543
FXUS66 KPDT 181747
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
947 AM PST TUE FEB 18 2025
UPDATED AVIATION DISCUSSION
AVIATION...18Z TAFS
MOST SITES (KDLS/KPDT/KYKM/KALW/KPSC) WILL
BE IN MVFR OR LESS THIS MORNING WITH KRDM/KBDN IN VFR. FOG IS
CURRENTLY OVER KDLS BUT MAY LIFT AROUND THIS AFTERNOON. FREEZING
RAIN AND FOG MAY DEVELOP DURING TOMORROW MORNING FOR KPDT/KPSC,
BUT CONFIDENCE IS LOW (<20%). DUE TO THE NEXT SYSTEM'S ARRIVAL
TOMORROW, THESE SITES WILL DETERIORATE FROM MVFR TO LIFR
CONDITIONS FROM RAIN, MIST AND LOW CLOUDS THUS LOWERING THEIR CIGS
AND/OR VSBYS. WINDS WILL BE LESS THAN 10 KTS. FEASTER/97
PREV DISCUSSION
/ISSUED 304 AM PST TUE FEB 18 2025/
SHORT TERM...TODAY THROUGH THURSDAY NIGHT...THE WINTER STORM
WARNING FOR THE NORTHERN BLUE MTNS IS SET TO EXPIRE AT 4 AM THIS
MORNING. THAT TIMING IS VERY REASONABLE AS LIGHT SNOW CONTINUES,
AS SEEN ON WSR-88D, AND ANY ADDITIONAL SNOW AMOUNTS THIS MORNING
WILL BE UP TO 3 INCHES AND MAINLY NORTH OF MEACHAM. AN UPPER LEVEL
RIDGE IS MOVING INLAND WITH THE AXIS OF THE RIDGE ALONG THE
COASTLINE. ISOLATED SHOWERS ARE ALSO OBSERVED ALONG THE WA AND
NORTHERN OR CASCADES. OTHERWISE, THERE WILL BE A BRIEF REPRIEVE IN
THE PRECIPITATION FOR MOST OF THE DAY. HOWEVER, THE WINTER WOES
RETURN WITH MIXED WINTRY PRECIPITATION TONIGHT.
TONIGHT, THE RIDGE WILL CONTINUE ITS TRACK EASTWARD, AND THE
FORECAST AREA WILL BE UNDER A SOUTHWEST FLOW TONIGHT THROUGH
WEDNESDAY MORNING. SNOW LEVELS WILL INCREASE OVERNIGHT TO AROUND
4500-5000 FEET IN CENTRAL AND NORTH CENTRAL OR, 3500-4500 FEET
FROM THE SOUTHERN BLUES DOWN TO THE JOHN DAY BASIN, BUT ONLY TO
AROUND 1500-2500 FEET ELSEWHERE. ON WEDNESDAY MORNING, SNOW LEVELS
WILL INCREASE AN ADDITIONAL 500-1000 FEET ACROSS MOST OF THE
AREA. THEREFORE, MOST OF THE HEAVIEST SNOW ALONG THE CASCADES AND
THE EASTERN MOUNTAINS WILL BE ABOVE PASS LEVELS AND CLOSER TO THE
HIGHER PEAKS. THE MAIN CONCERN WITH THIS SYSTEM WILL BE THE MIXED
SNOW, RAIN, AND LIGHT FREEZING RAIN. IT'S NOT A MAJOR WARM FRONT
OVERRIDING THE COLD AIR FOR SIGNIFICANT ICE ACCUMULATIONS.
HOWEVER, CONFIDENCE IS HIGH (80%) THAT THERE WILL BE AREAS OF
LIGHT FREEZING RAIN CREATING SLICK ROAD CONDITIONS WITH UP TO 0.05"
OF ICE. THIS IS SUPPORTED BY THE HREF, BUT NOT AS MUCH WITH THE
NBM WHERE PROBABILITIES ARE LOWER AND LESS COVERAGE. OVERNIGHT
LOWS WILL GENERALLY RANGE FROM 28-33F ACROSS THE COLUMBIA BASIN
AND SURROUNDING VALLEYS. IT'S NOT A SLAM DUNK FOR PINPOINTING
EXACT AREAS, BUT I FEEL A WINTER WEATHER ADVISORY FOR MANY OF OUR
LOWLAND ZONES IS NEEDED TO GIVE HEADS UP OF ICY ROADS. SNOW
AMOUNTS ALONG THE EAST SLOPES OF THE WA CASCADES IS ON THE LOW
END OF THE ADVISORY CRITERIA AND MAINLY ABOVE PASS LEVELS. IN
GENERAL, PROB OF 6" IS 60-80%, 8" IS 30-50%, AND 10" IS <20%.
THERE WILL BE ISOLATED COLD LOCATIONS ALONG THE OR CASCADE EAST
SLOPES SUCH AS SUNRIVER AND LA PINE AS WELL AS SANTIAM PASS THAT
WILL HAVE A GOOD CHANCE (60%) OF FREEZING RAIN MIXED WITH SNOW
TONIGHT.
THE MAIN UPPER TROUGH WILL EXIT THE REGION WEDNESDAY NIGHT
FOLLOWED BY ANOTHER SHORTWAVE RIDGE ON THURSDAY. A NW FLOW ALOFT
WILL CONTINUE TO BRING MOUNTAIN SNOW TO THE CASCADES AND THE
NORTHERN BLUES THURSDAY MORNING, DECREASING IN THE AFTERNOON. A
DRY FORECAST IS IN STORE THURSDAY NIGHT, BUT THERE WILL LIKELY BE
PATCHY FOG AND FREEZING FOG. WISTER/85
LONG TERM...FRIDAY THROUGH TUESDAY...DETERMINISTIC MODELS AND
ENSEMBLE CLUSTERS ARE IN EXCELLENT AGREEMENT ON THE 500 MB PATTERN
THROUGH THE PERIOD. ON FRIDAY A FLAT RIDGE WILL BE OVER THE REGION
AS AN EMBEDDED SHORTWAVE MOVES ACROSS THE AREA. IT WILL BE MOSTLY
DRY THOUGH THERE WILL BE A 30-40% CHANCE OF A LIGHT RAIN/SNOW MIX
ALONG THE CASCADE EAST SLOPES. THIS SCENARIO WILL CONTINUE INTO
SATURDAY.
SATURDAY NIGHT WSW FLOW ALOFT INCREASES SUBSTANTIALLY AND AN
ATMOSPHERIC RIVER EVENT IS FORECAST TO BEGIN ESPECIALLY IN THE
WASHINGTON CASCADES. WITH WARMING TEMPERATURES SNOW LEVELS WILL RISE
TO ABOVE 7000 FEET AND THE P-TYPE WILL BE ALL RAIN JUST ABOUT
EVERYWHERE...WITH PERIODS OF RAIN THROUGH MONDAY. QPF AMOUNTS ARE
FORECAST TO BE HEAVIEST ALONG THE EAST SLOPES OF THE WASHINGTON
CASCADES WHERE 2-3 INCHES OF RAIN MAY FALL. THE 24 HOUR PERIOD WITH
HEAVIEST RAINFALL FOR THE WASHINGTON CASCADES APPEARS TO BE THAT
ENDING 4 PM SUNDAY...WITH PROBABILITIES OF EXCEEDING 1.50 INCHES
RANGING FROM 40-60%. THE OREGON EAST SLOPES AND NORTHEAST MOUNTAINS
WILL SEE LESS RAIN BUT STILL MODERATE TO HEAVY AMOUNTS OF .75-1.50
INCHES.
WITH RECENT HEAVY SNOW IN THE MOUNTAINS AND THE WARMING TEMPERATURES
CONSIDERABLE MELTING IS EXPECTED WITH RAIN ON SNOW. LOOKING AT THE
LATEST HYDROGRAPHS FROM AREA RIVERS, MANY ARE SHOWING SHARP RISES
OVER THE WEEKEND INTO EARLY NEXT WEEK, WITH SEVERAL NEAR ACTION
STAGE. THIS SITUATION WILL HAVE TO BE MONITORED OVER THE COMING DAYS
TO SEE IF THE RIVER RESPONSE WILL BE HIGHER IN LATER FORECASTS FROM
THE NWRFC.
IT WILL BREEZY TO WINDY ALONG THE BLUE MOUNTAIN FOOTHILLS AND GRANDE
RONDE VALLEY SATURDAY AND SUNDAY WITH THE KBKE-KMEH PRESSURE
GRADIENT INCREASING TO AROUND 6 MB. PROBABILITIES OF GUSTS
EXCEEDING 45 MPH IN THESE AREAS ARE 30-40%. TEMPERATURES IN THE
LOWER ELEVATIONS WILL BE MUCH WARMER THAN WHAT THEY HAVE BEEN
RECENTLY WITH HIGHS MAINLY IN THE 50S, AND POSSIBLY A FEW LOWER 60S
ON MONDAY. 78
PRELIMINARY POINT TEMPS/POPS
PDT 43 29 43 34 / 10 20 90 50
ALW 39 30 41 34 / 30 10 100 70
PSC 41 30 40 31 / 0 20 90 40
YKM 42 32 39 29 / 0 60 100 40
HRI 44 31 43 33 / 10 20 90 50
ELN 42 30 39 31 / 0 60 100 30
RDM 46 33 50 27 / 0 40 70 30
LGD 42 29 39 31 / 30 20 90 70
GCD 42 30 45 30 / 0 30 100 70
DLS 49 36 46 38 / 10 70 100 60
PDT WATCHES/WARNINGS/ADVISORIES
OR...WINTER WEATHER ADVISORY FROM 2 AM TO NOON PST WEDNESDAY FOR
ORZ044-507.
WINTER WEATHER ADVISORY FROM 10 PM THIS EVENING TO NOON PST
WEDNESDAY FOR ORZ508-510.
WINTER WEATHER ADVISORY FROM 10 PM THIS EVENING TO 4 AM PST
THURSDAY FOR ORZ509.
WA...WINTER WEATHER ADVISORY FROM 2 AM TO NOON PST WEDNESDAY FOR
WAZ027>029.
WINTER WEATHER ADVISORY FROM 10 PM THIS EVENING TO NOON PST
WEDNESDAY FOR WAZ521.
WINTER WEATHER ADVISORY FROM 4 AM WEDNESDAY TO 4 AM PST THURSDAY
FOR WAZ522-523.
SHORT TERM...85
LONG TERM....78
AVIATION...97
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