324
FXUS66 KPDT 302316
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
316 PM PST TUE DEC 30 2025
DISCUSSION
KEY MESSAGES:
1. BREEZY GRANDE RONDE VALLEY TODAY.
*WIND ADVISORY ACTIVE*
2. HIGH PRESSURE DOMINATES THROUGH WEDNESDAY.
*AIR STAGNATION ADVISORIES ACTIVE*
3. PRECIPITATION RETURNS THURSDAY, POTENTIAL FOR FREEZING RAIN.
CURRENT RADAR AND VISIBLE SATELLITE IMAGERY SHOWS DRY CONDITIONS
AND MOSTLY CLEAR SKIES, WITH SOME POCKETS OF STRATUS ALONG THE
BASE OF THE BLUE MOUNTAINS AND OVER NORTH-CENTRAL OREGON. SURFACE
HIGH PRESSURE IS CENTERED ALONG THE IDAHO BORDER, WHICH IS
CREATING A SLIGHT PRESSURE GRADIENT OVER THE GRANDE RONDE VALLEY.
THIS HAS INITIATED BREEZY CONDITIONS EARLY THIS MORNING, AND IS
EXPECTED TO PERSIST THROUGH THE EVENING AS SUSTAINED WINDS OF
25-35 MPH AND GUSTS OF UP TO 55 MPH WILL BE POSSIBLE. MAXIMUM WIND
GUSTS OF 50 MPH HAVE BEEN OBSERVED AT THE CHARLES REYNOLDS REST
AREA WITHIN THE LAST HOUR. THUS, A WIND ADVISORY HAS BEEN ISSUED
FOR THE GRANDE RONDE VALLEY, SPECIFICALLY OVER THE LADD AND PYLES
CANYONS UNTIL 11PM THIS EVENING. NAM AND SREF GUIDANCE SUGGESTS
THAT PRESSURE GRADIENTS WILL TEMPORARILY SLACKEN BUT INCREASE
THROUGH THE EARLY MORNING HOURS ON WEDNESDAY, SO THIS ADVISORY MAY
NEED TO BE EXTENDED (40-50% CHANCE).
HIGH PRESSURE IS ALSO PRESENT IN THE MID-AND UPPER LEVELS OF THE
ATMOSPHERE, AS A RIDGE CONTINUES TO SLOWLY STRENGTHEN OVER THE
AREA BEFORE SLOWLY WEAKENING AND SHIFTING EAST ON WEDNESDAY. THIS
HAS PROVIDED MOSTLY CLEAR SKIES AND LOW WINDS ACROSS THE LOWER
COLUMBIA BASIN AS SINKING AIR KEEPS TEMPERATURES ABOUT 5 DEGREES
BELOW NORMAL FOR THIS TIME OF YEAR. HIGHS WILL PEAK IN THE MID-30S
THROUGH THURSDAY AS LOWS DIP IN TO THE LOW TO MID-20S ACROSS THE
COLUMBIA BASIN. THIS LACK OF MOVING AIR WILL NOT ONLY ALLOW FOR
THE POTENTIAL FOR DEVELOPING POCKETS OF FREEZING FOG DURING THE
MORNING HOURS, BUT WILL PROMOTE THE POTENTIAL FOR DEGRADING AIR
QUALITY. CURRENTLY, MODERATE (51-100 AQI) AIR QUALITY IS BEING
OBSERVED ACROSS CENTRAL OREGON, NORTH-CENTRAL OREGON, AND THE
YAKIMA VALLEY, WITH THIS TREND EXPECTED TO CONTINUE THROUGH
THURSDAY MORNING. AS A RESULT, AN AIR STAGNATION ADVISORY IS
ACTIVE THROUGH NOON ON THURSDAY.
THE UPPER LEVEL RIDGE CONTINUES TO WEAKEN AND PUSH TO OUR EAST
THURSDAY AS AN UPPER LEVEL LOW PRESSURE DROPS INTO THE EASTERN
PACIFIC FROM THE GULF OF ALASKA AND APPROACHES THE COAST.
THIS WILL ENHANCE SOUTHWEST FLOW ALOFT AND BRING MOISTURE INTO THE
REGION FROM THE SOUTH. THE RESIDENT COLD AIR WILL STILL BE PRESENT
ACROSS THE COLUMBIA BASIN, GORGE, YAKIMA/KITTITAS VALLEY, AND
PORTIONS OF CENTRAL OREGON AS THE MOISTURE MOVES IN THURSDAY
MORNING. THE WEAK FRONTAL SYSTEM THAT IS BRINGING THE MOISTURE
ONSHORE ALONG THE CALIFORNIA COAST WILL BREAK UP BEFORE REACHING
SOUTHERN OREGON, LEADING TO THE LACK OF SYNOPTIC FORCINGS TO
PROPERLY SCOUR THE COLD AIR FROM LOWER ELEVATIONS OF THE
AFOREMENTIONED AREAS. THIS WILL SET UP THE POTENTIAL FOR FREEZING
RAIN TO OCCUR, WITH CURRENT CONFIDENCE OF UP TO 0.10" OF ICE OVER
LOWER ELEVATIONS OF THE COLUMBIA BASIN (HERMISTON & TRI-CITIES) AT
50-60%. THE NBM IS SHOWING A VERTICAL PROFILE THAT WOULD ALLUDE TO
FREEZING RAIN POTENTIAL, WITH 850 MB TEMPERATURES OF 34-41
DEGREES, 925 MB TEMPERATURES OF AROUND FREEZING, AND SURFACE
TEMPERATURES BETWEEN 25-30 DEGREES. LREF SOUNDINGS ADVERTISE A
DEEP WARM NOSE OF TEMPERATURES UP TO AROUND 9000 FEET, SUGGESTING
LIQUID PRECIPITATION WITH NEAR SURFACE TEMPERATURES WELL BELOW
FREEZING - ESPECIALLY IN THE EARLY MORNING HOURS. 56% OF ENSEMBLES
CONFIRM AND SLIGHTLY LEAN TO EVEN COLDER SURFACE TEMPERATURES
THURSDAY MORNING ASSOCIATED WITH A WEAKER AND EARLIER TROUGH,
BETTER ALIGNING WITH COLD OVERNIGHT/EARLY MORNING TEMPERATURES.
THESE CONDITIONS MAY WARRANT THE NEED FOR AN ADVISORY IN THE NEXT
36 HOURS. 75
AVIATION...00Z TAFS
A PATCH OF LIFR STRATUS DEVELOPED LATE THIS MORNING IN THE VICINITY
OF PSC/ALW WHICH COMPLICATED AN OTHERWISE VFR SETUP ACROSS ALL
TERMINALS. WITH HIGH PRESSURE PATTERN REMAINING IN PLACE, THIS RISK
OF CEILINGS COULD RETURN OVERNIGHT, ALTHOUGH CONFIDENCE IS NOT HIGH,
MODEL ENSEMBLES ARE PRODUCING BETTER AREAL COVERAGE OF THE LOW
PROBABILITY (20-30%) RISK FOR 1/2SM VSBY AND LIFR CIGS AFTER ABOUT
6Z FOR ALW/PDT. LIGHT WINDS UNDER 5 KNOTS IS ANTICIPATED AT ALL
TERMINALS. RUSSELL/71
PRELIMINARY POINT TEMPS/POPS
PDT 22 36 22 34 / 0 0 0 20
ALW 25 34 25 34 / 0 0 0 20
PSC 25 34 22 34 / 0 0 0 10
YKM 23 37 22 35 / 0 0 0 10
HRI 24 34 23 34 / 0 0 0 10
ELN 20 34 19 34 / 0 0 0 10
RDM 25 49 24 44 / 0 0 10 30
LGD 30 43 29 43 / 0 0 0 30
GCD 30 48 29 45 / 0 0 10 50
DLS 27 38 27 37 / 0 0 0 20
PDT WATCHES/WARNINGS/ADVISORIES
OR...AIR STAGNATION ADVISORY UNTIL NOON PST THURSDAY FOR ORZ044-507-
508-510-511.
WIND ADVISORY UNTIL 11 PM PST THIS EVENING FOR ORZ049.
WA...AIR STAGNATION ADVISORY UNTIL NOON PST THURSDAY FOR WAZ026>029.
DISCUSSION...75
AVIATION...71
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