705
FXUS66 KPDT 171731
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
931 AM PST SUN NOV 17 2024
MORNING UPDATE
TODAY WILL MARK THE BIFURCATION POINT OF THIS
ONGOING WEATHER SYSTEM AS A COLD FRONT WILL MOVE IN AND DROP SNOW
LEVELS BACK DOWN TO PASS LEVEL AND LOWER, MAKING FOR HAZARDOUS
DRIVING CONDITIONS ACROSS MOST OF OUR MAJOR MOUNTAIN PASSES. SNOW
LEVELS WILL START OFF TODAY AT AROUND 4000 FEET, BEFORE DROPPING
DOWN TO LESS THAN 2000 FEET THIS EVENING AND OVERNIGHT INTO
TOMORROW, WITH SNOW EXPECTED TO PERSIST ACROSS OUR MOUNTAIN ZONES
UNTIL OUR ONGOING WINTER STORM WARNINGS EXPIRE BY LATE TOMORROW
NIGHT. EXPECT THE TRANSITION PERIOD FROM RAIN TO SNOW TO OCCUR
ACROSS OUR MOUNTAIN ZONES BETWEEN NOON AND 4 PM, WITH SNOW
PARTICULARLY PILING ON THIS EVENING AND OVERNIGHT, TAPERING OFF
DURING THE DAY TOMORROW. EXPECT BREEZY WINDS AND LIGHT RAIN TO
PREVAIL ACROSS MOST OF OUR LOWER ELEVATION AND VALLEY ZONES AS
WELL.
NO SUBSTANTIAL CHANGES WERE MADE TO THE FORECAST OR MESSAGING, BUT
DID UPDATE POPS AND SNOW LEVELS BASED ON LATEST TRENDS AND THE 12Z
HREF. EVANS/74
AVIATION...18Z TAFS
A MIX OF VFR TO MVFR CONDITIONS EXPECTED,
WITH POTENTIAL MVFR CATEGORIES EXPECTED WITH ANY RAIN OR SOME
POSSIBLE SNOW IN BDN/RDM TOMORROW MORNING. IF SNOW DOES OCCUR, IT
SHOULD BE ON THE LIGHT SIDE, BUT VIS OR POSSIBLE CIGS COULD DROP
TO MVFR STATUS. WITH LOW CONFIDENCE, HAVE USED PROB30 TO CONVEY
THIS UNCERTAINTY. OTHERWISE, PERIODS OF RAIN TODAY FOR ALL SITES
WITH CIGS BETWEEN 3-5K FEET, LIFTING TONIGHT AS THIS SYSTEM BEGINS
EXITING THE REGION, THOUGH ANOTHER ROUND OF PRECIPITATION POSSIBLE
AGAIN TOMORROW WITH CIGS DROPPING AGAIN BACK TO 5-10K FEET WITH
THIS NEXT ROUND. GOATLEY/87
PREV DISCUSSION
/ISSUED 321 AM PST SUN NOV 17 2024/
SHORT TERM...TODAY THROUGH TOMORROW... WINTER STORM WARNINGS WILL
REMAIN FOR THE WA CASCADES AND BLUE MOUNTAINS THROUGH MONDAY AT 10
PM. A WINTER STORM WARNING ALSO REMAINS IN EFFECT FOR THE OR
CASCADES THROUGH MONDAY EVENING.
A WARM FRONT WILL SWEEP ACROSS THE PACNW TODAY BEFORE THE UPPER
TROUGH TAKES OVER STARTING TONIGHT THROUGH TOMORROW. THIS WILL BRING
A BAND OF RAIN FOR THE LOWLANDS, MIXTURE OF MOUNTAIN RAIN/SNOW, AND
GUSTY WINDS FOR THIS PERIOD. QPF AMOUNTS WILL EXCEED UP TO 1" OVER
THE CREST OF THE WA/OR CASCADES WITH 0.75" OR LESS FOR THE BLUES
TODAY. THE LOWLANDS WILL HAVE LIGHTER QPF UP TO 0.25". TONIGHT INTO
TOMORROW, QPF MIGHT REMAIN THE SAME FOR THE AFOREMENTIONED MOUNTAIN
AREAS WITH THE WEAK COLD FRONT MOVING OVER WITH ANOTHER OF PRECIP,
INCLUDING FOR THE LOWLANDS DUE TO LINGERING SHOWERS LEFT BEHIND FROM
THE WARM FRONT (>50% CONFIDENCE).
AS THE TROUGH BEGINS ARRIVING OFF THE OR COAST WITH INCREASED
SOUTHWESTERLY WIND ALOFT, GUSTY WINDS (25-35 MPH) WILL OCCUR AT THE
CREST OF THE CASCADES, NORTHERN BLUES AND THE SIMCOE HIGHLANDS
THROUGH TOMORROW MORNING (50-80% PROBABILITY). THE PROB OF WIND
GUSTS EXCEEDING TO 40 MPH OR HIGHER IS MODERATE (<60%) FOR SANTIAM
PASS AND THE SIMCOE HIGHLANDS, WHICH COULD POTENTIALLY WARRANT FOR
AN WIND ADVISORY. OTHERWISE, THE REST OF THE FORECAST AREA WILL BE
BREEZY (15-25 MPH).
SNOW LEVELS TODAY WILL BE ABOVE 5KFT DUE TO THE PASSING WARM FRONT.
HOWEVER, THEY WILL THEN DECREASE STARTING TONIGHT ONWARDS TO 1.5-
2.2KFT AS THE TROUGH MOVES ACROSS THE PACNW. THERE IS >50% PROB OF
SNOW AT 10-12" FOR THE WA CASCADES AND 6-8" FOR THE BLUES TONIGHT
THROUGH TOMORROW EVENING. THE HIGH ELEVATIONS AT THE CREST OF THE OR
CASCADES WILL ALSO HAVE SNOW UP TO 18" THROUGH TOMORROW EVENING AS
WELL (>50% CONFIDENCE). FEASTER/97
LONG TERM...TUESDAY THROUGH SUNDAY...MODELS ARE COMING INTO GOOD
AGREEMENT THAT THE LONG TERM FORECAST PERIOD WILL BE DOMINATED BY A
MOIST SOUTHWEST FLOW ACROSS THE FORECAST AREA DUE TO ONSET OF AN
ATMOSPHERIC RIVER. THIS WILL LEAD TO A SEVERAL DAY WET PERIOD ACROSS
THE FORECAST AREA.
ON TUESDAY MODELS ARE SHOWING UPPER LEVEL TROUGH FROM THE GULF OF
ALASKA DROPPING INTO THE EASTERN PACIFIC OCEAN. A SURGE OF MOISTURE
COMING AROUND HE BOTTOM OF THE TROUGH WILL BE THE ONSET OF THE
ATMOSPHERIC RIVER AS THE SOUTHWEST FLOW POINTS IT AT NORTHERN
CALIFORNIA AND SOUTHERN OREGON LATE TUESDAY INTO WEDNESDAY. THIS
MOISTURE SPREAD ACROSS THE FORECAST AREA WEDNESDAY THROUGH FRIDAY
BEFORE THE ATMOSPHERIC RIVER WEAKENS AND SHIFTS FURTHER SOUTH INTO
CENTRAL CALIFORNIA. STILL THERE WILL BE MOISTURE CONTINUING IN THE
SOUTHWEST FLOW ACROSS THE REGION THROUGH THE WEEKEND MAINTAINING THE
WET PATTERN.
THE INITIAL ONSET OF PRECIPITATION TUESDAY NIGHT INTO WEDNESDAY COULD
BE A WINTERY MIX WITH VARYING SNOW LEVELS AND SOME POCKETS OF COLD
AIR TRAPPED IN SOME MOUNTAIN VALLEYS AND LOW LYING AREAS ALONG THE
EAST SLOPES OF THE CASCADES. INCREASING SOUTHERLY WINDS WILL BEGIN
TO SCOUR OUT THE POCKETS OF COLD AIR LATE TUESDAY NIGHT AND EARLY
WEDNESDAY AND BEGIN TO RAISE SNOW LEVELS. SNOW LEVELS WILL CONTINUE
TO RISE BECOMING 5000 TO 7000 FEET THURSDAY THROUGH FRIDAY BEFORE
BEGINNING TO LOWER OVER THE WEEKEND.
PRELIMINARY POINT TEMPS/POPS
PDT 54 31 44 27 / 90 70 30 20
ALW 52 34 46 29 / 100 80 50 30
PSC 55 38 50 32 / 70 30 10 20
YKM 52 25 47 21 / 40 20 10 20
HRI 55 35 48 30 / 90 40 10 20
ELN 49 26 44 22 / 80 40 20 20
RDM 52 26 40 24 / 70 70 50 20
LGD 41 27 39 21 / 100 100 60 40
GCD 49 26 38 21 / 100 90 60 50
DLS 53 35 48 31 / 80 60 50 50
PDT WATCHES/WARNINGS/ADVISORIES
OR...WINTER STORM WARNING UNTIL 10 PM PST MONDAY FOR ORZ502.
WINTER STORM WARNING UNTIL 10 PM PST MONDAY FOR ORZ509.
WA...WINTER STORM WARNING UNTIL 10 PM PST MONDAY FOR WAZ030-522.
SHORT TERM...74
LONG TERM....91
AVIATION...87
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