844
FXUS66 KPQR 212155
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
255 PM PDT MON SEP 21 2026
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 18Z TUESDAY
LOW STRATUS HAS DISSIPATED
ACROSS THE AREA, GIVING WAY TO MAINLY VFR CONDITIONS. HIGH LEVEL
CLOUDS STREAMING IN ALONG SOUTHWESTERLY UPPER LEVEL FLOW WILL
CONTINUE AS A WEAK FRONT MOVES THROUGH. VFR CONDITIONS
PERSIST UNTIL THE EVENING WITH NORTHERLY TO NORTHWESTERLY WINDS
5-10 KT. CONDITIONS THIS EVENING ARE EXPECTED TO BE SIMILAR TO THE
PAST FEW EVENINGS WITH STRATUS DEVELOPING BETWEEN 00-06Z TUESDAY
AND SPREADING THROUGH THE COAST RANGE GAPS AND ALONG THE COLUMBIA
RIVER INTO THE METRO AND WILLAMETTE VALLEY BETWEEN 08-12Z TUESDAY.
KPDX AND APPROACHES...LOW CLOUDS HAVE DISSIPATED WITH SOME HIGH
LEVEL CLOUDS MOVING OVER THE AREA. NORTHERLY WINDS AROUND 5 KT
EXPECTED. STRATUS DEVELOPS AND PUSHES EASTWARD AGAIN LATE TONIGHT
INTO TUESDAY MORNING WITH A PERIOD MVFR CIGS LIKELY (60-70%). -19
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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