666
FXUS66 KPDT 120953
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
253 AM PDT MON OCT 12 2026
KEY MESSAGES
- FRIGID MORNING TEMPERATURES CONTINUE THROUGH EARLY WEEK.
*FREEZE WARNINGS AND WATCHES ISSUED*
- LIGHT RAIN-SNOW ACROSS BLUE MOUNTAINS THIS MORNING.
- WARMING TREND THROUGH 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 COUNTY 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 /06Z TAFS THROUGH 06Z TUESDAY/
VFR CONDITIONS CURRENTLY ACROSS ALL SITES, WHICH WILL STAY THE
COURSE THROUGH THE PERIOD. WINDS ARE EXPECTED TO STAY LIGHT AND
BELOW 10KTS, AS CEILINGS IMPROVE THROUGH THE PERIOD. 75
PRELIMINARY POINT TEMPS/POPS
PDT 56 30 63 37 / 10 0 0 0
ALW 56 35 63 42 / 10 0 0 0
PSC 61 31 66 35 / 10 0 0 0
YKM 62 34 65 39 / 0 0 0 0
HRI 60 30 66 35 / 10 0 0 0
ELN 60 31 62 35 / 0 0 0 0
RDM 55 20 63 29 / 0 0 0 0
LGD 52 25 62 30 / 30 0 0 0
GCD 51 24 63 31 / 20 0 0 0
DLS 68 37 71 41 / 0 0 0 0
PDT WATCHES/WARNINGS/ADVISORIES
WA...FREEZE WATCH FROM THIS EVENING THROUGH TUESDAY MORNING FOR
WAZ026>029-521.
FREEZE WARNING UNTIL 9 AM PDT THIS MORNING FOR WAZ026-027.
OR...FREEZE WATCH FROM THIS EVENING THROUGH TUESDAY MORNING FOR
ORZ044-049-050-507-508-510.
DISCUSSION...75
AVIATION...75
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