251
FXUS66 KPDT 061108
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
408 AM PDT MON OCT 6 2025
DISCUSSION...AN UPPER-LEVEL RIDGE OF HIGH PRESSURE EXTENDS FROM
THE NORTHEASTERN PACIFIC OCEAN INTO THE PACIFIC NORTHWEST. BENEATH
THE RIDGE, CLEAR SKIES COUPLED WITH PREDOMINANTLY LIGHT WINDS AND
A DRY AIR MASS (PWATS OF 0.25-0.60") WILL FACILITATE EFFICIENT
RADIATIONAL COOLING. ISOLATED NEAR-FREEZING TO FREEZING TEMPERATURES
ARE EXPECTED (80% CONFIDENCE) THIS MORNING FOR LOW-LYING, COLD-
PRONE LOCATIONS WITHIN THE YAKIMA AND KITTITAS VALLEYS, COLUMBIA
BASIN, AND ALONG THE BLUE MOUNTAIN FOOTHILLS; NO FREEZE WARNINGS
HAVE BEEN ISSUED DUE TO LIMITED SPATIAL EXTENT. HOWEVER, HAVE
ADDED A MENTION OF FROST IN THE FORECAST THIS MORNING AS WELL AS
TUESDAY MORNING. ELSEWHERE, MORE WIDESPREAD SUB-FREEZING
TEMPERATURES ARE EXPECTED (80-100% CONFIDENCE) THIS MORNING FOR
CENTRAL OREGON, THE JOHN DAY BASIN, AND THE GRANDE RONDE AND
WALLOWA VALLEYS. FREEZE WARNINGS REMAIN IN EFFECT UNTIL 10 AM FOR
THE AFOREMENTIONED ZONES.
BY TUESDAY, THE RIDGE WILL FLATTEN AS A COUPLE VORT LOBES DROP
SOUTH FROM THE GULF OF ALASKA AND BC AND CARVE OUT AN OFFSHORE
CLOSED LOW. ANALYSIS OF ENSEMBLE CLUSTERS SUGGESTS A VERY HIGH
CHANCE (>90%) THAT THE LOW WILL DEEPEN AND SPIN OFFSHORE OF THE
PACIFIC NORTHWEST WEDNESDAY THROUGH THURSDAY. ANY PRECIPITATION
ASSOCIATED WITH THE LOW WILL LIKELY (75% CHANCE) REMAIN PINNED TO
THE CASCADES AND THEIR IMMEDIATE EAST SLOPES.
ENSEMBLE CLUSTERS INDICATE THE LONGWAVE PATTERN WILL ALMOST
CERTAINLY (>90% CHANCE) BECOME MORE PROGRESSIVE FRIDAY THROUGH
THE WEEKEND. WHILE SOME DIFFERENCES IN EXACT TIMING ARE APPARENT
AMONG ENSEMBLE CLUSTERS, ALL ENSEMBLE SYSTEMS TRACK THE CLOSED
LOW INLAND OVER THE PACIFIC NORTHWEST FRIDAY THROUGH SATURDAY,
WITH A SECOND SHORTWAVE TROUGH DIGGING SOUTHEAST OUT OF BC
SATURDAY THROUGH SUNDAY. THE COMBINATION OF THESE TWO SYSTEMS WILL
FACILITATE MEDIUM-HIGH CHANCES (55-85%) OF PRECIPITATION FOR THE
CASCADES AND BLUES WITH A LOW-MEDIUM CHANCE (20-50%) OF RAIN FOR
THE LOWER ELEVATIONS LATE FRIDAY THROUGH SUNDAY. SNOW LEVELS WILL
DROP SUFFICIENTLY LOW (4-5 KFT) OVER THE WEEKEND TO ALLOW A
MEDIUM-HIGH CHANCE (50-80%) OF MEASURABLE SNOW IN THE MOUNTAINS.
BREEZY WESTERLY WINDS ARE ALSO FORECAST SATURDAY INTO SUNDAY.
NBM PROBABILITIES SUGGEST A LOW-MEDIUM (30-60%) CHANCE OF WINDS
REACHING ADVISORY THRESHOLDS, AND THE ECMWF EFI FOR WIND AND WIND
GUSTS RANGES FROM 0.5-0.8 ACROSS WIND-PRONE AREAS OF THE COLUMBIA
GORGE/BASIN AND ADJOINING FOOTHILL AND VALLEY AREAS. PLUNKETT/86
AVIATION...12Z TAFS...VFR CONDITIONS WILL PREVAIL THROUGH THE
FORECAST PERIOD. CIGS WILL BE PRIMARILY SKC WITH VARIABLE LIGHT
WINDS AT ALL TAF SITES. BENNESE/90
PRELIMINARY POINT TEMPS/POPS
PDT 69 40 74 43 / 0 0 0 0
ALW 69 45 74 48 / 0 0 0 0
PSC 70 37 72 40 / 0 0 0 0
YKM 70 41 72 41 / 0 0 0 0
HRI 70 38 73 41 / 0 0 0 0
ELN 69 37 70 38 / 0 0 0 0
RDM 68 31 75 34 / 0 0 0 0
LGD 66 35 72 42 / 0 0 0 0
GCD 68 36 73 38 / 0 0 0 0
DLS 73 44 76 46 / 0 0 0 0
PDT WATCHES/WARNINGS/ADVISORIES
OR...FREEZE WARNING UNTIL 10 AM PDT THIS MORNING FOR ORZ049-050-505-
511.
WA...NONE.
SHORT TERM...86
LONG TERM....86
AVIATION...90
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