181
FXUS66 KPDT 301112
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
312 AM PST FRI JAN 30 2026
KEY MESSAGES
- OVERNIGHT VALLEY FOG THIS MORNING.
*DENSE FOG ADVISORIES ACTIVE*
- PERIODS OF MOUNTAIN PRECIPITATION INTO EARLY NEXT WEEK.
- HIGH PRESSURE MIDWEEK PROMOTES FOG AND STAGNANT AIR.
DISCUSSION
CURRENT RADAR AND INFRARED SATELLITE IMAGERY SHOWS LIGHT RETURNS
MOVING ACROSS THE LOWER COLUMBIA BASIN UNDER MOSTLY CLOUDY
SKIES. THESE LIGHT SHOWERS HAVE RESULTED IN A SATURATED LOWER
LEVEL ACROSS THE KITTITAS AND YAKIMA VALLEYS, RESULTING IN DENSE
FOG DEVELOPING AS VISIBILITIES OF ONE QUARTER OF A MILE ARE
BEING OBSERVED. THUS, A DENSE FOG ADVISORY HAS BEEN ISSUED FOR
THESE AREAS UNTIL NOON TODAY. THIS ADVISORY MAY NEED TO EXPAND
TO INCLUDE THE TRI-CITIES AREA LATER IN THE MORNING, BUT
CONFIDENCE IS LOW (20-30%) AT THIS TIME. THESE CONDITIONS ARE
IN RESPONSE TO AN APPROACHING UPPER LEVEL SHORTWAVE THAT WILL
PASS ALONG THE CANADIAN BORDER LATER IN THE DAY TODAY, BRINGING
LIGHT TO MODERATE PRECIPITATION PRIMARILY ACROSS THE CASCADES.
LOWER CHANCES (30-60%) RESIDE ALONG THE EAST SLOPES OF THE
CASCADE AND THE BLUE MOUNTAINS AS SLIGHT CHANCES (15-25%)
RESIDE ACROSS THE LOWER COLUMBIA BASIN AND BLUE MOUNTAIN
FOOTHILLS THROUGH THE AFTERNOON AND EARLY EVENING. THIS
SHORTWAVE WILL BRIEFLY FLATTEN THE PRESENT UPPER LEVEL RIDGE
THAT STRENGTHENED ACROSS THE AREA ON THURSDAY, LEADING TO AN
OVERALL LACK OF MOISTURE ASSOCIATED WITH ANY OF TODAY'S
PRECIPITATION. A WEAK WARM FRONT WILL ALSO CLIP THE AREA
ASSOCIATED WITH THE PASSING SHORTWAVE, INCREASING SNOW LEVELS TO
6000-7000 FEET THIS AFTERNOON. THESE VALUES WILL KEEP ANY
MOUNTAIN SNOW CONFINED TO HIGHER ELEVATIONS. RAIN AMOUNTS OF
0.10-0.25" ARE EXPECTED BETWEEN 4000-6000 FEET OVER THE
WASHINGTON CASCADES, WITH UP TO 0.10" OVER THE OREGON CASCADES.
THE UPPER LEVEL RIDGE REBUILDS BRIEFLY ON SATURDAY, BRINGING A
RETURN TO DRY CONDITIONS AND PARTLY CLOUDY SKIES. THIS RIDGE
SHIFTS EAST LATE SATURDAY AS ANOTHER SHORTWAVE APPROACHES AND
PASSES THROUGH THE PACIFIC NORTHWEST SUNDAY INTO MONDAY TO
RETURN MOUNTAIN PRECIPITATION TO THE AREA. SNOW LEVELS WILL DROP
TO BETWEEN 4500-5500 FEET ON SUNDAY AND LINGER AT THIS LEVEL
INTO MONDAY AS THE SHORTWAVE SLOWLY PASSES. AGAIN, DUE TO THE
PERIODIC RIDGING AND LACK OF MULTI-LEVELED SUPPORT IN THE FORM
OF A SUBSTANTIAL UPPER LEVEL TROUGH OR SURFACE FRONTAL SYSTEM,
OVERALL PRECIPITATION AMOUNTS WILL BE MINIMAL. ONLY UP TO AN
INCH OF SNOWFALL ACROSS HIGHER ELEVATIONS ARE EXPECTED BOTH
DAYS, WITH RAIN AMOUNTS OF BETWEEN 0.10-0.20" SUNDAY AND
0.05-0.15" MONDAY PRIMARILY ABOVE 3500 FEET.
ENSEMBLES ARE IN GOOD AGREEMENT REGARDING AN UPPER LEVEL RIDGE
BUILDING LATE MONDAY INTO TUESDAY AND CONTINUING THROUGH THE
MIDWEEK. THESE CONDITIONS WILL ALLOW FOR THE POTENTIAL FOR OVERNIGHT
FOG DEVELOPMENT ACROSS THE LOWER COLUMBIA BASIN, COLUMBIA GORGE,
BLUE MOUNTAIN FOOTHILLS, NORTH-CENTRAL OREGON, AND THE
YAKIMA/KITTITAS VALLEYS AS EARLY AS TUESDAY MORNING.
THIS ALIGNS WITH WPC'S SURFACE ANALYSIS, WHICH ADVERTISES
SURFACE HIGH PRESSURE BUILDING TUESDAY THROUGH THURSDAY. OVERALL
GUIDANCE STRUGGLES WITH FOG DEVELOPMENT AFTER DAY 3, BUT 58% OF
ENSEMBLE MEMBERS DO HIGHLIGHT A 40% CHANCE OR BETTER OF RELATIVE
HUMIDITY VALUES OF 90% OR GREATER FOR THE TRI-CITIES AREA
TUESDAY MORNING WITH ALL MEMBERS SUGGESTING THIS OCCURRING
ACROSS THE KITTITAS VALLEY (WHICH SHOULD BE THE FIRST LOCATION
IMPACTED BY SUBSIDENCE AND COLD POOLING). 75
AVIATION...12Z TAFS
VARIABLE CONDITIONS CURRENTLY ACROSS ALL
SITES, WITH VFR AT KPDT/KRDM/KBDN/KALW AND IFR AT KDLS/KYKM/KPSC
DUE TO REDUCED VISIBILITIES OF 1-2.5SM AND CEILINGS OF 500-1000
FEET OBSERVED AT KDLS/KYKM. THESE CONDITIONS ARE EXPECTED TO
CONTINUE TO DEGRADE OVERNIGHT, EVENTUALLY DIPPING INTO LIFR AS
VISIBILITIES OF 1/4-1/2SM ARE LIKELY TO PERSIST THROUGH THE
MORNING. CHANCES OF THIS OCCURRING ARE LOWEST AT KPSC (20-30%)
AND MAY BE ONLY FOR A COUPLE HOURS MID-MORNING. REDUCED
CEILINGS OF AROUND 300 FEET ARE ALSO EXPECTED FOR THESE SITES.
ELSEWHERE, VFR CONDITIONS PERSIST AS WINDS STAY LIGHT AND BELOW
10KTS FOR ALL TERMINALS. 75
PRELIMINARY POINT TEMPS/POPS
PDT 37 52 33 51 / 20 0 0 10
ALW 40 51 37 51 / 20 10 0 10
PSC 34 49 34 52 / 20 0 0 10
YKM 34 48 34 49 / 10 10 0 10
HRI 35 49 34 51 / 20 0 0 10
ELN 33 43 33 43 / 20 10 0 30
RDM 33 56 32 52 / 10 0 0 10
LGD 35 50 38 51 / 10 0 0 10
GCD 36 54 34 52 / 0 0 0 10
DLS 40 53 39 51 / 30 10 0 40
PDT WATCHES/WARNINGS/ADVISORIES
WA...DENSE FOG ADVISORY UNTIL NOON PST TODAY FOR WAZ026-027.
OR...NONE.
DISCUSSION...75
AVIATION...75
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