772
FXUS66 KPDT 191155
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
355 AM PST FRI DEC 19 2025
DISCUSSION
KEY MESSAGES:
1. ONGOING FLOODING AND HYDRO CONCERNS.
*ACTIVE FLOOD WARNINGS AND WATCHES*
2. SIGNIFICANT MOUNTAIN SNOWFALL THROUGH SATURDAY MORNING.
*ACTIVE WINTER STORM WARNINGS AND ADVISORIES*
3. LOWLAND HOLIDAY SNOW CHANCES.
CURRENT RADAR AND INFRARED SATELLITE IMAGERY SHOWS LIGHT TO MODERATE
RETURNS EXTENDING ACROSS THE REGION FROM THE OREGON CASCADES THROUGH
THE NORTHERN BLUE MOUNTAINS AND FOOTHILLS UNDER CLOUDY SKIES. THIS
IS IN RESPONSE TO THE PASSING OF AN UPPER LEVEL TROUGH AND ATTENDANT
COLD FRONT, WHICH BROUGHT ELEVATED WINDS THURSDAY EVENING THROUGH
THE OVERNIGHT LEADING TO A WIND ADVISORY THAT WAS CANCELLED AT 3:17
AM. A WEAK ATMOSPHERIC RIVER (AR) IS SUPPLYING THE MOISTURE FOR THIS
TROUGH PASSAGE, WITH SUBSTANTIAL VAPOR TRANSPORT OF JUST UNDER 750
KG/M*S. THIS VALUE IS ABOUT 100 KG/M*S HIGHER THAN THE SUNDAY/MONDAY
EVENT, JUST OVER A MUCH SHORTER DURATION. THE ORIENTATION OF THE AR
HAS BEEN FOCUSED ACROSS THE OREGON CASCADES AS 2-4 INCHES OF
RAINFALL HAS FALLEN OVER THE PAST 24 HOURS ACROSS THE CREST, WITH
ANOTHER INCH EXPECTED ALONG THE EAST SLOPES THROUGH THE MORNING
HOURS ON FRIDAY (70-90% CONFIDENCE). EVEN LOWER ELEVATIONS ALONG THE
97 CORRIDOR HAVE PICKED UP 1-2 INCHES OF RAINFALL IN THE LAST 24
HOURS.
THESE RAIN AMOUNTS HAVE WARRANTED THE ISSUANCE OF A FLOOD WATCH
ACROSS THE EAST SLOPES OF THE OREGON CASCADES THROUGH SATURDAY
AFTERNOON, WITH A FLASH FLOOD WARNING ALONG SHITIKE CREEK THROUGH 10
AM FRIDAY DUE TO A LOG JAM, AND A RIVER FLOOD WARNING ALONG THE
WHYCHUS CREEK NEAR SISTERS UNTIL 10 AM FRIDAY. A FLOOD WATCH IS ALSO
ACTIVE ACROSS THE EAST SLOPES OF THE WASHINGTON CASCADES UNTIL
FRIDAY EVENING AS SHOWERS RETURN ON THE BACKSIDE OF THE PASSING
UPPER LEVEL TROUGH. THE AR WILL CONTINUE TO SHIFT SOUTH INTO
CALIFORNIA, SO THE UPSLOPE PRECIPITATION WILL NOT BE ADDITIONALLY
ENHANCED. EARLIER PRECIPITATION HAS KEPT RIVER LEVELS ELEVATED, WITH
THE NACHES RIVER NEAR NACHES CURRENTLY IN MINOR FLOOD STAGE AND THE
YAKIMA RIVER AT KIONA EXPECTED TO REACH MINOR FLOOD STAGE LATE THIS
MORNING. THUS, A RIVER FLOOD WARNING IS ACTIVE FOR THE NACHES RIVER
NEAR NACHES UNTIL SATURDAY AFTERNOON AND FOR THE YAKIMA RIVER AT
KIONA UNTIL SUNDAY EVENING.
THE PASSING COLD FRONT WILL CONTINUE TO FOLLOW THE DROPPING AR
SOUTH, ADVECTING COLDER AIR INTO THE REGION AND DROPPING SNOW LEVELS
TO 1500-2500 FEET THIS AFTERNOON. PRECIPITATION WILL TRANSITION TO
SNOW THIS MORNING, LEADING TO SNOW AMOUNTS OF 6 TO 12 INCHES THROUGH
SATURDAY MORNING AND PEAKING TODAY BEFORE 4 PM ACROSS THE OREGON
CASCADES. THIS HAS PROMPTED THE ISSUANCE OF A WINTER STORM WARNING
ACROSS THE OREGON CASCADES UNTIL 10 AM SATURDAY, WITH 60-80%
CONFIDENCE OF RECEIVING WARNING CRITERIA SNOWFALL (8 INCHES OR MORE)
AT PASS LEVEL. SNOWFALL OVER THE WASHINGTON CASCADES IS EXPECTED TO
INCREASE THROUGH THE DAY TODAY AND CONTINUE THROUGH SATURDAY
AFTERNOON, WITH TOTAL SNOW AMOUNTS OF 10 TO 16 INCHES LIKELY AT PASS
LEVEL. THUS, A WINTER STORM WARNING HAS BEEN ISSUED UNTIL 4 PM
SATURDAY WITH 70-90% CONFIDENCE OF WARNING CRITERIA OF 12 INCHES OF
SNOWFALL OR MORE BEING REACHED AT PASS LEVEL. THE NORTHERN BLUE
MOUNTAINS ARE ALSO EXPECTED TO PICK UP 6 TO 10 INCHES OF SNOWFALL
ABOVE 3500 FEET. PRECIPITATION HAS ALREADY TRANSITIONED INTO
SNOWFALL VIA WEBCAMS, WITH CONTINUOUS SNOWFALL ANTICIPATED
THROUGH THE MORNING HOURS.
AFTER THIS WINTER EVENT SATURDAY, ENSEMBLES SUGGEST A DROPPING UPPER
LEVEL LOW OFF THE COAST OF BRITISH COLUMBIA WILL BRING WARMER AND
WETTER CONDITIONS SUNDAY THROUGH TUESDAY, AMOUNTING TO LIGHT LOWER
ELEVATION RAINFALL AND 1-4 INCHES OF DAILY MOUNTAIN SNOW ACROSS THE
CASCADES AND BLUE MOUNTAINS. ENSEMBLES HINT AT A STRENGTHENING OF
THE LOW AS IT DROPS OFF THE PACIFIC NORTHWEST COAST INTO
THURSDAY, ADVECTING COLDER AIR INTO THE REGION. THIS MAY BE ENOUGH
TO ALLOW FOR OVERNIGHT TEMPERATURES TO ALIGN WITH MOISTURE FOR
MEASURABLE SNOW CHANCES ACROSS LOWER ELEVATIONS OF THE COLUMBIA
BASIN WEDNESDAY NIGHT INTO THURSDAY MORNING. CURRENTLY CHANCES ARE
LOW 10-25% FOR THE TRI-CITIES, PENDLETON, HERMISTON, AND WALLA
WALLA TO PICK UP MEASURABLE SNOWFALL (0.01" OR GREATER), BUT IT
IS WORTH NOTING THAT 57% OF ENSEMBLE CLUSTERS CURRENTLY ADVERTISE
A 10% BETTER CHANCE FOR MEASURABLE SNOWFALL FOR TRI-CITIES. THIS
HINTS AT FUTURE FORECASTS POTENTIALLY TRENDING IN THAT DIRECTION,
WHICH MAY LEAD TO A WHITE CHRISTMAS MORNING FOR SOME PORTIONS OF
THE COLUMBIA BASIN AND BLUE MOUNTAIN FOOTHILLS. 75
AVIATION...12Z TAFS
ALL SITES WILL BE VFR WITH THE ONGOING LIGHT
RAIN OVER KDLS, KPDT, KRDM, KBDN, AND KALW ALONG WITH GUSTY WINDS OF
20-30KTS FROM THIS SYSTEM. RAIN MIGHT CONTINUE TO LINGER THROUGH
LATER THIS MORNING FOR THESE SITES (30% PROB). THAT SAID, THIS
SYSTEM MAY LEAVE BEHIND SOME LOW CLOUDS FOR KDLS, KRDM, AND KBDN IN
ADDITION TO LIGHT RAIN/SNOW MIX AT KRDM/KBDN. VSBYS AND CIGS COULD
DROP TO MVFR CONDITIONS OR POTENTIALLY LOWER FOR THE AFOREMENTIONED
SITES LATE THIS MORNING (30-40% CONFIDENCE). GUSTY WINDS OF 20-30KTS
WILL PERSIST THROUGH MOST OF TODAY FOR MOST SITES, BUT BRIEFLY FOR
KYKM. WINDS SHOULD GRADUALLY DECREASE STARTING LATE THIS AFTERNOON,
THOUGH WITH KPSC REMAINING GUSTING AT 20-25KTS FOR THE REST OF THIS
TAF PERIOD. FEASTER/97
PRELIMINARY POINT TEMPS/POPS
PDT 45 31 49 31 / 60 10 10 10
ALW 46 35 48 33 / 70 20 20 10
PSC 49 34 50 31 / 10 10 0 10
YKM 44 26 45 27 / 20 20 30 20
HRI 47 32 50 30 / 30 10 0 10
ELN 37 23 38 24 / 30 30 50 40
RDM 43 23 45 25 / 90 10 0 10
LGD 42 25 38 26 / 100 20 10 10
GCD 45 23 40 28 / 90 10 0 20
DLS 46 34 46 33 / 60 60 50 40
PDT WATCHES/WARNINGS/ADVISORIES
OR...WINTER WEATHER ADVISORY UNTIL 10 PM PST THIS EVENING FOR ORZ502.
FLOOD WATCH THROUGH SATURDAY AFTERNOON FOR ORZ509>511.
WINTER STORM WARNING UNTIL 10 AM PST SATURDAY FOR ORZ509.
WA...WINTER WEATHER ADVISORY UNTIL 10 PM PST THIS EVENING FOR WAZ030.
FLOOD WATCH THROUGH THIS EVENING FOR WAZ522-523.
WINTER STORM WARNING UNTIL 4 PM PST SATURDAY FOR WAZ522.
DISCUSSION...75
AVIATION...97
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