Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 221632
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
932 AM PDT FRI AUG 22 2014

.SYNOPSIS...UPPER LEVEL LOW PRESSURE CENTER CONTINUES TO SLIDE EAST
OF THE AREA TODAY. THERE WILL BE ENOUGH INSTABILITY ON THE WEST SIDE
OF THIS LOW TO BRING A SLIGHT THREAT FOR THUNDERSTORMS FOR THE SOUTH
WASHINGTON CASCADES AND EXTREME NORTH OREGON CASCADES THIS AFTERNOON.
NORTHERLY FLOW ALOFT CONTINUES OVER THE WEEKEND MAINTAINING ONSHORE
LOW-LEVEL FLOW AND NEAR TO SLIGHTLY ABOVE NORMAL HIGH TEMPERATURES.
HIGH PRESSURE STRENGTHENS JUST OFFSHORE BRINGING A WARM UP FOR THE
FIRST HALF OF NEXT WEEK.

&&

.UPDATE...REMNANTS OF AN OLD FRONT HAS RESULTED IN A VARIETY OF
CLOUDS ACROSS NW OREGON THIS MORNING...AND SOME SPOTTY DRIZZLE. RADAR
IMAGERY SHOWS LIGHT DRIZZLE MOVING THROUGH THE WILLAMETTE
VALLEY...CURRENTLY BETWEEN HILLSBORO AND SALEM. THIS DRIZZLE LOOKS TO
BE MOVING SOUTH AROUND 8 MILES PER HOUR. THERE HAS NOT BEEN ANY KNOWN
ACCUMULATION...BUT A TRACE OF PRECIPITATION WAS MEASURED AT
HILLSBORO.

HIGH PRESSURE IS BUILDING OVER THE AREA AND VISIBLE SATELLITE IMAGERY
SHOWS NORTHERLY FLOW CLEARING SKIES FROM NORTH TO SOUTH. HAVE
ADJUSTED TODAYS SKY FORECAST TO INCREASE SUNSHINE IN MOST AREAS.
THERE IS STILL A SLIGHT THREAT FOR THUNDERSTORMS THIS AFTERNOON FOR
THE WASHINGTON AND EXTREME NORTHERN OREGON CASCADES... MAINLY AROUND
MOUNT ADAMS...BUT THE THREAT LOOKS REALLY LOW. HAVE LIMITED SHOWERS
TO SCATTERED FOR THE CASCADES AND CASCADE FOOTHILLS FOR THIS
AFTERNOON AND EVENING. TJ

PREVIOUS SHORT TERM...TONIGHT THROUGH SUNDAY...LOW PRESSURE WILL
CONTINUE TO DEVELOP ACROSS THE INTERIOR PACNW TODAY RESULTING IN A
CHALLENGING FORECAST FOR THE NEXT 24 HOURS. A CLOSED LOW CENTER IS
BEGINNING TO WIND UP UNDER CYCLOGENESIS. THE COMPLEX DYNAMICS WITH
THE DEVELOPING LOW WERE ABLE TO WRING OUT SOME DRIZZLE ALONG THE
COAST WITH BOTH ASTORIA AND NEWPORT RECORDING AT LEAST AN HOUR OF
PRECIPITATION. NORTH ANS EAST OF THE DEVELOPING LOW CENTER...A
SIGNIFICANT AMOUNT OF NOCTURNAL CONVECTION THUS FAR HAS GENERATED
MOISTURE WHICH WILL GET WRAPPED AROUND TO MOISTEN UP THE WESTERN
FRINGES OF THE LOW. EXPECT THE NORTHEASTERN 1/3RD OF THE CWA WILL BE
IMPACTED BY THIS MOISTURE IN VARYING FORMS.

THE MOST SIGNIFICANT THREAT WILL BE FOR THUNDERSTORMS. STILL FEEL
MOST ACTIVITY WILL REMAIN CONFINED TO AREAS NORTHEAST OF THE
PORTLAND METRO AND CLOSER TO MT ADAMS. BOTH THE NAM AND GFS AGREE
THERE WILL BE SUFFICIENT SURFACE HEATING AND MOISTURE TO CREATE DEEP
CONVECTION AND THUNDERSTORMS. FURTHER SOUTH AND WEST THE MODELS HAVE
LIMITED AGREEMENT. THE BIG ISSUE WILL BE SURFACE DEW POINTS. THE NAM
AS OF THE LAST FEW YEARS HAS COMMONLY PRODUCE TOO MUCH SURFACE
MOISTURE AND THUS DEW POINTS TOO HIGH BY A FEW DEGREES.
CONVERSELY...THE GFS TENDS TO RUN A FEW DEGREES TO DRY.

THE 00Z MODEL RUNS ARE HOLDING TRUE TO EXPECTATIONS AT LEAST THROUGH
THE 09Z HOUR WITH REALITY LYING SOMEWHERE IN BETWEEN BUT A SLIGHT BIT
CLOSER TO THE GFS. DETERMINING WHAT REALITY WILL BRING IS WHERE THE
SPECIFIC CHALLENGE LIES. SKIN TEMPERATURES FROM BOTH MODEL FORECAST
SOUNDINGS ARE ALSO APPEARING TO BE TOO COOL AS IS OFTEN THE CASE.
BASED ON THE RAW MODEL SOUNDING DATA...THE GFS DOES NOT SHOW
CONVECTION VERY FAR AWAY FROM THE CASCADES WHILE THE NAM BRINGS A
THREAT TO THE METRO AND AS FAR WEST AS ABOUT KELSO/LONGVIEW.
ULTIMATELY LANDED ON ABOUT A 60/40 BLEND OF SURFACE DEW POINTS
FAVORING THE GFS. THIS COMBINED WITH MANUAL TEMPERATURE ADJUSTMENTS
TO THE SOUNDING SURFACE CONDITIONS PRODUCED A FIRST ESTIMATE OF
THUNDERSTORMS WITH CONFIDENCE AND ISOLATED COVERAGE ACROSS THE BULK
OF SKAMANIA COUNTY...LOWER CONFIDENCE SLIGHT CHANCE COVERAGE TO THE
EASTERN 1/4 OF COWLITZ COUNTY STRETCHING SOUTH TO INCLUDE THE GORGE
AND AREAS EAST OF SANDY AROUND MT HOOD...AND THEN A THREAT OF SHOWERS
ONLY MAINLY NORTH OF THE COLUMBIA RIVER. OBVIOUSLY WE ARE WALKING A
VERY FINE LINE TODAY BETWEEN NOTHING HAPPENING ACROSS OUR NORTHERN
TIER AND A DECENT COVERAGE OF THUNDERSTORMS SO FELT USING PROBABILITY
IN THE TRUEST SENSE WAS THE MOST PRUDENT COURSE OF ACTION TODAY
NOTING THAT A 20 PERCENT CHANCE REALLY MEANS 80 PERCENT OF THE TIME
IT WILL NOT HAPPEN. DID FEEL REASONABLY CONFIDENT THAT TEMPERATURES
NEED TO GET CLOSE TO THEIR FORECASTED HIGHS TODAY TO TRIGGER
CONVECTION IN ANY FORM. THUS WOULD NOT EXPECT TO SEE MUCH RAIN
FORMING UNTIL AFTER 2 PM. ALSO WOULD NOT EXPECT IT TO LAST VERY LONG
INTO THE EVENING BUT DID NOT HAVE AS MUCH CONFIDENCE TO SHUT OFF THE
THREAT BY 8 PM SO LEFT IT IN PLACE FOR THE ENTIRE EVENING.

THE UPPER LOW WILL SLOWLY MOVE EAST OVERNIGHT WHILE AN UPPER RIDGE
BUILDS OFFSHORE. THIS WILL MAINTAIN A TYPICALLY DRIER NORTHWESTERLY
TO NORTHERLY FLOW AND BRING UNEVENTFUL WEATHER FOR THE REST OF THE
WEEKEND ASIDE FROM CLOUDS AT THE COAST AND PERHAPS SOME BRIEF
MORNING CLOUDS INLAND. TEMPERATURES NEAR OR SLIGHTLY ABOVE
NORMAL WILL GRADUALLY WARM FURTHER. /JBONK

.LONG TERM...SUNDAY THROUGH THURSDAY...NO CHANGES. PREVIOUS
DISCUSSION FOLLOWS. UPPER LEVEL RIDGING WILL MOVE ONSHORE ALLOWING
TEMPERATURES TO INCREASE SLIGHTLY ABOVE SEASONAL NORMS FOR THE
BEGINNING PART OF NEXT WEEK. AS THE RIDGE BEGINS TO BREAKDOWN
AND BECOME MORE ZONAL WE WILL SEE AN INCREASE IN LOW AND MID LEVEL
MOISTURE. THIS WILL PROVIDE FOR AN INCREASE IN CLOUD COVER FOR THE
LATTER PART OF NEXT WEEK. DO NOT EXPECT ANY PRECIPITATION IN THE
NEAR FUTURE. /64

&&

.AVIATION...COASTAL STRATUS PRODUCING IFR CONDITIONS ALONG THE
COAST SHOULD GIVE WAY TO VFR CONDITIONS THIS AFTERNOON. CONTINUED
ONSHORE FLOW SHOULD PRODUCE ANOTHER ROUND OF IFR CONDITIONS ALONG
THE COAST TONIGHT AND INTO SATURDAY MORNING. FURTHER
INLAND...NORTH TO NORTHEASTERLY WINDS SHOULD BE STRONG ENOUGH TO
KEEP CONDITIONS VFR THROUGH 18Z SATURDAY.

KPDX AND APPROACHES...HIGH PRESSURE AND INCREASING NORTHEASTERLY
FLOW SHOULD PRODUCE VFR CONDITIONS THROUGH 18Z SATURDAY. /NEUMAN

&&

.MARINE...HIGH PRESSURE WILL CONTINUE OVER THE NORTHEAST PACIFIC
INTO THE FORESEEABLE FUTURE. HOWEVER...THERMAL LOW PRESSURE OVER
CALIFORNIA WILL SHIFT MORE SQUARELY OVER THE COAST SATURDAY AND
AGAIN EARLY NEXT WEEK...IN A PATTERN THAT HAS BEEN RELATIVELY RARE
THIS SUMMER. THIS SHOULD PRODUCE WIDESPREAD NORTHERLY WINDS OF 25
TO 30KT ESPECIALLY ACROSS THE CENTRAL OREGON WATERS. WITH A
WESTERLY SWELL REMAINING 4 FT OR LESS DURING THIS TIME...SEAS MAY
ALSO BECOME WIND DOMINATED...I.E. ESPECIALLY STEEP AND HAZARDOUS
ACROSS THE CENTRAL WATERS SO A SMALL CRAFT FOR HAZARDOUS SEAS WILL
BE POSSIBLE SATURDAY AND AGAIN EARLY NEXT WEEK. /NEUMAN

&&

.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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