873
FXUS66 KPDT 171112 AAA
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
311 AM PST MON FEB 17 2025
UPDATED AVIATION DISCUSSION
SHORT TERM...TODAY THROUGH WEDNESDAY NIGHT
WINTER WEATHER
CONTINUES TO IMPACT THE FORECAST AREA THIS MORNING WITH SNOW,
FREEZING RAIN, AND FREEZING FOG RESULTING IN MULTIPLE WINTER STORM
WARNINGS AND WINTER WEATHER ADVISORIES. AN UPPER LEVEL TROUGH OVER
THE PACNW IS AIDED BY A STRONG UPPER LEVEL JET ALONG THE BOTTOM
OF THE TROUGH AS WELL AS SEVERAL EMBEDDED SHORTWAVES BRINGING
WIDESPREAD PRECIPITATION. THE WARM FRONT YESTERDAY WAS WEAK AND
HAS DONE LITTLE TO PROVIDE MIXING OF THE COLD AIR ACROSS THE
COLUMBIA BASIN AND SURROUNDING VALLEYS. TEMPERATURES THROUGHOUT
THE BASIN AND BLUE MTN FOOTHILLS ARE IN THE LOWER 30S, THEREFORE
PRECIPITATION IS FALLING AS RAIN OR FREEZING RAIN. A WINTER
WEATHER ADVISORY WAS ISSUED FOR THE BLUE MTN FOOTHILLS OF WA WHERE
TEMPS ARE 30-32F AND ROAD TEMPS ALSO SHOWING SUBFREEZING TEMPS.
AN ADVISORY WAS ALSO ISSUED FOR THE GRANDE RONDE VALLEY WHERE
WARMER AIR IS CHANGING SNOW TO FREEZING RAIN, AND THE COMBINATION
WILL CAUSE SLICK ROAD CONDITIONS ALONG I-84.
THE CURRENT WINTER STORM WARNINGS FOR THE EAST SLOPES OF THE WA/OR
CASCADES AND THE NORTHERN BLUE MTNS IN ADDITION TO THE WINTER
WEATHER ADVISORIES FOR THE SOUTHERN BLUES AND OCHOCO-JOHN DAY
HIGHLANDS ARE SET TO EXPIRE AT 4 PM THIS AFTERNOON. THE UPPER
LEVEL SUPPORT AND ISENTROPIC LIFT WILL BRING SIGNIFICANT SNOW
TODAY, PARTICULARLY IN THE NORTHERN BLUES NORTH OF MEACHAM. NBM
PROB OF 12" WITH THIS EVENT IS 60% FOR TOLLGATE AND BLUEWOOD AND
20% FOR 18". THE MOST LIKELY SNOW AMOUNTS FOR THE EAST SLOPES OF
THE WA/OR CASCADES WILL BE 5-8". THE WINTER HIGHLIGHTS MAY NEED TO
BE EXTENDED INTO THE EVENING HOURS IF THE OROGRAPHIC LIFT
CONTINUES TO ENHANCE SNOWFALL.
A TRANSITORY RIDGE TONIGHT THROUGH TUESDAY WILL PROVIDE A BREAK
IN PRECIPITATION WITH WIDELY SCATTERED MOUNTAIN SNOW SHOWERS AND
DRY CONDITIONS ELSEWHERE. THE RIDGE WILL BE FORCED EASTWARD
TUESDAY NIGHT FOLLOWED BY ANOTHER STRONG UPPER LEVEL TROUGH ON
WEDNESDAY. THIS SYSTEM POSES CONCERNS FOR FREEZING RAIN ACROSS THE
COLUMBIA BASIN DOWN TO NORTH CENTRAL OR AND SOME OF THE MOUNTAIN
VALLEYS. SNOW LEVELS ARE NOT EXPECTED TO INCREASE
DRAMATICALLY...AROUND 2500-4500 FEET ON AVERAGE. COLD AIR THAT
HAS YET TO SCOUR OUT IN THE COLUMBIA BASIN WILL ALSO MEAN THE
THREAT OF FREEZING RAIN. GUIDANCE SHOWS OVERNIGHT LOWS IN THE
LOWER 30S, SO THIS ALSO DOESN'T APPEAR TO BE A MAJOR FREEZING RAIN
EVENT. NBM IS SHOWING MINIMAL CHANCE FOR FREEZING RAIN. HOWEVER,
IT SEEMS NECESSARY TO SHOW AT LEAST A CHANCE IN THE TUESDAY NIGHT
FORECAST. YAKIMA AND KITTITAS VALLEYS WILL HAVE SNOW
ACCUMULATIONS WHERE SNOW LEVELS WILL BE DOWN TO THE VALLEY FLOOR,
AND THERE IS A GOOD CHANCE (50%) OF 1-2". THIS WILL NOT BE A BIG
SNOW EVENT IN THE MOUNTAINS UNDER THIS TROUGH PATTERN AND WEAK
UPPER LEVEL FLOW, BUT SOME ADVISORIES MAY BE MET. WILL FOCUS ON
TODAY'S EVENT AND DECISIONS TO ISSUE WINTER STATEMENTS WILL BE
MADE IN THE UPCOMING SHIFTS. WISTER/85
LONG TERM...THURSDAY THROUGH MONDAY
DETERMINISTIC MODELS AND
ENSEMBLE CLUSTERS ARE IN GOOD AGREEMENT ON THE 500 MB PATTERN
THROUGH MUCH OF THE PERIOD...THOUGH THE ECMWF AND GFS SHOW SOME
DIFFERENCES IN THE HANDLING OF AN UPPER TROUGH NEXT WEEKEND. ON
THURSDAY AN UPPER LEVEL TROUGH WILL MOVE SE OF THE REGION DURING THE
DAY WITH DECREASING MOUNTAIN SNOW SHOWERS...AND POPS DROPPING BELOW
15% THURSDAY NIGHT. ON FRIDAY A SHORTWAVE WILL MOVE INTO A TRANSIENT
UPPER RIDGE OVER WA/ORE BUT WEAKEN AS IT DOES SO. THIS WILL CONFINE
PRECIPITATION CHANCES (30-40%) TO MAINLY THE WASHINGTON CASCADE
CREST AS A WEAK COLD FRONT DISSIPATES OVER THE AREA.
ON SATURDAY 500 MB HEIGHTS WILL RISE WITH FAST WSW FLOW ALOFT
DEVELOPING OVER THE REGION. INCREASING MOISTURE IN THIS FLOW WILL
LEAD TO THE DEVELOPMENT OF MAINLY RAIN SATURDAY EVENING AND
SATURDAY NIGHT. SNOW LEVELS ARE FORECAST TO RISE TO 7000 FEET.
LATEST ECMWF ENSEMBLE IS DEPICTING AN ATMOSPHERIC RIVER FOR SUNDAY
OVER THE CASCADES. ENSEMBLE CLUSTERS SHOW GOOD AGREEMENT ON
FORECASTING 1-2 INCHES OF RAIN FOR THE CASCADE EAST SLOPES
ESPECIALLY IN WASHINGTON. THIS MATCHES WELL WITH THE CURRENT WPC
QPF FORECAST. THE LATEST RFC FORECASTS DO NOT SHOW SHARP RISES ON
THE AREA RIVERS BUT THIS COULD CHANGE IN THE COMING DAYS AS
TEMPERATURES NEXT WEEKEND IN THE MOUNTAINS WARM INTO THE 40S
DURING THE DAY AND STAY NEAR OR ABOVE FREEZING AT NIGHT. THIS WILL
RESULT IN AMPLE MELTING OF THE SNOW PACK IN ADDITION TO RAIN
FALLING ON SNOW.
WINDS WILL NOT BE A SIGNIFICANT CONCERN THROUGH THE PERIOD EXCEPT
FOR SUNDAY ALONG THE BLUE MOUNTAIN FOOTHILLS AND GRANDE RONDE
VALLEY. THE KBKE TO KMEH PRESSURE GRADIENT IS FORECAST TO INCREASE
TO 5-6 MB WHICH WILL RESULT IN BREEZY TO WINDY CONDITIONS. NBM
PROBABILITIES OF WIND GUSTS EXCEEDING 45 MPH IN THESE AREAS ARE 30-
50%
TEMPERATURES WILL BE WARMING SUBSTANTIALLY IN THE LOWER ELEVATIONS
THROUGH THE PERIOD WITH HIGH TEMPERATURES IN THE 50S SATURDAY AND
SUNDAY...AND A 40-50% CHANCE OF REACHING 60 DEGREES OR HIGHER IN THE
LOWER BASINS ON MONDAY. 78
AVIATION...12Z TAFS
WIDESPREAD MVFR/IFR CONDITIONS ARE EXPECTED
THROUGH THE PERIOD. -FZRA AT KALW AND KPSC WILL END AROUND 16Z AS
TEMPERATURES RISE ABOVE FREEZING. OTHERWISE PRECIPITATION WILL
GENERALLY BE ON THE DOWNWARD TREND EXCEPT FOR THE MOUNTAINS THIS
AFTERNOON AND EVENING. WINDS WILL BE LIGHT EXCEPT OCCASIONAL WINDS
10-15 KT AT KBDN. 78
PRELIMINARY POINT TEMPS/POPS
PDT 40 32 43 32 / 70 40 20 40
ALW 37 33 40 31 / 90 70 40 20
PSC 39 28 42 31 / 60 20 10 40
YKM 41 28 41 32 / 40 10 10 70
HRI 42 31 44 32 / 50 20 10 40
ELN 40 29 41 31 / 40 10 10 70
RDM 45 24 46 31 / 40 10 0 40
LGD 41 33 42 30 / 90 70 20 30
GCD 41 30 43 31 / 80 50 10 50
DLS 47 35 48 36 / 60 30 10 70
PDT WATCHES/WARNINGS/ADVISORIES
OR...WINTER WEATHER ADVISORY UNTIL 10 AM PST THIS MORNING FOR ORZ049.
WINTER STORM WARNING UNTIL 4 PM PST THIS AFTERNOON FOR ORZ502-
509.
WINTER WEATHER ADVISORY UNTIL 4 PM PST THIS AFTERNOON FOR ORZ503-
506.
WA...WINTER WEATHER ADVISORY UNTIL 10 AM PST THIS MORNING FOR WAZ029.
WINTER STORM WARNING UNTIL 4 PM PST THIS AFTERNOON FOR WAZ030-
522.
WINTER WEATHER ADVISORY UNTIL 4 PM PST THIS AFTERNOON FOR WAZ523.
SHORT TERM...85
LONG TERM....76
AVIATION...78
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