587
FXUS66 KPDT 200005
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
405 PM PST TUE NOV 19 2024
SHORT TERM...TODAY THROUGH THURSDAY
KEY MESSAGES:
1. SUBSTANTIAL MOUNTAIN SNOWFALL THROUGH PERIOD.
*BLIZZARD WARNING IN EFFECT*
*WINTER STORM WARNING IN EFFECT*
*WINTER ADVISORIES IN EFFECT*
2. WINDY CONDITIONS THIS EVENING THROUGH WEDNESDAY MORNING.
*HIGH WIND WARNINGS IN EFFECT*
*WIND ADVISORY IN EFFECT*
3. WIDESPREAD RAINFALL TONIGHT THROUGH PERIOD.
CURRENT RADAR AND VISIBLE SATELLITE IMAGERY SHOWING LIGHT RETURNS
DEVELOPING ALONG THE CASCADE CREST AND EAST SLOPES UNDER MOSTLY
CLOUDY SKIES. THESE CONDITIONS ARE IN RESPONSE TO THE STRONG,
INTENSIFYING UPPER LEVEL LOW PRESSURE SYSTEM THAT IS STALLING OFF
THE WASHINGTON COAST THROUGH THE WEEK. AS THE SYSTEM CONTINUES TO
APPROACH THE COAST THIS EVENING, MOUNTAIN SNOW AND LOWER
ELEVATION RAIN CHANCES (50-90%) MATERIALIZE WEST TO EAST THIS
EVENING AHEAD OF WIDESPREAD CHANCES BY MIDNIGHT TONIGHT. SOUTHWEST
FLOW ALOFT WILL PROMOTE INCREASING SNOW LEVELS FROM 3000-4000
FEET OVERNIGHT TONIGHT TO 4000-5000 FEET WEDNESDAY AND 5000-7000
FEET ON THURSDAY. SIGNIFICANT MOUNTAIN SNOWFALL IS EXPECTED WITH
THIS SYSTEM, WHICH HAS WARRANTED THE ISSUANCE OF A WINTER STORM
WARNING OVER THE WASHINGTON CASCADES, AND WINTER WEATHER
ADVISORIES ACROSS THE OREGON CASCADES ABOVE 3500 FEET, NORTHERN
BLUE MOUNTAINS ABOVE 4000 FEET, AND THE KITTITAS VALLEY THROUGH 10
AM WEDNESDAY. THE WASHINGTON CASCADES ARE EXPECTED TO RECEIVE THE
MOST SNOWFALL AS 15-20 INCHES WILL BE POSSIBLE, WITH 6-8 INCHES
ANTICIPATED TO FALL OVER THE OREGON CASCADES AND THE NORTHERN BLUE
MOUNTAINS, AND 2-4 INCHES LIKELY OVER THE KITTITAS VALLEY.
CONFIDENCE IN THESE SNOW AMOUNTS IS HIGH (80-90%) AS THE NBM
SUGGESTS A 70-90% CHANCE OF 12 INCHES OR MORE OF SNOW ALONG THE
WASHINGTON CASCADES, A 50-75% CHANCE OF 7 INCHES OR MORE OF
SNOWFALL OVER SANTIAM PASS AND HIGHER ELEVATIONS OF THE NORTHERN
BLUE MOUNTAINS, AND A 35-65% CHANCE OF 3 INCHES OR MORE OF SNOW
ACROSS THE KITTITAS VALLEY. WINDY CONDITIONS WILL ALSO BE ARRIVING
THROUGH REMAINDER OF THE DAY TODAY AND EXTEND INTO WEDNESDAY
MORNING AND EARLY AFTERNOON. THESE ELEVATED WINDS WILL LEAD TO
TRAVEL CONCERNS WHERE SNOW IS PRESENT, ESPECIALLY ALONG THE
WASHINGTON CASCADES AND PASSES. WIND GUSTS OF UP TO 60 MPH WILL BE
POSSIBLE, WHICH COUPLED WITH ACTIVE SNOWFALL OR SNOW PRESENT ON
THE GROUND SURFACE, WILL LEAD TO REDUCED VISIBILITIES OF A QUARTER
OF A MILE OR LOWER. THUS, A BLIZZARD WARNING HAS BEEN ISSUED OVER
THE UPPER SLOPES OF THE WASHINGTON CASCADES ABOVE 2000 FEET
THROUGH 10 AM WEDNESDAY. CONFIDENCE IN THESE WINDS IS MODERATE
(50-60%) AS THE NBM SHOWCASES A 40-60% CHANCE OF WIND GUSTS OF 50
MPH OR GREATER OVER SNOQUALMIE PASS.
AS STATED EARLIER, THE APPROACHING UPPER LEVEL SYSTEM WILL ALLOW
PRESSURE GRADIENTS TO DEVELOP ALONG THE CASCADES AND BLUE
MOUNTAINS THAT WILL LEAD TO WIDESPREAD WINDY CONDITIONS ACROSS THE
AREA. WINDS ARE EXPECTED TO BE THE HIGHEST OVER CENTRAL OREGON,
NORTH-CENTRAL OREGON, AND THE BLUE MOUNTAIN FOOTHILLS AS
SUSTAINED SOUTH TO SOUTHEAST WINDS OF 30-40 MPH AND GUSTS OF UP TO
60 MPH. THUS, A HIGH WIND WARNING HAS BEEN ISSUED AND IS ACTIVE
UNTIL 10 AM WEDNESDAY. SLIGHTLY LOWER WINDS ARE ANTICIPATED OVER
THE LOWER COLUMBIA BASIN OF OREGON, JOHN DAY BASIN, AND THE GRANDE
RONDE VALLEY WITH SUSTAINED SOUTHEAST WINDS OF 25-35 MPH AND
GUSTS OF UP TO 50 MPH. THIS HAS ALSO WARRANTED THE ISSUANCE OF A
WIND ADVISORY THROUGH 10 AM WEDNESDAY. HIGH CONFIDENCE RESIDES
WITH THESE WIND VALUES, AS THE RAP, GFS, NAM, AND SREF ALL
INDICATE A CROSS-BASIN (KPDX-KGEG) GRADIENT OF 15-18 MB, WHICH IS
WELL ABOVE THE ADVISORY THRESHOLD OF 10 MB. FURTHER CONFIDENCE IS
GLEAMED FROM THE NBM, WHICH HIGHLIGHTS A 70-90% CHANCE OF GUSTS
REACHING 50 MPH OR MORE OVER THE WARNED AREA (CENTRAL OREGON,
NORTH-CENTRAL OREGON, AND THE BLUE MOUNTAIN FOOTHILLS) AND A
85-95% CHANCE OF GUSTS OF 45 MPH OR MORE OVER THE ADVISORY AREA
(LOWER COLUMBIA BASIN OF OREGON, JOHN DAY BASIN, AND THE GRANDE
RONDE VALLEY).
AS MENTIONED PREVIOUSLY, RAIN CHANCES WILL BE INCREASING WEST TO
EAST THIS EVENING AS RAIN BECOMES WIDESPREAD ACROSS THE AREA AFTER
10 PM TONIGHT. RAIN CHANCES WILL EXTEND THROUGH THE DAY ON
WEDNESDAY (30-60%) AND THURSDAY (40-80%). 0.25-0.50" OF RAINFALL
IS EXPECTED TO FALL TONIGHT ALONG THE BLUE MOUNTAIN FOOTHILLS AND
THE EAST SLOPES OF THE CASCADES, 0.10-0.25" OVER THE JOHN DAY
BASIN AND LOWER ELEVATIONS OF THE BASIN, AND 0.01-0.10" OVER
CENTRAL OREGON AND THROUGH THE EASTERN GORGE. WEDNESDAY'S RAIN
AMOUNTS ARE MUCH LESS, ONLY AMOUNTING TO 0.25-0.50" OVER THE
CASCADES AND NORTHERN BLUE MOUNTAINS, AND 0.01-0.15" OVER LOWER
ELEVATIONS OF THE BASIN, EASTERN GORGE, CENTRAL OREGON, AND THE
YAKIMA/KITTITAS VALLEYS. THERE LOOKS TO BE AN EMBEDDED SHORTWAVE
OCCURRING ON THURSDAY COUPLED WITH THE BEGINNING OF AN
ATMOSPHERIC RIVER, WHICH WILL HELP TO ELEVATE RAIN AMOUNTS AND
SNOW LEVELS. RAIN AMOUNTS ON THURSDAY WILL REACH 0.30-0.60" ACROSS
THE BASIN, CENTRAL OREGON, AND THE FOOTHILLS WITH 0.75-1.5" AT
ELEVATION OVER THE CASCADES AND NORTHERN BLUE MOUNTAINS. 75
LONG TERM...FRIDAY THROUGH TUESDAY
MOISTURE TRANSPORTATION FROM
A WEAKENING ATMOSPHERIC RIVER WILL CONTINUE OVER THE WEEKEND INTO
EARLY NEXT WEEK, BUT MODEL UNCERTAINTY WILL RISE AS THE DEEP LOW
THAT IS BRINGING THE SIGNIFICANT WEATHER TO THE REGION DURING THE
EARLY TO MID PORTION OF THIS WEEK WILL BEGIN TO DECAY AND EJECT
INTO MULTIPLE SMALLER SYSTEMS.
AS THE DEEP OFFSHORE LOW BEGINS TO FINALLY WEAKEN OVER THE
WEEKEND, WE SHOULD SEE MOISTURE CONTINUE TO FLOW AND BRING
WIDESPREAD RAIN AND HIGH ELEVATION SNOW THROUGH SATURDAY. AFTER
THIS, THE LOW WILL BEGIN SPLITTING OFF INTO MULTIPLE SEPARATE
SMALLER SYSTEMS, AND ENSEMBLES ARE HAVING DIFFICULTY
DISTINGUISHING THESE FEATURES AND DETERMINING WHERE WE MIGHT SEE
PERIODS OF FURTHER PRECIPITATION AND WHERE SOME DRYING AND CALMER
CONDITIONS MAY OCCUR. ENSEMBLES GENERALLY GET THE BROAD PATTERN
AGREED UPON WITH BROAD TROUGHING OVER THE WEST COAST, BUT INTO
EARLY NEXT WEEK EVEN THE CLUSTER ANALYSIS OF THE ENSEMBLES
INDICATES GROWING DIFFERENCES IN THE EVOLUTION OF THE REMNANTS OF
THIS SYSTEM.
THIS UNCERTAINTY IS HEAVILY REFLECTED IN THE NBM, WITH THE MODEL
DATA INDICATING A BROAD SWATH OF SLIGHT CHANCE TO CHANCE OF
PRECIPITATION ACROSS OUR REGION OUTSIDE OF THE MOUNTAINS WITH MORE
LIKELY PRECIPITATION FORECAST. THIS IS INDICATIVE THAT WITH
VARIOUS MODELS ALL SHOWING PRECIPITATION POSSIBLE AT SOME POINT
BEYOND SATURDAY, A BLEND OF GENERAL POPS IS OCCURRING. THE
TAKEAWAY FROM THIS FORECAST SHOULD BE TO EXPECT PERIODS OF
LESSENING PRECIPITATION ONCE WE MOVE PAST SATURDAY, WITH WAVES OF
SHOWERS STILL POSSIBLE HOWEVER, AND TEMPERATURES DROPPING WITH
COOLER AIR FINALLY DESCENDING WITH THE SYSTEM. WINDS MAY ALSO BE
BREEZY ONCE AGAIN EARLY ON FRIDAY AS THE PRESSURE GRADIENT REMAINS
TIGHTENED WITH THIS SYSTEM, BUT AS IT WEAKENS AND BROADENS WINDS
SHOULD FINALLY RELAX THROUGH THE REST OF THE LONG TERM. OVERALL
THERE IS LOW TO MODERATE CONFIDENCE (30-60%) IN THE EXTENDED
FORECAST, WITH THIS CONFIDENCE LOWER EACH DAY PAST SATURDAY.
GOATLEY/87
AVIATION...00Z TAFS
A MIX OF FLIGHT CATEGORIES EXPECTED DUE TO
RAIN MOVING ACROSS THE REGION, WITH AREAS OF MVFR TO NEARING IFR
POSSIBLE DUE TO LOWERED CIGS, RAIN AND/OR MIST, AND PERIODS OF
BLOWING RAIN FROM STRONG WINDS. ON THE NOTE OF WINDS, EVERY SITE
WILL SEE 25-45+ KNOT GUSTS AS THIS SYSTEM MOVES THROUGH, WEAKEST
AT YKM, AND STRONGEST PDT/ALW. WIND SHEAR IS ALSO NOTED AND EVERY
SITE OUTSIDE OF YKM ALSO INCLUDES PERIODS OF WIND SHEAR THIS
EVENING AND OVERNIGHT. CLOUD DECKS WILL RANGE BETWEEN 1.5-10K
FEET, LOWEST YKM WHERE LIGHTER WINDS MAY ALLOW FOR LIGHT RAIN AND
MIST. GOATLEY/87
PRELIMINARY POINT TEMPS/POPS
PDT 39 52 37 49 / 80 30 40 60
ALW 40 53 39 51 / 90 60 50 60
PSC 43 55 40 48 / 90 30 40 50
YKM 32 46 31 43 / 90 50 50 60
HRI 42 56 38 48 / 80 30 40 60
ELN 29 44 30 43 / 90 60 40 50
RDM 37 49 34 50 / 60 30 40 70
LGD 32 42 35 45 / 80 60 60 80
GCD 32 45 37 48 / 80 50 80 80
DLS 38 52 39 48 / 80 40 50 70
PDT WATCHES/WARNINGS/ADVISORIES
OR...WIND ADVISORY UNTIL 10 AM PST WEDNESDAY FOR ORZ044-049-505.
HIGH WIND WARNING UNTIL 10 AM PST WEDNESDAY FOR ORZ507-508-510-
511.
WINTER WEATHER ADVISORY UNTIL 10 AM PST WEDNESDAY FOR ORZ509.
WA...HIGH WIND WARNING UNTIL 10 AM PST WEDNESDAY FOR WAZ029.
WINTER WEATHER ADVISORY UNTIL 10 AM PST WEDNESDAY FOR WAZ026.
WINTER WEATHER ADVISORY FROM 10 PM THIS EVENING TO 10 AM PST
WEDNESDAY FOR WAZ030.
BLIZZARD WARNING UNTIL 10 AM PST WEDNESDAY FOR WAZ522.
WINTER STORM WARNING UNTIL 10 AM PST WEDNESDAY FOR WAZ523.
SHORT TERM...75
LONG TERM....87
AVIATION...87
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