056
FXUS66 KPQR 291725
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
1025 AM PDT SAT AUG 29 2026
UPDATED AVIATION DISCUSSION.
SYNOPSIS
THE REGION REMAINS UNDER THE INFLUENCE OF A
PROGRESSIVE ONSHORE FLOW PATTERN WITH LITTLE TO NO NOTABLE
WEATHER IMPACTS THROUGH THE NEXT WEEK. A WEAK FRONTAL PASSAGE
THIS MORNING WILL USHER IN OCCASIONAL LIGHT RAIN, MAINLY ALONG
THE COAST AND IN HIGHER TERRAIN. AFTER A RETURN TO DRIER AND
WARMER WEATHER SUNDAY INTO MONDAY, THE FORECAST TRENDS TOWARDS
MORE WIDESPREAD RAINFALL CHANCES BY THE MIDDLE OF NEXT WEEK,
WITH SOME UNCERTAINTY REMAINING IN RAINFALL TIMING AND AMOUNTS.
SHORT TERM...NOW THROUGH TUESDAY
THROUGH THE FIRST HALF OF
THE WEEKEND UPPER-LEVEL TROUGHING REMAINS THE DOMINANT FEATURE
OVER THE FAR ENE PACIFIC WHILE HELPING TO KEEP PERSISTENT
ONSHORE FLOW IN PLACE. THIS UPPER-LEVEL TROUGH FEATURE WILL
DRAG A WEAK COLD FRONT ACROSS THE NORTHERN PORTIONS OF OUR CWA
WHICH COULD LEAD TO A PERIOD OF LIGHT SHOWERS/AGGRESSIVE
DRIZZLE. OVERALL THE BEST RELATIVE CHANCE FOR LIGHT RAIN
(20-50%) APPEARS TO BE ALONG THE COAST, COAST RANGE/WILLAPA
HILLS, AND SOUTHWEST WASHINGTON, PARTICULARLY IN THE CASCADES
AND CASCADE FOOTHILLS, WHERE OROGRAPHIC FORCING IS PRESENT.
CAN'T COMPLETELY RULE OUT AREAS AROUND THE PORTLAND/VANCOUVER
METRO RECEIVING A SHOWER IN THE MORNING AS WELL (15-25% CHANCE)
BUT CONFIDENCE IS HIGH ANY RAINFALL AMOUNTS STAY RATHER LIGHT
(<0.05 INCHES). THE ADDITIONAL ONSHORE FLOW WILL KEEP WIDESPREAD
CLOUD COVER OVER THE MAJORITY OF THE CWA, LEADING TO DAYTIME
HIGHS IN THE LOW TO MID 70S FOR INLAND VALLEYS, LOW TO UPPER 60S
ALONG THE COAST AND UPPER 50S TO MID 60S FOR THE CASCADES.
SUNDAY, A SHORTWAVE RIDGE WILL BUILD OVER THE PAC NW, RESULTING
IN A BRIEF WARMING PERIOD FOR SUNDAY AND MONDAY. DAYTIME HIGHS
ON SUNDAY ARE EXPECTED TO WARM INTO THE MID TO UPPER 70S FOR
INLAND VALLEYS, MID TO UPPER 60S ALONG THE COAST AND UPPER 60S
TO LOW 70S FOR THE CASCADES. MONDAY, IS ON TRACK TO BE AROUND
7-10 DEGREES WARMER THAN SUNDAY. THIS WARM UP LOOKS TO BE RATHER
SHORT LIVED AS BY LATE MONDAY/EARLY TUESDAY, A BROAD TROUGH/
ALASKAN LOW IS EXPECTED TO REPLACE THE SHORTWAVE RIDGE AS THE
DOMINANT SYNOPTIC FEATURE OVER THE PAC NW. MODELS ARE DEPICTING
A WEAK FRONTAL SYSTEM MOVING INTO THE REGION EARLY TUESDAY AND
COULD BRING SOME VERY LIGHT RAIN, BUT THE BIGGER STORY COMES
FROM WHAT COULD ENTER INTO THE REGION TUESDAY NIGHT AND INTO THE
LATTER PART OF NEXT WEEK. -42/99
LONG TERM...TUESDAY NIGHT THROUGH FRIDAY
LOOKING INTO THE
MIDDLE OF NEXT WEEK, ENSEMBLE GUIDANCE CONTINUES TO HEAVILY
FAVOR THE DEVELOPMENT OF AN EARLY FALL-LIKE, COOLER AND WETTER
WEATHER PATTERN. WHILE THE GENERAL CONSENSUS OF THE ENSEMBLES
ARE SUPPORTIVE OF THIS PATTERN, THE FINER DETAILS SUCH AS:
PLACEMENT OF THE UPPER LEVEL LOW ALONG WITH THE AMPLITUDE OF
THE UPPER LEVEL LOW IS WHAT IS DRIVING THE OVERALL UNCERTAINTY
WITHIN THE FORECAST AS A WHOLE. FOR EXAMPLE, SOME ENSEMBLES
BRING INCREASING RAINFALL AS EARLY AS TUESDAY MORNING (WEAKER
TROUGH FEATURE), WHILE OTHERS HOLD IT OFF UNTIL LATER TUESDAY
AND WEDNESDAY (STRONGER TROUGH). WITH THAT SAID, AT THIS POINT
ALMOST ALL DETERMINISTIC MODELS AND THEIR RESPECTIVE ENSEMBLES
SHOW AT LEAST A WETTING RAIN (0.25 INCHES OR MORE IN A 12 HOUR
PERIOD) SOMETIME IN THE LATE TUESDAY THROUGH LATE THURSDAY NIGHT
TIMEFRAME. LOOKING AT THE LATEST NBM PROBABILISTIC GUIDANCE,
THERE IS A 70-85% CHANCE FOR GREATER THAN 0.5 INCHES OF RAINFALL
ACROSS THE ENTIRE REGION, AND EVEN A 50-75% CHANCE FOR GREATER
THAN 1.0 INCH OF RAINFALL AND A 25-50% CHANCE FOR 1.25 INCHES
OVER THAT SAME 48 HR TIMEFRAME.
OVERALL, WHILE THIS MID-WEEK SYSTEM ISN'T SHAPING UP TO BE A
"FIRE SEASON ENDER" (UNLESS PRECIPITATION AMOUNTS TREND MUCH
HIGHER), THE FORECAST RAINFALL WILL DEFINITELY WORK TO HEAVILY
MODERATE FIRE WEATHER RELATED CONCERNS FOR OUR SIDE OF THE
CASCADES ASSUMING THE FORECAST REMAINS ON TRACK AS MORE HIGH
RESOLUTION MODELS COME ONLINE. -42/99
AVIATION...THROUGH 18Z SUNDAY
SCATTERED RAIN SHOWERS CONTINUE
TO TRACK EASTWARD ACROSS THE AIRSPACE AS AN UPPER-LEVEL LOW
MOVES INLAND OVER WASHINGTON STATE LATE THIS MORNING. LIGHT RAIN
MAY BRIEFLY REACH THE GROUND AT AREA TERMINALS, BUT AVIATION
IMPACTS ARE UNLIKELY. OTHERWISE, LARGELY VFR CONDITIONS PERSIST
AS SKIES TREND CLEARER AND SHOWERS END THIS AFTERNOON AS THE LOW
DEPARTS TO THE EAST. ADDITIONAL MARINE STRATUS WILL YIELD SCT-
BKN SKIES AFTER 06-12Z SUN, WITH HIGH CHANCES FOR MVFR CIGS AT
COASTAL TERMINALS AND MODEST CHANCES, 30-60%, AT INLAND SITES.
LIGHT SOUTHWEST WINDS THIS MORNING WILL BUILD OUT OF THE
NORTHWEST TO NORTH AT 5-10 KT THIS AFTERNOON, THEN EASE BELOW
3-5 KT AGAIN AFTER 06Z SUN.
KPDX AND APPROACHES...VFR CONDITIONS FAVORED TO PERSIST
THROUGHOUT THE PERIOD. LIGHT RAIN SHOWERS ARE POSSIBLE THROUGH
21-24Z SAT, BUT ANY PRECIPITATION WOULD BE VERY LIGHT AND
TERMINAL IMPACTS ARE NOT ANTICIPATED. SKIES TREND CLEARER AFTER
00Z SUN, UNTIL MARINE STRATUS BUILDS INLAND FROM THE COAST NEAR
12Z SUN YIELDING 60% CHANCES OF MVFR CIGS LATE IN THE PERIOD.
WINDS WILL BUILD OUT OF THE NORTHWEST TO 5-10 KT THIS AFTERNOON,
THEN EASE BELOW 3-5 KT THIS EVENING. -36
MARINE
A BROAD, UPPER LEVEL TROUGH WILL CONTINUE TO PUSH
EASTWARD THROUGH TODAY AND MAINTAIN NORTH/NORTHWEST WINDS ACROSS
THE COASTAL WATERS INTO EARLY NEXT WEEK. A WEAK FRONT PUSHES
ACROSS THE NORTHERN WATERS THIS MORNING WITH LITTLE TO NO IMPACT
EXPECTED. WINDS ARE GENERALLY EXPECTED TO REMAIN AROUND 15 KT
OR LESS, WITH PREDOMINATELY WIND DRIVEN SEAS REMAIN AT AROUND 3
TO 5 FT.
THE PATTERN LOOKS TO BECOME MORE ACTIVE BY THE MIDDLE OF NEXT
WEEK AS A SERIES OF STRONGER FRONTAL SYSTEMS APPROACH THE REGION
TUESDAY INTO WEDNESDAY, FOLLOWED BY LOW PRESSURE MOVING SOUTHEAST
FROM THE GULF OF ALASKA. THERE IS AT LEAST A 50% CHANCE THAT THIS
SYSTEM BRINGS LOW END GALE FORCE, SOUTHERLY WIND GUSTS IN EXCESS
OF 34 KT, AS WELL AS RESULTING IN SEAS BUILDING TOWARDS 10-12 FT
BY THE MIDDLE/LATTER PART OF NEXT WEEK. /42
PQR WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
PZ...NONE.
WWW.WEATHER.GOV/PORTLAND
INTERACT WITH US VIA SOCIAL MEDIA:
WWW.FACEBOOK.COM/NWSPORTLAND
X.COM/NWSPORTLAND
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page