864
FXUS66 KPDT 201935
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
1135 AM PST WED NOV 20 2024
MORNING UPDATE
A DEEP CLOSED LOW CONTINUES TO SPIN OFFSHORE IN
THE PACIFIC NEAR 48.3N, 132.4W. THROUGH THE DAY, THE LOW WILL
RETROGRADE NORTHWESTWARD, RELAXING PRESSURE GRADIENTS ACROSS THE
REGION. MOREOVER, 12Z HREF GUIDANCE SUGGESTS LOW- TO MID-LEVEL
WINDS WILL SLACKEN THROUGH THE DAY SUCH THAT THE SUPPORT FOR
WIDESPREAD WARNING-LEVEL WINDS MIXING TO THE SURFACE WILL BE LOW
(<30% CHANCE) THIS AFTERNOON. HOWEVER, WINDS ARE STILL SUPPORTIVE
OF ADVISORIES ALONG THE BASE OF THE NORTHERN BLUE MOUNTAINS OF
OREGON AND THROUGH THE SOUTHERN GRANDE RONDE VALLEY, SO HAVE
OPTED TO RE-ISSUE WIND HIGHLIGHTS FOR THOSE AREAS THROUGH THIS
EVENING.
WITH REGARD TO PRECIPITATION CHANCES, STRONG SOUTHWESTERLY FLOW
IS ADVECTING A PLUME OF MOISTURE INTO THE OR CASCADES. EXPECTING
SNOWFALL TO CONTINUE ACROSS THE OR CASCADES TODAY, BUT CONFIDENCE
IN AMOUNTS REACHING ADVISORY LEVELS IS MEDIUM-HIGH (50-70%) FOR
AREAS ABOVE 4500 FT, NOT QUITE HIGH ENOUGH TO EXTEND THE ADVISORY
THAT WAS IN PLACE THIS MORNING. PLUNKETT/86
PREV DISCUSSION
/ISSUED 1007 AM PST WED NOV 20 2024/
UPDATED FOR AVIATION...
18Z TAFS...VFR CONDITIONS TO START AT ALL SITES, BEFORE
DETERIORATING CONDITIONS OVERNIGHT AND TOWARD MORNING WILL BRING
WIDESPREAD MVFR AND POSSIBLY IFR. GUSTY WINDS ARE EXPECTED MAINLY
AT PDT AND ALW WITH WINDS IN THE 30 TO 35 KT RANGE BEFORE
DECREASING THIS EVENING TO 10 KTS OR LESS. ELSEWHERE, WINDS WILL
MAINLY BE 10 KTS OR LESS THROUGH THE PERIOD.
PREV DISCUSSION... /ISSUED 335 AM PST WED NOV 20 2024/
SHORT TERM...TODAY THROUGH FRIDAY...
BOTTOM LINE UP FRONT
1. PROGRESSIVELY WET PATTERN CONTINUES THROUGH FRIDAY
2. WINDS WILL RETURN THURSDAY NIGHT WITH THE PASSAGE OF A FRONT
MODELS REMAIN IN FIRM AGREEMENT WITH THE DEEP LOW CONTINUING TO
REMAIN PARKED OFF SHORE WITH THE UPPER LEVEL SOUTHWEST FLOW
CONTINUING TO BRING IN PRECIPITATION. THE PASSAGE OF THE WARM
FRONT AND THE CONTINUED SOUTHWESTERLY FLOW BRINGING WARM AIR
ADVECTION, SNOW LEVELS WILL CONTINUE TO RISE THROUGH THE NIGHT.
HOWEVER, MODELS DO SHOW THE SNOW LEVELS TO TAKE THEIR TIME RISING
ALONG THE WA CASCADES AND BLUE MOUNTAINS. THIS WILL ALLOW THE
CONTINUED PRECIPITATION OVERNIGHT TO REMAIN AS SNOW ABOVE 3000 FT.
WITH THE RISING SNOW LEVELS PROGRESSIVELY MOVING NORTHWARDS, MUCH
OF THE PRECIPITATION WILL FALL AS RAIN BELOW 3500 FT KEEPING THE
SNOW CAPPED ALONG THE CRESTS OF THE CASCADES AND BLUES. SNOW
AMOUNTS TODAY WILL REMAIN PRIMARILY ABOVE 3500-4000 FT WITH 70-90%
SHOWING NEAR 6 INCHES OR MORE ALONG THE OR CASCADE CRESTS, 80-90%
SHOWS THE SNOQUALMIE PASS AREA NEARING 1 INCHES, 80-90% SHOWING
WHITE PASS NEARING 1.5-2.0 INCHES, 80-90% MEACHAM AND THE I-84
CORRIDOR WILL SEE 0.1-0.5 INCHES AND THE PEAKS AND TOLLGATE WILL
SEE NEAR 4 INCHES. SNOW WILL GRADUALLY TAPPER OFF AND REMAIN
LOCKED TO THE CRESTS THROUGH FRIDAY. AS FOR THE LOWER ELEVATIONS,
EXPECT RAIN ACROSS THE REGION. TODAYS RAIN TOTALS WILL BE THE
LIGHTEST OF THE FORECAST PERIOD WITH 80-100% OF THE ENSEMBLES
SHOWING A MINIMUM OF 0.50 INCHES OF RAIN ACROSS CENTRAL OR,
YAKIMA/KITTITAS VALLEYS AND PORTIONS OF THE BASIN AND FOOTHILLS,
WHILE THE REMAINDER OF THE REGION WILL SEE ANYWHERE FROM 0.10-0.30
INCHES AND HIGHER AMOUNTS ALONG THE CRESTS. AMOUNTS WILL INCREASE
TOMORROW WITH 20-30% PROBABILITIES OF THE BASIN SEEING 0.20
INCHES, 50-80% PROBABILITIES OF 0.30 INCHES THROUGH CENTRAL AND
NORTH CENTRAL OR, 30-50% PROBABILITIES OF 0.30-0.50 INCHES THROUGH
THE GORGE FOOTHILLS OF THE BLUES, SIMCOE HIGHLANDS AND THE
OCHOCO-JOHN DAY HIGHLANDS. RAIN WILL CONTINUE THROUGH FRIDAY WITH
A BIT OF REPRIEVE FOR CENTRAL OR WHILE ELSEWHERE WILL SEE
0.20-0.30 ADDITIONAL INCHES OF RAIN. ITS GOING TO BE A WET ONE.
WINDS WILL SETTLE TODAY YET REMAINING WITH A EAST AND SOUTHEAST
COMPONENT. WINDS WILL HOWEVER REMAIN SLIGHTLY ELEVATION THROUGH
THE GRANDE RONDE VALLEY AND ALONG THE FOOTHILLS OF THE BLUES
WITH RAW ENSEMBLES SHOWING 30-60% PROBABILITIES OF 30 MPH
SUSTAINED WINDS ALONG THE FOOTHILLS OF THE SOUTHERN BLUES, 80-100%
FOR THE FOOTHILLS OF THE NORTHERN BLUES AND THROUGH GRANDE RONDE
VALLEY. WINDS WILL RETURN TO NEAR NORMAL THURSDAY BEFORE UPTICKING
AGAIN THURSDAY NIGHT. MODELS SHOW A COLD FRONT GEARING UP TO MOVE
ACROSS THE REGION BEGINNING THURSDAY NIGHT. MUCH OF THE BREEZY
WINDS WILL REMAIN ALONG THE SOUTHERN PORTION OF THE REGION AND
ACROSS THE FOOTHILLS OF THE BLUES WITH 50-70% CHANCES OF SUSTAINED
WINDS GREATER THAN 20 MPH. BENNESE/90
LONG TERM...SATURDAY THROUGH WEDNESDAY...MODELS ARE COMING INTO
BETTER AGREEMENT WITH THE SYNOPTIC PATTERN THROUGH THE WEEKEND,
BUT THERE ARE SOME NOTABLE DIFFERENCES IN DAYS 6-8. THE LARGE
UPPER LEVEL TROUGH OVER THE EASTERN PACIFIC AND THE GULF OF ALASKA
WILL PUSH EASTWARD ACROSS THE PACNW FRIDAY AND WILL FLATTEN IN
RESPONSE TO AN INCREASING WESTERLY FLOW ALONG 40N. THEREFORE,
SATURDAY WILL PREDOMINANTLY BE MET WITH A WESTERLY FLOW ALOFT.
SHOWERS WILL BE NUMEROUS (70-90% POPS) OVER THE MOUNTAINS AND A
CHANCE (20-40% POPS) ELSEWHERE. THE COOLER AIR WITH THE WESTERLY
FLOW WILL LOWER SNOW LEVELS DOWN TO NEAR 3500 FEET BY THE
AFTERNOON. AN ATMOSPHERIC RIVER WILL BE SOUTH OF OREGON AIDED BY A
150KT JET, ALTHOUGH THE ECMWF EFI HAS MOST OF EASTERN OREGON IN
ABOVE AVERAGE QPF RELATIVE TO REFORECASTS. CURRENT FORECAST WILL
SHOW 3-6 INCHES OF NEW SNOW SATURDAY IN THE WALLOWA MOUNTAINS AND
THE ELKHORNS AS WELL AS THE CASCADE CREST.
BASED ON THE DETERMINISTIC AND ENSEMBLE MEANS, THE FORECAST AREA
WILL BE BETWEEN SYSTEMS AND UNDER A SHORTWAVE RIDGE SATURDAY NIGHT
THROUGH SUNDAY NIGHT. ANY CHANCE OF PRECIPITATION WILL BE 15-30%
EXCEPT 40-60% ALONG THE CASCADE CREST. SNOW LEVELS IN SOUTHEAST WA
WILL BE NEAR 2500 FEET SLOPING UPWARDS TO 3500 FEET IN CENTRAL
OREGON WITH VERY LIGHT SNOW ACCUMULATIONS, IF ANY AT ALL. THE
BENIGN WEATHER MAY CONTINUE INTO MONDAY AS WELL, ALTHOUGH THE
ENSEMBLE MEMBERS ARE IN GENERAL AGREEMENT THAT AN OFFSHORE TROUGH
WILL NUDGE INLAND ON MONDAY. THIS WILL INCREASE THE SW FLOW ALOFT.
DESPITE THE AGREEMENT IN THE H5 PATTERN, ABOUT 50% OF THE
ENSEMBLES KEEP THE BRUNT OF PRECIPITATION WEST OF THE CASCADES.
FOR NOW, I WOULD STATE THAT THERE IS A CHANCE OF PRECIPITATION ON
MONDAY (SNOW LEVELS 2500-3500 FEET) BUT IT'S NOT A SLAM DUNK.
THE TUESDAY-WEDNESDAY FORECAST IS A MORE MESSY WITH AN UNCERTAIN
FORECAST. THE CHALLENGE IS WHAT THE OFFSHORE TROUGH WILL DO. ITS
POSITION VARIES SIGNIFICANTLY AMONGST THE DETERMINISTIC AND
ENSEMBLES. THE NBM FAVORS LOW CHANCE POPS (20-40%) ALONG WITH
SEASONAL TO BELOW SEASONAL TEMPERATURES. WISTER/85
PRELIMINARY POINT TEMPS/POPS
PDT 53 38 52 38 / 40 60 40 90
ALW 54 41 52 41 / 60 70 60 80
PSC 55 41 49 42 / 50 70 30 80
YKM 44 31 45 33 / 60 60 40 90
HRI 56 40 51 40 / 50 70 30 80
ELN 43 30 43 33 / 70 50 40 80
RDM 48 36 51 42 / 60 70 50 70
LGD 44 36 45 41 / 70 70 70 80
GCD 46 36 48 41 / 70 90 90 90
DLS 50 41 51 42 / 70 70 50 90
PDT WATCHES/WARNINGS/ADVISORIES
OR...WIND ADVISORY UNTIL 6 PM PST THIS EVENING FOR ORZ049-507.
WA...NONE.
MORNING UPDATE...86
SHORT TERM...90
LONG TERM....85
AVIATION...77
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