049
FXUS66 KPDT 161128
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
330 AM PST SUN FEB 16 2025
UPDATED AVIATION DISCUSSION
SHORT TERM...TODAY THROUGH TUESDAY
MESSY WEATHER CURRENTLY
IMPACTING THE FORECAST AREA AS A WARM FRONT LIFTS THROUGH THE
INTERIOR NORTHWEST, FOLLOWED BY STRONG ZONAL FLOW WHICH IS EXPECTED
TO BATTER THE MOUNTAINS WITH HEAVY SNOW. LATEST RADAR IMAGERY FILLS
IN THE BASIN WITH LIGHT RETURNS, AND OBS SHOW A MIX OF SNOW AND
FREEZING RAIN OCCURRING ACROSS THE BASIN. AS WARM AIR FILLS IN
BEHIND THE FRONT, PRECIP IS EXPECTED TO TRANSITION TO ALL RAIN
ACROSS THE LOWLANDS, WHILE THE MOUNTAINS SEE PERSISTENT SNOWFALL
THROUGH MONDAY.
TOUGHEST PART OF THE FORECAST HAS BEEN NAILING DOWN QPF AND PRECIP
TYPE ACROSS THE BASIN. WARM AIR ADVECTION AHEAD OF THE WARM FRONT
APPEARS TO BE A BIT WEAKER THAN WHAT GUIDANCE INITIALLY HINTED AT.
THIS SHOULD BE OF LITTLE SURPRISE, AS EVEN HI-RES GUIDANCE TENDS TO
UNDERESTIMATE THE STRENGTH OF THE COLD POOL, HENCE WHY THE TRI-
CITIES AND HERMISTON HAVE MOSTLY REPORTED SNOW OVERNIGHT. THIS IS
EVENTUALLY EXPECTED TO CHANGE TO FREEZING RAIN AS THE WARM NOSE
BECOMES BETTER DEFINED, BUT WILL THERE BE ENOUGH QPF LEFT OVER FOR
ICING? CAMS HAVE TRENDED DOWNWARD OVERALL WITH REGARDS TO BASIN
PRECIP, HOWEVER RADAR AND OBS SHOW AMOUNTS GENERALLY RUNNING ABOVE
GUIDANCE THUS FAR. THINK THAT THE WORST OF THE ICE THREAT SHOULD
SHIFT CLOSER TO THE FOOTHILLS, ESPECIALLY AS WESTERLY WINDS INVITE
COLDER AIR INTO THE AREA, BUT STILL ANTICIPATE THE LOWER BASIN TO AT
LEAST RECEIVE INTERMITTENT REPORTS OF FREEZING RAIN THROUGH THE LATE
MORNING BEFORE TRANSITIONING TO ALL RAIN. FORECAST FOR SNOW IN THE
YAKIMA AND KITTITAS VALLEYS STILL LOOKS GOOD, ALTHOUGH AMOUNTS MAY BE
A LITTLE BIT LOWER THAN ORIGINALLY FORECASTED BASED ON LATEST
TRENDS. CENTRAL OREGON AND THE ADJACENT VALLEYS ARE EXPECTED TO
REMAIN AT OR ABOVE FREEZING WITH LIMITED ICE IMPACTS. GRANDE RONDE
VALLEY LOOKS TO WAVER RIGHT AROUND FREEZING, BUT WITH GUSTY WINDS IN
THE AREA, HELD OFF ON ANY MAJOR CHANGES TO THE FORECAST AS WINDS
SHOULD INTERFERE WITH PRECIP EFFICIENCY.
WEBCAMS SHOW SNOW PILING UP IN THE MOUNTAINS, ESPECIALLY ACROSS THE
CASCADE PASSES. SNOW IS EXPECTED TO ENCOMPASS MORE OF THE EASTERN
MOUNTAINS LATER IN THE DAY SUNDAY INTO MONDAY BEHIND THE WARM FRONT
AS STRONG ZONAL FLOW IN THE MID-LEVELS SUPPORTS ROBUST UPSLOPE SNOW.
QPF ACROSS GUIDANCE LOOKS TO BE FAIRLY PERSISTENT DESPITE OPPOSITE
TRENDS IN THE LOWER ELEVATIONS, SO ONGOING WINTER STORM WARNINGS
LOOK GOOD. TRANSITORY RIDGING THEN BUILDS IN FOR TUESDAY, WITH ONLY
LIGHT LINGERING PRECIP IN THE MOUNTAINS EXPECTED, BEFORE ANOTHER LOW
PRESSURE SYSTEM ARRIVES ON WEDNESDAY, BRINGING ANOTHER CHANCE FOR
WIDESPREAD PRECIP TO THE FORECAST AREA. EVANS/74
LONG TERM...WEDNESDAY THROUGH SUNDAY
THE EXTENDED FORECAST IS A
BIT OF A CHALLENGE DUE TO MODEL INCONSISTENCIES AND LATEST
DIFFERENCES--NOT AS NOTICEABLE IN THE 500MB HEIGHTS BUT IN THE MSLP
PATTERN. THE GFS HAS HAD THE POOREST RUN-TO-RUN CONTINUITY COMPARED
TO ITS PREVIOUS RUNS. OVERALL CONFIDENCE IN THE LONG TERM FORECAST
IS MODERATE.
WIDESPREAD PRECIPITATION IS STILL ANTICIPATED FOR WEDNESDAY. WHILE
ALL THE MODELS ARE ADVERTISING A FAIRLY STRONG SHORTWAVE TROUGH, THE
GFS AND ABOUT 47% OF THE GEFS MEMBERS ARE STRONGER WITH THE SYSTEM
AND SLOWER. THE GFS ALSO MAINTAINS A DEEP SURFACE LOW ALONG THE WA
COAST WHILE THE OTHER MODELS FILL THE SURFACE LOW DURING THE DAY.
CONFIDENCE IS HIGH THAT WEDNESDAY WILL BE A WET DAY. THERE WILL BE A
MOIST SOUTH-SOUTHWEST FLOW AHEAD OF THE SHORTWAVE IN THE MORNING
FOLLOWED BY COLD AIR ADVECTION ALOFT WITH THE TROUGH PASSAGE IN THE
AFTERNOON. SNOW LEVELS WILL BE AROUND 1500-2500 FEET IN SOUTH
CENTRAL WA, 3000-4000 FEET IN SOUTHEAST WA AND NORTHEAST OR, AND
4500-5000 FEET IN CENTRAL OR DURING THE AFTERNOON. HOWEVER, THIS
WILL CHANGE IF THE MODELS TREND SLOWER, AND WEDNESDAY COULD BE
WARMER WITH HIGHER SNOW LEVELS. THIS WILL ALSO MEAN THE THREAT OF
LIGHT FREEZING RAIN IN THE MORNING. NBM SHOWS AROUND 10% OF
FREEZING RAIN OVER THE EASTERN MOUNTAIN VALLEYS AND NORTH CENTRAL
OR, THEREFORE TOO LOW TO INCLUDE IN THE FORECAST. SNOWFALL AMOUNTS
ALONG THE CASCADES AND THE EASTERN MOUNTAINS WILL GENERALLY RANGE
FROM 2-5" WITH HIGHER AMOUNTS ALONG THE PEAKS.
MODEL DIFFERENCES CONTINUE INTO THURSDAY, BUT NOT AS PRONOUNCED.
AFTER THE TROUGH EXITS THE REGION, A SHORTWAVE RIDGE WILL FOLLOW.
PRECIPITATION WILL BE LIGHT OVER MOST OF THE MOUNTAIN ZONES. UNLIKE
THE GFS, THE ECMWF AND CANADIAN ADVERTISE A WARM FRONT OVER NORTHWEST
WA THAT WOULD BRING MODERATE SNOW NORTH OF SNOQUALMIE PASS. POPS ON
THURSDAY NIGHT DECREASE TO 10-30% (HIGHEST ALONG THE WA CASCADES) AS
THE UPPER LEVEL RIDGE STRENGTHENS.
THE UPPER RIDGE IS PROGGED TO FLATTEN ON FRIDAY, RESULTING IN A
WESTERLY FLOW THAT CONTINUES THROUGH SUNDAY. ONCE AGAIN, THERE ARE
UNCERTAINTIES IN THE FORECAST. THE GFS IS FARTHER NORTH WITH THE
POLAR JET COMPARED TO THE ECMWF AND CANADIAN, AND THESE DIFFERENCES
PLAY A ROLE IN THE SENSIBLE WEATHER. THE ECMWF ALSO ADVERTISES AN
ATMOSPHERIC RIVER NOSING INLAND ON SATURDAY UNLIKE THE GFS. EVEN
THOUGH THE DETERMINISTIC GFS APPEARS TO BE THE OUTLIER, THERE IS A
SMALL PERCENTAGE OF THE EC AND CANADIAN ENSEMBLES WITH SIMILAR
SYNOPTIC CHARACTERISTICS. AT THIS TIME, FRIDAY THROUGH THE WEEKEND
WILL BE MET WITH NEAR TO ABOVE AVERAGE SEASONAL TEMPERATURES, BREEZY
TO LOCALLY WINDY CONDITIONS, SNOW LIKELY (50-70%) OVER THE
MOUNTAINS, AND A CHANCE (20-40%) OF RAIN OR RAIN/SNOW MIX IN THE
LOWER ELEVATIONS. WISTER/85
AVIATION...12Z TAFS
LOW CLOUDS, MIXED PRECIPITATION, AND FOG WILL
MAKE FOR MULTIPLE AVIATION CONCERNS FOR THE NEXT 24 HOURS. RDM AND
BDN ARE THE ONLY SITES THAT ARE VFR THIS MORNING, BUT THE PASSAGE OF
THE UPPER LEVEL TROUGH THIS AFTERNOON WILL BRING SHOWERS TO CENTRAL
OR WITH MVFR CONDITIONS EXPECTED FROM 20Z-03Z. THE OTHER TERMINAL
AIRPORTS ARE IFR OR LIFR WITH MIXED PRECIPITATION. -FZRA MIXED
WITH SNOW HAS BEEN OBSERVED AT PDT, ALW, AND PSC. SNOW AND RAIN
MIXED HAVE BEEN OBSERVED AT DLS AND YKM. ANY IMPROVEMENT THIS
AFTERNOON WILL BE BRIEF AS MIXED PRECIPITATION WILL BE OBSERVED
AGAIN THIS EVENING. FORTUNATELY, THE FREEZING RAIN WILL BE PATCHY,
AND A PROB30 GROUP WAS ADDED TO PSC AFTER 06Z. WINDS WILL BE 10 KTS
OR LESS FOR THE NEXT 24 HOURS. WISTER/85
PRELIMINARY POINT TEMPS/POPS
PDT 40 33 43 33 / 80 80 80 50
ALW 37 33 41 33 / 90 90 90 70
PSC 37 30 42 31 / 50 60 50 30
YKM 37 29 42 28 / 30 40 20 10
HRI 38 30 45 32 / 60 70 60 30
ELN 37 28 41 29 / 50 40 30 20
RDM 44 30 45 25 / 60 60 40 10
LGD 39 32 42 33 / 100 100 90 80
GCD 43 32 41 30 / 90 90 80 30
DLS 41 35 48 35 / 80 80 70 20
PDT WATCHES/WARNINGS/ADVISORIES
OR...WINTER WEATHER ADVISORY UNTIL 10 AM PST THIS MORNING FOR ORZ044-
507.
WINTER STORM WARNING UNTIL 4 PM PST MONDAY FOR ORZ502-509.
WA...WINTER WEATHER ADVISORY UNTIL 10 AM PST THIS MORNING FOR WAZ026-
028-029.
WINTER STORM WARNING UNTIL 4 PM PST MONDAY FOR WAZ030-522.
WINTER WEATHER ADVISORY UNTIL 4 AM PST MONDAY FOR WAZ523.
SHORT TERM...74
LONG TERM....85
AVIATION...85
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