228
FXUS66 KPQR 041821 AAB
AFDPQR
AREA FORECAST DISCUSSION...UPDATE
NATIONAL WEATHER SERVICE PORTLAND OR
1121 AM PDT FRI SEP 4 2026
UPDATED AVIATION DISCUSSION
SYNOPSIS
AN UNSETTLED AIRMASS REMAINS OVERHEAD INTO THE
WEEKEND WITH LINGERING SHOWERS GRADUALLY DIMINISHING DAY TO DAY.
THEN CONDITIONS TREND DRIER BY THE EARLY TO MIDDLE PORTION OF
NEXT WEEK AS TEMPERATURES SLOWLY CLAW THEIR WAY BACK NEAR NORMAL
FOR EARLY SEPTEMBER. HOWEVER, UNCERTAINTY IN THE LARGE SCALE
PATTERN GROWS NOTICEABLY AROUND THE MIDDLE PORTION OF NEXT WEEK.
DISCUSSION...FRIDAY THROUGH THURSDAY
RADAR IMAGERY AROUND
12:30 AM PT ON FRIDAY SHOWS RAIN SHOWERS HAVE MOSTLY CLEARED
NORTH OF SALEM WITH SHOWERS CONTINUING SOUTH OF SALEM. THE
VERTICALLY STACKED UPPER-LEVEL AND SURFACE CLOSED LOW PRESSURE
SYSTEM IS SPINNING JUST OFF OF THE CENTRAL OR COAST WITH A
SHORTWAVE PRODUCING THE CURRENT SHOWERS. ENSEMBLE GUIDANCE IS IN
AGREEMENT THAT THE CORE OF THE UPPER LOW HAS STOPPED PUSHING
SOUTH AND WILL SLOWLY MOVE EAST AND INLAND INTO WEST-CENTRAL OR
TODAY. WITH THE CORE OF THE LOW BEGINNING TO MOVE OVERHEAD, CAMS
INDICATE SHOWERS WILL BE LESS WIDESPREAD TODAY THAN YESTERDAY,
WITH BETTER CHANCES SOUTH OF THE PORTLAND METRO AREA AND OVER
THE COAST RANGE AND CASCADES. AS DAYTIME HEATING INCREASES
TODAY, CONVECTIVE POTENTIAL INCREASES, AS WELL. DETERMINISTIC
MODEL SOUNDS ALONG WITH THE HREF INDICATE JUST ENOUGH CAPE
EXTENDING INTO THE MIX-PHASED REGION OF THE ATMOSPHERE FOR A
LIGHTNING STRIKE OR TWO TO BE PRODUCED IN STRONGER CELLS
GENERALLY AFTER 10 AM. HOWEVER, A GLARING LACK OF VERTICAL
SHEAR MEANS ANY STORMS WHICH DO DEVELOP WILL BE SHORT-LIVED AND
PULSE-LIKE. INFREQUENT LIGHTNING, HEAVY RAIN, AND GUSTY OUTFLOW
WINDS ARE THE PRIMARY IMPACTS. ANY ACTIVITY THEN QUICKLY
DECREASES AFTER SUNSET INTO FRIDAY NIGHT.
OVER THE WEEKEND, THE MAJORITY OF DETERMINISTIC AND ENSEMBLE
MEMBERS CONTINUE TO SHOW THE BROAD UPPER-LEVEL CLOSED LOW
PRESSURE SYSTEM HOLDING FIRM OVER THE PACIFIC NORTHWEST WITH
MULTIPLE SHORTWAVES WITHIN THE FLOW. THIS WILL CAUSE LINGERING
SHOWER CHANCES OVER NW OR AND SW WA, MOST LIKELY DURING THE
DAYTIME HOURS AND OVER TERRAIN FEATURES AS DIURNAL HEATING
LIKELY PLAYS A MAJOR ROLE IN SHOWER GENERATION. ALSO CAN'T RULE
OUT STRONGER CELLS AND A THUNDERSTORM OR TWO FORMING IN THE
AFTERNOON AND EVENING HOURS WITH SIMILAR IMPACTS TO FRIDAY.
CONFIDENCE IS HIGH THAT TEMPERATURES REMAIN BELOW NORMAL FOR
THIS TIME OF YEAR WITH UPPER 60S TO MID 70S IN THE INTERIOR
LOWLANDS, 60S ALONG THE COAST, AND 40S TO LOW 60S OVER THE
CASCADES (COLDEST AT HIGHER ELEVATIONS). IT MIGHT BE WORTH
PACKING A JACKET/COAT IF YOU PLAN ON VENTURING INTO THE
MOUNTAINS THIS WEEKEND.
THE MAJORITY OF ENSEMBLE MEMBERS FINALLY SHOW THE UPPER LOW
BEGINNING TO ACCELERATE EASTWARD ON MONDAY, FAVORING THE RETURN
OF DRY CONDITIONS BY TUESDAY AND A GRADUAL WARMING TREND. AFTER
TUESDAY, ENSEMBLES BEGIN TO DEVIATE FROM ONE ANOTHER WHEN
TRYING TO RESOLVE THE UPPER-LEVEL PATTERN, PARTICULARLY IN
REGARDS TO A RIDGE OF HIGH PRESSURE TRYING TO DEVELOP OVER THE
ROCKIES INTO SOUTHEAST OREGON WHILE A TROUGH AMPLIFIES OVER THE
EASTERN PACIFIC. CURRENTLY AROUND 60% OF ENSEMBLES FAVOR A
WARMER/DRIER SOLUTION WITH HIGHS ABOVE NORMAL (MID 80S) BY
WEDNESDAY/THURSDAY WHILE THE REMAINING 40% POINT TO A SOMEWHAT
COOLER SOLUTION (LOW TO MID 70S). WILL HAVE TO SEE HOW GUIDANCE
TRENDS AS WE GET CLOSER TO NEXT WEEK. -03/99
AVIATION...THROUGH 18Z SATURDAY
A LOW PRESSURE SYSTEM REMAINS
OVER THE REGION TODAY WITH MOIST, SOUTHERLY FLOW ACROSS THE AREA.
THIS WILL MAINTAIN BROKEN CLOUDS WITH SCATTERED SHOWERS THROUGH
THIS AFTERNOON. EXPECT PREDOMINATELY VFR CONDITIONS THROUGH THE
TAF PERIOD, EXCEPT FOR BRIEF REDUCTIONS TO MVFR WITH HEAVIER
SHOWERS AT TIMES. THERE IS ALSO AROUND A 60% CHANCE FOR MVFR CIGS
AT KONP BETWEEN 20-03Z TODAY. CHANCES FOR THUNDERSTORMS (15-30%)
RETURN AFTER 18Z THIS AFTERNOON, ENDING BY 02-03Z SATURDAY. ANY
STORMS THAT DO DEVELOP WILL HAVE THE POTENTIAL TO PRODUCE
LIGHTNING, GUSTY/ERRATIC WINDS, AND SMALL HAIL. GENERALLY EXPECT
LIGHT AND VARIABLE WINDS INLAND WITH SOUTHEASTERLY WINDS LESS THAN
10 KT ALONG THE COAST.
KPDX AND APPROACHES...VFR EXPECTED THROUGH THE PERIOD WITH
SCATTERED SHOWERS TODAY. THERE IS A 15% CHANCE OF THUNDERSTORMS
THIS AFTERNOON. LIGHT WINDS EXPECTED THROUGH THE TAF PERIOD. /DH
MARINE
A LOW PRESSURE SYSTEM WILL CONTINUE TO WEAKEN AT THE
SURFACE INTO FRIDAY MORNING AS IT SITS OFF OF THE CENTRAL OR
COAST. WINDS OVER THE COASTAL WATERS HAVE EASED BELOW 20 KTS AND
ARE MORE EASTERLY. WINDS WILL CONTINUE TO EASE THROUGH FRIDAY
MORNING, BECOMING NORTHERLY FRIDAY EVENING THEN MORE LIGHT AND
VARIABLE BY SATURDAY MORNING. SEAS HAVE FALLEN BELOW 10 FT AND
WILL CONTINUE TO SUBSIDE TO 4 TO 5 FT BY FRIDAY EVENING. ALSO, A
15% CHANCE FOR THUNDERSTORMS EXISTS ACROSS THE INNER WATERS SOUTH
OF CAPE FOULWEATHER FRIDAY AFTERNOON, WHICH COULD PRODUCE
LIGHTNING AND GUSTY/ERRATIC WINDS.
LIGHT OFFSHORE FLOW BECOMES NORTHERLY LATER SATURDAY INTO SUNDAY
AS WEAK HIGH PRESSURE REBUILDS OVER THE WATERS. SEAS WILL REMAIN
AROUND 3-5 FT THROUGH THE WEEKEND. CONDITIONS LOOK TO REMAIN
RATHER BENIGN INTO EARLY NEXT WEEK. -03/DH
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
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