682
FXUS66 KPDT 162237
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
237 PM PST SUN FEB 16 2025
SHORT TERM...THIS AFTERNOON THROUGH TUESDAY NIGHT
MULTIPLE
SHORTWAVES EMBEDDED WITHIN AN AMPLIFIED, MOIST QUASI-ZONAL FLOW
ARE EVIDENT OFFSHORE IN THE PACIFIC. THE PARENT CIRCULATION
CENTER/VORT MAX IS LOCATED FARTHER NORTHWEST, WEST OF VANCOUVER
ISLAND. OVERNIGHT THROUGH MONDAY MORNING, THESE SHORTWAVES WILL
RIPPLE ONSHORE OVER SOUTHERN OREGON WITH THE MAIN VORT MAX
PUNCHING ACROSS THE OREGON CASCADES MONDAY AFTERNOON. THE RESULT
WILL BE PERSISTENT MOUNTAIN SNOW THROUGH MONDAY AFTERNOON. IN THE
LOWLANDS, LIGHT SNOW OR RAIN/SNOW MIX IS FORECAST FOR THE YAKIMA
AND KITTITAS VALLEYS AND NORTHERN PORTIONS OF THE LOWER COLUMBIA
BASIN ROUGHLY FROM THE TRI-CITIES NORTH. CONFIDENCE IS HIGH
(70-90%) THAT SNOW ACCUMULATION IN THE YAKIMA AND KITTITAS
VALLEYS WILL REMAIN BELOW ADVISORY LEVELS OF 2". MOSTLY RAIN, WITH
SOME AREAS OF WINTRY MIX, IS FORECAST TO THE SOUTH AND EAST IN
CENTRAL/NORTH-CENTRAL OREGON AND THE BLUE MOUNTAIN FOOTHILLS.
SNOW CHANCES WILL GRADUALLY TAPER OFF MONDAY NIGHT THROUGH
TUESDAY MORNING AS A BRIEF SHORTWAVE RIDGE MOVES OVER THE PACIFIC
NORTHWEST. NBM PROBABILITIES INDICATE A 70-90% CHANCE OF WARNING-
LEVEL (10" OR MORE) SNOW ABOVE 5000 FEET IN THE NORTHERN BLUE
MOUNTAINS THROUGH TUESDAY MORNING, WHILE THE OREGON CASCADES HAVE
AN 80-95% CHANCE OF WARNING-LEVEL SNOW (8" OR MORE) ABOVE 4500
FEET ALONG THE CREST. SYNOPTIC SUPPORT APPEARS WEAKER FOR THE
WASHINGTON CASCADES WHERE THERE IS ONLY HAS A 50% CHANCE OF
OBTAINING ADDITIONAL ADVISORY-LEVEL AMOUNTS (6" OR GREATER).
THE MAIN CHANGE IN THE FORECAST THIS AFTERNOON WAS TO ISSUE WINTER
WEATHER ADVISORIES THROUGH 4PM MONDAY FOR THE SOUTHERN BLUE
MOUNTAINS AND OCHOCO-JOHN DAY HIGHLANDS FOR AREAS ABOVE 4000 FEET.
HIGHEST SNOW TOTALS (2-9") ARE FORECAST ABOVE 4500 FEET WITH
LIGHTER AMOUNTS BETWEEN 4000 AND 4500 FEET (SEE WINTER WEATHER
HIGHLIGHTS FOR DETAILS).
THE ARRIVAL OF A SHORTWAVE RIDGE OF HIGH PRESSURE ALOFT TUESDAY
SHOULD FACILITATE A BREAK IN PRECIPITATION BY TUESDAY AFTERNOON
FOR MOST AREAS, PERHAPS SAVE THE NORTHERN BLUE MOUNTAINS AND
CASCADE CREST WHERE THERE IS A 20-50% CHANCE OF LIGHT UPSLOPE
SNOW.
TUESDAY EVENING THROUGH TUESDAY NIGHT, A RETURN TO ACTIVE WINTER
WEATHER IS STRONGLY SUGGESTED BY ENSEMBLE GUIDANCE (AT LEAST 90%
CHANCE) AS AN UPPER-LEVEL TROUGH AND ATTENDANT SURFACE LOW AND
FRONTAL SYSTEM ARRIVE FROM THE PACIFIC. OF NOTE, SIGNIFICANT
SPREAD EXISTS IN ENSEMBLE SOLUTIONS REGARDING PATTERN DETAILS
SUCH AS THE MAGNITUDE/TRACK OF THE SURFACE LOW, REMNANT COLD AIR
TRAPPED TO THE LEE OF THE CASCADES, AND THERMAL PROFILES. AS
SUCH, CONFIDENCE IN FORECAST DETAILS INCLUDING PRECIPITATION TYPE
AS WELL AS SNOW AND ICE ACCUMULATIONS FOR THE LOWER ELEVATIONS IS
ONLY MEDIUM (50%).
TUESDAY NIGHT INTO WEDNESDAY MORNING, CALIBRATED PROBABILITIES
FROM THE NBM SUGGEST A 5-10% CHANCE OF 1" OF SNOW FOR CENTRAL AND
NORTH-CENTRAL OR, THE BLUE MOUNTAIN FOOTHILLS, AND MUCH OF THE
SOUTHERN AND EASTERN PORTIONS OF THE LOWER COLUMBIA BASIN. IN
CONTRAST, THE YAKIMA AND KITTITAS VALLEYS AND COLUMBIA RIVER GORGE
HAVE A 20-60% CHANCE OF 1" OF SNOW. THE BEST CHANCE OF REACHING
ADVISORY-LEVEL SNOW (2" OR GREATER) OR WARNING-LEVEL SNOW (4" OR
GREATER) IS FOR THE YAKIMA AND KITTITAS VALLEYS AT 20-40% AND
5-10% FOR ADVISORY AND WARNING, RESPECTIVELY. PLUNKETT/86
LONG TERM...WEDNESDAY THROUGH SUNDAY
WEDNESDAY WILL START OUT
WITH ACTIVE WEATHER AS AN AREA OF LOW PRESSURE MOVES INTO
WASHINGTON AND THE ASSOCIATED TROUGH MOVES INTO THE PACIFIC
NORTHWEST. THIS SYSTEM WILL BRING, PREDOMINANTLY SNOW TO THE
MOUNTAINS AND A MIX OF WINTRY PRECIPITATION AND RAIN TO THE LOWER
ELEVATIONS. AS IS COMMON FOR LATE FEBRUARY, TEMPERATURES AT NIGHT
WILL BE CLOSE TO FREEZING SO EITHER SNOW OR FREEZING RAIN ARE
POSSIBILITIES IN THE THE LOWER ELEVATIONS AND TEMPERATURES WILL
RISE ABOVE FREEZING DURING THE DAY SO A CHANGE TO ALL RAIN IS
EXPECTED.
LIQUID EQUIVALENT QPF AMOUNTS WILL GENERALLY BE BETWEEN 0.25 AND
0.33 INCHES IN THE LOWER ELEVATIONS AND BETWEEN 0.50 AND 0.75
INCHES IN THE MOUNTAINS, THOUGH THERE COULD BE AMOUNTS UPWARDS OF
AN INCHES ALONG THE CRESTS. SNOW AMOUNTS OF 4 TO 8 INCHES LOOK
POSSIBLE, ESPECIALLY AT THE HIGHER ELEVATIONS.
THIS SYSTEM WILL MOVE OUT THURSDAY MORNING AND MOST OF THE REGION
WILL BE DRY THROUGH FRIDAY, EXCEPT FOR SOME LINGERING
PRECIPITATION IN THE CASCADES, AS RIDGING BUILDS OVER THE
NORTHWEST.
BY SATURDAY, THE FLOW BECOMES MORE ZONAL AND THE GUIDANCE WANTS TO
BRING IN ANOTHER SYSTEM THAT COULD BRING IN ANOTHER ROUND OF
PRECIPITATION, THAT COULD IMPACT THE MOUNTAINS, BUT ALSO
POTENTIALLY THE LOWER ELEVATIONS AS WELL. THERE IS STILL SOME
UNCERTAINTY AS TO WHETHER THIS SYSTEM GOES MORE NORTH AND HOW
STRONG IT IS AND ALSO HOW STRONG THE RIDGE IS. ONE THING THAT IS
FAIRLY CERTAIN IS THAT THIS WILL BE A MUCH WARMER SYSTEM.
THERE WILL BE DIURNAL BREEZES WEDNESDAY INTO THURSDAY, WITH THE
TROUGH, WITH GUSTS IN THE 26 TO POSSIBLY 30 MPH RANGE. NBM
PROBABILITIES OF WIND GUSTS >=25 MPH ARE BETWEEN 60 AND 90 PERCENT
OVER A GOOD PORTION OF OUR AREA. HOWEVER, PROBABILITIES OF WIND
GUSTS >=39 MPH ARE FAIRLY LOW, GENERALLY NO MORE THAN 30 PERCENT.
BEGINNING THURSDAY, TEMPERATURES WILL BEGIN A STEADY WARMING
TREND. HIGHS ON THURSDAY IN THE LOWER ELEVATIONS WILL BE IN THE
40S TO NEAR 50 DEGREES. ON FRIDAY, HIGHS WILL RANGE FROM THE MID
40S TO MID 50S IN CENTRAL OREGON. MOST LOCATIONS WILL BE IN THE
50S ON SATURDAY, AND BY SUNDAY EVERYONE WILL BE WELL INTO THE 50S,
WITH BOTH CENTRAL OREGON AND THE COLUMBIA BASIN PUSHING 60
DEGREES. HIGHS WILL GO FROM ABOUT 5 TO 10 DEGREES BELOW NORMAL ON
WEDNESDAY TO CLOSE TO 10 DEGREES ABOVE NORMAL ON SUNDAY.
AVIATION...00Z TAFS
MVFR AND LOWER CONDITIONS ARE EXPECTED
THROUGH THE PERIOD. MOST SITES WILL DETERIORATE TO IFR OR LOWER
THIS EVENING AND OVERNIGHT. HOWEVER, CONFIDENCE ON ACTUAL FLIGHT
CATEGORY AT ANY GIVEN SITE IS LOWER THAN AVERAGE AS THERE HAS BEEN
A LOT OF FLUCTUATION. BUT, THE TREND FOR POOR FLYING CONDITIONS
AND SUB-MVFR CONDITIONS WILL CONTINUE AND CONFIDENCE IS HIGH FOR
THAT THROUGH THE PERIOD. TEMPERATURES AND PRECIPITATION TYPE ARE
ONCE AGAIN A CONCERN ESPECIALLY FOR PDT/ALW.
WINDS WILL GENERALLY BE LESS THAN 10 KTS AT ALL SITES EXCEPT
RDM/BDN WHICH COULD SEE WINDS IN THE 10 TO 15 KT RANGE THIS
EVENING BEFORE DECREASING OVERNIGHT.
PRELIMINARY POINT TEMPS/POPS
PDT 33 41 33 44 / 80 90 50 20
ALW 33 37 33 42 / 90 90 70 40
PSC 32 40 29 44 / 70 60 20 10
YKM 31 41 28 43 / 40 30 10 10
HRI 31 43 31 47 / 70 70 30 10
ELN 30 41 28 41 / 40 30 10 10
RDM 30 45 24 46 / 50 50 10 0
LGD 31 41 33 42 / 100 90 80 30
GCD 32 41 30 43 / 90 80 30 10
DLS 34 47 36 48 / 80 70 20 20
PDT WATCHES/WARNINGS/ADVISORIES
OR...WINTER STORM WARNING UNTIL 4 PM PST MONDAY FOR ORZ502-509.
WINTER WEATHER ADVISORY UNTIL 4 PM PST MONDAY FOR ORZ503-506.
WA...WINTER STORM WARNING UNTIL 4 PM PST MONDAY FOR WAZ030-522.
WINTER WEATHER ADVISORY UNTIL 4 AM PST MONDAY FOR WAZ523.
SHORT TERM...86
LONG TERM....77
AVIATION...77
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