128
FXUS66 KPDT 181751
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
951 AM PST TUE NOV 18 2025
UPDATED AVIATION...18Z TAFS
LOW CIGS WILL LINGER AROUND FOR
KRDM (IFR) AND KBDN (MVFR) BEFORE CLOUD COVERAGE DECREASES INTO
THIS AFTERNOON. EVEN THOUGH KRDM/KBDN MAY RETURN TO VFR FOR THE
REST OF THE DAY, LOW CLOUDS COULD DEVELOP LATER THIS EVENING
(40-50% CONFIDENCE). OTHERWISE, VFR CONDITIONS ARE ANTICIPATED FOR
THE REMAINING SITES WITH LIGHT WINDS. FEASTER/97
PREV DISCUSSION... /ISSUED 306 AM PST TUE NOV 18 2025/
DISCUSSION
TODAY THROUGH WEDNESDAY: A SHORTWAVE TROUGH TO THE
NORTH CONTINUES TO DRAG A COLD FRONT BOUNDARY ACROSS THE FAR
EASTERN WA TONIGHT, WITH LIGHT SHOWERS NOW DIMINISHING IN THE
LOWER COLUMBIA BASIN. BREEZY WINDS HAVE DEVELOPED WITH THE FRONTAL
PASSAGE, WITH BREEZY WINDS ALONG THE BLUE MOUNTAIN FOOTHILLS AND
PORTIONS OF THE COLUMBIA BASIN EXPECTED TO CONTINUE THROUGH
SUNRISE THIS MORNING. OTHERWISE, PLENTY OF CLEARING HAS OCCURRED
BEHIND THE FRONTAL PASSAGE, WITH THE BACK END OF THE ASSOCIATED
STRATUS LAYER ENTERING EASTERN PORTIONS OF THE BASIN.
THE NEXT IN A SERIES OF SHORTWAVES WILL PASS OVER THE PACNW TODAY,
HOWEVER A LACK OF MOISTURE WITH THIS SYSTEM WILL ONLY RESULT IN
LIGHT PRECIP ALONG THE WA CASCADE CREST AND INTERIOR NORTHERN
BLUES THROUGH THIS AFTERNOON, WITH PRECIP CONSISTING OF SNOW OR A
RAIN/SNOW MIX NEAR PASS LEVELS. A COLDER AND DRIER AIRMASS WILL
FILTER INTO AREAS EAST OF THE CASCADE CREST TONIGHT, AND COUPLED
WITH CLEARING SKIES, LOWER ELEVATION LOCATIONS AND MOUNTAIN
VALLEYS WILL BE LOOKING AT MORNING LOW TEMPERATURES BELOW FREEZING
WEDNESDAY. THERE IS MODERATE-HIGH CONFIDENCE (65-85%) THAT AREAS
OF THE EASTERN COLUMBIA RIVER GORGE WILL SEE THEIR FIRST FREEZE OF
THE FALL/WINTER, WHICH HAS RESULTED IN A SEASON ENDING FREEZE
WARNING FOR WEDNESDAY MORNING. IN TANDEM WITH THE CLEARING SKIES
AND LOWER TEMPERATURES, MORE MOIST CONDITIONS NEAR THE SURFACE MAY
ALSO RESULT IN AREAS OF PATCHY DENSE FOG/FREEZING FOG DEVELOPING ACROSS
THE LOWER ELEVATION AND MOUNTAIN VALLEYS (CONFIDENCE 40-65%)
WEDNESDAY MORNING, THOUGH CONFIDENCE IS LOW (15-25%) IN THE
DETAILS FOR WHERE AND WHEN FOG MAY DEVELOP. WEDNESDAY, A
TRANSIENT UPPER RIDGE WILL SLIDE OVER THE PACNW, RESULTING IN DRY,
COOL CONDITIONS WITH LIGHT WINDS.
THURSDAY THROUGH SATURDAY: A SEMI-ACTIVE WEATHER PATTERN, THOUGH
WITH LIGHT PRECIPITATION, WILL CONTINUE THROUGH THE LATTER HALF OF
THE WORK WEEK INTO THE WEEKEND. ENSEMBLE GFS AND ECMWF GUIDANCE
ARE IN AGREEMENT OF AN UPPER TROUGH APPROACHING THE PACNW
WEDNESDAY NIGHT, THEN TRANSITIONING INTO A CLOSED LOW THAT WILL
DIVE SOUTH ALONG THE COAST AND INTO CA THURSDAY. THE CLOSED LOW
WILL CLIP THE WESTERN AND SOUTHERN PORTIONS OF THE FORECAST AREA,
RESULTING IN LIGHT RAIN AND MOUNTAIN SNOW ACROSS THE CASCADE
CREST AS WELL AS ACROSS PORTIONS OF CENTRAL OR AND THE BLUES
(CONFIDENCE 50-70%). DRY CONDITIONS WILL BRIEFLY DEVELOP THURSDAY
NIGHT AS THE LOW MOVES FURTHER SOUTH OF THE REGION, BUT LIGHT
RAIN WITH LIGHT SNOW MAINLY ABOVE 5KFT TO 6KFT WILL REDEVELOP
ALONG THE CASCADE CREST AND NORTHERN BLUES FRIDAY THROUGH THE
WEEKEND AS ZONAL FLOW DEVELOPS ALOFT (CONFIDENCE 50-75%).
SUNDAY THROUGH MONDAY: ENSEMBLE CLUSTER GUIDANCE SHOWS GOOD
AGREEMENT THAT THE ZONAL FLOW ALOFT WILL PERSIST THROUGH SUNDAY
AFTERNOON, WITH A SOUTHERLY COMPONENT DEVELOPING AS A TROUGH
DIVES DOWN THE BC COAST. SUNDAY NIGHT THROUGH MONDAY, ENSEMBLE
GUIDANCE COMES INTO DISAGREEMENT IN TIMING AND STRENGTH OF THE
TROUGH PASSAGE. ONE SOLUTION (GFS MEMBER MAJORITY) HAS THE TROUGH
AXIS OVERHEAD BY MONDAY AFTERNOON, WHILE ANOTHER SOLUTION (ECMWF
MEMBER MAJORITY) HAS THE TROUGH AXIS STILL OFFSHORE. THE LATTER
SOLUTION WOULD DELAY MORE WIDESPREAD PRECIP WHILE THE FORMER
WOULD RESULT IN WIDESPREAD PRECIP CHANCES BY EARLY MONDAY MORNING.
WHAT THESE SOLUTIONS DO AGREE UPON IS THAT SNOW CHANCES WOULD
BE LIMITED TO THE MOUNTAIN ZONES. THAT SAID, THERE IS YET ANOTHER
SOLUTION (MADE UP OF ECMWF AND GFS MEMBERS) THAT WOULD ARRIVE WITH
A MUCH COLDER AIRMASS AND WIDESPREAD LIGHT SNOW OR RAIN/SNOW MIX
TO THE LOWER ELEVATIONS MONDAY. WHILE CONFIDENCE IS MODERATE
(40-65%) IN WIDESPREAD PRECIPITATION CHANCES ACROSS THE FORECAST
AREA SUNDAY NIGHT INTO MONDAY, CONFIDENCE IS LOW (10-20%)
PRECIPITATION TYPE AND AMOUNTS. LAWHORN/82
PRELIMINARY POINT TEMPS/POPS
PDT 50 30 48 31 / 0 0 0 10
ALW 49 34 48 34 / 10 10 0 10
PSC 52 29 49 31 / 0 0 0 10
YKM 50 29 49 31 / 0 0 0 10
HRI 51 30 48 31 / 0 0 0 10
ELN 47 27 46 29 / 10 10 0 20
RDM 48 21 51 26 / 0 0 0 20
LGD 50 29 51 33 / 10 10 0 10
GCD 50 31 54 34 / 0 10 0 20
DLS 52 34 50 37 / 0 0 0 30
PDT WATCHES/WARNINGS/ADVISORIES
OR...FREEZE WARNING FROM 11 PM THIS EVENING TO 10 AM PST WEDNESDAY
FOR ORZ041.
WA...FREEZE WARNING FROM 11 PM THIS EVENING TO 10 AM PST WEDNESDAY
FOR WAZ024.
DISCUSSION...82
AVIATION...97
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