800
FXUS66 KPDT 181758
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
958 AM PST MON NOV 18 2024
MORNING UPDATE
LOOKING AT ONGOING PRECIPITATION, THE CURRENT
FORECAST SEEMS TO BE DOING A GOOD JOB OF CONVEYING WHAT WE'RE
ALREADY SEEING. MEANWHILE, MADE SOME MINOR CHANGES TO THE
TEMPERATURES TO ACCOUNT FOR OVERNIGHT LOWS. MAIN UPDATES FROM THIS
MORNING WERE TO WINDS TUESDAY EVENING THROUGH EARLY WEDNESDAY
MORNING WITH OUR NEXT SIGNIFICANT SYSTEM FOR THE REGION. MODELS
ARE COMING IN MUCH HIGHER ON WINDS, PARTICULARLY IN THE WA
CASCADES WHERE WE EXPECT NOTEWORTHY SNOW TO OCCUR. TO CONVEY THIS,
WANTED TO AT LEAST INCREASE WINDS A BIT, BUT EXPECT THAT IF MODELS
CONTINUE THIS TREND THAT WE WILL SEE ANOTHER BUMP IN FORECAST
CONDITIONS WITH THE AFTERNOON UPDATE. WANTED TO CONVEY THIS NOW AS
WE'RE LESS THAN 48 HOURS FROM ONSET AND DUE TO ONGOING PRODUCTS
FROM THE CURRENT WINTER SYSTEM, WE DO NOT HAVE ANY WATCHES OUT
FOR THIS NEXT SYSTEM, SO PUSHING OUT A FORECAST UPDATE WILL BE THE
WAY TO GO. GOATLEY/87
AVIATION...18Z TAFS
VFR CONDITIONS CURRENTLY AT ALL SITES, BUT
ARE EXPECTED TO DEGRADE TO MVFR FOR KDLS/KRDM/KBDN DUE TO LIGHT
SNOWFALL LEADING TO REDUCED VISIBILITIES DURING THE EARLY MORNING
HOURS ON TUESDAY. CEILINGS WILL ALSO DROP LATE IN THE PERIOD AS A
RESULT OF THE INCOMING SYSTEM, WITH KDLS DROPPING THE LOWEST TO
OVC025. WINDS WILL BE BREEZY THIS AFTERNOON FOR
KDLS/KPDT/KRDM/KBDN/KALW/KPSC WITH SUSTAINED WINDS OF 10-15 KTS AND
GUSTS OF 20-25 KTS. WINDS WILL DECREASE THIS EVENING AND CONTINUE TO
DISSIPATE THROUGH THE END OF THE PERIOD. 75
PREV DISCUSSION
/ISSUED 316 AM PST MON NOV 18 2024/
SHORT TERM...TODAY THROUGH WEDNESDAY...FOLLOWING YESTERDAYS COLD
FRONTAL PASSAGE THE FORECAST AREA WILL BE UNDER A COOL WESTERLY FLOW
TODAY AS THE UPPER LEVEL TROUGH PASSES. THIS WESTERLY FLOW WILL
CONTINUE TO PROVIDE SNOW SHOWERS TO THE CASCADE CREST WHERE WINTER
STORM WARNINGS REMAIN IN EFFECT THROUGH THIS EVENING. AN ADDITIONAL
4 TO 8 INCHES OF ACCUMULATIONS WILL BE POSSIBLE MAINLY ALONG THE
CASCADE CREST AT PASS LEVELS WITH LIGHTER AMOUNTS ALONG THE LOWER
EASTERN SLOPES. THE NORTHERN BLUE MOUNTAINS WILL SEE SOME LINGERING
SHOWERS BUT WITH ONLY ADDITIONAL ACCUMULATIONS OF 2 TO 5 INCHES SO
THE WARNINGS WILL BE DROPPED WITH THE MORNING FORECAST ISSUANCE.
OVERALL, WILL SEE SOME LINGERING SHOWERS MONDAY NIGHT THROUGH
TUESDAY AS THE WESTERLY FLOW BEGINS TO TRANSITION TO A SOUTHWEST
FLOW AHEAD OF THE NEXT SYSTEM EXPECTED TO ARRIVE TUESDAY NIGHT INTO
WEDNESDAY. THIS SYSTEM WILL BE SUPPORTED BY A DEEPENING UPPER LEVEL
TROUGH OVER THE EASTERN PACIFIC. A SURGE OF MOISTURE COMING AROUND
THE BOTTOM OF THE TROUGH WILL TAP INTO SOME TROPICAL MOISTURE TO
FORM AN ATMOSPHERIC RIVER THAT MOVES INTO THE PACIFIC NW COAST LATE
TUESDAY INTO WEDNESDAY. THIS IN TURN WILL PUSH A WARM FRONT ACROSS
THE FORECAST AREA TUESDAY NIGHT. INITIAL SNOW LEVELS WILL START OUT
BETWEEN 1500 TO 3000 FEET THEN RISE INTO WEDNESDAY TO 3000 TO 4500
FEET. THE LOWEST SNOW LEVELS WILL BE FOCUSED ALONG THE EASTERN
SLOPES OF THE WASHINGTON CASCADES TUESDAY NIGHT THROUGH WEDNESDAY
WHERE A POOL OF COLD AIR WILL TRAPPED. OTHER THAN THE LOWER
ELEVATIONS OF THE LOWER COLUMBIA BASIN THERE WILL BE SOME INITIAL
SNOW BEFORE TURNING TO RAIN TUESDAY NIGHT OR EARLY WEDNESDAY.
HOWEVER, THE EASTERN SLOPES OF THE WASHINGTON CASCADES COULD SEE A
PROLONGED SNOW EVENT RESULTING IN SOME ADVISORY AND POSSIBLE WARNING
TYPE SNOW ACCUMULATIONS. THE WARM FRONT WILL ALSO BE ACCOMPANIED BY
SOME WINDY SOUTHERLY WINDS MAINLY ACROSS EASTERN OREGON. HIGH WIND
WATCHES HAVE BEEN ISSUED AND ARE IN EFFECT FOR TUESDAY NIGHT THROUGH
WEDNESDAY MORNING.
LONG TERM...THURSDAY THROUGH MONDAY...
BOTTOM LINE UP FRONT
1. RAIN, RAIN AND MORE RAIN
2. SOUTHWEST FLOW WILL BRING 'WARMER' TEMPERATURES RISING SNOW LEVELS
3. LOCALIZED AREAS OF FLOODING POSSIBLE
THE LONG TERM WILL BE A BIT WET AS AS MODELS SHOW AN UPPER LEVEL LOW
WILL REMAIN PARKED OFF THE COAST. CLUSTERS SHOW THAT THE ONLY
VARIANCE IN THE LONG TERM IS WITH THE POSITION OF THE UPPER LEVEL
LOW UNTIL THE LATER PORTION OF THE LONG TERM. SOUTHWESTERLY FLOW
INTO THE REGION WILL KEEP A CONTINUOUS FLOW MOISTURE ACROSS THE AREA
WITH AN EMBEDDED ATMOSPHERIC RIVER THAT WILL REMAIN THROUGH AT LEAST
SATURDAY. WITH THAT SAID, THE LONG TERM WILL REMAIN UNDER WET
CONDITIONS THROUGH THE ENTIRE LONG TERM PERIOD WITH WHAT APPEARS TO
BE LITTLE TO NO BREAK IN PRECIPITATION EXCEPT ON SATURDAY FOR MOSTLY
FOR THE BASIN, CENTRAL OR AND NORTH CENTRAL OR. NBM SHOWS 70-100%
PROBABILITIES OF 0.40 INCHES OF PRECIPITATION ALONG THE CASCADES AND
BLUES WITH HIGHER AMOUNTS ALONG THE CRESTS AND 0.30-0.40 INCHES
ELSEWHERE THROUGH THE CWA. FRIDAY, PROBABILITIES DROP SLIGHTLY TO 50-
80% FOR THE SAME AMOUNT OF PRECIPITATION AS THURSDAY. FRIDAY SHOWS
THE FIRST SIGNS OF A DECREASE WITH CENTRAL OR SEEING 0.08-0.20
INCHES WITH 50-70% PROBABILITIES, 30-60% FOR THE BASIN AND FOOTHILLS
OF THE BLUES TO SEE 0.25-0.35 INCHES AND 80-100% FOR ABOVE 0.50
INCHES ALONG THE MOUNTAINS TOPS. ITS GOING TO BE A VERY WET LATER
PART OF THE WORK WEEK.
MODELS SHOW THE SOUTHWEST FLOW TO CONTINUE THROUGH THE PERIOD WHICH
WILL ALLOW TEMPERATURES TO REMAIN SEASONAL THROUGH THE PERIOD WITH
THE NBM SHOWING TEMPERATURES TO HOVER IN THE UPPER 40S TO LOW 50S
FOR MUCH OF THE LOWER AND MID ELEVATIONS WHILE THE HIGHER ELEVATIONS
WILL HOVER IN THE LOW TO MID 30S. EVEN THROUGH SATURDAY ELEVATIONS
BELOW 3000 FT WILL REMAIN ABOVE FREEZING. THE SOUTHWEST FLOW WILL
ALSO AID IN KEEPING THE SNOW LEVELS A BIT HIGHER WITH MOSTLY THE
HIGHER CRESTS SEEING ANY SNOWFALL. HOWEVER, MODELS DO SHOW THAT
BEGINNING FRIDAY NIGHT AND SATURDAY MORNING, THE UPPER LEVEL LOW
WILL BEGIN TO MAKES ITS WAY ONSHORE AND MAKE ITS WAY ACROSS THE
REGION. THIS WILL DECREASE THE TEMPERATURES ACROSS THE MID AND
HIGHER TERRAINS WITH SNOW EXPECTED TO REACH AS LOW AS 2500 FT WITH
15-20% PROBABILITIES OF NEAR 2 INCHES ALONG THE I-84 CORRIDOR OF THE
BLUE MOUNTAINS AND 40-60% CHANCE OF NEAR 3 INCHES ALONG THE I-80
CORRIDOR OF THE CASCADES. HOWEVER, CLUSTERS ARE BIT OUT OF SINK WITH
THE TIMING OF THE UPPER LEVEL LOW MOVING INLAND.
WITH ALL THAT SAID AND THE FACT THAT THE EFI IS SIGNALING THIS TO BE
A WELL ABOVE NORMAL RAINFALL EVENT, ALONG WITH THE MODERATE TO HIGH
CONFIDENCE IN THE FORECAST, SOME LOCALIZED FLOODING COULD OCCUR DUE
TO THE RAIN AMOUNTS COUPLED WITH SOME SLIGHT SNOW MELT. WHILE NO
WIDESPREAD FLOODING IS EXPECTED, BE PREPARED AS THIS WILL SURE BE A
WET ONE. BENNESE/90
PRELIMINARY POINT TEMPS/POPS
PDT 46 27 47 40 / 20 20 20 70
ALW 47 30 48 40 / 20 20 20 80
PSC 51 32 49 42 / 10 10 20 80
YKM 48 24 42 31 / 10 10 30 100
HRI 50 30 50 42 / 10 10 20 70
ELN 43 22 38 28 / 10 10 30 90
RDM 41 24 43 36 / 20 20 20 90
LGD 39 19 36 31 / 50 30 20 80
GCD 38 19 40 33 / 50 30 20 90
DLS 49 30 48 39 / 30 20 50 90
PDT WATCHES/WARNINGS/ADVISORIES
OR...HIGH WIND WATCH FROM TUESDAY AFTERNOON THROUGH WEDNESDAY MORNING
FOR ORZ507-508-510-511.
WINTER STORM WARNING UNTIL 10 PM PST THIS EVENING FOR ORZ509.
WA...WINTER STORM WARNING UNTIL 10 PM PST THIS EVENING FOR WAZ522.
SHORT TERM...91
LONG TERM....90
AVIATION...75
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