519
FXUS66 KPDT 141024
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
324 AM PDT SAT MAR 14 2026
KEY MESSAGES
- MOUNTAIN SNOWFALL CONTINUES ACROSS CASCADE AND BLUE MOUNTAINS.
*ACTIVE WINTER STORM WARNING & ADVISORY*
- HYDRO CONCERNS THROUGH SUNDAY, POTENTIALLY RETURNING MIDWEEK.
- MOUNTAIN PRECIPITATION AND WARMING TEMPERATURES THROUGH WEEK.
DISCUSSION
CURRENT RADAR AND INFRARED SATELLITE IMAGERY SHOWS MODERATE TO HEAVY
RETURNS ACROSS THE CASCADES, BLUE MOUNTAINS, AND THE COLUMBIA BASIN
UNDER CLOUDY SKIES. THIS IS IN RESPONSE TO AN INCOMING UPPER LEVEL
SHORTWAVE TROUGH, SURFACE COLD FRONT, AND WEAK TO MODERATE
ATMOSPHERIC RIVER THAT CONTINUES TO IMPACT THE AREA THROUGH MUCH OF
THE DAY. THE COLD FRONT IS POISED TO PASS THROUGH THE AREA EARLY
THIS MORNING, ADVECTING COLD AIR INTO THE REGION AND PLUMMETING
SNOW LEVELS TO AROUND 2000 FEET BY MID- MORNING. THIS WILL USHER
IN A TRANSITION FROM RAIN TO SNOW OVER THE NORTHERN BLUE
MOUNTAINS EARLY THIS MORNING AS THE ATMOSPHERIC RIVER SLOWLY
SAGS SOUTH. THERE SHOULD BE ENOUGH MOISTURE TO PROVIDE AN
ADDITIONAL 6 TO 9 INCHES OF SNOWFALL THROUGH THE AFTERNOON AS
TEMPERATURES WILL BE SLOW TO WARM IN THE WAKE OF THE DEPARTING
COLD FRONT. THUS, A WINTER WEATHER ADVISORY HAS BEEN ISSUED
ACROSS THE NORTHERN BLUE MOUNTAINS UNTIL 8 PM THIS EVENING FOR
ELEVATIONS ABOVE 4000 FEET.
LIGHT SNOWFALL IS STILL OCCURRING OVER THE WASHINGTON CASCADES,
AND IS BEGINNING TO INTENSIFY AS THE PUGET SOUND CONVERGENCE
ZONE HAS DEVELOPED AND EXTENDS OVER THE WASHINGTON CASCADE
CREST. THIS WILL KEEP LIGHT TO MODERATE SNOW OVER WASHINGTON
CASCADE PASSES THROUGH THE MORNING, WHICH HAS WARRANTED THE
EXTENSION OF THE WINTER STORM WARNING UNTIL 11 AM TODAY AS AN
ADDITIONAL 4 INCHES WILL BE POSSIBLE. CURRENTLY, THE SNOQUALMIE
PASS/I-90 CORRIDOR IS CLOSED IN BOTH DIRECTIONS DUE TO MULTIPLE
SPINOUTS AND COLLISIONS.
THE PASSING UPPER LEVEL SHORTWAVE, COUPLED WITH THE SURFACE HIGH
PRESSURE PUSHING INLAND OVER THE WASHINGTON COAST LATER THIS
MORNING, WILL ALLOW A PRESSURE GRADIENT TO DEVELOP ALONG THE
CASCADES AND BLUE MOUNTAINS TO ENHANCE WINDS ALONG THE EAST SLOPES
OF THE WASHINGTON CASCADES, BLUE MOUNTAIN FOOTHILLS, AND BLUE
MOUNTAIN VALLEYS AS GUSTS OF UP TO 40 MPH WILL BE POSSIBLE.
BOTH THE HREF AND NBM HIGHLIGHT AREAS OF THE SOUTHERN BLUE MOUNTAIN
FOOTHILLS AS EXPERIENCING THE BEST CHANCES OF GUSTS REACHING 40 MPH
WITH A 70-90% CHANCE OF OCCURRENCE. PEAK WINDS ARE EXPECTED TO
COINCIDE WITH THE PASSING OF THE COLD FRONT BETWEEN 6AM AND 9AM THIS
MORNING.
THE SUBSTANTIAL MOISTURE RELATED TO THE ATMOSPHERIC RIVER, AND THE
RAIN-ON-SNOW OCCURRING AHEAD OF THE COLD FRONT PASSAGE HAS LEAD
TO RIVER RISES ON SOME AREA RIVERS. MOST NOTABLY IS THE
UMATILLA RIVER NEAR GIBBON AND THE WALLA WALLA RIVER NEAR
TOUCHET, WHICH ARE ANTICIPATED TO CREST IN MINOR FLOOD STAGE
LATER TODAY. AS A RESULT, A RIVER FLOOD WARNING HAS BEEN ISSUED
UNTIL 11 PM TODAY FOR THE UMATILLA RIVER NEAR GIBBON AND A RIVER
FLOOD WATCH HAS BEEN ISSUED BETWEEN SATURDAY AFTERNOON THROUGH
SUNDAY AFTERNOON FOR THE WALLA WALLA RIVER NEAR TOUCHET. OTHER
RIVER REACHES ARE FORECAST TO RISE ABOVE ACTION/BANKFULL STAGE
THAT INCLUDE THE GRANDE RONDE RIVER AT TROY AND THE NACHES RIVER
NEAR NACHES LATER TODAY. MAKE SURE TO USE CAUTION IN LOW-LYING
AREAS NEAR THESE RIVERS AND FIND AN ALTERNATE ROUTE IF
ENCOUNTERING FLOODED ROADWAYS.
THE UPPER LEVEL SHORTWAVE CONTINUES EAST AND DEEPENS AS AN UPPER
LEVEL RIDGE MOVES ONSHORE AND OVER THE AREA ON MONDAY. THIS WILL
BRING DRIER CONDITIONS OVER LOWER ELEVATIONS OF THE COLUMBIA BASIN
AND CENTRAL OREGON, BUT WEAK EMBEDDED SHORTWAVES WILL KEEP LIGHT
MOUNTAIN PRECIPITATION THROUGH THE EARLY PART OF THE WEEK AS SNOW
LEVELS INCREASE FROM 1000-3000 FEET SUNDAY AFTERNOON TO AROUND 8500
FEET BY MONDAY AFTERNOON. ENSEMBLES ARE IN GOOD AGREEMENT WITH THE
DEVELOPMENT OF AN UPPER LEVEL LOW PRESSURE OFF THE GULF OF ALASKA,
WHICH ENHANCES THE BACKSIDE OF THE UPPER LEVEL RIDGE TO ALLOW A WEAK
TO MODERATE ATMOSPHERIC RIVER EVENT TO UNFOLD THROUGH MUCH OF NEXT
WEEK. BOTH THE GEFS AND ECMWF SUGGEST A WEAK ATMOSPHERIC RIVER
DEVELOPING MONDAY BEFORE ENHANCING TO A WEAK TO MODERATE EVENT
WEDNESDAY TO THURSDAY. THE INITIAL TRAJECTORY LOOKS TO FOCUS MORE
ALONG THE SOUTHERN BRITISH COLUMBIA AND NORTHERN WASHINGTON COASTS
EARLY IN THE WEEK BEFORE SAGGING SOUTH WEDNESDAY. DIFFERENCES DO
ARISE RELATED TO THE STRENGTH OF THE UPPER RIDGE AND LOW OFF THE
COAST OF ALASKA, WITH THE RESULT LEADING TO MORE WIDESPREAD AND
LOWER ELEVATION RAINFALL ASSOCIATED WITH A WEAKER UPPER LEVEL LOW
AND WARMER TEMPERATURES WITH A STRONGER UPPER LEVEL LOW. CURRENTLY,
51% OF ENSEMBLES HINT AT A WEAKER LOW AND MORE WIDESPREAD RAINFALL.
EVEN WITH THIS MARGINAL DISCREPANCY, PERIODS OF LIGHT LOWER
ELEVATION SHOWERS ARE LIKELY MIDWEEK ONWARD AS HIGH TEMPERATURES
BREAK INTO THE LOW TO MID-70S ACROSS LOWER ELEVATIONS OF THE
COLUMBIA BASIN AND CENTRAL OREGON. 75
AVIATION /06Z TAFS THROUGH 06Z SUNDAY/
VFR CONDITIONS CURRENTLY ACROSS THE MAJORITY OF SITES, WITH THE
EXCEPTION OF MVFR CONDITIONS AT KALW AND IFR CONDITIONS AT KPSC DUE
TO REDUCED CEILINGS OF 2500 FEET AND 700 FEET RESPECTIVELY.
THESE CONDITIONS ARE EXPECTED TO SLOWLY IMPROVE THROUGH THE MORNING
AS A COLD FRONT PASSES AND DEPARTS TO OUR SOUTHEAST.
CEILINGS ARE EXPECTED TO LIFT DURING THIS TIME, BUT WIDESPREAD
BREEZY WINDS OF 20-30KTS WILL OCCUR ACROSS ALL SITES THROUGH MUCH OF
THE DAY. WINDS WILL START TO SUBSIDE THIS EVENING AS HIGH PRESSURE
BEGINS TO MOVE ONSHORE. 75
PRELIMINARY POINT TEMPS/POPS
PDT 49 26 51 39 / 60 10 0 20
ALW 48 29 50 41 / 80 10 0 40
PSC 53 28 53 38 / 20 0 0 10
YKM 48 26 48 33 / 0 0 0 20
HRI 53 28 53 39 / 20 0 0 10
ELN 41 23 42 31 / 10 0 0 40
RDM 48 23 55 35 / 40 0 0 0
LGD 47 25 49 38 / 100 20 0 50
GCD 47 25 52 38 / 80 0 0 20
DLS 51 32 50 38 / 0 0 0 20
PDT WATCHES/WARNINGS/ADVISORIES
WA...WINTER WEATHER ADVISORY UNTIL 8 PM PDT THIS EVENING FOR WAZ030.
WINTER STORM WARNING UNTIL 11 AM PDT THIS MORNING FOR WAZ522.
OR...WINTER WEATHER ADVISORY UNTIL 8 PM PDT THIS EVENING FOR ORZ502.
DISCUSSION...75
AVIATION...75
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