165
FXUS66 KPDT 160617
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
1017 PM PST SAT FEB 15 2025
AVIATION...06Z TAFS
A WEATHER SYSTEM MOVING INTO THE AREA WILL
BRING DETERIORATING CONDITIONS IN THE NEXT FEW HOURS ALONG WITH A
MIX OF -SN, -FZRA AND -RA TO ALL TAF SITES FOR MUCH OF THE NEXT
24 HOURS. -FZRA IS MOST LIKELY (60-70%) AT KPSC AND KALW, POSSIBLE
(40- 50%) AT KPDT AND LESS LIKELY (20-40%) AT KYKM, KRDM AND
KBDN. -FZRA WILL BE POSSIBLE FROM 06Z-10Z AT KYKM AND FROM 08Z-18Z
AT THE OTHER TAF SITES. IN GENERAL, -SN WILL BE THE PRIMARY
PRECIP TYPE THROUGH 18Z AND THEN TEMPERATURES WILL WARM
SUFFICIENTLY TO SWITCH OVER TO RA. KPDT, KALW, KRDM AND KBDN ARE
CURRENTLY AT VFR CONDITIONS ASIDE FROM MVFR VSBY AT KALW. THOSE
TAF SITES WILL HAVE MVFR/IFR CIGS AND VSBY AFTER 10Z-14Z THROUGH
06Z. OTHER TAF SITES ALREADY HAVE HAVE MVFR/IFR CIGS/VSBY AND THIS
WILL CONTINUE THROUGH 06Z TOMORROW EVENING. WINDS WILL REMAIN
BELOW 12 KTS FOR THE NEXT 24 HOURS. PERRY/83
PREV DISCUSSION
/ISSUED 309 PM PST SAT FEB 15 2025/
SHORT TERM...THIS AFTERNOON THROUGH MONDAY NIGHT...ACTIVE WINTER
WEATHER IS FORECAST TO CONTINUE THROUGH THE FORECAST PERIOD AS A
ROBUST LOW-PRESSURE SYSTEM IMPACTS THE REGION.
THE MAIN CHALLENGE HAS BEEN FORECASTING PRECIPITATION TYPE FOR
THE LOWER ELEVATIONS TONIGHT THROUGH SUNDAY MORNING AS A WEAK WARM
FRONT LIFTS ACROSS THE PACIFIC NORTHWEST. CAMS SUGGEST MANY
SHELTERED VALLEYS WILL STAY BELOW FREEZING (OR DROP BELOW FREEZING
AGAIN TONIGHT), AND SURFACE OBSERVATIONS SHOW TEMPERATURES HAVE
BEEN NEAR OR BELOW FREEZING IN MUCH OF THE COLUMBIA BASIN AND
ADJOINING VALLEYS THIS AFTERNOON. LIGHT SNOW HAS BEEN OBSERVED IN
THE YAKIMA AND KITTITAS VALLEYS, WHERE MOSTLY SNOW IS FORECAST TO
TRANSITION TO RAIN (YAKIMA) AND A RAIN/SNOW MIX (KITTITAS) THROUGH
SUNDAY. FARTHER SOUTH, FREEZING RAIN IS MOST LIKELY IN FAR
SOUTHERN WASHINGTON AND NORTHERN OREGON IN THE LOWER COLUMBIA
BASIN, WALLA WALLA VALLEY, AND PORTIONS OF THE ADJOINING FOOTHILLS
OF THE BLUE MOUNTAINS WHERE FORECAST SOUNDINGS FROM THE HREF SHOW
A WARM NOSE ALOFT OF 1-3 DEGREES CELSIUS. UP TO ONE-TENTH OF AN
INCH OF ICE ACCUMULATION IS FORECAST FOR THE WALLA WALLA VALLEY
AND PORTIONS OF THE LOWER COLUMBIA BASIN, SO HAVE EXPANDED THE
WINTER WEATHER ADVISORY TO INCLUDE THE FOOTHILLS OF THE NORTHERN
BLUE MOUNTAINS, MAINLY TARGETING THE WALLA WALLA VALLEY.
CONFIDENCE IN AT LEAST MEASURABLE (0.01") FREEZING RAIN IS
GENERALLY 50-80%. WILL NOTE THAT LIGHT FREEZING RAIN IS FORECAST
ELSEWHERE IN SHELTERED VALLEY LOCATIONS, BUT CONFIDENCE IN
SIGNIFICANT ICE IS TOO LOW (30% OR LESS) TO ISSUE ANY ADVISORIES.
IN THE WAKE OF THE WARM FRONTAL PASSAGE, A PERSISTENT, MOIST
WESTERLY THEN NORTHWESTERLY ALOFT WILL KEEP PRECIPITATION CHANCES
"LIKELY" (75% OR GREATER) ACROSS THE MOUNTAINS INTO MONDAY NIGHT.
THE LOWER ELEVATIONS WILL SEE PERIODS OF MOSTLY RAIN SUNDAY
AFTERNOON AND MONDAY. PLUNKETT/86
LONG TERM...TUESDAY WILL SEE A TRANSITORY RIDGE OVER
THE PACIFIC NORTHWEST, BEFORE THE NEXT WEATHER SYSTEM MOVES OVER
THE REGION WEDNESDAY INTO WEDNESDAY NIGHT. THIS SYSTEM WILL
BRING ANOTHER ROUND OF MIXED PRECIPITATION TO MANY PARTS OF THE
REGION AND MAINLY SNOW IN THE MOUNTAINS. ANY PRECIPITATION
BEGINNING OVERNIGHT WILL BE SNOW OR MIXED PRECIPITATION. HOWEVER,
DURING THE DAYLIGHT HOURS, TEMPERATURES SHOULD RISE ABOVE FREEZING
IN MOST NOT MOUNTAIN AREAS. HOWEVER, THERE IS STILL SOME
UNCERTAINTY AS TO HOW WARM TEMPERATURES GET ON WEDNESDAY.
PRECIPITATION CHANCES WILL DECREASE BY THURSDAY MORNING, OUTSIDE
OF THE MOUNTAINS BUT TEMPERATURES WILL FALL TO AROUND OR JUST
BELOW FREEZING, SO ANY LINGERING PRECIPITATION WOULD BE OF THE
MIXED VARIETY ONCE AGAIN. THE ECMWF EFI DOES KEY IN ON A QPF
ANOMALY OF 0.7 TO 0.8 CENTERED ON THE GORGE AND BASIN ON
WEDNESDAY, AND AN ANOMALY FOR SNOW AROUND 0.6 TO 0.7 CENTERED MORE
ON THE WASHINGTON BASIN.
IT WILL BE BREEZY WITHE THE WEDNESDAY SYSTEM, WITH WIND GUSTS
GENERALLY UPWARDS OF 20 TO POSSIBLY 25 MPH. THE NBM PROBABILITIES
OF WIND GUSTS >=25 MPH RANGES FROM 30 TO 80% ACROSS THE REGION.
HOWEVER, THE NBM PROBABILITIES OF WIND GUSTS >=39 MPH IS <20%.
QPF VALUES LOOK TO RANGE FROM AROUND 0.10 INCHES IN CENTRAL OREGON
AND THE YAKIMA AND KITTITAS VALLEYS TO AROUND 0.25 INCHES IN MOST
OTHER LOWER ELEVATION LOCATIONS TO AROUND 0.25 TO 0.50 INCHES IN
THE MOUNTAINS. SOME MODERATE SNOW AMOUNTS OF 5 INCHES PLUS ARE
POSSIBLE ESPECIALLY ALONG THE CRESTS OF THE CASCADES AND BLUE
MOUNTAINS. BUT CONFIDENCE IN THESE AMOUNTS AT THIS TIME IS ONLY 40
TO 60%.
AFTER THURSDAY, PRECIPITATION CHANCES ARE GREATLY DECREASED WITH
BOTH THE GFS AND ECMWF DETERMINISTIC BASICALLY DRY OUTSIDE OF
POSSIBLY THE CASCADES, WHILE THE NBM HAS SOME LOW POPS IN SOME
AREAS AND SEEMS OVERDONE DUE TO THE RIDGING, AGAIN OUTSIDE OF
THE CASCADES.
HIGH TEMPERATURES ARE EXPECTED TO WARM UP AFTER WEDNESDAY AND BY
SATURDAY, HIGHS ARE FORECAST TO BE A FEW DEGREES ABOVE NORMAL.
NORMAL HIGHS BY THE END OF THE WEEK ARE GENERALLY IN THE UPPER 40S
TO AROUND 50 DEGREES.
PRELIMINARY POINT TEMPS/POPS
PDT 29 41 34 42 / 60 70 80 80
ALW 28 38 33 39 / 70 80 90 90
PSC 26 38 31 42 / 70 50 60 40
YKM 26 38 29 43 / 70 30 40 20
HRI 27 38 32 45 / 60 60 70 60
ELN 26 38 28 42 / 80 50 40 30
RDM 28 44 30 45 / 20 50 30 40
LGD 28 39 33 42 / 80 80 100 90
GCD 28 43 33 42 / 70 70 80 80
DLS 32 42 36 47 / 70 70 70 60
PDT WATCHES/WARNINGS/ADVISORIES
OR...WINTER WEATHER ADVISORY UNTIL 10 AM PST SUNDAY FOR ORZ044-507.
WINTER STORM WARNING UNTIL 4 PM PST MONDAY FOR ORZ502-509.
WA...WINTER WEATHER ADVISORY UNTIL 10 AM PST SUNDAY 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...86
LONG TERM....77
AVIATION...83
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