590
FXUS66 KPQR 211042
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
330 AM PDT MON SEP 21 2026
SYNOPSIS
TEMPERATURES TREND COOLER THROUGH THE WORKWEEK AS
BROAD UPPER-LEVEL TROUGHING DEVELOPS OVER THE GULF OF ALASKA. DRY
WEATHER WITH AREAS OF MORNING FOG AND LOW CLOUDS GIVING WAY TO
AFTERNOON WILL CONTINUE THROUGH WEDNESDAY. THE BROAD UPPER-LEVEL
TROUGH OVER THE GULF OF ALASKA WILL DEEPEN AND PROGRESS TOWARDS
WESTERN WASHINGTON AND OREGON LATE THURSDAY INTO FRIDAY, BRINGING
INCREASING CHANCES FOR WIDESPREAD RAIN. TRENDING DRY OVER THE WEEKEND
IN THE WAKE OF THIS TROUGH.
SHORT TERM...NOW THROUGH WEDNESDAY NIGHT
THE SHORT TERM FORECAST
IS HIGHLIGHTED BY CONTINUED DRY WEATHER, NEAR NORMAL TO SLIGHTLY
BELOW NORMAL TEMPERATURES, AND AREAS OF MORNING FOG AND LOW CLOUDS
GIVING WAY TO INCREASING AFTERNOON SUN. EXPECT DAILY HIGH
TEMPERATURES IN THE LOW TO MID 70S OVER 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.
IN REGARDS TO THE LARGE SCALE WEATHER PATTERN, MODEL ENSEMBLE
GUIDANCE REMAINS IN GOOD AGREEMENT FOR INCREASING SOUTHWEST FLOW
ALOFT AHEAD OF BROAD UPPER LEVEL TROUGHING OVER THE GULF OF ALASKA.
THIS TROUGH WILL GENERALLY NOT BE AMPLIFIED ENOUGH YET TO BRING RAIN
BACK INTO NORTHWEST OREGON OR SOUTHWEST WASHINGTON THROUGH WEDNESDAY
NIGHT, AS THE MAIN WEATHER SYSTEM ASSOCIATED WITH THIS TROUGH WILL BE
IMPACTING THE BRITISH COLUMBIA COAST. 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.
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. THIS WILL ALLOW TEMPERATURES TO COOL
SLIGHTLY EACH DAY MONDAY THROUGH WEDNESDAY, HOWEVER ONLY BY A DEGREE
OR TWO EACH DAY. -23
LONG TERM...THURSDAY THROUGH SUNDAY NIGHT
TROUGHING OVER THE
GULF OF ALASKA WILL APPROACH THE REGION IN EARNEST LATE THURSDAY INTO
FRIDAY AS THE TROUGH BECOMES MORE AMPLIFIED AND PROGRESSES EASTWARD
TOWARDS WASHINGTON AND OREGON. AS SUCH, THE 24-HOUR PROBABILITY FOR
PRECIPITATION REMAINS FAIRLY HIGH DURING THAT TIME, RANGING BETWEEN
55-65%. THE MAIN REASON PROBABILITIES ARE NOT HIGHER THAN THAT IS DUE
TO A SUBSET OF ENSEMBLE GUIDANCE THAT REMAINS DRY, MAINLY WITH THE
GEPS AS THIS ENSEMBLE SYSTEM SHOWS A HIGHER LIKELIHOOD OF THE TROUGH
DEAMPLIFYING AFTER MOVING INLAND WITH THE BULK OF THE PRECIPITATION
FALLING FARTHER TO THE NORTH OVER NORTHWEST WASHINGTON. WHILE THIS IS
NOT THE MOST LIKELY OUTCOME, IT IS WORTH MENTIONING AS IT IS STILL
WITHIN THE REALM OF POSSIBILITIES. 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. IF RAIN DOES FALL, DO NOT
EXPECT ANY FLOODING IMPACTS AS RAIN AMOUNTS WOULD MOST LIKELY RANGE
SOMEWHERE BETWEEN 0.1-0.6 INCHES, HIGHEST IN THE MOUNTAINS AND LOWEST
OVER THE WILLAMETTE VALLEY. THE WETTEST MODEL SOLUTIONS PRODUCE
0.5-1.2 INCHES OF RAIN, HOWEVER CHANCES FOR RAIN AMOUNTS THIS HIGH
ARE ONLY AT 10% AS SUGGESTED BY THE NBM 90TH PERCENTILE. EVEN THESE
RAIN AMOUNTS WOULD NOT BE ENOUGH TO PRODUCE FLOODING GIVEN THE
EXTENDED DURATION.
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. -23
AVIATION...THROUGH 06Z TUESDAY
AS OF 1030Z MONDAY, LOW MARINE
STRATUS REMAINED IN PLACE ALONG THE COAST WITH CEILINGS AROUND
1000 FT. AREAS OF FOG HAVE DEVELOPED OVER THE SOUTHERN WILLAMETTE
VALLEY, INCLUDING AT KEUG WHERE SURFACE VISIBILITIES ARE FALLING
AS LOW AS 1/4-1/2 SM AT TIMES. SIMILAR TO PREVIOUS MORNINGS,
EXPECT AREAS OF FOG AND LOW STRATUS TO EXPAND IN COVERAGE OVER THE
WILLAMETTE VALLEY BETWEEN 12-18Z MONDAY, BRINGING INCREASING
CHANCES FOR LIFR TO IFR FLIGHT CONDITIONS. HOWEVER, FOG AND LOW
STRATUS IS NOT EXPECTED TO BE QUITE AS WIDESPREAD AS WHAT WAS
OBSERVED YESTERDAY MORNING. AS SUCH, SOME TAF SITES MAY SEE VFR
CONDITIONS REMAIN IN PLACE THROUGH THE MORNING HOURS OR ONLY SEE A
BRIEF PERIOD OF FOG. OVERALL CONFIDENCE IN FOG AND LOW STRATUS
DEVELOPMENT IS HIGHEST TO THE SOUTH OF KSLE AND LOWEST NORTH OF
KSLE. REGARDLESS OF HOW WIDESPREAD FOG AND LOW STRATUS BECOMES
LATER THIS MORNING, EXPECT CLEARING TO OCCUR SOMETIME BETWEEN
18-20Z MONDAY WITH VFR CONDITIONS RETURNING THEREAFTER.
KPDX AND APPROACHES...CLEAR SKIES WILL GIVE WAY TO INCREASING
CHANCES FOR LOW STRATUS BETWEEN 13-16Z MONDAY. THIS IS WHEN
PROBABILITIES FOR CEILINGS BELOW 1000 FT INCREASE TO 30% AND
PROBABILITIES FOR CEILINGS BELOW 500 FT INCREASE TO 20%. IF LOW
STRATUS DOES EXPAND OVER THE TERMINAL LATER THIS MORNING, EXPECT
VFR CONDITIONS TO RETURN SOMETIME BETWEEN 18-20Z MONDAY AS SKIES
CLEAR BACK OUT. -23
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
UNDER 20 KT THROUGH FRIDAY, EVEN WITH THE TWO FRONTAL PASSAGES.
SEAS ARE EXPECTED TO INCREASE TO 6 TO 8 FT MONDAY EVENING INTO
MONDAY NIGHT WITH THE ARRIVAL OF A LONG PERIOD WEST-NORTHWESTWERLY
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. -23
PQR WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
PZ...NONE.
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