536
FXUS66 KPDT 121753 CCA
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
1053 AM PDT MON OCT 12 2026
KEY MESSAGES
- COLD MORNING TEMPERATURES CONTINUE THROUGH EARLY WEEK.
*FREEZE WARNINGS ISSUED*
- WARMING TREND THROUGH THE WEEK, MOUNTAIN SHOWERS LATE IN
WEEK.
DISCUSSION
CURRENT RADAR AND INFRARED SATELLITE IMAGERY SHOWS VERY LIGHT
RETURNS ACROSS THE NORTHERN BLUE MOUNTAINS AS LOW-TO-MID-LEVEL
CLOUDS LINGER ACROSS MOUNTAIN ZONES OF THE CASCADE AND BLUE
MOUNTAINS. THIS IS IN RESPONSE TO AN UPPER LEVEL LOW PRESSURE
THAT IS CURRENTLY OVER THE COLUMBIA BASIN, WHICH ORIGINATED OVER
NORTHERN BRITISH COLUMBIA AND THE GULF OF ALASKA LAST WEEK. THE
PROGRESSION OF THIS SYSTEM OVER THE PAST SEVERAL DAYS HAS LED
TO A COOLING TREND, AS IT ADVECTS A COLD AIRMASS INTO THE
REGION. THE RESULT HAS BEEN CONSECUTIVE DAYS OF FREEZE PRODUCTS
AS A FREEZE WARNING IS CURRENTLY ACTIVE ACROSS THE YAKIMA AND
KITTITAS VALLEYS UNTIL 9 AM TODAY. CONFIDENCE IN FREEZING
TEMPERATURES BEING REACHED THIS MORNING IS BEST ACROSS THE
KITTITAS VALLEY, AS THE NBM ADVERTISES A 60-90% CHANCE OF
FREEZING TEMPERATURES FOR THORP AND ELLENSBURG. THE YAKIMA
VALLEY HAS BETTER CHANCES TO FREEZE EAST OF TOPPENISH (35-55%)
VERSUS IN AND AROUND YAKIMA (5-15%) VIA THE NBM. THIS SLOWLY
DROPPING SYSTEM WILL ALSO ATTRIBUTE TO LIGHT RAIN-SNOW SHOWERS
ACROSS THE BLUE MOUNTAINS THIS MORNING. THE NBM ADVERTISES A
40-60% CHANCE OF MEASURABLE SNOWFALL BEFORE 11 AM, DROPPING TO A
20-40% CHANCE THROUGH THE AFTERNOON. OVERALL SNOW AMOUNTS ARE
EXPECTED TO STAY BELOW AN INCH, WITH ONLY A 25% CHANCE OF AN
INCH OR MORE OVER THE ELKHORNS. SNOW LEVELS WILL BE INCREASING
THROUGH THE DAY FROM 3500 FEET THIS MORNING TO 4500 FEET BY THIS
AFTERNOON.
THE SYSTEM WILL CONTINUE TO SLIDE SOUTH AND INTO NORTHERN
NEVADA THROUGH THE DAY, ENHANCING THE COLD AIRMASS AND ALLOWING
AN INCOMING UPPER LEVEL RIDGE TO BEGIN TO INFILTRATE FROM THE
COAST. THIS RIDGE OF HIGH PRESSURE WILL CLEAR SKIES AND SHIFT
FLOW ALOFT TO MORE OF A NORTH-NORTHEAST DIRECTION. THESE TWO
ADDED FACTORS WILL ATTRIBUTE TO MORE WIDESPREAD FREEZING
CONCERNS ACROSS THE COLUMBIA BASIN, BLUE MOUNTAIN FOOTHILLS, AND
UNION/WALLOWA COUNTIES AS A FREEZE WATCH HAS BEEN ISSUED MONDAY
EVENING THROUGH TUESDAY MORNING. BEST CHANCES FOR FREEZING
TEMPERATURES TUESDAY MORNING ARE HIGHLIGHTED ACROSS UNION AND
WALLOWA COUNTIES WITH A 90-95% CHANCE VIA THE NBM. THE NEXT
HIGHEST PERCENTAGES FROM THE NBM ARE EXPECTED ALONG THE NORTHERN
BLUE MOUNTAIN FOOTHILLS AT A 65-85% CHANCE. CHANCES ARE
ADVERTISED AS MORE SPORADIC ACROSS THE COLUMBIA BASIN AS THE NBM
HIGHLIGHTS A 60-80% CHANCE OF FREEZING FOR SUNNYSIDE AND
HERMISTON, BUT ONLY 10-20% CHANCE FOR YAKIMA, TRI-CITIES, AND
THE DALLES.
THE ECMWF AND GFS AI ENSEMBLES PASS A WEAK UPPER LEVEL
SHORTWAVE THROUGH CENTRAL BRITISH COLUMBIA AND ALBERTA ON
TUESDAY AND WEDNESDAY, SHIFTING THE DEPARTING UPPER LEVEL LOW
PRESSURE EAST INTO THE FOUR CORNERS AREA. FLOW ALOFT BECOMES
MORE FROM THE WEST DUE TO THE COASTAL RIDGE SUPPRESSING AS THE
CANADIAN SHORTWAVE NEARS THE NORTHERN BRITISH COLUMBIA COAST. AS
A RESULT, HIGH TEMPERATURES WILL INCREASE 5 TO 8 DEGREES ON
TUESDAY. THE CANADIAN SHORTWAVE MOVES QUICKLY INTO ALBERTA
WEDNESDAY MORNING, WHICH MAY ALLOW FOR LIGHT SHOWERS OVER HIGHER
TERRAIN OF THE WASHINGTON CASCADES. 47% OF ENSEMBLE MEMBERS
SUGGEST ONLY MINIMAL AMOUNTS OF ANY PRECIPITATION, AS INCUMBENT
DRY AIR, ASSOCIATED WITH THE PRESENT RIDGE OF HIGH PRESSURE, AND
SNOW LEVELS AROUND 8000-9000 FEET WILL INHIBIT ANY RAIN OR SNOW
AMOUNTS APART FROM HIGHER TERRAIN.
GUIDANCE IS IN AGREEMENT WITH THE COASTAL RIDGE STRENGTHENING
AND PUSHING FURTHER INLAND THURSDAY AND FRIDAY, SHIFTING FLOW
ALOFT TO SOUTHWEST AND RETURNING HIGH TEMPERATURES INTO THE
MID-TO-UPPER-70S ACROSS THE COLUMBIA BASIN AND CENTRAL OREGON.
THE RIDGE AXIS SHIFTS EAST FRIDAY ALLOWING AN UPPER LEVEL LOW
PRESSURE TO ATTEMPT TO DROP SOUTH FROM THE GULF OF ALASKA ON
SATURDAY. ENSEMBLE MEMBERS ALIGN WITH THE MAJORITY OF
PRECIPITATION BEING CONFINED TO THE CASCADES, BUT THERE IS
UNCERTAINTY IN HOW FAR MOISTURE WILL EXTEND INTO THE EAST
SLOPES AND VALLEYS. THE TWO FACTORS THAT WOULD LEAD TO SHOWERS
PUSHING EAST INTO THE KITTITAS AND YAKIMA VALLEYS ARE TIMING
AND STRENGTH. THE EARLY AND STRONGER DROPPING SYSTEM IS
SUGGESTED TO BRING A BETTER CHANCE OF PRECIPITATION INTO THE
EAST SLOPES OF THE WASHINGTON CASCADES. HOWEVER, THIS SCENARIO
ONLY AMOUNTS TO 20-30% OF ENSEMBLE MEMBERS. THIS SYSTEM DOES
LOOK TO SET THE STAGE FOR A SECOND, MORE PROMISING UPPER LEVEL
TROUGH TO DROP INTO THE AREA FROM THE GULF OF ALASKA, BUT THE
SAME INCONSISTENCIES OF STRENGTH AND TIMING ARISE. CURRENTLY,
41% OF ENSEMBLE MEMBERS ADVERTISE WIDESPREAD RAINFALL, WITH THE
MAJORITY (59%) KEEPING IT ALONG THE CASCADES AND EAST SLOPES
LATE SUNDAY INTO MONDAY. 75
AVIATION /18Z TAFS THROUGH 18Z TUESDAY/
VFR CONDITIONS AND LIGHT WINDS OF 10 KTS OR LESS ARE FORECAST
AT ALL SITES THROUGH THE PERIOD.
PRELIMINARY POINT TEMPS/POPS
PDT 56 29 64 36 / 10 0 0 0
ALW 56 34 65 41 / 20 0 0 0
PSC 61 31 67 36 / 0 0 0 0
YKM 62 34 65 40 / 0 0 0 0
HRI 60 29 66 36 / 0 0 0 0
ELN 60 30 62 35 / 0 0 0 0
RDM 55 22 66 31 / 0 0 0 0
LGD 52 25 64 31 / 20 0 0 0
GCD 51 24 64 33 / 20 0 0 0
DLS 68 37 70 41 / 0 0 0 0
PDT WATCHES/WARNINGS/ADVISORIES
WA...FREEZE WARNING FROM 11 PM THIS EVENING TO 9 AM PDT TUESDAY FOR
WAZ026>029-521.
OR...FREEZE WARNING FROM 11 PM THIS EVENING TO 9 AM PDT TUESDAY FOR
ORZ044-049-050-507-508-510.
DISCUSSION...75
AVIATION...86
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