Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 210320 AAA
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND
820 PM PDT MON APR 20 2015

.SYNOPSIS...INCREASING ONSHORE FLOW WILL RESULT IN COOLER CONDITIONS
TUESDAY AND THEN CONTINUING FOR THE REMAINDER OF THE WEEK. DAYTIME
TEMPERATURES WILL FALL TO NEAR AVERAGE VALUES. A WEAK FRONTAL SYSTEM
WILL MOVE ACROSS THE AREA TUESDAY NIGHT...WHICH WILL REINFORCE THE
MARINE LAYER. A WETTER PATTERN LOOKS TO DEVELOP LATE SATURDAY AND
SUNDAY...WITH PERHAPS ANOTHER ROUND OF WET WEATHER EARLY NEXT WEEK.

&&

.SHORT TERM...00Z LOCAL SURFACE ANALYSIS SHOWED THE THERMALLY-INDUCED
SURFACE TROUGH ALONG THE EAST SLOPES OF THE WASHINGTON CASCADES...
THROUGH THE CENTRAL COLUMBIA GORGE AND EXTENDING ALONG THE OREGON
CASCADE FOOTHILLS. AS EXPECTED...THE 00Z MON NAM WAS TOO FAST MOVING
THE THERMAL TROUGH EAST. LAST AVAILABLE VISIBLE SATELLITE IMAGES
SHOWED A FAIRLY SHALLOW MARINE LAYER ALONG THE OREGON COASTAL
STRIP...BUT STARTING TO PUSH INTO THE DOUGLAS COUNTY COASTAL VALLEYS.
THE 12Z HI RES ARW MODEL LOOKS TO DEPICT THE MARINE LAYER RATHER
WELL. AT 03Z THE MODEL SHOWS 90 PCT OR GREATER BOUNDARY LAYER
MOISTURE STARTING TO PUSH INTO THE CENTRAL COASTAL VALLEYS. ANOTHER
SIGN OF INCREASING ONSHORE FLOW IS THE S-SW WIND AT KMMV. AT 02Z THE
TEMP HAD DROPPED TO 69...WHILE THE KPDX METRO AREA WAS STILL IN THE
MID TO UPPER 70S. TYPICALLY...WITH A SW MARINE SURGE...THE SRN
WILLAMETTE VALLEY PICKS UP A SW BREEZE DURING THE EVENING. AS OF 02Z
KEUG WAS SHOWING CALM CONDITIONS. HOWEVER...AT 03Z KSLE AND KUAO
OBSERVED SW-W WIND UP TO 11 KT. THE HI RES ARW STILL HINTS AT A SW
MARINE SURGE THROUGH THE LANE COUNTY COASTAL GAPS OVERNIGHT. IT ALSO
DEPICTS ANOTHER INTRUSION DOWN THE COLUMBIA RIVER. EXPECT KKLS TO
BECOME OVERCAST LATE TONIGHT OR AROUND SUNRISE TUE.

850 MB TEMPS FALL FROM 12.2C TODAY (00Z KSLE SOUNDING) TO 3-4C BY 00Z
WED. MODELS SHOWING A TIGHT 850 MB TEMP GRADIENT FROM THE CASCADE
CREST TO THE WILLAMETTE VALLEY AND CLARK COUNTY IN SW WA 18Z TUE. THE
MAIN RESULT...OTHER THAN SIGNIFICANT COOLING...WILL BE INCREASED
WIND...ESPECIALLY EAST OF KCZK AND THROUGH COAST RANGE GAPS. SHALLOW
INSTABILITY AND MOISTURE MAY PRODUCE A FEW VERY LIGHT SHOWERS TUESDAY
NIGHT INTO EARLY WEDNESDAY...PARTICULARLY ACROSS THE NORTH AND IN THE
UPSLOPE AREAS...BUT CONFIDENCE IS LOW. NAM...GFS AND ECMWF SURFACE
PATTERN WED AFTERNOON SUGGEST IT COULD END UP PARTLY CLOUDY ACROSS
THE S HALF AS ALL AFOREMENTIONED MODELS HAVE A N-NE SURFACE ISOBAR
CONFIGURATION. WOULD EXPECT LIMITED CLEARING OVER THE N...ESPECIALLY
THE SW WA ZONES CLOSEST TO THE PASSING UPER TROUGH. ANOTHER WEAKENING
FRONT MAY BRING INCREASING PRECIP CHANCES TO THE FAR NORTHWEST ZONES
ON THURSDAY. ALL IN ALL...MOST LOCATIONS LOOK TO REMAIN GENERALLY DRY
THE NEXT FEW DAYS WITH TEMPERATURES TOPPING OUT NEAR AVERAGE.
WEISHAAR

.LONG TERM...THURSDAY NIGHT THROUGH MONDAY...MODELS CONTINUE TO
STRUGGLE ON THE DETAILS...BUT SUGGEST ONSHORE FLOW WILL CONTINUE NEAR
AVERAGE TEMPERATURES WITH A CHANCE FOR SOME LIGHT SHOWERS THURSDAY
NIGHT AND FRIDAY. WHILE MODELS DIFFER ON TIMING...BUT THE GFS AND EC
SUGGEST A WETTER FRONTAL STORM SYSTEM WILL SLOWLY SAG SOUTHWARD
ACROSS THE AREA LATE SATURDAY THROUGH SUNDAY NIGHT. AS A
RESULT...POPS WERE INCREASED IN THE LIKELY TO CATEGORICAL RANGE FOR
THE PRIME WINDOW OF SATURDAY NIGHT AND SUNDAY. BOTH MODELS SUGGEST
ANOTHER STORM SYSTEM IS LIKELY NEXT WEEK...BUT ONCE AGAIN DIFFER ON
TIMING SO POPS WERE TRENDED MORE INTO THE HIGH END CHANCE TO LOW END
LIKELY RANGE. /NEUMAN

&&

.AVIATION...MOSTLY VFR UNDER HAZY SKIES THROUGH THIS EVENING. THE
FLOW PATTERN WILL CONTINUE TO TURN ONSHORE THIS AFTERNOON AS A
WEAK FRONT APPROACHES THE REGION ALLOWING MARINE STRATUS TO FILL
BACK IN ALONG THE COAST - EXPECT IFR CIGS BETWEEN 500 AND 1000 FT
AND REDUCED VSBY THROUGH LATE TUE MORNING. LOW CLOUDS WILL
CONTINUE TO PUSH INLAND TONIGHT...WITH INTERIOR SITES LIKELY
SEEING MVFR CIGS BETWEEN 1500 AND 2000 FT BY 15Z. CONDITIONS TURN
VFR UNDER MOSTLY CLOUDY SKIES TUE AFTERNOON.

KPDX AND APPROACHES...VFR UNDER HAZY SKIES THROUGH THIS EVENING.
LOWER CLOUDS RETURN TONIGHT...WITH MVFR STRATUS AROUND 2000 FT
AFFECTING THE TERMINAL BY 14Z. VFR RETURNS BY AROUND 18Z TUESDAY
WITH NW WINDS PICKING UP MID AFTERNOON.

&&

.MARINE...INCREASED FORECAST WINDS SLIGHTLY OVER THE NEXT 24
HOURS TO NUDGE CLOSER TO OBS AS WELL AS RUC. BUOY 29 HAS BEEN
GUSTING TO AROUND 20 KT FOR A FEW HOURS BUT SINCE WINDS ARE
INCREDIBLY MARGINAL AND PROBABLY OVER JUST A SMALL AREA...WILL
NOT MOVE UP THE BEGINNING OF THE SMALL CRAFT ADVISORY FOR WINDS. WILL
HAVE A LAST VERY STRONG EBB ON THE COLUMBIA BAR TUESDAY
MORNING...SO ISSUED A SMALL CRAFT ADVISORY FOR ROUGH BAR DURING
THE MORNING EBB AND THEN AGAIN FOR THE TUESDAY EVENING EBB WITH
INCREASE IN SWELL AND WINDS. BOWEN

PREVIOUS DISCUSSION...A WEAK FRONT WILL MOVE ACROSS THE WATERS
TOMORROW MORNING BRINGING GUSTY NORTHWESTERLY WINDS AND BUILDING
SEAS. EXPECT GUSTS TO 30 KT AND SEAS AROUND 11 FT FROM TUE
MORNING TO WED. HIGH PRES BRIEFLY RETURNS WED AFTERNOON BEFORE
ANOTHER WEAK FRONT MOVES ACROSS THE WATERS ON THU. NOT EXPECTING
MUCH IN THE WAY OF IMPACTS WITH THIS SECOND FRONT. A MUCH STRONGER
FRONT LOOKS TO MOVE ACROSS THE WATERS OVER THE WEEKEND AND WILL
LIKELY BRING GUSTY SOUTHERLY WINDS AND ANOTHER ROUND OF BUILDING
SEAS.

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...NONE.
WA...NONE.
PZ...SMALL CRAFT ADVISORY FOR WINDS FROM 7 AM TUESDAY TO NOON PDT
     WEDNESDAY FOR WATERS FROM CAPE SHOALWATER WA TO CASCADE
     HEAD OR FROM 10 TO 60 NM-WATERS FROM CASCADE HEAD TO
     FLORENCE OR FROM 10 TO 60 NM.

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

     SMALL CRAFT ADVISORY FOR WINDS FROM 1 PM TUESDAY TO NOON PDT
     WEDNESDAY FOR COASTAL WATERS FROM CAPE SHOALWATER WA TO
     CASCADE HEAD OR OUT 10 NM-COASTAL WATERS FROM CASCADE HEAD
     TO FLORENCE OR OUT 10 NM.

     SMALL CRAFT ADVISORY FOR ROUGH COLUMBIA RIVER BAR FROM 6 AM TO
     10 AM PDT TUESDAY.

     SMALL CRAFT ADVISORY FOR ROUGH COLUMBIA RIVER BAR FROM 7 PM TO
     10 PM PDT TUESDAY.

     SMALL CRAFT ADVISORY FOR ROUGH COLUMBIA RIVER BAR FROM 5 AM TO
     10 AM PDT WEDNESDAY.

&&

$$

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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