709
FXUS66 KPDT 280518
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
1018 PM PDT TUE OCT 27 2026
KEY MESSAGES
- MOUNTAIN SNOW OVERNIGHT, BECOMING LIGHT THROUGH THE WEEK.
*WINTER WEATHER ADVISORY ISSUED*
- BREEZY WINDS TODAY AND WEDNESDAY.
- COOLING, BELOW NORMAL TEMPERATURES THROUGH WEEK.
DISCUSSION
CURRENT RADAR AND VISIBLE SATELLITE IMAGERY SHOWS LIGHT RETURNS
ALONG THE CASCADE AND BLUE MOUNTAINS UNDER MOSTLY CLOUDY SKIES.
THIS IS IN RESPONSE TO AN UPPER LEVEL SHORTWAVE PASSING THROUGH
THE AREA. THIS SHORTWAVE HAS PRODUCED CONTINUED LIGHT MOUNTAIN
RAIN AND BRIEF SHOWERS ACROSS THE COLUMBIA BASIN, CENTRAL
OREGON, AND JOHN DAY BASIN. 12 HOUR RAIN TOTALS ARE OBSERVED
BETWEEN 0.20-0.40" ACROSS THE CASCADE AND BLUE MOUNTAINS,
0.10-0.20" THROUGH THE BLUE MOUNTAIN FOOTHILLS, AND 0.01-0.05"
ACROSS CENTRAL OREGON, COLUMBIA GORGE, AND THE JOHN DAY BASIN.
PRECIPITATION CHANCES WILL PERSIST ACROSS OUR MOUNTAIN ZONES AS
AN UPPER LEVEL LOW PRESSURE DROPS SOUTH AND OFFSHORE ALONG THE
BRITISH COLUMBIA COAST. THIS ENHANCES NORTHWEST FLOW AND ADVECTS
A COOLER AIRMASS INTO THE REGION, EFFECTIVELY TRANSITIONING
PRECIPITATION TO SNOW ACROSS THE WASHINGTON CASCADES. SNOW
LEVELS WILL PLUMMET TO AROUND 3500 FEET TONIGHT INTO WEDNESDAY
MORNING AS 3 TO 7 INCHES OF SNOWFALL IS EXPECTED AT ELEVATIONS
AT OR ABOVE 4000 FEET. THUS, A WINTER WEATHER ADVISORY HAS BEEN
ISSUED FOR THE UPPER SLOPES OF THE WASHINGTON CASCADES THROUGH 5
PM WEDNESDAY, WHICH INCLUDES WHITE PASS. CONFIDENCE IN THESE
SNOW AMOUNTS IS HIGH AS THE HREF AND NBM ADVERTISES AN 85-95%
CHANCE OF 3 INCHES OF SNOW, 75-85% CHANCE OF 5 INCHES OR MORE,
AND 30-60% CHANCE OF 7 INCHES OF SNOW OR MORE AT WHITE PASS.
MOUNTAIN SNOW SHOWERS TAPER OFF THROUGH WEDNESDAY AFTERNOON AS
THE LOW PRESSURE SYSTEM CONTINUES TO DROP SOUTH ALONG THE
WASHINGTON COAST AND WEAKENS.
ALONG WITH COOLER TEMPERATURES AND MOUNTAIN SNOWFALL, THE
INCOMING SYSTEM WILL ALSO ENHANCE WINDS AS IT TIGHTENS ISOBARS
ON ITS APPROACH. THIS WILL LEAD TO SUSTAINED WINDS OF 15-25 MPH
WITH GUSTS OF 35-40 MPH ACROSS PORTIONS OF THE COLUMBIA GORGE
AND SIMCOE HIGHLANDS. THE NBM HIGHLIGHTS A 60-80% CHANCE OF 35
MPH WIND GUSTS AND A 40-60% CHANCE OF 40 MPH WIND GUSTS TONIGHT
THROUGH WEDNESDAY MORNING ACROSS THESE AREAS. WINDS ARE
EXPECTED TO PEAK BETWEEN 11 PM TONIGHT AND 3 AM WEDNESDAY
MORNING.
TEMPERATURES WILL CONTINUE TO DROP THROUGH THE END OF THE WEEK,
BOTTOMING OUT AHEAD OF A LOW PRESSURE PASSAGE ON SATURDAY
MORNING. MORNING LOW TEMPERATURES ARE EXPECTED TO DROP TO OR
BELOW FREEZING ACROSS THE COLUMBIA BASIN. THE FINAL FREEZE
WARNINGS OF THE SEASON MAY BE NEEDED FOR AREAS STILL AWAITING
THEIR FIRST FREEZE OF THE SEASON - WHICH WOULD INCLUDE THE
COLUMBIA GORGE AND OREGON BLUE MOUNTAIN FOOTHILLS. THE NBM
SUGGESTS THAT THE FOOTHILLS HAVE A 50-80% CHANCE OF FREEZING AS
EARLY AS THURSDAY MORNING, BUT THE UNDERLYING CONCERN WILL BE
RELATED TO CLOUD COVER. THIS LEADS TO THE BEST CHANCE OF LITTLE
TO NO CLOUD COVER BEING ON SATURDAY MORNING.
GUIDANCE IS IN AGREEMENT THAT THE LOW PRESSURE WILL STALL OFF
THE OREGON/WASHINGTON COASTS THURSDAY, CONTINUING TO WEAKEN ON
FRIDAY AS AN UPPER LEVEL RIDGE BEHIND THIS FEATURE APPROACHES
AND STRENGTHENS. HOWEVER, THIS IS WHERE GUIDANCE BEGINS TO
STRUGGLE IN THE INCOMING RIDGE'S STRENGTH AND SUBSEQUENT
WEAKENING OF THE OFFSHORE LOW. IT WILL ALSO RESULT IN TIMING
DIFFERENCES OF WHEN THE WEAKEN LOW PRESSURE IS PUSHED THROUGH
THE AREA, WITH CURRENT TIMING OF LATE SATURDAY NIGHT INTO EARLY
AFTERNOON ON SUNDAY. CURRENTLY, 61% OF ENSEMBLES FAVOR AN
EARLIER MORE WEAKENED SYSTEM PASSAGE, BRINGING LIGHT RAINFALL TO
OUR MOUNTAIN ZONES SATURDAY EVENING VERSUS EARLY MORNING ON
SUNDAY. AFTER THIS PASSAGE, THE UPPER LEVEL RIDGE MOVES THROUGH
THE AREA OVER THE EARLY PART OF THE WEEK.
TEMPERATURES WILL CONTINUE TO DROP THROUGH THE END OF THE WEEK,
BOTTOMING OUT AHEAD OF THIS LOW PRESSURE PASSAGE ON SATURDAY
MORNING. MORNING LOW TEMPERATURES ARE EXPECTED TO DROP TO OR
BELOW FREEZING ACROSS THE COLUMBIA BASIN. THE FINAL FREEZE
WARNINGS OF THE SEASON MAY BE NEEDED FOR AREAS STILL AWAITING
THEIR FIRST FREEZE OF THE SEASON - WHICH WOULD INCLUDE THE
COLUMBIA GORGE AND OREGON BLUE MOUNTAIN FOOTHILLS. THE NBM
SUGGESTS THAT THE FOOTHILLS HAVE A 50-80% CHANCE OF FREEZING AS
EARLY AS THURSDAY MORNING, BUT THE UNDERLYING CONCERN WILL BE
RELATED TO CLOUD COVER. THIS LEADS TO THE BEST CHANCE OF LITTLE
TO NO CLOUD COVER BEING ON SATURDAY MORNING. 75
AVIATION /06Z TAFS THROUGH 06Z THURSDAY/
VFR CONDITIONS INITIALIZE EXPECTED TO PREVAIL THROUGH THE REST
OF THE PERIOD. REDUCED FEW AND SCT CLOUDS AT 2500 TO 3000 FEET
THROUGH MOST TAF SITES WITH THE ON-SET OF LIGHT TO MODERATE RAIN
SHOWERS THROUGH MORNING AND AFTERNOON HOURS. A 15-30% CHANCE
REMAINS AT EACH SITE EXCEPT FOR BDN/RDM THAT MVFR CONDITIONS
DEVELOP AND PERSIST FOR A FEW HOURS. THE GREATEST CHANCES OCCUR
WHERE/WHEN THE HEAVIEST SHOWERS OCCUR. WINDS IN GENERAL WILL BE
ELEVATED WITH THE STRONGEST WINDS IN PSC/ALW WITH GUSTS AT 20
TO 30 KNOTS POSSIBLE THROUGH THE OVERNIGHT HOURS INTO THE AFTERNOON
HOURS.
PRELIMINARY POINT TEMPS/POPS
PDT 33 54 32 52 / 10 30 10 0
ALW 39 53 35 53 / 50 60 30 0
PSC 37 59 30 54 / 10 10 0 0
YKM 33 56 26 52 / 20 30 0 0
HRI 37 57 30 52 / 10 20 10 0
ELN 28 48 21 47 / 70 60 10 0
RDM 28 49 20 48 / 0 10 0 0
LGD 31 52 26 54 / 60 30 20 0
GCD 29 51 25 55 / 20 0 0 0
DLS 39 56 31 55 / 70 90 40 0
PDT WATCHES/WARNINGS/ADVISORIES
WA...WINTER WEATHER ADVISORY UNTIL 5 PM PDT WEDNESDAY FOR WAZ522.
OR...NONE.
DISCUSSION...75
AVIATION...95
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