061
FXUS66 KPDT 131121
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
421 AM PDT MON APR 13 2026
KEY MESSAGES
- AN UPPER LOW WILL BRING WIDESPREAD LOWER ELEVATION RAIN AND
MOUNTAIN SNOW CHANCES ACROSS THE REGION LATE TUESDAY THROUGH
WEDNESDAY
- TEMPERATURES WILL DROP TO 5 TO 10 DEGREES BELOW NORMAL
WEDNESDAY AND THURSDAY, WITH OVERNIGHT LOWS IN THE MID 20S TO
MID 30S
- DRIER CONDITIONS RETURN LATE IN THE WORK WEEK, BUT LIGHT
PRECIP CHANCES DEVELOP ACROSS THE AREA OVER THE WEEKEND
DISCUSSION
TODAY THROUGH TUESDAY MORNING: RADAR AND
SATELLITE IMAGERY TONIGHT SHOW AN UPPER LOW CENTERED OVER
CENTRAL ID WITH AN ASSOCIATED DEFORMATION BAND OVER NORTHEAST OR
AND SOUTHEAST WA. THE UPPER LOW AND IT'S ASSOCIATED DEFORMATION
BAND WILL CONTINUE TO SHIFT EAST TODAY IN RESPONSE TO A
SHORTWAVE DIVING ACROSS THE PACNW. THIS WILL RESULT IN LOW
ELEVATION PRECIPITATION TAPERING OFF BY THIS AFTERNOON, WITH
ONLY MOUNTAIN SHOWERS CONTINUING THROUGH THE EVENING. COLD AIR
ADVECTION WITH THE SHORTWAVE PASSAGE WILL ALSO RESULT IN A
TIGHTENING OF THE CROSS-CASCADE PRESSURE GRADIENT, RESULTING IN
BREEZY WINDS 15-25MPH AND GUSTS UP TO 40MPH DEVELOPING THROUGH
THE CASCADE GAPS AND PORTIONS OF THE COLUMBIA BASIN AND BLUE
MOUNTAIN FOOTHILLS. STRONGEST WINDS ARE EXPECTED TO DEVELOP
THROUGH THE KITTITAS VALLEY, WITH A 50-65% CHANCE OF GUSTS
EXCEEDING 45MPH LATE THIS MORNING THROUGH THE AFTERNOON.
LATER THIS EVENING, THE SHORTWAVE WILL EXIT TO THE SOUTHEAST OF
THE FORECAST AREA, RESULTING IN SHOWER CHANCES RETREATING TO THE
CASCADE CREST UNDER A WESTERLY FLOW ALOFT. WINDS WILL LIGHTEN AS
THE CROSS-CASCADE PRESSURE GRADIENT ALSO WEAKENS WITH THE DEPARTURE
OF THE SHORTWAVE, THOUGH BREEZY CONDITIONS ARE EXPECTED TO
REMAIN THROUGH THE CASCADE GAP AREAS. LIGHT CASCADE CREST
SHOWERS WITH LOCALLY BREEZY CONDITIONS WILL CONTINUE INTO
TUESDAY.
TUESDAY AFTERNOON THROUGH THURSDAY: A STRONG UPPER LOW WITH A
LEADING COLD FRONT DROPPING OUT OF THE GULF OF ALASKA WILL MOVE
ACROSS THE PACNW, BRINGING WITH IT WIDESPREAD RAIN AND MOUNTAIN
SNOW CHANCES (CONFIDENCE 80-85%). THE BEST PRECIPITATION CHANCES
IN THE LOWER ELEVATIONS WILL BE ASSOCIATED WITH THE COLD FRONT
PASSAGE TUESDAY NIGHT THROUGH WEDNESDAY AFTERNOON, WITH CHANCES
TAPERING OFF LATE WEDNESDAY THROUGH THURSDAY. THE UPPER LOW AND
COLD FRONT WILL BRING A MUCH COLDER AIRMASS TO THE REGION,
RESULTING IN SNOW LEVELS STEADILY DROPPING TO BETWEEN 1.5KFT TO
2KFT BY WEDNESDAY EVENING, LIMITING LIGHT SNOW IMPACTS TO
CENTRAL OR BY WEDNESDAY EVENING. OTHERWISE, MODERATE TO LOCALLY
HEAVY SNOW SHOWERS WILL DEVELOP ACROSS THE CASCADE CREST AND
THE NORTHERN BLUES TUESDAY NIGHT THROUGH THURSDAY. OVER A 48-HR
PERIOD ENDING THURSDAY AFTERNOON, SNOQUALMIE PASS, WHITE PASS,
AND THE NORTHERN BLUES ABOVE 4.5KFT WILL SEE A 65-80% CHANCE OF
SNOW ACCUMULATIONS OVER 6 INCHES. FURTHER SOUTH, SANTIAM PASS IS
EXPECTED TO SEE THE HEAVIEST SNOW ACCUMULATIONS, WITH >90%
CHANCE OF ACCUMULATIONS EXCEEDING 10 INCHES THROUGH THURSDAY.
FOR NOW, A WINTER STORM WATCH WAS ISSUED FOR THE OR CASCADE EAST
SLOPES ABOVE 4KFT.
BREEZY WINDS WILL CONTINUE TO IMPACT THE REGION THROUGH THE
MIDWEEK AS THE COLD FRONT PASSAGE AND CONTINUED COLD AIR
ADVECTION INTO THE FORECAST AREA RESULT IN TIGHTENED PRESSURE
GRADIENTS. CONFIDENCE IS MODERATE-HIGH THAT WESTERLY WINDS WILL
REMAIN BETWEEN 15-25MPH AND GUSTS 25-40MPH THROUGH THE MIDWEEK.
OTHERWISE, TEMPERATURES WILL DROP TO BETWEEN 5 TO 10 DEGREES
BELOW NORMAL BY WEDNESDAY AND THURSDAY. THIS WILL RESULT IN
MORNING LOWS IN THE MID 20S TO MID 30S ACROSS THE LOWER TO MID
ELEVATION AREAS IN THE FORECAST AREA. OF PARTICULAR CONCERN ARE
THE KITTITAS AND YAKIMA VALLEYS, WHERE THERE IS 65-85% CHANCE OF
MORNING LOWS BELOW FREEZING THURSDAY MORNING.
FRIDAY THROUGH THE WEEKEND: ENSEMBLE GUIDANCE IS IN GOOD
AGREEMENT OF UPPER LEVEL RIDGING SLIDING ACROSS THE PACNW WITH
DRY CONDITIONS AND LIGHT WINDS BY FRIDAY (CONFIDENCE 55-65%).
THE FORECAST AREA WILL REMAIN UNDER THE INFLUENCE OF THE RIDGE
THROUGH SATURDAY AFTERNOON, BUT DISAGREEMENT GROWS IN TIMING AND
STRENGTH OF THE NEXT LOW PRESSURE SYSTEM ARRIVING TO THE PACNW.
WHILE MOST SOLUTIONS FAVOR LIGHT RAIN AND HIGH MOUNTAIN SNOW
RETURNING THE REGION SATURDAY NIGHT THROUGH SUNDAY, SOME
SOLUTIONS (~29% OF ENSEMBLE CLUSTER MEMBERS) FAVOR MORE MODERATE
SNOW/PRECIP ACCUMULATIONS THROUGH SUNDAY AFTERNOON. LAWHORN/82
AVIATION /12Z TAFS THROUGH 12Z TUESDAY/
VFR CONDITIONS TO
PREVAIL THROUGH THE PERIOD. LIGHT RAIN IMPACTS WILL CONTINUE AT
SITE ALW THROUGH 14Z. SITES IMPACTED BY LOW TO MID-LEVEL CIGS
WILL SEE IMPROVEMENT THROUGH THE MORNING, WITH CIGS STAYING 5KFT
OR HIGHER THROUGH THE REMAINDER OF THE PERIOD. WINDS OF 15-25KTS
WITH GUSTS 25-35KTS WILL IMPACT SITES DLS/PDT THROUGH THIS
AFTERNOON, BECOMING 12-20KTS WITH GUSTS AROUND 25KTS THE
REMAINDER OF THE PERIOD AT THOSE SITES. OTHERWISE, ALL OTHER
SITES WILL SEE WINDS 12-20KTS WITH GUSTS TO AROUND 25KTS THROUGH
EARLY THIS EVENING. WINDS WILL REMAIN BETWEEN 12-15KTS AT SITES
ALW/PSC INTO THE NIGHTTIME HOURS. LAWHORN/82
PRELIMINARY POINT TEMPS/POPS
PDT 58 36 59 42 / 40 0 10 60
ALW 59 41 58 44 / 70 10 10 80
PSC 67 41 61 45 / 10 0 10 40
YKM 64 36 58 38 / 0 0 10 60
HRI 63 39 61 43 / 20 0 0 30
ELN 55 36 52 32 / 0 0 20 60
RDM 54 27 57 35 / 10 0 0 40
LGD 53 33 58 40 / 90 20 10 90
GCD 52 31 58 38 / 80 10 0 70
DLS 60 41 58 42 / 10 0 20 80
PDT WATCHES/WARNINGS/ADVISORIES
WA...NONE.
OR...WINTER STORM WATCH FROM TUESDAY AFTERNOON THROUGH LATE
WEDNESDAY NIGHT FOR ORZ509.
DISCUSSION...82
AVIATION...82
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