339
FXUS66 KPDT 182315
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
315 PM PST MON NOV 18 2024
SHORT TERM...TONIGHT THROUGH WEDNESDAY
LINGERING SHOWERS AND
SNOW SHOWERS ARE NOTED ACROSS THE MOUNTAINS THIS EVENING AS WE
WRAP UP ON THE BACK SIDE OF A TROUGH EXITING THE REGION, BUT ZONAL
FLOW THROUGH TUESDAY MORNING WILL CONTINUE TO PROMOTE MOISTURE
MOVING INTO THE CASCADES WITH PERIODS OF LIGHT SNOWFALL POSSIBLE
ALONG AND JUST PAST THE CRESTS.
THE REAL STORY NOW FOR THE SHORT TERM COMES IN THE FORM OF A VERY
STRONG OFFSHORE LOW THAT WILL DESCEND FROM THE GULF OF ALASKA AND
DEEPEN CONSIDERABLY NEAR THE OFFSHORE BORDERS OF CANADA AND THE
US. MAJOR MODELS ARE ALL INDICATING THIS SYSTEM WILL NEAR OR DROP
JUST BELOW 940MB, BRINGING HURRICANE FORCE OFFSHORE WINDS AND A
STEADY STREAM OF SOUTHERLY FLOW TO OUR INLAND REGION. ALTHOUGH
FRICTIONAL EFFECTS WILL HELP TO ALLEVIATE SOME OF THE STRENGTH OF
THESE WINDS, CAMS AND ENSEMBLE SOLUTIONS ALL AGREE WE'RE LOOKING
AT A NOTEWORTHY WIND EVENT FOR OUR AREA, WITH WIDESPREAD GUSTS OF
45-60+ MPH POSSIBLE DURING THE OVERNIGHT TUESDAY INTO WEDNESDAY
MORNING TIMEFRAME. THE MOUNTAINS IN PARTICULAR WILL BE IMPACTED
BY THESE WINDS, AND COMBINED WITH FALLING OR ALREADY LAID GROUND
SNOW WILL PRESENT A SIGNIFICANT REDUCTION OF VISIBILITIES. THE
ECMWF ENSEMBLES ALL SHOW A WIDESPREAD AGREEMENT ON WIND GUSTS OF
55-60 MPH DURING THAT TIMEFRAME FOR SNOQUALMIE PASS FOR EXAMPLE,
AND THIS ALONGSIDE SHORT TERM MODEL AGREEMENT HAS LED TO A
BLIZZARD WARNING BEING ISSUED FOR THE WASHINGTON CASCADES.
MEANWHILE, THE EAST SLOPES OF THE WASHINGTON CASCADES AND THE
OREGON CASCADES WILL SEE NOTEWORTHY SNOWFALL ALONGSIDE VERY GUSTY
WINDS, BUT BLIZZARD LEVEL CONDITIONS OF LIMITED VISIBILITIES
SHOULD BE MUCH MORE LIMITED FOR THESE LOCATIONS, BUT STILL EXPECT
SIGNIFICANT HINDRANCES TO TRAVEL FOR THESE AREAS.
ON THE NOTE OF PRECIPITATION, THE INITIAL HEAVIEST WAVE OF RAIN
AND MOUNTAIN SNOW WILL ARRIVE WITH THAT STRONGER PUSH OF WINDS
OVERNIGHT TUESDAY INTO WEDNESDAY. BY THE TIME WE REACH THE END OF
WEDNESDAY, ALMOST EVERY LOCATION ACROSS THE CWA IS EXPECTED TO
HAVE RECEIVED 0.1+ INCH OF NEW RAINFALL OUTSIDE OF THE COLUMBIA
BASIN AND PORTIONS OF CENTRAL OREGON, WITH THE NBM GIVING A HIGH
PROBABILITY TO THIS OCCURRING AT 50-100% CHANCE. OTHERWISE,
SOUTHWESTERLY FLOW ALOFT WILL BEGIN TO OVERSPREAD WARMER AIR AND
INCREASE OUR TEMPERATURES, ALLOWING SNOW LEVELS TO RISE AND LIMIT
FUTURE SNOWFALL TO THE CRESTS AND PEAKS AS WE MOVE INTO THE END OF
THE WEEK. GOATLEY/87
LONG TERM...THURSDAY THROUGH MONDAY
KEY MESSAGES:
1. WIDESPREAD RAIN CHANCES THROUGH PERIOD.
2. ABOVE NORMAL TEMPERATURES EXTEND INTO WEEKEND.
3. LOCALIZED FLOODING POSSIBLE.
THE EXTENDED PERIOD IS CHARACTERIZED BY A STRONG, UPPER LEVEL LOW
PRESSURE SYSTEM THAT STALLS OFF THE WASHINGTON/OREGON COASTS BEFORE
MOVING ONSHORE AND THROUGH THE PACIFIC NORTHWEST LATE IN THE
WEEKEND. SOUTHWEST FLOW ALOFT WILL BE DOMINANT UNDER THIS SYNOPTIC
PATTERN, LEADING TO WIDESPREAD RAIN CHANCES EACH DAY AS A WEAK
ATMOSPHERIC RIVER SETS UP THROUGH THE WORKWEEK. THE ECMWF EFI
INDICATES FRIDAY'S RAINFALL AS BEING ABOVE THE CLIMATOLOGICAL NORMAL
AND THE WETTEST DAY IN THE FORECAST, BUT RAIN AMOUNTS ON THURSDAY
WILL BE RATHER SIMILAR. RAIN AMOUNTS OF 0.25-0.45" ARE EXPECTED
ACROSS LOWER ELEVATIONS OF THE BASIN, CENTRAL OREGON, AND THE BLUE
MOUNTAIN FOOTHILLS WITH 0.35-0.85" OF RAINFALL EXPECTED AT HIGHER
ELEVATIONS OF THE CASCADE EAST SLOPES, JOHN DAY HIGHLANDS, AND THE
BLUE MOUNTAINS BOTH THURSDAY AND FRIDAY. CONFIDENCE IN THESE RAIN
AMOUNTS IS MODERATE TO HIGH (60-80%) AS THE NBM SUGGESTS A 25-55%
CHANCE OF 0.25" OF RAIN OR MORE OVER LOWER ELEVATIONS OF THE BASIN
AND A 50-75% CHANCE ALONG THE BLUE MOUNTAIN FOOTHILLS THURSDAY AND
FRIDAY. THE UPPER LEVEL LOW OPENS AND BROADENS OUT ON SATURDAY AHEAD
OF MOVING ONSHORE MID-TO LATE SUNDAY. THIS WEAKENED AND LESS
ORGANIZED SYSTEM WILL STILL BRING WIDESPREAD RAIN SHOWERS ACROSS THE
AREA. RAIN AMOUNTS OF 0.50-0.75" AT ELEVATION OVER THE CASCADE AND
BLUE MOUNTAINS, 0.20-0.40" ALONG THE BLUE MOUNTAIN FOOTHILLS, AND
0.01-0.10" ACROSS LOWER ELEVATIONS OF THE BASIN AND CENTRAL OREGON
ARE EXPECTED ON SATURDAY. CONDITIONS WILL CONTINUE TO DRY OUT INTO
SUNDAY, WITH LOWER ELEVATIONS OF THE BASIN STAYING DRY AS RAIN
AMOUNTS STAY CONFINED TO OUR FOOTHILLS AND MOUNTAIN ZONES. SNOW
LEVELS WILL HOVER BETWEEN 5000-6000 FEET THURSDAY AND FRIDAY,
DROPPING TO 3500-4500 FEET SATURDAY AND 2500-3500 FEET SUNDAY. THESE
VALUES WILL KEEP SNOWFALL OVER OUR MOUNTAINOUS TERRAIN OF THE
CASCADES, BLUE MOUNTAINS, JOHN DAY/OCHOCO HIGHLANDS, AND THE SIMCOE
HIGHLANDS THROUGH THE PERIOD. 1-5 INCHES OF SNOWFALL IS ANTICIPATED
TO OCCUR ACROSS THE CASCADE PASSES THURSDAY AND SATURDAY.
SOUTHWEST FLOW ALOFT WILL HELP TO BRING IN A WARMER AND WETTER
AIRMASS THROUGH THE WEEK. THIS WILL KEEP HIGH TEMPERATURES IN THE
UPPER 40S TO LOW 50S THROUGH THE PERIOD, WHICH WILL BE 2-5 DEGREES
ABOVE NORMAL FOR THIS TIME OF YEAR. OVERNIGHT LOWS WILL ALSO BE
RATHER MILD THROUGH THE WORKWEEK, WITH MORNING TEMPERATURES DROPPING
INTO THE UPPER 30S TO LOW 40S THURSDAY AND FRIDAY. A COOLING TREND
DEVELOPS OVER THE WEEKEND AS THE SYSTEM OFFSHORE OPENS, WEAKENS,
AND BEGINS TO PUSH ONSHORE. MONDAY MORNING TEMPERATURES WILL DROP TO
NEAR OR BELOW FREEZING OVER THE BASIN, WITH VALUES DROPPING INTO THE
MID TO UPPER 20S ACROSS CENTRAL OREGON. CONFIDENCE IN EXPERIENCING
FREEZING MORNING TEMPERATURES ON MONDAY IS MODERATE (50-70%) AS THE
NBM SUGGESTS A 40-70% ACROSS LOWER ELEVATIONS OF THE BASIN AND A 75-
95% CHANCE OVER CENTRAL OREGON.
THERE ARE SIGNIFICANT RAIN AMOUNTS IN THE LONG-TERM FORECAST, WHICH
MAY LEAD TO ISOLATED OR LOCALIZED AREAS OF FLOODING - PRIMARILY IN
AND AROUND URBAN AND LOW-LYING AREAS. SNOWPACK IS NOT YET
ESTABLISHED, SO THE PROBABILITY OF RAIN-ON-SNOW EVENTS IS LOW AS
SNOW LEVELS BEGIN TO DECREASE SATURDAY. HOWEVER, THERE MAY BE TIMES
WHEN CELLS TRAIN AND PERSISTENT MODERATE TO HEAVY RAINFALL MAY LEAD
TO PONDING ON ROADWAYS AND LOCALIZED FLOODING NEAR BODIES OF WATER.
75
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
PRELIMINARY POINT TEMPS/POPS
PDT 27 47 36 52 / 20 20 90 70
ALW 30 47 37 52 / 30 30 90 80
PSC 33 49 41 55 / 30 20 90 50
YKM 23 43 29 46 / 30 60 100 60
HRI 31 51 40 55 / 40 20 90 50
ELN 23 40 29 44 / 30 60 100 70
RDM 24 43 35 49 / 50 20 90 60
LGD 21 37 31 42 / 20 40 90 90
GCD 20 40 32 44 / 50 50 100 90
DLS 32 46 39 52 / 60 80 100 80
PDT WATCHES/WARNINGS/ADVISORIES
OR...WIND ADVISORY FROM 4 PM TUESDAY TO 10 AM PST WEDNESDAY FOR
ORZ044-049-505.
HIGH WIND WARNING FROM 4 PM TUESDAY TO 10 AM PST WEDNESDAY FOR
ORZ507-508-510-511.
WINTER WEATHER ADVISORY FROM 4 PM TUESDAY TO 10 AM PST WEDNESDAY
FOR ORZ509.
WA...WINTER WEATHER ADVISORY FROM 4 PM TUESDAY TO 10 AM PST WEDNESDAY
FOR WAZ026.
BLIZZARD WARNING FROM 4 PM TUESDAY TO 10 AM PST WEDNESDAY FOR
WAZ522.
WINTER STORM WARNING FROM 4 PM TUESDAY TO 10 AM PST WEDNESDAY
FOR WAZ523.
SHORT TERM...87
LONG TERM....75
AVIATION...75
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