO TRIM THEM EVEN MORE.
WEISHAAR

.LONG TERM...THE LONG TERM STARTS OUT WET WITH THE NEXT SYSTEM MOVING
INTO THE FORECAST AREA MON NIGHT. THIS SYSTEM CONTAINS THE REMNANTS
OF HURRICANE ANA...THAT SKIRTED HAWAII LAST WEEK. MODELS MAY BE
UNDER DOING THE PRECIPITATON POTENTIAL WITH THIS ONE. A STRONG JET
STREAM WILL REMAIN DIRECTED AT WA AND NRN OREGON THROUGH TUE NIGHT.
MODELS SHOW LARGE VARIATIONS BEGINNING WED...BUT EXPECT THE ACTIVE
PATTERN TO CONTINUE. THE ECMWF AND GFS SHOW A TREND TOWARD DRIER
CONDITIONS LATE NEXT WEEK AS A DEEP LOW IN THE GULF OF ALASKA
AMPLIFIES THE DOWNSTREAM RIDGE OVER THE INTERMOUNTAIN WEST. WEISHAAR

&&

.AVIATION...MAINLY VFR CONDITIONS WITH LIGHT RAIN THROUGH 07Z.
OCCASIONAL PERIODS OF MVFR AND IFR CIGS ARE POSSIBLE. EXPECT RAIN
CHANCES TO DECREASE AFTER 08Z AS THE WARM FRONT MOVES INTO WA. VFR
CONDITIONS EXPECTED AFTER 10Z. HOWEVER...THERE IS A 30 PERCENT CHANCE
OF FOG AND MIST DEVELOPING TOMORROW MORNING.

KPDX AND APPROACHES...VFR CONDITIONS EXPECTED THROUGH TOMORROW
AFTERNOON. LIGHT RAIN POSSIBLE THROUGH 06Z. WINDS WILL LIKELY TURN
TO THE EAST AFTER 23Z. HOWEVER...TIMING MAY NEED TO BE ADJUSTED.
/64

&&

.MARINE...A DEEPENING LOW PRES SYSTEM WILL APPROACH FROM THE SW
LATE TONIGHT AND MOVE THROUGH THE COASTAL WATERS ON SAT BEFORE
MOVING INLAND ON LATE SAT. GALE FORCE WINDS ARE EXPECTED TO START
LATE TONIGHT IN THE CENTRAL OR WATERS AND LAST THROUGH TOMORROW
EVENING. IN THE NORTHERN OR AND SOUTHER WA WATERS EXPECT GALE
CONDITIONS TO BEGIN EARLY TOMORROW MORNING AND CONTINUE THROUGH
TOMORROW NIGHT. STEEP SEAS ARE EXPECTED WITH THE GALES WITH WAVE
HEIGHTS PEAKING AT AROUND 15 FT SATURDAY EVENING.

AS THE LOW MOVES INLAND WINDS WILL BECOME W AND DECREASE WITH SEAS
LOWERING TO AROUND 7 TO 9 FT AS HIGH PRES BUILDS INTO THE PAC NW.
ANOTHER SHORTWAVE EXPECTED TO APPROACH THE REGION EARLY NEXT WEEK
WITH SEAS OF 10 TO 12 FT POSSIBLE. /64

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...NONE.
WA...NONE.
PZ...GALE WARNING FROM 2 AM TO 11 PM PDT SATURDAY FOR COASTAL WATERS
     FROM CAPE SHOALWATER WA TO CASCADE HEAD OR OUT 60 NM.

     GALE WARNING FROM 11 PM THIS EVENING TO 5 PM PDT SATURDAY FOR
     COASTAL WATERS FROM CASCADE HEAD OR TO FLORENCE OR OUT 60 NM.

     SMALL CRAFT ADVISORY FOR ROUGH COLUMBIA RIVER BAR UNTIL 8 PM
     PDT THIS EVENING.

     SMALL CRAFT ADVISORY FOR ROUGH COLUMBIA RIVER BAR FROM 3 AM TO
     8 AM PDT SATURDAY.

     SMALL CRAFT ADVISORY FOR ROUGH COLUMBIA RIVER BAR FROM 2 PM
     SATURDAY TO 5 AM PDT SUNDAY.

&&

$$

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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