Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 202122
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
220 PM PDT WED AUG 20 2014

.SYNOPSIS...NORTHWEST FLOW WILL CONTINUE OVER THE REGION FOR MUCH
OF THE WEEK. AN UPPER LEVEL LOW PRESSURE DROPPING SOUTHEAST ACROSS
THE INLAND NORTHWEST ON FRIDAY...COULD RESULT IN A SOME LIGHT
PRECIPITATION TO THE 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...TONIGHT THROUGH SATURDAY...MORNING STRATUS LAYER HAS
TRANSFORMED INTO A BROKEN STRATOCUMULUS FIELD WITH CIGS GENERALLY 035
TO 045. MODERATE TO STRONG ONSHORE LOW-LEVEL FLOW CONTINUES TONIGHT
THROUGH THURSDAY...AND EXPECT SIMILAR DRIZZLE COVERAGE TONIGHT AND
THURSDAY MORNING COMPARED TO TODAY. SW WA LOWLANDS... OREGON
COAST...AND WEST SLOPES OF THE COAST RANGE SOME OF THE MORE FAVORED
DRIZZLE AREAS. KTTD-KDLS GRADIENT UP TO 4.0 MB AS OF 20Z...WHICH
NORMALLY RESULTS IN AT LEAST 25-30 MPH GUSTS NEAR HOOD RIVER.
AUGSPURGER...AN ELEVATED BPA SITE ON THE WASHINGTON SIDE OF THE
GORGE...GUSTING TO 35 MPH. EXPECT SIMILAR CONDITIONS THURSDAY.

MAIN FORECAST CHANGES CENTER ON LATE THURSDAY NIGHT THROUGH FRIDAY
PERIOD. LATEST NAM AND ECMWF CONTINUE TO INDICATE AREAS OF LIGHT QPF
FURTHER WEST THAN PREVIOUS COUPLE OF RUNS. BOTH MODELS SHOW THE UPPER
TROUGH DIGGING AS A REINFORCING SHORT-WAVE DROPS SOUTH INTO THE
TROUGH BASE...AIDED BY A 80-100 KT 300 MB JET STREAK. NAM SHOWS
FAIRLY ROBUST 700 MB OMEGA FOCUSED OVER SW WA AND EXTREME NW OREGON
12Z FRI. WOULD EXPECT A MUCH DEEPER MARINE LAYER WITH ENOUGH LIFT FOR
AT LEAST AREAS OF DRIZZLE LATE THU NIGHT THROUGH FRI MORNING IN THE
LOWLANDS AND POSSIBLY SPOTTY LIGHT SHOWERS OVER ELEVATED TERRAIN. ANY
DRIZZLE OR LIGHT SHOWERS SHOULD BE CONFINED TO THE NORTHERN
TWO-THIRDS OF THE FORECAST AREA.

THERE IS STILL SOME VARIABILITY AMONG THE MODEL SOLUTIONS WITH REGARD
TO THE ACTUAL LOW TRACK BUT MODELS GENERATE ENOUGH INSTABILITY OVER
THE S WA AND FAR N OREGON CASCADES FRI AFTERNOON FOR A SLIM THREAT OF
THUNDERSTORMS. 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 LOW LEVEL MARINE INFLUENCED LOW
LEVELS. CYCLONIC JET FROM THE DEPARTING LOW CLOSE ENOUGH TO THE
CASCADE CREST TO LEAVE SLIGHT CHANCE POPS THERE SAT...PRIMARILY IN
THE MORNING. WEISHAAR


.LONG TERM...SATURDAY NIGHT THROUGH TUESDAY...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 A SLIGHT 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...GENERALLY VFR CONDITIONS THIS AFTERNOON WITH SCT CLOUDS
AND SOME CIGS 3000 TO 4000 FT. CLEARING TREND WILL CONTINUE INTO
THE OVERNIGHT HOURS INLAND WHILE ONSHORE FLOW BRINGS MVFR CIGS
BACK TO COAST AFT 02Z. MARINE STRATUS WILL PUSH INLAND AGAIN
TONIGHT WITH CIGS AROUND 2500 FT BUT LATEST GUIDANCE SHOWS BEST
LIKELIHOOD ON THE NORTH SIDE OF THE RIVER. COULD SEE SOME
SCATTERED CLOUDS FARTHER SOUTH IN THE VALLEY BUT GENERALLY VFR
CONDITIONS SHOULD PREVAIL SOUTH OF PDX.

KPDX AND APPROACHES...VFR WITH CLEARING SKIES THIS AFTERNOON.
COULD SEE SOME MVFR CIGS AROUND 2500 FT THURSDAY MORNING AFTER
13Z BUT NOT AS WIDESPREAD AS THIS MORNING. BOWEN

&&

.MARINE...BUOYS SHOWING 4 TO 6 FT SEAS AT 10 SECONDS BUT THERE`S
ALSO ENERGY AT 8 SECONDS SO SEAS WILL BE A BIT STEEP THROUGH THIS
EVENING. NW WINDS REMAIN RATHER LIGHT...LESS THAN 15 KT. VERY
LITTLE CHANGE IN THE PATTERN THROUGH THE WEEKEND WITH CONTINUED NW
WIND AND SWELL. PRESSURE GRADIENT TIGHTENS SOME FRIDAY AND
SATURDAY AFTERNOONS AS HIGH PRESSURE OVER THE NE PACIFIC
STRENGTHENS A BIT WITH THERMAL LOW OVER NORTHERN
CALIFORNIA...INCREASING WINDS TO 15 TO 20 KT WITH SLIGHTLY HIGHER
GUSTS. BOWEN

&&

.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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