153
FXUS66 KPDT 201807
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
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
AVIATION...12Z TAFS...STRONG WINDS AND LLWS CONTINUE TO BE THE MAIN
AVIATION CONCERNS FOR TODAY. WINDS WILL GRADUALLY DECREASE AS THE
DAY PROGRESSES, BUT THERE WILL REMAIN SSE WINDS SUSTAINED AT 25-35KT
GUSTING TO 40-50KT AT PDT AND ALW THROUGH THE MORNING HOURS.
ALTHOUGH SURFACE WINDS ARE CONSIDERABLY LESS AT THE OTHER TERMINALS,
THERE IS LLWS THAT INCREASES +20-25 KTS AROUND 2000 FT AGL. DLS AND
YKM ARE THE ONLY TWO LOCATIONS THAT WILL NOT HAVE THESE WIND
CONCERNS. CONDITIONS ARE CURRENTLY VFR AS PRECIPITATION IS MAINLY
WEST OF THE CASCADES AND FROM THE BLUE MTNS EASTWARD. HOWEVER,
PRECIPITATION WILL INCREASE FROM THE SSW TONIGHT AND WIDESPREAD RAIN
AND MOUNTAIN SNOW WILL LOWER CONDITIONS TO MVFR OR LESS. WINDS
TONIGHT WILL BE 5-15KTS. WISTER/85
PRELIMINARY POINT TEMPS/POPS
PDT 37 49 38 55 / 60 40 90 90
ALW 39 51 41 57 / 60 60 90 100
PSC 39 48 42 51 / 60 30 80 90
YKM 29 43 33 48 / 50 50 90 90
HRI 39 48 40 52 / 60 30 90 90
ELN 31 43 33 47 / 50 60 90 90
RDM 34 50 42 54 / 50 60 80 70
LGD 36 45 41 50 / 70 80 90 100
GCD 36 48 41 52 / 90 90 90 100
DLS 40 48 42 52 / 70 60 90 90
PDT WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
SHORT TERM...86
LONG TERM....85
AVIATION...77
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