901
FXUS66 KPDT 210620
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
1020 PM PST WED NOV 20 2024
UPDATED AVIATION DISCUSSION
AVIATION...06Z TAFS
KDLS/KYKM ARE CURRENTLY IN MVFR WHEREAS
THE REMAINING SITES ARE IN VFR. AS THE SYSTEM PASSES, WIDESPREAD
PRECIPITATION WILL CONTINUE ACROSS THE PACNW. ALL SITES WILL HAVE
MVFR/IFR CIGS AND VSBYS BETWEEN 11Z AND 01Z DUE TO RAIN. KPSC MAY
EXPERIENCE LIFR CONDITIONS, RELATED TO CIG AT 300FT STARTING AT
13Z BUT CONFIDENCE IS LESS THAN 30% ON WHETHER OR NOT IT WILL
PERSIST. WINDS AT MOST SITES WILL BE LESS THAN 10KTS WITH THE
EXCEPTION OF KALW GUSTING AT 24KTS THROUGH OVERNIGHT. FEASTER/97
PREV DISCUSSION
/ISSUED 827 PM PST WED NOV 20 2024/
UPDATE...CURRENT RADAR AND INFRARED SATELLITE IMAGERY SHOWING
SCATTERED LIGHT RETURNS PASSING THROUGH THE BASIN AND ACROSS THE
BLUE MOUNTAINS FROM THE SOUTHWEST UNDER CLOUDY SKIES. THIS IS A
RESULT OF THE STRONG UPPER LEVEL SYSTEM OFF OF THE WASHINGTON
COAST, WHICH IS EXPECTED TO STALL OFFSHORE THROUGH THE REMAINDER
OF THE WEEK.
EDITS ASSOCIATED WITH THIS EVENING'S FORECAST UPDATE
INCLUDE RAIN CHANCES, SKY COVER, AND WINDS OVER THE NEXT 24 HOURS
TO BETTER ACCOUNT FOR CURRENT CONDITIONS AND RECENT GUIDANCE.
THE MAJORITY OF THE EDITS WERE RELATED TO WINDS ALONG THE
NORTHERN BLUE MOUNTAIN FOOTHILLS (SPECIFICALLY AROUND CABBAGE
HILL), WHICH ARE LINGERING LONGER THAN EXPECTED. THIS HAS
WARRANTED THE EXTENSION OF THE WIND ADVISORY TO 9 PM. THIS MAY
NEED TO BE EXTENDED ONCE AGAIN AS CURRENT OBSERVATIONS ARE
REGISTERING SUSTAINED EAST WINDS OF 30-40 MPH AND GUSTS BETWEEN
48-52 MPH. THE HRRR IS THE LONE PIECE OF GUIDANCE THAT IS
INITIALIZING WELL WITH THESE EAST WINDS ALONG THE FOOTHILLS,
WHICH HINTS AT DECREASING WINDS BETWEEN 11 PM AND MIDNIGHT
TONIGHT. OTHERWISE, THE FORECAST IS ON TRACK AS THIS PERIOD OF
UNSETTLED WEATHER CONTINUES. 75
PREV DISCUSSION
/ISSUED 428 PM PST WED NOV 20 2024/
SHORT TERM...TONIGHT THROUGH FRIDAY NIGHT
ENSEMBLE NWP
GUIDANCE IS IN EXCELLENT AGREEMENT THAT AN ACTIVE WEATHER PATTERN
WILL CONTINUE THROUGH THE PERIOD, WITH CONCERNS STEMMING FROM A
DEEP CLOSED LOW OFFSHORE THAT IS LOCATED IN THE EASTERN PACIFIC.
A WIND ADVISORY REMAINS IN EFFECT UNTIL 6PM THIS EVENING FOR THE
BASE OF THE NORTHERN BLUE MOUNTAINS OF OREGON. TONIGHT, WINDS ARE
EXPECTED TO SLACKEN AS THE STRONG OFFSHORE SURFACE LOW NEAR 48.8N,
132.2W RETROGRADES NORTHWESTWARD INTO THE PACIFIC. MOREOVER, 12Z
HREF GUIDANCE SUGGESTS THE LOW- TO MID-LEVEL WIND FIELD WILL
WEAKEN THIS EVENING AND OVERNIGHT SUCH THAT THE SUPPORT FOR
WIDESPREAD ADVISORY-LEVEL WINDS MIXING TO THE SURFACE WILL BE LOW
(<20% CHANCE).
PRECIPITATION CONCERNS THIS EVENING AND OVERNIGHT WILL BE PLACED
ALONG THE SOUTHERN PORTION OF OUR CWA FROM THE CENTRAL OR CASCADES
TO THE HIGHER TERRAIN OF THE OCHOCO-JOHN DAY HIGHLANDS IN GRANT
COUNTY. A STRONG SOUTHWESTERLY UPPER-LEVEL JET REMAINS OVERHEAD,
AND MID-LEVEL WAA IS CURRENTLY FACILITATING A BROAD REGION OF
LIGHT PRECIPITATION. WHILE THE BEST MOISTURE WILL REMAIN ON THE
WEST SIDE OF THE CASCADES FROM SOUTHERN OREGON TO NORTHERN
CALIFORNIA, ENSEMBLE MEAN PWAT ANOMALIES RANGE FROM 150-200% OF
NORMAL. THIS REGION IS CO-LOCATED WITH A BROAD AREA OF ENSEMBLE
AGREEMENT IN ANOMALOUS QPF FROM THE SOUTHERN BLUES INTO SOUTHEAST
OR FROM 00Z THURSDAY UNTIL 00Z FRIDAY. WHILE THE HIGHEST VALUES OF
THE ECMWF EFI (0.8-0.9) LIE ACROSS NORTHERN HARNEY AND MALHEUR
COUNTIES, SOUTHERN GRANT COUNTY IS ALSO WITHIN THE BULLSEYE.
MOREOVER, THE EFI FOR SNOW IS 0.6-0.8 FOR THE AFOREMENTIONED
REGION. A HIGH PERCENTAGE OF CAMS ARE QUITE AGGRESSIVE WITH A BAND
OF PRECIPITATION SETTING UP, BUT CONFIDENCE IN THE TEMPERATURES
WITHIN THE BAND (AND PRECIPITATION TYPE FOR AREAS SUCH AS THE BEAR
VALLEY AND THE BROADER OCHOCO-JOHN DAY HIGHLANDS ZONE) IS TOO LOW
TO ISSUE ANY WINTER WEATHER PRODUCTS WITH THE AFTERNOON FORECAST
PACKAGE. HIGH-END SNOW AMOUNTS (1-IN-10 CHANCE) COULD BE 5-8",
WHILE LOW-END AMOUNTS (9-IN-10 CHANCE) ARE 0.5-1.5".
SHIFTING FOCUS WESTWARD, CONFIDENCE IN IMPACTFUL SNOWFALL FOR THE
CENTRAL OR CASCADES ABOVE 4500 FEET IS HIGH ENOUGH (80%) TO ISSUE
A WINTER WEATHER ADVISORY ABOVE 4500 FEET, VALID UNTIL 4AM PDT
THURSDAY. FORECAST SNOWFALL AMOUNTS ARE 3-7", LOCALLY HIGHER.
THURSDAY, ENSEMBLE GUIDANCE ADVERTISES THE DEVELOPMENT OF ANOTHER
SURFACE LOW AS A VORTICITY LOBE TRACKS AROUND THE BASE OF ITS
PARENT UPPER-LEVEL LOW AND INTERACTS WITH A BAROCLINIC ZONE OFFSHORE
IN THE EASTERN PACIFIC. WHILE ALL ENSEMBLE SYSTEMS ARE IN
EXCELLENT AGREEMENT THAT IT THE RESULTANT SURFACE LOW WILL TRACK
TOWARDS THE PACNW THURSDAY THROUGH FRIDAY, THERE IS STILL A RANGE
OF SOLUTIONS IN TERMS OF HOW CLOSE IT WILL TRACK TO THE COAST.
THIS WILL HAVE AN IMPACT ON THE MAGNITUDE OF WINDS ACROSS THE
FORECAST AREA, AS WELL AS PRECIPITATION TOTALS. FORECAST
UNCERTAINTY ASIDE, A WARM FRONTAL PASSAGE IS LIKELY (90% CHANCE OR
GREATER) THURSDAY NIGHT THROUGH FRIDAY MORNING. WITH AMPLIFIED
SOUTHERLY TO SOUTHWESTERLY FLOW ALOFT, THIS PATTERN FAVORS WINDS
THROUGH THE GRANDE RONDE VALLEY AND ALONG THE BLUE MOUNTAIN
FOOTHILLS. CONFIDENCE IN WIND HIGHLIGHTS IS MEDIUM (50-70%) AT
THIS TIME FOR WIND-PRONE ZONES. WHILE WIDESPREAD PRECIPITATION IS
FORECAST, RISING SNOW LEVELS WITH THE WARM FRONT WILL LIFT
CONCERNS ABOVE PASS LEVELS, AND LIKELY ABOVE THE HIGHEST
ELEVATIONS FOR WHICH WE WARN (>5000-5600 FT).
FRIDAY AFTERNOON THROUGH FRIDAY NIGHT, LOWERING SNOW LEVELS AND
WIDESPREAD PRECIPITATION MAY FACILITATE SOME WINTER WEATHER
CONCERNS FOR AREA MOUNTAINS ABOVE 4500 FT, BUT CONFIDENCE IS LOW
(<40%) IN THE NEED FOR ANY HEADLINES AT THIS TIME. PLUNKETT/86
LONG TERM...SATURDAY THROUGH WEDNESDAY
SOUTHWESTERLY FLOW
AROUND LOW PRESSURE OFF THE BRITISH COLUMBIA COAST WILL START
THE DAY ON SATURDAY. HOWEVER, AS THE LOW MOVES MORE NORTHWARD, THE
FLOW WILL BECOME MORE WESTERLY AND DRIER CONDITIONS ARE EXPECTED
OUTSIDE OF THE MOUNTAINS. BRIEF RIDGING MOVES IN LATER SATURDAY
INTO SUNDAY, BEFORE SOUTHWEST FLOW RETURNS SUNDAY NIGHT INTO
MONDAY.
ANOTHER UPPER LOW WILL APPROACH THE COAST OF SOUTHWEST
OREGON/NORTHERN CALIFORNIA TUESDAY OR WEDNESDAY. THIS WILL BRING
ANOTHER ROUND OF INCREASED PRECIPITATION, MAINLY FOR THE
MOUNTAINS.
HOWEVER, EVEN THOUGH THERE ARE LOW POPS OVER THE WEEKEND INTO EARLY
NEXT WEEK, QPF VALUES ARE GENERALLY LOW AND FORECAST UNCERTAINTY IS
HIGH DUE TO THE POSITION OF THE LOW. MOST AREAS WON'T SEE MORE
THAN A FEW HUNDREDTH OF AN INCH OF PRECIPITATION, AND EVEN THE
CASCADES (WHICH WILL LIKELY SEE THE MOST) MAY NOT SEE MORE THAN
0.25 TO 0.30 INCHES, EXCEPT AT THE HIGHER PEAKS.
THE ECMWF EFI DOES INDICATE QPF IN THE 0.7 TO 0.8 OVER THE BLUE
MOUNTAINS ON SATURDAY, THOUGH QPF AMOUNTS ARE ONLY IN THE 0.5 TO
0.20 INCH RANGE.
AT 00Z MONDAY, THE ENSEMBLE CLUSTERS SLIGHTLY FAVOR THE ECMWF
SOLUTION (36%). BY 00Z TUESDAY, THERE IS NO REAL FAVORED SOLUTION
WITH ALL OF THE CLUSTERS ABOUT EQUAL. BY 00Z WEDNESDAY, THERE IS
A FASTER AND SLOWER SOLUTION WITH RESPECT TO THE TROUGH/LOW AND
THE PROBABILITIES ARE ABOUT EQUAL AT THIS POINT.
PRELIMINARY POINT TEMPS/POPS
PDT 39 50 38 55 / 60 50 90 90
ALW 41 50 41 57 / 70 60 80 100
PSC 42 48 42 51 / 70 40 80 90
YKM 32 44 33 48 / 70 40 90 90
HRI 41 50 40 52 / 70 40 80 90
ELN 30 42 33 47 / 60 50 80 90
RDM 36 49 42 54 / 70 60 70 70
LGD 37 44 41 50 / 70 70 80 100
GCD 37 47 41 52 / 90 90 90 100
DLS 41 50 42 52 / 70 40 90 90
PDT WATCHES/WARNINGS/ADVISORIES
OR...WIND ADVISORY UNTIL MIDNIGHT PST TONIGHT FOR ORZ507.
WINTER WEATHER ADVISORY UNTIL 4 AM PST THURSDAY FOR ORZ509.
WA...NONE.
SHORT TERM...86
LONG TERM....77
AVIATION...97
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