738
FXUS66 KPDT 262235
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
235 PM PST FRI DEC 26 2025
DISCUSSION...TONIGHT THROUGH FRIDAY. KEY MESSAGES
- MOUNTAIN SNOW IN THE WA/OR CASCADES AND NORTHERN BLUES WITH
SNOWFALL MOST LIKELY 6-12 INCHES.
- BREEZY TO LOCALLY WINDY CONDITIONS THIS EVENING INTO THE SMALL
HOURS TOMORROW MORNING WITH PEAK GUSTS 35-45 MPH ACROSS THE
LOWER ELEVATIONS.
- DRY CONDITIONS SUNDAY TO MID WEEK WITH AN INCREASED RISK FOR
PATCHY TO AREAS OF FOG IN CLIMO-PRONED AREAS OF THE COLUMBIA
BASIN AND ADJACENT VALLEYS.
- NEXT ROUND OF UNSETTLED WINTER WEATHER POSSIBLE LATE NEXT WEEK
(30-50% CHANCE), MAINLY FOR THE WA/OR CASCADES WITH POSSIBLE
NUISANCE TO MINOR WINTER IMPACTS.
LATEST DAY CLOUD PHASE SATELLITE IMAGERY SHOWS A CLEARING ACROSS
MUCH OF NORTHERN OR AND SOUTH CENTRAL WA AHEAD OF THE LAST OF
MULTIPLE SHORTWAVE TROUGHS ENTERING THE REGION. LATEST WATER
VAPOR IMAGERY SHOWS THIS SHORTWAVE TROUGH ENTERING EASTERN WA WITH
A LIMITED MOISTURE TAP. ITS ATTENDANT COLD FRONT IS ANTICIPATED
TO MOVE INTO THE AREA LATE THIS AFTERNOON CROSSING OVERNIGHT
WHILE WEAKENING OVER TIME AS IT MOVES INTO THE NORTHERN
INTERMOUNTAIN WEST.
THE LARGE SCALE PATTERN IS CHARACTERIZED BY AN ELONGATE DEEP,
AMPLIFIED TROUGH ACROSS BC TO OFFSHORE THE WEST COAST WITH
MULTIPLE EMBEDDED SHORTWAVES TROUGHS. THE NORTHERNMOST
DISTURBANCE THAT IS ENTERING THE REGION WILL DEEPEN AND PUSH
ACROSS THE NORTHERN ROCKIES BY EARLY TOMORROW AND IS THE PRIMARY
WEATHER FOCUS REST OF TODAY-EARLY TOMORROW. DESPITE LIMITED
MOISTURE, MODERATE TO LOCALLY HEAVY SNOW IS EXPECTED ACROSS THE
WA/OR CASCADES AND OR/WA NORTHERN BLUES (ABOVE 4.5 KFT). THE
LATTER SEEING A BRIEF REPRIEVE NOW UNTIL THIS EVENING BEFORE SNOW
RESUMES. CURRENT THINKING IS AFTER THE INITIAL SYNOPTIC FORCING,
POST-FRONTAL CAA UPSLOPE SNOW WILL ALLOW SNOW TO CONTINUE INTO
EARLY TOMORROW. OF NOTE, OROGRAPHIC ENHANCEMENT ACROSS THE
NORTHERN BLUES IS PROVIDING A HIGHER RANGE IN POSSIBILITIES.
LATEST HREF (ALBEIT 10:1) AND NBM V5.0 SHOW GREATER LIKELIHOOD
FOR AMOUNTS IN EXCESS OF 10 INCHES ROUGHLY 50-80%, RESPECTIVELY.
THIS COMBINED WITH MORE ROBUST, PROTRACTED LIFT AND SATURATION IN
THE DGZ OVERNIGHT BASED ON PROXIMITY SOUNDINGS FAVOR THE BETTER
SNOW POTENTIAL/HIGH-END POSSIBILITY IN THE NORTHERN BLUES HIGHER
ELEVATIONS ABOVE 4.5 KFT. AS SUCH, THERE IS MODERATE CONCERN
FOR HIGHER SNOWFALL AMOUNTS OF 10 INCHES OR MORE THAT COULD BE
REALIZED (CONFIDENCE 50-80%). THIS SIGNAL IS NOT AS STRONG
ELSEWHERE OVER THE WA/OR CASCADES, SUCH AS SANTIAM PASS OR
SNOQUALMIE PASS. MEANTIME, THE FRONTAL PASSAGE WILL PROMOTE BREEZY
TO LOCALLY WINDY CONDITIONS ACROSS THE LOWER ELEVATIONS. CURRENT
THINKING IS PEAK GUSTS 35-45 MPH THIS EVENING POSSIBLE; GUSTS
MORE COMMONLY 25-35 MPH RANGE EVENING-OVERNIGHT. OF WHICH, THESE
HIGHER WINDS IN TANDEM WITH SNOWFALL IN THE MOUNTAINS WILL FURTHER
PROMOTE LOW VISIBILITY AND HAZARDOUS WINTER CONDITIONS.
AFTER THE UPPER TROUGH EVOLVES EASTWARD, AN AMPLIFIED UPPER-LEVEL
RIDGE WILL BUILD ACROSS THE WEST COAST THIS WEEKEND. THIS WILL
SET THE STAGE FOR DRY CONDITIONS AND A COOLING TREND IN THE LOWER
ELEVATIONS WITH HIGHS FEW TO SEVERAL DEGREES BELOW AVERAGE SUNDAY
TO MID-WEEK. IN TANDEM WITH THE COOLER AIR MASS, THIS UPPER-LEVEL
RIDGE THAT IS BUILDING WILL PUSH 500 MB HEIGHTS ACROSS THE
INTERIOR NORTHWEST APPROACHING THE 99TH PERCENTILE. THIS SYNOPTIC
PATTERN WILL LIMIT MOISTURE AND COULD RESULT IN THE DEVELOPMENT
AND MAINTENANCE OF PERSISTENT COLD POOLS IN PARTS OF THE COLUMBIA
BASIN AND VALLEYS THAT RING THE BASIN. OF WHICH, THERE WILL BE
POTENTIAL FOR FOG/LOW STRATUS EARLY-MID WEEK, ESPECIALLY THE
CLIMO-PRONE AREAS.
BEGINNING THURSDAY-FRIDAY, INCREASED CONFIDENCE IN THE RIDGE
BREAKING DOWN (CONFIDENCE 75%) WITH THE RETURN OF PRECIPITATION
CHANCES AT THE END OF THE WORK WEEK, MOUNTAIN SNOW AND LOWLAND
RAIN MOST LIKELY. OF WHICH, THERE REMAINS SUFFICIENT SPREAD AND
THERE ARE APPRECIABLE DIFFERENCES IN AMPLITUDE AND TIMING OF THE
UPPER TROUGH/ITS EVOLUTION. FRIDAY LOOKS MORE LIKELY TO BE THE
START OF UNSETTLED WEATHER THAN THURSDAY AT THE PRESENT. MOISTURE
LOOKS TO BE A LIMITING FACTOR WITH PROBS FOR IVT > 250 KG/MS FOR
THE EPS AROUND 30-50% IN TERMS OF MOISTURE PENETRATING INLAND. OF
WHICH, THE DIRECTION IS LARGELY NORMAL TO THE SOUTHERN WA
CASCADES/NORTHERN OR CASCADES, AND NOT A FAVORABLE PATHWAY FOR
INTERIOR MOUNTAINS. THIS WOULD LIMIT PRECIPITATION EAST OF THE
CASCADES. THE POTENTIAL SETUP AND SPREAD IN FORECASTS IN TANDEM
WITH THE POSSIBLE MOISTURE CONTENT/IVT PROBS PROMOTE THE CASCADES
AS THE MAIN AREA TO WATCH FOR WINTER WEATHER. OF WHICH. PROB. WSSI
SHOWS MINOR IMPACTS AT A CHANCE OF 40-50% OVER THE SOUTHERN
WA/NORTHERN-CENTRAL OR CASCADES ENDING FRIDAY AFTERNOON. THIS
SEEMS REASONABLE BASED ON ENSEMBLE GUIDANCE AT THIS TIME.
AVIATION...00Z TAFS
VFR CONDITIONS CURRENTLY AT ALL TAF SITES
WITH CONCERNS TURNING TO WINDS LATE TODAY-EARLY TOMORROW. SATELLITE
SHOWS CLEARING ACROSS MOST TERMINALS WITH NEXT SHORTWAVE TROUGH
AND ITS COLD FRONT APPROACHING THE AREA NOW. THIS FRONTAL PASSAGE
WILL PROMPT BREEZY TO LOCALLY WINDY CONDITIONS WITH WINDS
INCREASED ALREADY OUT AHEAD OF IT. GUSTS 25 KTS OR MORE HIGHLY
LIKELY KPSC, KPDT, KDLS, AND KALW THIS AFTERNOON INTO EARLY
MORNING WITH PEAK GUSTS ANTICIPATED AS HIGH AS 30-35 KTS. KYKM AND
CENTRAL OR TERMINALS EXPECTED TO SEE WINDS MORE SO 20-25 KTS.
THERE IS SOME POTENTIAL FOR PRECIP AT KPDT, KALW, AND KDLS
TERMINALS 00Z-06Z WITH LOWER CHANCES (UNDER 30%). WHILE LOW-END
VFR CEILINGS ARE POSSIBLE AT KDLS, KPDT, AND KALW, ESPECIALLY WITH
PRECIP, CONFIDENCE IS NOT SUFFICIENT TO INCLUDE IN TAFS AT THIS
TIME.
PRELIMINARY POINT TEMPS/POPS
PDT 30 38 24 37 / 70 40 0 0
ALW 31 36 25 35 / 80 50 0 0
PSC 30 39 22 34 / 40 10 0 0
YKM 25 40 21 35 / 20 0 0 0
HRI 31 41 24 36 / 60 20 0 0
ELN 23 34 18 31 / 40 0 0 0
RDM 24 38 18 39 / 20 10 0 0
LGD 28 33 21 34 / 90 70 0 0
GCD 28 34 21 37 / 80 50 0 0
DLS 35 43 30 39 / 60 20 0 0
PDT WATCHES/WARNINGS/ADVISORIES
OR...WINTER WEATHER ADVISORY UNTIL 7 AM PST SATURDAY FOR ORZ502.
WINTER WEATHER ADVISORY UNTIL 7 AM PST SATURDAY FOR ORZ509.
WA...WINTER WEATHER ADVISORY UNTIL 7 AM PST SATURDAY FOR WAZ030.
WINTER WEATHER ADVISORY UNTIL 7 AM PST SATURDAY FOR WAZ522.
SHORT TERM...80
LONG TERM....80
AVIATION...80
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