778
FXUS66 KPDT 171107
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
307 AM PST MON NOV 17 2025
DISCUSSION
TODAY THROUGH WEDNESDAY: A BAND OF LIGHT SHOWERS
ASSOCIATED WITH A PASSING SHORTWAVE CONTINUES TO TRANSIT EASTERN
PORTIONS OF THE COLUMBIA BASIN TONIGHT, WHILE PATCHES OF DENSE FOG
WITH VISIBILITIES DOWN TO A QUARTER MILE AND LOW STRATUS HAVE
DEVELOPED ACROSS WESTERN PORTIONS OF THE COLUMBIA BASIN, INCLUDING
ADJACENT VALLEYS AND THE EASTERN GORGE. MEANWHILE, VERY LIGHT
SHOWERS STRADDLING THE OR CASCADE CREST ARE CURRENTLY PUSHING
NORTH AND NEARING THE OR/WA BORDER. THESE SHOWERS ARE ASSOCIATED
WITH A TROUGH CENTERED OFFSHORE THE WESTERN CONUS.
BY MID-MORNING, A BRIEF LULL IN PRECIP ACTIVITY WILL DEVELOP
ACROSS THE FORECAST AREA AS THE MAIN LOW CIRCULATION IN THE TROUGH
OFFSHORE DIVES SOUTH, LEAVING BEHIND A WEAKER LOW CIRCULATION
OVER VANCOUVER ISLAND. SOME LIGHT PRECIP WILL CONTINUE ACROSS THE
CASCADE CREST, NORTHERN BLUES, AND WALLOWA MOUNTAINS THROUGH THIS
MORNING. THE LOW WILL TRANSIT THE PACNW LATE THIS AFTERNOON AND
TONIGHT, PROVIDING MAINLY LIGHT PRECIP TO THE WA CASCADES AND
NORTHERN BLUES, THOUGH LOW CHANCES (15-35%) OF LIGHT RAIN WILL BE
POSSIBLE INTO PORTIONS OF THE COLUMBIA BASIN NORTH OF THE HORSE
HEAVEN HILLS AND RATTLESNAKE MOUNTAIN, AND ALONG THE NORTHERN BLUE
MOUNTAIN FOOTHILLS. SNOW LEVELS WILL FALL TO PASS LEVEL TONIGHT,
RESULTING IN A TRANSITION FROM RAIN TO RAIN/SNOW MIX, THEN TO SNOW
BY MIDDLE OF THE NIGHT. A SHORTWAVE TROUGH WILL QUICKLY FOLLOW-
UP THE LOW AS IT EXITS TO THE NORTHEAST TUESDAY AFTERNOON, THOUGH
PRECIP WILL BE MUCH LIGHTER, WITH MAINLY SNOW OR RAIN/SNOW MIX
DEVELOPING ACROSS THE CASCADE CREST AND BLUE MOUNTAINS. TUESDAY
NIGHT, PRECIP CHANCES WILL COME TO AN END ACROSS THE FORECAST AREA
AS A TRANSIENT RIDGE OF HIGH PRESSURE MOVES INLAND, WITH DRY
CONDITIONS CONTINUING INTO THE OVERNIGHT HOURS. CLEARING CLOUD
COVER AND A COLDER AIRMASS FILTERING INTO THE REGION WILL RESULT
IN NEAR TO BELOW FREEZING LOW TEMPERATURES ACROSS THE LOWER
ELEVATIONS OF THE FORECAST AREA, WITH MODERATE CONFIDENCE (60-75%)
THAT PORTIONS OF THE EASTERN COLUMBIA RIVER GORGE WILL SEE THEIR
FIRST FREEZE OF THE FALL/WINTER.
THURSDAY THROUGH SUNDAY:AN ACTIVE WEATHER PATTERN, THOUGH WITH
LIGHT PRECIPITATION, WILL CONTINUE THROUGH THE LATTER HALF OF THIS
WEEK. ENSEMBLE 00Z GUIDANCE IS IN BETTER AGREEMENT TONIGHT OF AN
UPPER TROUGH APPROACHING THE PACNW, THEN TRANSITIONING INTO A
CLOSED LOW THAT WILL DIVE SOUTH ALONG THE COAST AND INTO CA. THE
CLOSED LOW WILL CLIP THE FORECAST AREA, RESULTING IN LIGHT RAIN
AND MOUNTAIN SNOW DEVELOPING ACROSS THE CASCADE CREST AS WELL AS
ACROSS PORTIONS OF CENTRAL OR AND THE BLUES. DRY CONDITIONS WILL
BRIEFLY DEVELOP THURSDAY NIGHT AS THE LOW MOVES FURTHER SOUTH OF
THE REGION, BUT LIGHT RAIN AND HIGH ELEVATION SNOW WILL REDEVELOP
ALONG THE CASCADE CREST AND FAR NORTHERN BLUES FRIDAY THROUGH THE
WEEKEND AS ZONAL FLOW DEVELOPS ALOFT (CONFIDENCE 45-70%).
AVIATION...PREVIOUS DISCUSSION...06Z TAFS
VARIABLE CONDITIONS
ARE FORECAST FOR THE NEXT 24 HOURS AS A WEATHER SYSTEM BRINGS
ISOLATED TO SCATTERED SHOWERS AND PERIODS OF SUB-VFR CIGS/VSBYS
INTO MONDAY.
CONFIDENCE IN SHOWERS RANGES FROM 30 TO 50 PERCENT AT TAF SITES,
HIGHEST AT BDN/RDM OVERNIGHT INTO MONDAY MORNING.
RECENT RAIN HAS PRODUCED NEAR-SATURATED SURFACE CONDITIONS FOR
MUCH OF THE COLUMBIA BASIN, AND PATCHY FOG AS LOW AS 1/4SM HAS
ALREADY BEEN OBSERVED THIS EVENING. CONFIDENCE IN AT LEAST SOME
AREAS OF FOG OVERNIGHT THROUGH MONDAY MORNING IS HIGH (80
PERCENT), BUT CONFIDENCE IN TIMING/MAGNITUDE OF VSBY DROPS AT TAF
SITES WAS GENERALLY TOO LOW TO INCLUDE A MENTION OTHER THAN 6SM BR
IN THE 06Z TAFS.
WINDS OF 10 KTS OR LESS ARE FORECAST FOR ALL SITES, EXCEPT MONDAY
AFTERNOON AND EVENING AT DLS WHEN WESTERLY WINDS RAMP THROUGH THE
GORGE.
OVERALL, HAVE LOWER-THAN-AVERAGE CONFIDENCE IN FORECAST DETAILS.
PRELIMINARY POINT TEMPS/POPS
PDT 58 38 50 30 / 40 30 20 0
ALW 56 42 49 34 / 50 40 30 10
PSC 57 38 52 30 / 20 20 10 0
YKM 56 33 51 29 / 30 30 0 0
HRI 58 39 51 30 / 30 30 10 0
ELN 53 33 47 27 / 50 50 10 0
RDM 56 30 48 20 / 40 10 0 0
LGD 56 38 50 27 / 60 30 30 10
GCD 57 36 51 29 / 50 20 20 10
DLS 56 40 53 34 / 60 20 10 0
PDT WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
DISCUSSION...82
AVIATION...86
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