907
FXUS66 KPDT 211754
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
1054 AM PDT TUE OCT 21 2025
AVIATION...18Z TAFS
VFR CONDITIONS ARE FORECAST THROUGH THE
VALID PERIOD FOR ALL SITES. DIURNALLY/TERRAIN-DRIVEN WINDS OF 10
KTS OR LESS AND SOME MID- AND HIGH-LEVEL CLOUD ARE EXPECTED (>80%
CONFIDENCE). THERE IS LOW CONFIDENCE (<30%) IN FORMATION OF IFR
OR LIFR STRATUS OR FG OVERNIGHT IN THE VICINITY OF DLS AND PSC.
PREV DISCUSSION
/ISSUED 430 AM PDT TUE OCT 21 2025/
DISCUSSION...TODAY THROUGH THURSDAY...UPPER LEVEL RIDGING WILL
CONTINUE TO BUILD ACROSS THE FORECAST AREA TODAY, BRINGING WITH IT
A PERIOD OF DRY CONDITIONS AND MOSTLY LIGHT WINDS. HOWEVER, A WEAK
PRESSURE GRADIENT DEVELOPING ACROSS THE BLUE MOUNTAINS WILL LEAD
TO BREEZY SOUTHERLY WINDS RETURNING TO THE GRANDE RONDE VALLEY AS
WELL AS DOWNSLOPING WINDS ALONG THE NORTHERN BLUE MOUNTAIN
FOOTHILLS THROUGH THIS MORNING, AND REDEVELOPING AGAIN LATER
TONIGHT.
BY WEDNESDAY AFTERNOON, THE UPPER RIDGE AXIS WILL PUSH EAST INTO
THE NORTHERN ROCKIES, ALLOWING A WEAKENING SHORTWAVE TROUGH AND
COLD FRONT TO QUICKLY LIFT NORTHEAST ACROSS THE PACNW THE LATTER
HALF OF WEDNESDAY. ANY PRECIPITATION CHANCES WILL BE LIMITED TO
THE WA CASCADE CREST, WITH DRY CONDITIONS PERSISTING ELSEWHERE.
THE BLUE MOUNTAIN PRESSURE GRADIENT WILL ALSO WEAKEN WITH THE
SYSTEM PASSAGE WEDNESDAY, WITH THE BREEZY CONDITIONS DECREASING
ALONG THE NORTHERN BLUE'S FOOTHILLS AND IN THE SOUTHERN GRANDE
RONDE VALLEY. OTHERWISE, LOCALLY BREEZY WINDS WILL DEVELOP IN THE
COLUMBIA BASIN AND THROUGH THE CASCADE GAPS. DRY CONDITIONS AND
LIGHT WINDS WILL REDEVELOP AREA-WIDE AS ZONAL FLOW DEVELOPS OVER
THE PACNW THURSDAY.
FRIDAY THROUGH SUNDAY: HIGH CONFIDENCE (75-85%) THAT A DEEP
TROUGH WILL DEVELOP OFF THE PACNW AND WILL FACILITATE THE PASSAGE
OF A LEADING COLD FRONT AND A SERIES OF SHORTWAVE TROUGHS ACROSS
THE REGION. FRIDAY THROUGH THE WEEKEND PERIOD, WIDESPREAD
PRECIPITATION CHANCES WILL DEVELOP ACROSS THE FORECAST AREA WITH
BREEZY TO LOCALLY WINDY WEST TO SOUTHWEST WINDS (GUSTS 30-45 MPH)
DEVELOPING IN THE LOWER ELEVATIONS BY EARLY SATURDAY (CONFIDENCE
55-70%). THERE IS A 55-90% CHANCE OF AT LEAST 0.2 INCHES OF
PRECIPITATION IN THE LOWER ELEVATIONS, A 50-90% CHANCE OF AT LEAST
0.5 INCHES OF LIQUID EQUIVALENT PRECIPITATION ACROSS THE EASTERN
MOUNTAIN ZONES, AND A 55-85% CHANCE OF AT LEAST 1 INCH OR MORE OF
LIQUID EQUIVALENT PRECIPITATION ACROSS THE CASCADE CREST AND EAST
SLOPES. A COLDER AIRMASS WILL ALSO SEEP INTO THE PACNW THROUGH THE
WEEKEND, ALLOWING SNOW LEVELS TO DROP TO 4000-5000 FEET
SATURDAY (CONFIDENCE 60-90%), AND 3500-4000 FEET ON SUNDAY
(CONFIDENCE 55-80%). THIS WILL RESULT IN LIGHT TO MODERATE
SNOWFALL IN THE MOUNTAINS, WITH GENERALLY A 75-90% CHANCE OF 6
INCHES OR GREATER OF SNOW ACROSS SANTIAM AND WHITE PASSES, BUT
ONLY A 30-50% CHANCE AT PASS LEVEL IN SNOQUALMIE PASS (CHANCES
60-80% ALONG RIDGES IN THE PASS). THERE IS ALSO A 50-80% CHANCE OF
6 INCHES OR GREATER FROM THE AREAS AROUND AND BETWEEN SKI
BLUEWOOD AND TOLLGATE. OTHERWISE, AREAS ON THE OUTSKIRTS OF BEND
MAY SEE THEIR FIRST SNOWFALL OF THE YEAR, THOUGH CHANCES OF
ANYTHING GREATER THAN AN INCH OF SNOW IS AROUND 30-40%, WHILE THE
REMAINDER OF THE US97 CORRIDOR TO THE DESCHUTES SOUTHERN BORDER
WILL SEE A 50-70% CHANCE.
MONDAY: ENSEMBLE GUIDANCE FAVORS ZONAL FLOW DEVELOPING IN THE
WAKE OF THE TROUGH EXIT BY LATE MONDAY MORNING. HOWEVER,
DISAGREEMENT GROWS AS TO THE EXTENT OF DRY CONDITIONS DEVELOPING
ACROSS THE LOWER ELEVATIONS. OTHERWISE, LIGHT MOUNTAIN SNOW/RAIN
WILL CONTINUE THROUGH MONDAY (CONFIDENCE 50-60%) WHILE LIGHT RAIN
MAY CONTINUE ACROSS THE BLUE MOUNTAIN FOOTHILLS AND ELEVATED
AREAS OF CENTRAL/NORTH CENTRAL OR (CONFIDENCE 35-45%). LAWHORN/82
PRELIMINARY POINT TEMPS/POPS
PDT 63 37 62 41 / 0 0 0 0
ALW 63 41 62 45 / 0 0 0 0
PSC 62 34 61 39 / 0 0 0 0
YKM 63 36 63 39 / 0 0 0 0
HRI 63 36 61 41 / 0 0 0 0
ELN 60 33 60 36 / 0 0 0 10
RDM 69 33 70 33 / 0 0 0 0
LGD 65 39 67 36 / 0 0 0 0
GCD 68 37 71 36 / 0 0 0 0
DLS 67 41 66 47 / 0 0 0 10
PDT WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
DISCUSSION...82
AVIATION...86
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page