658
FXUS66 KPDT 232147
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
147 PM PST SUN NOV 23 2025
DISCUSSION
SNOW LEVELS WILL DROP LATER THIS AFTERNOON THROUGH
TONIGHT AS A COLD FRONT FROM THE PACIFIC SWEEPS ACROSS THE
REGION. NO WINTER HIGHLIGHTS ARE IN EFFECT, BUT DO HAVE MEDIUM-
HIGH CONFIDENCE (60-80 PERCENT) IN ONE-HALF INCH TO TWO INCHES OF
SNOW FOR MOUNTAIN PASSES IN THE CASCADES AND NORTHERN BLUE
MOUNTAINS. ADDITIONALLY, BREEZY TO LOCALLY WINDY WESTERLY WINDS OF
15-25 MPH ACCOMPANIED BY GUSTS OF 25-40 MPH ARE FORECAST ACROSS
WIND-PRONE PORTIONS OF THE COLUMBIA PLATEAU WITH AND BEHIND FROPA,
PERSISTING THROUGH MONDAY AS A SHORTWAVE TROUGH MOVES OVERHEAD.
TUESDAY AFTERNOON THROUGH THURSDAY, FORECAST DETAILS ARE STILL
FUZZY AS ENSEMBLE GUIDANCE STRUGGLES TO RESOLVE FEATURES OF A
PROGRESSIVE WEATHER PATTERN, INCLUDING THE MAGNITUDE AND AXIS OF
MOISTURE TRANSPORT INTO THE PACIFIC NORTHWEST, FOCUSING MECHANISMS
FOR PRECIPITATION (FRONTS, SURFACE LOWS, ETC.), AND ANY WINTRY
PRECIPITATION FOR THE MOUNTAINS AND LOWLANDS. THAT SAID, NWP
GUIDANCE IS PRESENTING A RANGE OF SOLUTIONS THAT IS FAVORABLE FOR
WINTER WEATHER ACROSS PORTIONS OF OUR FORECAST AREA. WINTER
WEATHER CONDITIONS ARE MOST LIKELY ALONG THE WASHINGTON CASCADES
AND THEIR ADJACENT EASTERN SLOPES AS WELL AS THE YAKIMA AND
KITTITAS VALLEYS, WITH LOWER CHANCES FOR THE NORTHERN BLUE
MOUNTAINS AND BLUE MOUNTAIN BASINS SUCH AS THE GRANDE RONDE AND
WALLOWA VALLEYS.
TO DIVE INTO SPECIFICS FOR TUESDAY THROUGH THURSDAY, ENSEMBLE
SOLUTIONS GENERALLY DRAPE A WARM FRONT OVER THE FORECAST AREA BY
TUESDAY AFTERNOON, WITH THE LOCATION PRESENTED BY MEMBERS RANGING
FROM NORTH-CENTRAL OREGON TO SOUTH-CENTRAL WASHINGTON. MEANWHILE,
NEAR- TO SUB-FREEZING AIR AT THE SURFACE IS POSSIBLE (50-80
PERCENT CONFIDENCE) ACROSS THE AFOREMENTIONED AREAS OF SOUTH-
CENTRAL WASHINGTON AND NORTHEAST OREGON. SOLUTIONS THEN RANGE FROM
A SLOW-MOVING OR EVEN QUASI-STATIONARY FRONTAL BOUNDARY PERSISTING
ACROSS THE FORECAST AREA THROUGH WEDNESDAY NIGHT TO A FASTER-
MOVING FRONTAL BOUNDARY THAT PUSHES INTO NORTHERN WASHINGTON
(OUT OF OUR FORECAST AREA) BY WEDNESDAY AFTERNOON. THERMODYNAMIC
PROFILES IN NWP GUIDANCE ARE SUPPORTIVE OF SNOW OR LIGHT FREEZING
RAIN WHERE COLD AIR REMAINS TRAPPED, WITH PRECIPITATION TYPE
LARGELY DEPENDING ON THE LOCATION OF THE WARM FRONT, WARM AIR
ALOFT, AND SURFACE TEMPERATURES.
TO BETTER QUANTIFY THE RANGE OF SOLUTIONS IN GUIDANCE, ONE CAN
LOOK AT CLUSTERS OF ENSEMBLE MEMBERS THAT PRESENT SIMILAR
SOLUTIONS. IN THIS CASE, EXAMINING CLUSTERS BASED ON QPF OUTPUT
INDICATES ROUGHLY 45 PERCENT OF ENSEMBLE VARIANCE CAN BE EXPLAINED
BY LOCATION AND/OR TIMING DIFFERENCES IN THE AFOREMENTIONED WARM
FRONT, WHILE AN ADDITIONAL 22 PERCENT IS DRIVEN BY THE MAGNITUDE
OF QPF ACROSS WASHINGTON AND FAR NORTHERN OREGON. MOREOVER, 65
PERCENT OF ENSEMBLE SOLUTIONS PLACE THE AXIS OF QPF OVER NORTH-
CENTRAL OREGON TO SOUTH-CENTRAL WASHINGTON, WHILE THE REMAINING 35
PERCENT ADVERTISE MOSTLY DRY CONDITIONS FOR OREGON WITH THE QPF
AXIS SHIFTED NORTH TO WASHINGTON.
SO WILL IT SNOW IN THE LOWLANDS? THE NBM SUGGESTS A LOW
PROBABILITY (5-15 PERCENT) OF 1 INCH OR GREATER SNOWFALL FOR THE
24-HR PERIOD ENDING 10 AM PST WEDNESDAY FOR THE YAKIMA, KITTITAS,
AND GRANDE RONDE VALLEYS. BASED ON EXPERIENCE, THESE PROBABILITIES
ARE LIKELY TOO LOW GIVEN THE SYNOPTIC SETUP, AND WOULD
SUBJECTIVELY INCREASE THEM TO 10-50 PERCENT, HIGHEST FOR THE
KITTITAS VALLEY. IN THE EASTERN HALF OF THE COLUMBIA BASIN AND
FARTHER SOUTH INTO CENTRAL OREGON, GUIDANCE IS MORE CONFIDENT IN A
WARMER AIR MASS (SOUTH OF THE WARM FRONTAL BOUNDARY), RESULTING
IN VERY LOW PROBABILITIES OF MEASURABLE SNOWFALL (LESS THAN 5
PERCENT). WHILE PROBABILITIES FROM THE NBM ARE STILL QUITE LOW
(UP TO 10 PERCENT), THE SYNOPTIC PATTERN DOES SUPPORT SOME
POTENTIAL FOR MEASURABLE FREEZING RAIN TUESDAY NIGHT AND WEDNESDAY
IN SHELTERED VALLEYS ALONG THE EAST SIDE OF THE WASHINGTON
CASCADES, THE GRANDE RONDE VALLEY, AND SHELTERED LOCATIONS WITHIN
THE NORTHERN BLUE MOUNTAINS AS WARM AIR OVERRIDES COLDER AIR AT
THE SURFACE.
COMPARED TO THE LOWLANDS, WINTER WEATHER IS MORE LIKELY FOR THE
MOUNTAIN PASSES, THOUGH 48-HR NBM PROBABILITIES OF ADVISORY-
LEVEL SNOWFALL ARE STILL JUST MEDIUM (40-50 PERCENT) FOR THE
WASHINGTON CASCADES INCLUDING SNOQUALMIE AND WHITE PASSES WITH
LOWER PROBABILITIES OF 5-10 PERCENT FOR THE NORTHERN BLUE
MOUNTAINS.
LOOKING AHEAD, AN ARCTIC AIR MASS IS POSSIBLE (A SOLUTION
PRESENTED BY ROUGHLY 60 PERCENT OF ENSEMBLE MEMBERS) BY THE
WEEKEND INTO EARLY NEXT WEEK. WILL LOWLAND SNOW ACCOMPANY THIS
COOLER AIR MASS? CONFIDENCE IS STILL TOO LOW TO DISCUSS DETAILS,
SO STAY TUNED FOR MORE DETAILS IN THE COMING DAYS.
AVIATION...00Z TAFS
TEMPORARY SUB-VFR CIGS/VSBYS MAY OCCUR
(30-60% CONFIDENCE, HIGHEST AT ALW/PDT) THIS EVENING INTO THE
EARLY OVERNIGHT PERIOD AS A COLD FRONT BRINGS RAIN AND LOWERING
CEILINGS. LIGHT AND VARIABLE WINDS WILL BECOME GUSTY SOUTHWESTERLY
TO WESTERLY LATER THIS AFTERNOON THROUGH TONIGHT, PERSISTING INTO
OR THROUGH MONDAY (SITE-DEPENDENT) AS A 500-HPA SHORTWAVE TROUGH
MOVES OVER PACIFIC NORTHWEST. VFR CONDITIONS ARE THEN FORECAST FOR
ALL SITES BY EARLY MONDAY MORNING.
PRELIMINARY POINT TEMPS/POPS
PDT 35 47 26 45 / 90 20 0 10
ALW 37 46 31 44 / 90 40 10 10
PSC 34 51 26 42 / 70 10 0 10
YKM 29 49 26 42 / 30 0 0 10
HRI 36 50 26 43 / 80 10 0 10
ELN 29 45 24 39 / 30 0 0 10
RDM 27 46 20 48 / 60 10 0 10
LGD 33 45 24 43 / 90 50 10 10
GCD 34 45 24 47 / 60 40 0 10
DLS 38 50 32 43 / 80 10 0 30
PDT WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
DISCUSSION...86
AVIATION...86
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