407
FXUS66 KPQR 051725
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
1025 AM PDT SAT SEP 5 2026
UPDATED AVIATION DISCUSSION.
SYNOPSIS
EXPECT A SHOWERY, UNSETTLED AIRMASS TO REMAIN
OVERHEAD INTO THE WEEKEND WITH COOLER THAN NORMAL TEMPERATURES
PERSISTING. CONDITIONS TREND DRIER BY THE EARLY TO MIDDLE
PORTION OF NEXT WEEK AS HIGH TEMPERATURES GRADUALLY RISE BACK
CLOSER TO NORMAL FOR EARLY SEPTEMBER. HOWEVER, UNCERTAINTY IN
THE LARGE SCALE PATTERN GROWS NOTICEABLY AROUND THE MIDDLE TO
END OF NEXT WEEK.
DISCUSSION...SATURDAY THROUGH FRIDAY
THE UPPER LEVEL LOW
PRESSURE SYSTEM REMAINS SITUATED OVER THE PACNW THIS WEEKEND AS
THE SURFACE LOW HAS WEAKENED OVER THE COAST. VERY LIGHT WINDS
EARLY SATURDAY MORNING THROUGH SUNDAY MORNING WITH CLEARING
UPPER LEVEL CLOUDS WILL LEAD TO THE POTENTIAL OF LOW STRATUS OR
FOG DEVELOPMENT IN THE MORNING HOURS EACH DAY ALONG THE COAST
AND INTERIOR LOWLANDS. MULTIPLE WEAK SHORTWAVES EMBEDDED
WITHIN THE LARGER UPPER LOW PRESSURE CIRCULATION WILL BRING
ADDITIONAL 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 OR A PULSE-LIKE THUNDERSTORM OR
TWO FORMING IN THE AFTERNOON AND EVENING HOURS EACH DAY. BRIEF
HEAVY RAIN, SMALL HAIL, AND GUSTY WINDS ARE POSSIBLE WITH ANY
STRONG SHOWER OR THUNDERSTORM THAT FORMS. CONFIDENCE REMAINS
HIGH THAT TEMPERATURES HOLD 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). IF YOU'RE VENTURING UP IN THE MOUNTAINS TO
ENJOY THE WEEKEND IT MAY BE WORTH PACKING A JACKET.
ENSEMBLE GUIDANCE IS IN HIGH AGREEMENT THAT THE UPPER LOW WILL
FINALLY MOVE EASTWARD MONDAY INTO TUESDAY, INTO IDAHO BY LATE
MONDAY AND SOUTHERN CANADA BY TUESDAY. THIS WILL BRING DRY
CONDITIONS BY MIDDAY MONDAY AND TEMPERATURES WARMING BACK TO
NEAR NORMAL BY TUESDAY AS MOST ENSEMBLE MEMBERS INDICATE ZONAL
FLOW BEGINS TO TAKE SHAPE OVER THE PACNW.
WEDNESDAY INTO THURSDAY, ENSEMBLES BEGIN TO DEVIATE FROM ONE
ANOTHER OVER THE PACNW AS THEY TRY TO RESOLVE THE UPPER-LEVEL
PATTERN, PARTICULARLY IN REGARDS TO A RIDGE OF HIGH PRESSURE
OVER THE CENTRAL US TRYING TO AMPLIFY NORTHWEST OVER THE ROCKIES
INTO SOUTHEAST OREGON WHILE A TROUGH AMPLIFIES OVER THE EASTERN
PACIFIC. ABOUT 80% OF ENSEMBLE MEMBERS INDICATE AT LEAST ZONAL
FLOW IF NOT SLIGHT RIDGING OVER THE AREA ON WEDNESDAY, LEADING
TO THE WARMEST TEMPERATURES OF THE WEEK WITH A 75-85% CHANCE OF
INTERIOR LOWLAND TEMPERATURES EXCEEDING 80 DEGREES AND A 40-60%
CHANCE FOR EXCEEDING 85 DEGREES. BY THURSDAY, ABOUT 50% OF THE
MEMBERS HOLD ON TO THIS PATTERN WITH THE OTHER 50% INDICATING
WEAK TO MODERATE TROUGHING DEVELOPING OVER THE AREA. BY FRIDAY,
ABOUT 70-80% OF THE ENSEMBLE MEMBERS SUGGEST TROUGHING IMPACTING
THE REGION, THOUGH PRECIPITATION CHANCES WITH THIS ARE EXTREMELY
VARIABLE. THIS TROUGH FEATURE COULD BE INFLUENCED BY THE
EVENTUAL NORTHERLY PROGRESSION OF REMNANTS FROM HURRICANE MARIE
IN THE EASTERN PACIFIC WITH AROUND 50-60% OF ENSEMBLE MEMBERS
SUGGESTING THIS IN THE THURSDAY/FRIDAY TIMEFRAME. HOWEVER, HOW
MUCH MOISTURE LINGERS FROM MARIE AND HOW MUCH THIS WILL IMPACT
THE PACNW IS VERY UNCERTAIN AT THIS POINT. WILL BE KEEPING AN
EYE ON THIS AS MARIE PROGRESSES THROUGH THE PACIFIC OVER THE
NEXT WEEK. -03/99
AVIATION...THROUGH 18Z SUNDAY
A LOW PRESSURE SYSTEM CONTINUES
TO MEANDER OVERHEAD, BRING CONTINUED MOIST CONDITIONS WITH LIGHT
WINDS AND PERSISTENT LOW CHANCES FOR RAIN SHOWERS. NONETHELESS,
VFR CONDITIONS ARE FAVORED AT ALL TERMINALS AFTER 19-21Z SAT,
WITH REMAINING LOW CIGS EXPECTED TO LIFT AS DIURNAL MIXING
STRENGTHENS. TERMINAL IMPACTS FROM ANY SHOWERS ARE UNLIKELY, AND
WOULD BE VERY BRIEF IF THEY DO OCCUR. SHOWERS ARE MORE LIKELY
IN AREAS OF TERRAIN, PARTICULARLY THE CASCADES, WITH 15-25%
CHANCES FOR AN ISOLATED THUNDERSTORM WHICH COULD PRODUCE LOCALLY
HEAVY RAIN, GUSTY AND ERRATIC WINDS, AND SMALL HAIL THROUGH
THIS AFTERNOON. OTHERWISE, VFR CIGS/VIS CONTINUE WITH LIGHT
WINDS OF 5 KT OR LESS ACROSS THE AREA. CHANCES FOR LOW CLOUDS
AND ADDITIONAL RAIN SHOWERS INCREASE AFTER 06-12Z SUN.
KPDX AND APPROACHES...LOW CLOUDS THIS MORNING MAY RESULT IN
BRIEF MVFR/IFR CONDITIONS, BUT DIURNAL MIXING WILL
INCREASINGLY FAVOR VFR CIGS THROUGH 20-21Z SAT. LIGHT WINDS
BELOW 5 KT EXPECTED THROUGH THE PERIOD, INITIALLY OUT OF THE
NORTHWEST AND BECOMING VARIABLE TONIGHT AFTER 06Z SUN. LOW
CHANCES, <10%, FOR RAIN SHOWERS PERSIST THROUGH MUCH OF THE DAY,
BUT INCREASE TO 25-35% AFTER 12Z SUN. -36
MARINE
SURFACE LOW PRESSURE WILL CONTINUE TO WEAKEN INTO
EARLY SATURDAY MORNING AS IT SITS OFF THE OR COAST. NORTHERLY
WINDS THAT DEVELOPED ACROSS THE WATERS OVERNIGHT ARE BECOMING
LIGHT AND VARIABLE THIS MORNING. SEAS HAVE FALLEN TO AROUND 4 TO
5 FT AT 10 SECONDS.
NORTHERLY WINDS RETURN LATER TODAY INTO SUNDAY AS WEAK HIGH
PRESSURE REBUILDS OVER THE WATERS. WINDS ARE EXPECTED TO PEAK AT
AROUND 15 KT OR LESS. SEAS REMAIN AT AROUND 3 TO 6 FT THROUGH THE
WEEKEND. CONDITIONS LOOK TO REMAIN RATHER BENIGN INTO EARLY NEXT
WEEK, THOUGH HIGH PRESSURE MAY STRENGTHEN TOWARD THE MIDDLE OF
NEXT WEEK. -DH/03
PQR WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
PZ...NONE.
WWW.WEATHER.GOV/PORTLAND
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