492
FXUS66 KPDT 131031
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
331 AM PDT FRI MAR 13 2026
KEY MESSAGES
- MODERATE TO HEAVY MOUNTAIN SNOW THROUGH THE DAY
*WINTER STORM WARNINGS ACTIVE*
- BREEZY WINDS TODAY AND SATURDAY
*WIND ADVISORY ACTIVE*
- ABOVE NORMAL TEMPERATURES EXPECTED NEXT WEEK
DISCUSSION
CURRENT RADAR AND INFRARED SATELLITE IMAGERY SHOWS MODERATE TO
HEAVY RETURNS ACROSS THE WASHINGTON CASCADES AND THE NORTHERN
BLUE MOUNTAINS AS SNOW CONTINUES TO FALL UNDER MOSTLY TO PARTLY
CLOUDY SKIES. THESE CONDITIONS ARE ASSOCIATED WITH THE PASSING
OF AN EMBEDDED UPPER LEVEL TROUGH SUPPLIED BY A WEAK ATMOSPHERIC
RIVER THAT IS TAPPING SUBTROPICAL MOISTURE. THIS HAS PROVIDED
AMPLE SNOWFALL AND PERIODS OF HEAVY SNOW ACROSS THE WASHINGTON
CASCADES, AS 12 INCHES OF SNOWFALL HAS ACCUMULATED AT WHITE PASS
AND 10 INCHES HAS FALLEN OVER SNOQUALMIE PASS IN THE LAST 24
HOURS. ADDITIONAL SNOWFALL OF 1-2 FEET IS EXPECTED TO OCCUR
THROUGH THE DAY TODAY OVER THE WASHINGTON CASCADE PASSES.
CONFIDENCE IN THESE SNOW AMOUNTS ARE HIGH AS BOTH THE NBM AND
HREF ADVERTISE AN 80-95% CHANCE OF 12 INCHES OR MORE AND A
45-65% CHANCE OF 18 INCHES OR MORE SNOWFALL THROUGH 5 AM
SATURDAY MORNING ACROSS THE WASHINGTON CASCADE PASSES. SNOTEL
SITES ACROSS THE NORTHERN BLUE MOUNTAINS HAVE PICKED UP 5-7
INCHES OF SNOWFALL OVER THE LAST 24 HOURS, WITH AN ADDITIONAL
3-5 EXPECTED THROUGH THE DAY TODAY. CONFIDENCE IN THESE AMOUNTS
ARE MORE MARGINAL AS THE NBM AND HREF SUGGEST A 50-80% CHANCE OF
4 INCHES OF SNOWFALL THROUGH THE DAY TODAY. THESE SNOW
ACCUMULATIONS, COUPLED WITH EXPECTED ADDITIONAL AMOUNTS THROUGH
TODAY, WARRANT THE CONTINUATION OF ACTIVE WINTER STORM WARNINGS
ACROSS THE WASHINGTON CASCADES UNTIL 5 PM TODAY AND UNTIL 5 AM
SATURDAY OVER THE NORTHERN BLUE MOUNTAINS.
THE WEAK ATMOSPHERIC RIVER WILL ALSO LEAD TO WIDESPREAD RAINFALL
ACROSS LOWER ELEVATIONS THROUGH THE DAY TODAY, AND DROPPING
FURTHER SOUTH AS THE DAY PROGRESSES. RAIN CHANCES WILL PEAK
TONIGHT INTO EARLY SATURDAY MORNING AS RAIN AMOUNTS OF 0.25-
0.50" ARE EXPECTED ACROSS LOWER ELEVATIONS OF THE COLUMBIA
BASIN AND BETWEEN 0.75-1.25" OVER THE NORTHERN BLUE MOUNTAIN
FOOTHILLS. LIMITED RAINFALL IS ANTICIPATED ACROSS CENTRAL
OREGON WITH BETWEEN 0.01-0.07" LIKELY. THE HREF AND NBM SUGGEST
A 30-50% CHANCE OF 0.50" OR MORE RAINFALL FOR THE TRI- CITIES
AND HERMISTON AREAS, AND A 50-90% CHANCE ACROSS THE NORTHERN
BLUE MOUNTAIN FOOTHILLS THROUGH 5 AM SATURDAY. PRECIPITATION
WILL BECOME MORE CONFINED TO MOUNTAINOUS TERRAIN AS SATURDAY
MORNING PROGRESSES, WITH DRY CONDITIONS EXPECTED FOR THE
COLUMBIA BASIN, CENTRAL OREGON, AND BLUE MOUNTAIN FOOTHILLS BY
NOON. MOUNTAIN SNOWFALL WILL ALSO DISSIPATE THROUGH SATURDAY
EVENING AS AN UPPER LEVEL RIDGE BUILDS IN FROM THE COAST AND
SURFACE HIGH PRESSURE TRAVERSES THE CANADIAN BORDER.
A STATIONARY FRONT WILL CAMP OUT ACROSS THE OREGON/WASHINGTON
BORDER TODAY, WHICH WILL ALLOW SURFACE LOW PRESSURE TO DEVELOP
OVER THE COLUMBIA BASIN, AS A SURFACE HIGH PRESSURE INFILTRATES
INTO CENTRAL OREGON. THESE TWO FEATURES WILL CREATE A PRESSURE
GRADIENT ALONG THE SOUTHERN BLUE MOUNTAINS, WHICH WILL LEAD TO
BREEZY WINDS ALONG THE OREGON CASCADE CREST, CENTRAL OREGON,
NORTH-CENTRAL OREGON, SIMCOE HIGHLANDS, AND MOST FOCUSED ACROSS
THE SOUTHERN BLUE MOUNTAIN FOOTHILLS AS GUSTS OF UP TO 50 MPH
WILL BE POSSIBLE. THUS, A WIND ADVISORY HAS BEEN ISSUED FOR THE
SOUTHERN BLUE MOUNTAINS THROUGH 5 PM TODAY. CONFIDENCE IN
ADVISORY LEVEL WINDS (45 MPH OR GREATER) BEING MET IS HIGH AS
BOTH THE HREF AND NBM HIGHLIGHT A 70-90% CHANCE OF OCCURRENCE.
ANOTHER AREA THAT MAY BE IMPACTED BY BREEZY, ADVISORY-LEVEL
WINDS IS ALONG THE HIGHWAY 97 CORRIDOR BETWEEN SHANIKO AND GRASS
VALLEY. THIS AREA WILL NEED TO BE FURTHER MONITORED AS GUSTS OF
25-35 MPH HAVE ALREADY BEEN OBSERVED THIS MORNING.
THE APPROACHING EMBEDDED UPPER LEVEL TROUGH WILL PASS OVERNIGHT
TONIGHT INTO SATURDAY MORNING, COUPLED WITH A COLD FRONT THAT
WILL PASS THROUGH THE AREA FROM NORTHWEST TO SOUTHEAST. THIS
FRONTAL SYSTEM WILL ALLOW FOR ANOTHER PRESSURE GRADIENT TO
DEVELOP ALONG THE BLUE MOUNTAINS AS A SURFACE HIGH PRESSURE
FOLLOWS IN ITS WAKE. AS A RESULT, ANOTHER BREEZY DAY IS EXPECTED
SATURDAY ACROSS THE BLUE MOUNTAIN FOOTHILLS AND VALLEYS.
CURRENTLY, THE NBM ADVERTISES A 40-70% CHANCE OF ADVISORY-LEVEL
WINDS ACROSS THE NORTHERN/SOUTHERN BLUE MOUNTAIN FOOTHILLS,
WALLOWA COUNTY, AND THE GRANDE RONDE VALLEY. AT THIS TIME
CONFIDENCE IS LACKING, BUT A WIND PRODUCT MAY BE WARRANTED IF
GUIDANCE CONTINUES TO SUGGEST A STRONGER GRADIENT ASSOCIATED
WITH THE PASSING FRONTAL BOUNDARY.
THE UPPER LEVEL RIDGE THAT BUILDS ALONG THE COAST ON SUNDAY WILL
SLOWLY MOVE OVER THE PACIFIC NORTHWEST MONDAY BEFORE SLOWLY
CONTINUING EAST THROUGH THE BEGINNING PART OF THE WEEK. A LESS
SUBSTANTIAL UPPER LEVEL LOW WILL DEVELOP OVER THE GULF OF ALASKA
AND DEEPEN THE BACKSIDE OF THE UPPER LEVEL RIDGE, PUSHING IT
INTO THE SUBTROPICS AND DEVELOPING A MODERATE ATMOSPHERIC RIVER
AS INDICATED BY THE GEFS. THE ECMWF CATEGORIZES THE ATMOSPHERIC
RIVER AS WEAK, BUT BOTH INDICATE A INTEGRATED VAPOR TRANSPORT
MAGNITUDE (IVT) OF BETWEEN 400-650 KG/M*S. THIS EVENT DOES SEEM
TO FOCUS MORE ALONG THE BRITISH COLUMBIA AND WASHINGTON COASTS,
BUT LOOKS TO SAG SOUTH AS IT WEAKENS ON TUESDAY AND LINGERS
THROUGH THURSDAY. ENSEMBLES ARE IN GOOD AGREEMENT WITH THE
OVERALL PATTERN, WITH MINOR DIFFERENCES IN THE STRENGTH OF THE
GULF OF ALASKA UPPER LOW. THIS PRIMARILY RELATES TO
PRECIPITATIONCHANCES EXTENDING INTO THE COLUMBIA BASIN TUESDAY
AND WEDNESDAY, AS WELL AS HIGH TEMPERATURES BREAKING INTO THE
LOW TO MID-70S ACROSS LOWER ELEVATIONS WEDNESDAY AND THURSDAY.
97% OF ENSEMBLES SUGGEST LOWER ELEVATION RAIN TUESDAY AND
WEDNESDAY (ALBEIT LIGHT ACCUMULATIONS OF LESS THAN 0.05"), BUT
ONLY 36% OF MEMBERS ADVERTISE HIGH TEMPERATURES BREAKING INTO
THE 70S BOTH WEDNESDAY AND THURSDAY. SNOW LEVELS WILL ALSO BE ON
THE RISE STARTING ON SUNDAY, REACHING 7000 FEET MONDAY BEFORE
CLIMBING TO ABOVE 8000 FEET ON TUESDAY. 75
AVIATION /06Z TAFS THROUGH 06Z SATURDAY/
VFR CONDITIONS CURRENTLY ACROSS ALL SITES, WITH THE EXCEPTION OF
MVFR AT KPSC/KYKM DUE TO REDUCED CEILINGS OF 2000-2500 FEET.
THESE CONDITIONS ARE EXPECTED TO PERSIST THROUGH THE MORNING
HOURS AS STATIONARY FRONT LINGERS OVER THE AREA, WHICH WILL ALSO
KEEP LIGHT RAIN OVER ALL TERMINAL THROUGH MUCH OF THE DAY. THE
ONLY EXCEPTION WILL BE ACROSS KRDM/KBDN, WHICH IS EXPECTED TO
ARRIVE TOWARD THE END OF THE PERIOD. BREEZY WINDS ARE ALSO
ANTICIPATED FOR KRDM/KBDN/KPDT WITH GUSTS OF 20-30KTS. 75
PRELIMINARY POINT TEMPS/POPS
PDT 57 36 47 28 / 80 90 60 10
ALW 53 37 48 30 / 90 100 70 20
PSC 55 36 54 29 / 80 80 30 0
YKM 53 30 49 28 / 90 70 10 0
HRI 58 38 53 29 / 70 80 40 0
ELN 44 28 43 24 / 90 70 10 0
RDM 58 36 49 24 / 10 60 30 0
LGD 56 37 47 26 / 80 100 90 30
GCD 58 39 47 26 / 20 70 80 10
DLS 58 38 53 33 / 90 90 30 0
PDT WATCHES/WARNINGS/ADVISORIES
WA...WINTER STORM WARNING UNTIL 5 PM PDT THIS AFTERNOON FOR WAZ030-
523.
WINTER STORM WARNING UNTIL 5 AM PDT SATURDAY FOR WAZ522.
OR...WINTER STORM WARNING UNTIL 5 PM PDT THIS AFTERNOON FOR ORZ502.
WIND ADVISORY UNTIL 5 PM PDT THIS AFTERNOON FOR ORZ508.
DISCUSSION...75
AVIATION...75
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