Area Forecast Discussion
Issued by NWS Portland, OR

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000
FXUS66 KPQR 211013
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
312 AM PDT THU AUG 21 2014

.SYNOPSIS...NORTHWEST FLOW WILL CONTINUE OVER THE REGION THROUGH THE
REST OF THIS WEEK. AN UPPER LEVEL LOW PRESSURE DROPPING SOUTHEAST
ACROSS THE INLAND NORTHWEST ON FRIDAY COULD RESULT IN A SOME LIGHT
PRECIPITATION...MAINLY IN OUR NORTHERN ZONES...AND A SLIM THREAT OF
THUNDERSTORMS ACROSS THE SOUTH WASHINGTON AND NORTH OREGON CASCADES.
NORTHWEST TO NORTH FLOW ALOFT CONTINUES OVER THE WEEKEND MAINTAINING
ONSHORE LOW-LEVEL FLOW AND NEAR NORMAL OR SLIGHTLY BELOW NORMAL
DAYTIME TEMPERATURES. HIGH PRESSURE STRENGTHENS JUST OFFSHORE EARLY
NEXT WEEK...WHICH MAY RESULT IN SOME LIGHT OFFSHORE LOW-LEVEL FLOW.

&&

.SHORT TERM...TODAY THROUGH SATURDAY...SKIES HAVE REMAINED LARGELY
CLEAR ACROSS MOST OF THE CWA THUS FAR. FEEL LIKE WE ARE WALKING A
FINE LINE BETWEEN RADIATIONAL STRATUS DEVELOPMENT AND CLEAR SKIES.
ONLY SEEING STRATUS FROM ABOUT SEASIDE AND NORTH ALONG THE COAST
PLUS SOME SPOTTY ACTION NEARER THE WASHINGTON CASCADE FOOTHILLS.
HAVE ALSO SEEN SOME PATCHY FOG  FURTHER SOUTH ALONG THE COAST WITH
TILLAMOOK AIRPORT REPORTING IT WITH OTHER COASTAL VALLEY LOCATIONS
LIKELY SATURATING AS WELL. DO EXPECT SOME OTHER AREAS WILL FILL IN
BEFORE MID MORNING BUT DO NOT HAVE SOLID CONFIDENCE AS TO WHERE.
THUS EXPECT SOME UPDATING WILL BE NECESSARY AS THE MORNING WEARS ON.

NEXT TURNED ATTENTION TO THE APPROACHING SHORTWAVE AND CLOSING LOW
SLIDING DOWN THE BC COAST. AM VERY TORN WITH HOW TO HANDLE LATE
THURSDAY NIGHT AND EARLY FRIDAY MORNING. THE EC AND NAM CONTINUE TO
SHOW VERY LIGHT QPF AMOUNTS ACROSS THE SOUTHWESTERN 2/3RDS OF THE
CWA WHILE THE GFS AND THE GEM DO NOT. FURTHER COMPLICATING MATTERS
IS A DISTINCT LACK OF WIDESPREAD SATURATED LAYERS FROM JUST ABOUT
ALL BUT THE NAM. FOR NOW...RELUCTANTLY LEANED ON THE NIGHER
RESOLUTION NAM AND BROUGHT A DRIZZLE MENTION ACROSS MUCH OF THE AREA
DURING THE MORNING HOURS AS THE OTHER MODELS ARE AT LEAST GIVING
MINIMAL LOW LEVEL CLOUD SUPPORT FOR AT LEAST FEW AREAS.

LATER FRIDAY...THE MODELS CONTINUE TO CLOSE OFF THE UPPER LOW AND
HAVE REASONABLE AGREEMENT BY PLACING THE LOW CENTER NEAR THE
WASHINGTON/OREGON/IDAHO TRIPLE POINT BY 00Z SATURDAY. HAVE NOT SEEN
MUCH VARIATION FROM YESTERDAYS RUNS ASIDE FROM A BIT MORE STRENGTH
TO THE LOW CIRCULATION. STILL LOOKING AT THE BEST THUNDER THREAT TO
REMAIN NEAR THE MT ADAMS AREA FRIDAY AFTERNOON WITH RAPIDLY
DIMINISHING CHANCES HEADING SOUTH THROUGH THE LATE AFTERNOON AND
EARLY EVENING. ANY STORMS WHICH DO DEVELOP AND TRY TO MOVE WEST TO
SOUTHWEST OFF THE HIGHER TERRAIN WILL RUN INTO A MORE STABLE AIR
MASS OVERALL ON TOP OF THE ALREADY STABLE MARINE INFLUENCED LOWER
LEVELS. FEEL WE REALLY NEED THE CUMULATIVE EFFECTS OF SOLAR HEATING
TO DRIVE CONVECTION OVERNIGHT FRIDAY INTO EARLY SATURDAY SO DECIDED
TO REMOVE THE SHOWER THREAT AFTER MIDNIGHT SATURDAY. /JBONK

.LONG TERM...SATURDAY NIGHT THROUGH TUESDAY...NO CHANGES...PREVIOUS
DISCUSSION FOLLOWS. A SHORTWAVE ON THE BACK SIDE OF THE TROUGH WILL
PASS OVER OUR AREA SATURDAY NIGHT...SEEN AT 500 AND 850 MB. THIS
WILL ONLY BRING AN OUTSIDE CHANCE OF RAIN IN THE NORTH OREGON AND
SOUTHERN WASHINGTON CASCADES...AS MOISTURE IS VERY LIMITED FROM
NORTHERLY CONTINENTAL FLOW AND NEGATIVE VORTICITY ADVECTION WILL
PROMOTE DOWNWARD MOTION OVER THE WESTERN 2/3 OF OUR AREA. AS THE
LONGWAVE TROUGH PROGRESSES EASTWARD...THE RIDGE CURRENTLY OVER A
GOOD PORTION OF THE NORTH PACIFIC WILL MOVE ONSHORE OVER THE WEST
COAST WHICH WILL BRING TEMPERATURES UP AND DRY CONDITIONS EARLY NEXT
WEEK. -MCCOY

&&

.AVIATION...VFR CONDITIONS UNDER CLEAR SKIES ACROSS MOST OF THE
REGION WITH TWO PRIMARY EXCEPTIONS. FIRST...AN MVFR DECK OF
MARINE STRATUS AT AROUND 2000 FT HAS DEVELOPED ALONG THE S
WASHINGTON AND N OREGON COAST. EXPECT THIS TO BUILD A BIT FURTHER
S AND ALSO PUSH UP THE COLUMBIA...BUT WITH WEAKER ONSHORE
GRADIENTS THIS MAY NOT GET MUCH PAST KKLS. MEANWHILE...CLOUD DECK
DEVELOPING NEAR THE S WASHINGTON CASCADE FOOTHILLS AT AROUND 3500
FT. THIS DECK SHOULD EXPAND S AND BUILD W TOWARDS THE N WILLAMETTE
VALLEY. EXPECT VARIABLE SCATTERED TO BROKEN DECK PRIMARILY N OF
COLUMBIA RIVER BUT MAY DRIFT AS FAR S AS KPDX/KTTD.
OTHERWISE...EXPECT PRIMARILY CLEAR DAY THU ACROSS THE
INTERIOR...WITH COASTAL LOCATIONS LIKELY VFR WITH ONLY A SCATTERED
DECK FROM 19Z ONWARD.

KPDX AND APPROACHES...VFR CONTINUES TODAY. MAY SEE A CLOUD DECK
AROUND 3500 FT BUILD S AND E FROM CASCADE FOOTHILLS...PERHAPS
SLIGHTLY LOWER OVER ERN APPROACHES. LESS CONFIDENCE IN CIGS
DEVELOPING AT TERMINAL. AFT 17Z EXPECT VFR UNDER MOSTLY CLEAR
SKIES THROUGH AT LEAST 06Z FRI.  CULLEN

&&

.MARINE...SEAS REMAIN IN THE 4 TO 5 FT RANGE...BUT STILL SOMEWHAT
STEEP WITH DOMINANT PERIODS REMAINING AROUND 8 SECONDS. LIGHT WNW
WINDS CONTINUE EARLY THIS MORNING. A WEAK FRONT AND ASSOCIATED LOW
PRES MOVES THROUGH THE WATERS LATER TODAY...WHICH WILL BRING A
PERIOD OF S WINDS..BUT SPEEDS REMAIN LIGHT AT 15 KT OR LESS.
LITTLE CHANGE IN THE PATTERN THROUGH EARLY NEXT WEEK WITH HIGH
PRES OVER NE PAC AND A THERMAL LOW BUILDING OVER NORTHERN
CALIFORNIA. WINDS WILL BE STRONGEST IN THE AFTERNOON AND
EVENINGS...WITH GUSTS TO AROUND 20 KT...AND PRIMARILY S OF CASCADE
HEAD. FORECAST MODELS SUGGEST A STRENGTHENING THERMAL TROUGH THAT
MAY PUSH N INTO OREGON BY MIDWEEK...INCREASING SURFACE PRES
GRADIENTS AND BRINGING THE POTENTIAL FOR ADVISORY LEVEL WINDS
ACROSS THE WATERS.   CULLEN


&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...NONE.
WA...NONE.
PZ...NONE.
&&

$$

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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