211
FXUS66 KPDT 191722
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
922 AM PST WED FEB 19 2025
UPDATE
A WINTER WEATHER ADVISORY HAS BEEN ISSUED ACROSS THE
KITTITAS VALLEY UNTIL NOON TODAY AS ADDITIONAL SNOWFALL OF 1 TO 2
INCHES WILL BE POSSIBLE. SNOWFALL AND THE FREEZING RAIN THREAT
WILL BE DISSIPATING ACROSS THE BASIN AND YAKIMA/KITTITAS VALLEYS
THROUGH THE MORNING AS PRECIPITATION TRANSITIONS TO RAIN WITH
TEMPERATURES WARMING INTO THE UPPER 30S TO LOW 40S THROUGH THE
AFTERNOON. WINTER WEATHER ADVISORIES WILL STILL BE ACTIVE ACROSS
THE EAST SLOPES OF THE CASCADES AND NORTHERN BLUE MOUNTAINS
THROUGH THE EARLY MORNING HOURS ON THURSDAY DUE TO CONSISTENT
SNOWFALL. 75
AVIATION...18Z TAFS
CONCERNS THROUGH THE PERIOD WILL BE
PRIMARILY AT THE START. THIS WILL BE DUE TO FREEZING RAIN AND FOG AT
TAF SITES PDT/ALW AND SNOW AT YKM AND THESE TAF SITES WILL SEE
VARYING FLIGHT CATEGORIES FROM LIFR-MVFR THROUGH AT LEAST 4Z.
CENTRAL TAF SITES BDN/RDM WILL SEE RAIN AND REMAIN VFR THROUGH THE
PERIOD WITH WINDS 10-15 KTS AND GUSTS TO 20 KTS. CONDITIONS ARE
EXPECTED TO IMPROVE GRADUALLY 04-09Z AT KYKM, KPSC, AND KDLS. THOUGH
SOME CONCERNS REMAIN (60-70% CONFIDENCE) THAT KPDT AND KALW WILL SEE
LOW CEILINGS AND FOG PERSIST OVERNIGHT. BENNESE/90
PREV DISCUSSION
/ISSUED 422 AM PST WED FEB 19 2025/
SHORT TERM...TODAY THROUGH FRIDAY...SATELLITE AND RADAR IMAGERY
TONIGHT SHOW A WARM FRONT WITH A BAND OF RAIN/SNOW LIFTING ACROSS
THE FORECAST AREA, WHILE AN UPPER TROUGH APPROACHES THE PACNW. AT
THE SURFACE, MANY AREAS ALONG THE BLUE MOUNTAIN FOOTHILLS
EXTENDING OUT TO NORTH CENTRAL OR HAVE COOLED TO OR A COUPLE
DEGREES BELOW FREEZING TONIGHT, WHILE THE REMAINDER OF THE LOWER
ELEVATIONS ARE AT OR ABOUT 2-4 DEGREES ABOVE FREEZING.
A WARM FRONT BOUNDARY WILL CONTINUE TO MOVE ACROSS THE FORECAST
AREA THIS MORNING, THEN FOLLOWED BY AN UPPER TROUGH PASSAGE THIS
AFTERNOON AND OVERNIGHT. THE WARM FRONT PASSAGE THIS MORNING
PRESENTS THE BIGGEST CHALLENGE IN THE SHORT-TERM FORECAST, AS
HIGH-RES SHORT TERM GUIDANCE MAKING UP THE HREF INDICATE THE
POTENTIAL FOR LIGHT FREEZING RAIN TO DEVELOP IN AREAS OF NORTH
CENTRAL OR, THE BLUE MOUNTAIN FOOTHILLS, AND THE COLUMBIA BASIN.
CONFIDENCE IS HIGHEST (70-80%) IN NORTH-CENTRAL OR AND THE BLUE
MOUNTAIN FOOTHILLS, WHERE CURRENT TEMPERATURES ARE NEAR TO BELOW
FREEZING DUE TO TRAPPING OF COLD AIR IN THESE AREAS. ACROSS THE
COLUMBIA BASIN, CONFIDENCE IS LOWER (40-60%) FOR MEASURABLE
FREEZING RAIN AS TEMPERATURES ARE JUST ABOVE FREEZING, AND WEAKER
WARM AIR ADVECTION ALOFT WILL BE PRESENT ACROSS OUR WA ZONES. THE
WARMER AIRMASS IS EXPECTED TO MIX TO THE SURFACE ACROSS THESE
AREAS BY THE AFTERNOON, RESULTING IN PRECIPITATION TRANSITIONING
MOSTLY TO LIGHT RAIN THEN TAPERING OFF THROUGH THE EVENING. AS FOR
THE YAKIMA/KITTITAS VALLEYS, THE EXPECTATION IS FOR LIGHT SNOW
THIS MORNING TO TRANSITION TO A RAIN/SNOW MIX THAT WILL TAPER OFF
LATE THIS EVENING. MODERATE TO LOCALLY HEAVY MOUNTAIN SNOW WILL
ALSO ACCOMPANY THE FRONTAL/TROUGH PASSAGE THROUGH LATE THURSDAY
MORNING. CONFIDENCE IS HIGH (90%) THAT SNOW AMOUNTS WILL GENERALLY
BE 5 TO 10 INCHES ACROSS THE CASCADE EAST SLOPES AND IN THE
NORTHERN BLUES, WITH HIGHER AMOUNTS ABOVE PASS LEVEL, THROUGH
THURSDAY MORNING.
THE APPROACHING WARM FRONT WILL ALSO BRING A TIGHTENING PRESSURE
GRADIENT ACROSS THE BLUE MOUNTAINS THROUGH THIS MORNING, WITH
PRESSURE GRADIENT SHIFTING TO THE COLUMBIA BASIN AND CENTRAL OR
LATE THIS AFTERNOON AND EVENING. THE INCREASED PRESSURE GRADIENTS
WILL RESULT IN BREEZY WINDS 15-25MPH WITH GUSTS TO 40MPH ALONG
THE SLOPES OF THE BLUE MOUNTAIN FOOTHILLS AND THROUGH THE SOUTHERN
GRANDE RONDE VALLEY THIS MORNING. BREEZY WEST TO SOUTHWEST WINDS
15-25MPH WITH GUSTS UP TO 35MPH WILL DEVELOP ACROSS NORTH CENTRAL
OR AND PORTIONS OF THE COLUMBIA BASIN AND BLUE MOUNTAIN FOOTHILLS.
BY THURSDAY AFTERNOON, PRECIPITATION ACROSS THE FORECAST AREA WILL
TAPER OFF AS UPPER LEVEL RIDGING BUILDS INTO THE PACNW. LOCALLY
BREEZY WINDS WILL CONTINUE IN PORTIONS OF THE COLUMBIA BASIN AND
NORTHERN BLUE MOUNTAIN FOOTHILLS IN THE AFTERNOON AS PRESSURE
GRADIENTS WEAKEN. DRY AND CALMER CONDITIONS WILL DEVELOP THURSDAY
NIGHT AND PERSIST THROUGH FRIDAY MORNING.
FRIDAY AFTERNOON AND NIGHT, THE RIDGE WILL FLATTEN AS A WEAK
FRONTAL BOUNDARY AND SHORTWAVE TROUGH SLIDE ACROSS THE PACNW.
PRECIPITATION CHANCES WILL MAINLY BE CONFINED TO THE CASCADES AND
BLUES, WITH SNOW LEVELS RISING TO AROUND 4KFT TO 5KFT BY FRIDAY
EVENING. THAT SAID, THE LACK OF EVEN A MODERATE MOISTURE PLUME
WILL RESULT IN LIGHT SNOW ACCUMULATIONS IN THE MOUNTAINS,
GENERALLY LESS 2-3 INCHES (CONFIDENCE 60-80%).
LASTLY, WARMING TEMPERATURES BEHIND TODAY'S WARM FRONT PASSAGE
WILL RESULT IN AFTERNOON TEMPERATURES WARMING TO NEAR NORMAL
VALUES BY THURSDAY (MID TO UPPER 40S LOWER ELEVATIONS...MID 30S TO
LOWER 40S ELSEWHERE). WHILE THE WARMING TREND WILL BE WELCOMED BY
SOME, CONCERNS WILL SWITCH TO INCREASED SNOW MELT ACROSS THE
MOUNTAINS AND INCREASING RIVER LEVELS AREA-WIDE INTO EARLY NEXT
WEEK. LAWHORN/82
LONG TERM...SATURDAY THROUGH WEDNESDAY...KEY MESSAGES...
- RISING RIVER LEVELS PEAKING EARLY NEXT WEEK, HOWEVER, LOW
CONFIDENCE (< 30%) IN RIVER FLOODING AND HYDRO IMPACTS.
- UNSETTLED WEATHER AND MOUNTAIN RAIN LATE SATURDAY-MONDAY.
- ABOVE AVERAGE HIGHS AND LOWS BY 10-20 DEGREES SUNDAY AND MONDAY.
A LARGELY UNSETTLED PATTERN LATE SATURDAY INTO TUESDAY BUTTRESSED BY
A EXTENSIVE PLUME OF MOISTURE DIRECTED INTO THE PACIFIC NORTHWEST.
THE LARGE SCALE PATTERN EARLY SATURDAY CAN BE CHARACTERIZED BY BROAD
SOUTHWEST FLOW ACROSS THE EASTERN NORTH PACIFIC WITH AN UPPER-LEVEL
RIDGE OVER CA INTO SOUTHWEST CANADA AND MEAN TROUGHING OVER AK AND
THE NORTHERN EASTERN NORTH PACIFIC. AN EXTENSIVE EXPORT OF MOISTURE
WITH AN APPRECIABLE FETCH IS ANTICIPATED TO BECOME SET UP WITH ITS
PRECIPITABLE WATER AND IVT AXIS EXTENDING NORTH OF HI TO THE PACNW
COAST BY SATURDAY. THROUGH MONDAY, TWO EMBEDDED DISTURBANCES WITHIN
THE UPPER-FLOW TAKE A NORTHERLY TRACK INTO EXTREME SOUTHWEST CANADA
THAT SUPPORT MOISTURE CURVING ANTICYCLONICALLY INTO THE REGION AS
MEAN UPPER-LEVEL RIDGING PREVAILS OVER THE WESTERN CONUS.
EPS MEAN IVT FORECASTS ARE IN GOOD AGREEMENT WITH ITS MAGNITUDE WITH
IVT FORECASTS EXCEEDING 90TH AND 97.5TH %TILE RELATIVE TO CLIMO FOR
THIS TIME OF YEAR SATURDAY TO SUNDAY NIGHT OVER THE INTERIOR PACNW.
FURTHER, EPS AND GEFS ARE IN GOOD AGREEMENT WITH MOISTURE DIRECTED
INTO OUR AREA SHOWN VIA IVT > 150 KG/M/S CHANCES ALONG AN INLAND
TRANSECT HAVING HIGH PROBABILITIES, EXCEEDING 80%, OVER THE SATURDAY
NIGHT INTO EARLY MONDAY. THE BEST IVT SURGE EXISTS SUNDAY WHERE ODDS
FOR 250 KG/M/S EXCEED 60% OVER A 24-HR PERIOD. WHILE THERE ARE SOME
MINOR DIFFERENCES SEEN IN CLUSTERING SCENARIOS IN THE PRECIPITABLE
WATER AXIS, THERE IS HIGH CONFIDENCE (80%) IN THE FOCUS OF THIS
MOISTURE MORE ON OR CASCADES THAN EXTENDING INTO THE OLYMPICS OR THE
WA CASCADES. MEANTIME, THE NORTHERLY TRACK OF THESE WAVES, LENDS A
WARM FLAVOR TO THIS LONG-DURATION AR EVENT (24-48-HRS) WITH SNOW
LEVELS INCREASING ABOVE 6 KFT AREA WIDE AND HIGHER SATURDAY AND
PERSISTING THROUGH SUNDAY. SNOW LEVELS START TO SEE SOME LOWER
MONDAY THOUGH RANGE FROM ~4.5 KFT IN SOUTH CENTRAL WA TO ~6 KFT IN
THE CENTRAL OR MOUNTAINS.
MOUNTAIN RAIN WITH SNOW MELT/RUNOFF IS EXPECTED TO BE THE PRIMARY
SENSIBLE WEATHER HIGHLIGHT THIS WEEKEND INTO EARLY NEXT WEEK OWING
TO THE PRECIPITATION. CURRENT RIVER FORECASTS SHOW RESPONSES SHOULD
LEAD TO RISING RIVER LEVELS AND HIGHER FLOWS PEAKING MONDAY-TUESDAY
IN EASTERN OR AND THE CASCADES. OF NOTE, CONFIDENCE IN HYDRO IMPACTS
STEMMING FROM RIVER FLOODING ARE PRESENTLY LOW (LESS THAN 30%) BASED
ON CURRENT FORECASTS. IN TERMS OF PRECIPITATION, THE CASCADES WILL
SEE THE GREATEST TOTALS, ESPECIALLY NEAR THE CREST, OWING IN PART TO
THE STRONG WESTERLY COMPONENT/NORMAL TO THE CASCADES THE MOISTURE
GAINS AS IT EVOLVES SUNDAY. ELSEWHERE, LOWER TOTALS ARE EXPECTED IN
THE NORTHERN BLUES GIVEN THE STRONG WEST COMPONENT. NBM GUIDANCE
DENOTE 24-HR CHANCES FOR 1” OR MORE SATURDAY NIGHT-SUNDAY PEAK 75%
ACROSS THE CREST OF THE CASCADES AND ITS FAR UPPER EASTERN SLOPES;
ELSEWHERE PROBS PEAK 30-50% IN THE NORTHERN BLUES. THERE IS GOOD
AGREEMENT WITH THESE CHANCES WHEN COMPARED TO RAW PROBS COMPRISED OF
THE GEFS, EPS, AND CMC. ACCOUNTING FOR A LARGER 48-HR WINDOW, 4 AM
SAT – 4 AM MON, PARTS OF THE CASCADE CRESTS HAVE CHANCES OF 30-80%
FOR 2 INCHES OR MORE. ELSEWHERE, LOWER ELEVATIONS ARE EXPECTED TO
SEE LARGER UNDER A QUARTER INCH, EXCEPT HIGHER AMOUNTS POSSIBLE
ACROSS PARTS OF THE FOOTHILLS OF THE NORTHERN BLUES AND IN CENTRAL
OR.
MEANWHILE, A WARMING TREND WILL BE UNDERWAY PEAKING SUNDAY AND
MONDAY WITH HIGHS AROUND 10 DEGREES ABOVE NORMAL IN TANDEM WITH MILD
LOWS 10-20 DEGREES ABOVE NORMAL THAT PERSIST INTO TUESDAY. ANOTHER
STRONGER UPPER TROUGH IS EXPECTED TO APPROACH LATE MONDAY/EARLY
TUESDAY THAT WILL BRING ADDITIONAL PRECIP CHANCES BUT WITH LOWER
PRECIPITATION AMOUNTS COMPARED TO EARLIER IN THE LONG TERM.
AFTERWARDS, GUIDANCE SHOWS AN UPPER RIDGE RE-BUILDING ACROSS THE
WESTERN CONUS WITH A DRIER PATTERN TAKING HOLD LATE TUESDAY-
WEDNESDAY.
PRELIMINARY POINT TEMPS/POPS
PDT 43 32 47 27 / 90 70 20 0
ALW 41 33 45 29 / 90 80 20 0
PSC 40 30 48 28 / 90 40 10 10
YKM 39 28 46 28 / 90 30 0 0
HRI 42 31 49 28 / 90 40 10 0
ELN 39 29 45 28 / 90 40 0 0
RDM 50 25 49 24 / 60 20 0 0
LGD 39 29 42 21 / 90 90 20 0
GCD 44 25 42 21 / 90 60 10 0
DLS 45 36 50 33 / 90 50 10 0
PDT WATCHES/WARNINGS/ADVISORIES
OR...WINTER WEATHER ADVISORY UNTIL NOON PST TODAY FOR ORZ044-507-508-
510.
WINTER WEATHER ADVISORY UNTIL 4 AM PST THURSDAY FOR ORZ502-509.
WA...WINTER WEATHER ADVISORY UNTIL NOON PST TODAY FOR WAZ026>029-521.
WINTER WEATHER ADVISORY UNTIL 4 AM PST THURSDAY FOR WAZ030-522-
523.
UPDATE...75
SHORT TERM...82
LONG TERM....80
AVIATION...90
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