832
FXUS66 KPQR 220602
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
1102 PM PDT MON SEP 21 2026
.UPDATED AVIATION DISCUSSION.
SYNOPSIS
MAINLY DRY AND SEASONABLE WEATHER EXPECTED THROUGH
AT LEAST WEDNESDAY AS ONSHORE FLOW PERSISTS. TEMPERATURES
GRADUALLY TREND TREND COOLER THROUGH THE WEEK WITH AREAS OF
MORNING FOG AND LOW CLOUDS GIVING WAY TO AFTERNOON SUN. UPPER
LEVEL TROUGHING OVER THE GULF OF ALASKA DEEPENS ON THURSDAY,
APPROACHING THE REGION THROUGH FRIDAY, BRINGING INCREASING
CHANCES FOR WIDESPREAD RAIN. CONDITIONS EXPECTED TO TREND DRIER
ON SATURDAY WITH CHANCES FOR RAIN RETURNING LATE WEEKEND INTO
EARLY NEXT WEEK.
SHORT TERM...NOW THROUGH WEDNESDAY NIGHT
SATELLITE IMAGERY
THIS AFTERNOON SHOWS LOW STRATUS BEGINNING TO CLEAR, WHICH WILL
ALLOW FOR INLAND TEMPERATURES TO WARM INTO THE MID-70S TODAY.
EXPECT DRY WEATHER WITH NEAR TO SLIGHTLY BELOW NORMAL
TEMPERATURES TO CONTINUE THROUGH WEDNESDAY AS AREAS OF MORNING
FOG AND LOW CLOUDS GIVE WAY TO INCREASING AFTERNOON SUN. DESPITE
THE LACK OF PRECIPITATION, 500 MB HEIGHTS AND TEMPERATURES
ALOFT WILL BE ON A GRADUAL DECREASE AS THE TROUGH BEGINS TO
DEEPEN TOWARDS THE MIDDLE OF THE WEEK. TEMPERATURES COOL
SLIGHTLY THROUGH THE NEXT 2 DAYS, WITH DAILY HIGHS IN THE LOWER
70S ACROSS INLAND VALLEYS AND 60S AT THE COAST. MORNING LOWS
WILL GENERALLY RANGE ANYWHERE FROM THE MID 40S TO MID 50S,
WARMEST OVER URBAN AREAS AND COOLEST OVER RURAL AREAS.
MODEL ENSEMBLE GUIDANCE REMAINS IN GOOD AGREEMENT FOR INCREASING
SOUTHWEST TO WESTERLY FLOW ALOFT AHEAD OF BROAD UPPER LEVEL
TROUGHING OVER THE GULF OF ALASKA. A FRONTAL SYSTEM WILL REMAIN
NORTH OF OUR AREA, MAINLY IMPACTING THE BRITISH COLUMBIA COAST
THROUGH MID-WEEK. THE ONLY POTENTIAL EXCEPTION TO THAT IS TUESDAY
NIGHT THROUGH WEDNESDAY MORNING ALONG THE SOUTH WASHINGTON AND FAR
NORTH OREGON COAST WHEN THERE IS A VERY LOW CHANCE (5-10%) FOR LIGHT
RAIN WITH AN INITIAL WEAK WAVE AND ATTENDANT DECAYING SURFACE FRONT.
DH/23
LONG TERM...THURSDAY THROUGH MONDAY
RAIN IS APPEARING MORE LIKELY
LATER THIS WEEK AS MORE AMPLIFIED UPPER LEVEL TROUGHING INTERACTS
WITH A PLUME OF MOISTURE OVER THE PACIFIC. BY THURSDAY, A STRONG JET
STREAK WILL CAUSE THE UPPER TROUGH OVER THE GULF OF ALASKA TO DIG
SOUTHWARD, BECOMING MORE AMPLIFIED OFF THE COAST OF THE PACIFIC NW.
THIS WILL INTERACT WITH AN AREA OF WEAK LOW PRESSURE ASSOCIATED WITH
A PLUME OF MOISTURE, POTENTIALLY STRENGTHENING THE SURFACE LOW AS IT
MOVES TOWARD THE COAST. BUT, THERE STILL REMAINS QUITE A BIT OF
UNCERTAINTY REGARDING THE POSITIONING AND STRENGTH OF THIS LOW
PRESSURE SYSTEM.
FIRST, WILL DISCUSS THE PRECIPITATION POTENTIAL, AS THE
PROBABILITIES FOR RAIN CONTINUE TO INCREASE ACROSS THE AREA FOR
LATER THURSDAY INTO FRIDAY. LATEST NBM GUIDANCE SUGGESTS THERE IS AT
LEAST AN 80% CHANCE FOR MEASURABLE RAINFALL ACROSS NW OREGON AND SW
WASHINGTON, BUT RAINFALL AMOUNTS REMAIN QUITE UNCERTAIN, THOUGH HAVE
BEEN TRENDING HIGHER IN THE LATEST MODEL RUNS. THERE IS STILL A 10-
20% CHANCE THAT CONDITIONS REMAIN DRY. THERE IS ALSO A 10% CHANCE
THAT 24-HOUR RAINFALL AMOUNTS EXCEED 1 INCH ANYWHERE ACROSS THE
FORECAST AREA. THOSE WITH OUTDOOR PLANS LATE THURSDAY OR FRIDAY
SHOULD MONITOR THE FORECAST OVER THE COMING DAYS TO SEE IF RAIN
CHANCES TREND UP OR DOWN.
WHILE THE PROBABILITY FOR IMPACTFUL WIND WITH THIS SYSTEM IS SMALL,
IT IS STILL WORTH NOTING. A HANDFUL OF ENSEMBLE MEMBERS, INCLUDING
THE LATEST 12Z ECMWF OPERATIONAL RUN, DEVELOPS A SLIGHTLY STRONGER
LOW THAT LIFTS NE TOWARD THE NORTHERN OR COAST. THERE IS AROUND A
10% CHANCE FOR WIND GUSTS EXCEEDING 40 MPH ALONG THE COAST AND
WITHIN THE CENTRAL WILLAMETTE VALLEY.
UPPER-LEVEL HEIGHTS LOOK TO REBOUND QUICKLY IN THE WAKE OF THE
SHORTWAVE TROUGH, WITH HIGH CONFIDENCE FOR DRY WEATHER AND SLIGHTLY
WARMER TEMPERATURES ON SATURDAY GIVEN CHANCES FOR RAIN FALL BELOW
10%. HOWEVER, HIGH PRESSURE BUILDING IN BEHIND THIS TROUGH FRIDAY
NIGHT INTO THE WEEKEND WILL BRING CLEARING SKIES AND CALM WINDS
DURING THE OVERNIGHT HOURS. THIS WILL BRING AN IDEAL SET-UP FOR
RADIATIONAL COOLING AND CHILLIER OVERNIGHT LOW TEMPERATURES. ASIDE
FROM THE HIGH CASCADES, OVERNIGHT LOWS WILL BE COLDEST IN THE UPPER
HOOD RIVER VALLEY WHERE FROST DEVELOPMENT IS POSSIBLE FRIDAY NIGHT,
SATURDAY NIGHT, AND SUNDAY NIGHT. THE NBM IS SHOWING A 30-50% CHANCE
FOR MORNING LOWS BELOW 36-37 DEGREES FRIDAY NIGHT AND SATURDAY NIGHT
NEAR PARKDALE AND A 5-10% CHANCE NEAR ODELL. THOSE WITH OUTDOOR
VEGETATION THAT IS SUSCEPTIBLE TO FROST DAMAGE SHOULD MONITOR THE
FORECAST OVER THE COMING DAYS.
CHANCES FOR PRECIPITATION RETURN SUNDAY INTO MONDAY NEXT WEEK, BUT
THERE EXISTS QUITE A BIT OF UNCERTAINTY BETWEEN THE CLUSTERS WITH
SOME INDICATING WEAK RIDGING BUILDING IN BUT OTHERS MAINTAINS MORE
ZONAL TO WEAK TROUGHING PERSISTING. DH/23
AVIATION...THROUGH 06Z WEDNESDAY
LATE THIS EVENING, STRATUS IS
BEGINNING TO FILL IN ACROSS THE REGION WITH A MIX OF IFR TO MVFR
CIGS ALONG THE COAST, AND LOW-END VFR TO MVFR CIGS INLAND. AS THE
NIGHT GOES ON, CONFIDENCE IS HIGH THIS LOW CLOUD COVER WILL
INCREASE FURTHER, BECOMING RATHER PROLIFIC BY 10-12Z. BY THE
SUNRISE HOURS CIGS LIKELY (60-80%) DROP INTO THE 1.5-2.5KFT AT ALL
INLAND TERMINALS WITH MVFR CONDITIONS PREVAILING THROUGH AT LEAST
19-20Z. DURING THE ~12-16Z TIME PERIOD CHANCES FOR IFR CONDITIONS
HOLD AROUND 15-20%, HIGHEST AT KTTD AND KEUG. COME THE MIDDAY AND
AFTERNOON HOURS MVFR CIGS LIFT AND BREAK UP FOLLOWED BY THE
RETURN OF VFR CONDITIONS 20-22Z ONWARD. THAT SAID, CONFIDENCE IN
THE EXACT TIMING OF THIS IMPROVEMENT IS ONLY LOW TO MODERATE AT
THIS TIME. WINDS STAY FAIRLY LIGHT, GENERALLY LESS THAN 5-10
KNOTS.
KPDX AND APPROACHES...SATELLITE OBSERVATIONS SHOW STRATUS
BEGINNING TO FILL IN AROUND THE PORTLAND METRO ALTHOUGH LOW-END
VFR CONDITIONS ARE EXPECTED TO PERSIST THROUGH A GOOD CHUNK OF THE
NIGHT BEFORE DROPPING TO MVFR IN THE 09-12Z TIMEFRAME. ONCE THIS
OCCURS MVFR CIGS LIKELY HOLD THROUGH THE MORNING HOURS BEFORE
GRADUALLY LIFTING AND CLEARING BETWEEN 20-22Z. -99
MARINE
HIGH PRESSURE WILL MAINTAIN PREDOMINATELY NORTHERLY
WINDS ACROSS THE WATERS THROUGH THURSDAY. AN EXCEPTION WOULD BE
TUESDAY AFTERNOON TO WEDNESDAY MORNING, WHEN WINDS MAY TURN MORE
WESTERLY FOR THE WATERS NORTH OF CAPE FALCON WITH THE PASSAGE
OF A WEAK FRONT. WINDS BECOME MORE NORTHWESTERLY AND INCREASE
SLIGHTLY IN STRENGTH OVER ALL OF THE COASTAL WATERS THURSDAY
NIGHT INTO FRIDAY WITH THE PASSAGE OF ANOTHER FRONT. THIS FRONT
WILL BE RELATIVELY STRONGER THAN THE FRONTAL PASSAGE EARLIER IN
THE WEEK, WITH WIDESPREAD RAIN LIKELY. WIND GUSTS SHOULD
GENERALLY STAY BELOW 20 KT THROUGH THE WEEK. THE HIGHEST
PROBABILITIES COME LATE THURSDAY INTO FRIDAY WITH A 15-40%
CHANCE, HIGHEST IN THE NORTHERN OUTER WATERS.
SEAS ARE EXPECTED TO INCREASE TO 6 TO 8 FT THIS EVENING INTO
THE OVERNIGHT WITH THE ARRIVAL OF A LONG PERIOD WEST-
NORTHWESTERLY SWELL. SEAS THEN REMAIN NEAR THAT RANGE THROUGH
FRIDAY, BUT ARE NOT EXPECTED TO BE PARTICULARLY STEEP AT ANY POINT
IN TIME DUE TO THE DOMINANT WAVE PERIODS OF 10 TO 13 SECONDS.
-19/23
PQR WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
PZ...NONE.
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