840
FXUS66 KPDT 291816
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
1016 AM PST MON DEC 29 2025
UPDATE
AVIATION
STRONG HIGH PRESSURE IS PROMOTING LIGHT TO CALM WINDS AT ALL
TERMINALS THIS MORNING WHICH WILL CONTINUE. LOW STRATUS WAS
IMPACTING THE RDM TERMINAL AND BASED ON HREF (ENSEMBLES)
PROBABILITY TRENDS, THIS SHOULD BE DISSIPATING IN THE NEXT COUPLE
OF HOURS (BY 20Z). A RETURN IS POSSIBLE BY AS EARLY AS 04 UTC WITH
20-50% PERCENT CONFIDENCE IN THE VICINITY FOR SUB 1000FT CEILINGS
AND SUB 1 MILE VSBY. STRATUS IS ALSO PRONE IN THE FOOTHILLS OF THE
BLUES AND IN VCTY OF THE ALW TERMINAL, BUT CONFIDENCE4 HERE IS
LOWER AT THIS TIME AND WILL LEAVE OUT OF THE TAF. HIGH CONFIDENCE
(90%) FOR VFR CONDITIONS ELSEWHERE.
PREV DISCUSSION
/ISSUED 238 AM PST MON DEC 29 2025/
DISCUSSION...
AN UPPER LEVEL RIDGE OF HIGH PRESSURE WILL CONTINUE TO BUILD INTO
THE WESTERN CONUS TODAY AND WILL PEAK OVER THE REGION ON TUESDAY
BEFORE GRADUALLY BEING PUSHED EASTWARD ON WEDNESDAY. THIS HIGH
PRESSURE WILL BRING DRY WEATHER, BUT THE POTENTIAL FOR LOW CLOUDS
AND FOG WILL PERSIST THROUGH MIDWEEK. ADDITIONALLY, WITH THE
STRONG HIGH AND LIGHT WINDS, AIR STAGNATION COULD ALSO BECOME A
CONCERN.
EXCEPT FOR CENTRAL OREGON, TEMPERATURES WILL BE ABOUT 5 DEGREES
BELOW NORMAL THROUGH WEDNESDAY.
AS THE HIGH MOVES EASTWARD, A MORE SOUTH TO SOUTHWEST FLOW WILL
DEVELOP DURING WEDNESDAY. THIS FLOW WILL ALLOW FOR MOISTURE TO
MOVE IN FROM CALIFORNIA BY THURSDAY.
THERE ARE STILL SOME MODEL DIFFERENCES BETWEEN THE GUIDANCE AS TO
WHEN THE MOISTURE ARRIVES, WITH THE DETERMINISTIC ECMWF BRINGING
MOISTURE IN BY WEDNESDAY NIGHT AND THE OTHER GUIDANCE MAINLY
WAITING UNTIL THURSDAY.
QPF DURING THIS TIME LOOKS TO BE FAIRLY LIGHT, PROBABLY NO MORE
THAN A FEW HUNDREDTHS TO PERHAPS 0.10 TO 0.20 INCHES OVER THE
MOUNTAINS. SOME GUIDANCE SUGGESTS, THERE WILL BE A LULL ON FRIDAY
BEFORE LOW PRESSURE MOVES NORTH OFF THE PACIFIC NORTHWEST COAST
AND SWINGS A TROUGH THROUGH WITH ANOTHER SHOT OF PRECIPITATION
LATER FRIDAY INTO SATURDAY. ONCE AGAIN, THIS PRECIPITATION WILL BE
MAINLY IN THE MOUNTAINS. DURING THIS TIME QPF COULD BE 0.25 TO
0.30 INCHES OVER THE MOUNTAINS AND ONLY A FEW HUNDREDTHS MOST
ELSEWHERE.
LOW CHANCE (30 TO 40 PERCENT) POPS WILL REMAIN OVER THE MOUNTAINS
SATURDAY INTO SUNDAY WITH DRY WEATHER EXPECTED FOR THE REMAINDER
OF THE AREA AS YET ANOTHER SYSTEM COULD BRING ADDITIONAL MOISTURE.
TOTAL LIQUID EQUIVALENT QPF FROM MIDWEEK THROUGH THE WEEKEND LOOKS
TO BE AROUND 0.50 INCHES IN THE BLUE MOUNTAINS AND 0.75 TO 1.00
INCH ALONG THE CREST OF THE CASCADES. NBM PROBABILITIES OF 0.05
INCHES OF LIQUID EQUIVALENT PRECIPITATION DURING ANY ONE 24 HOUR
PERIOD ARE NEVER MORE THAN 40 TO 50 PERCENT IN THE WASHINGTON
CASCADE CREST AND NO HIGHER THAN 10 TO 20 PERCENT IN THE LOWER
ELEVATIONS.
SNOW LEVELS THURSDAY MORNING WILL RANGE FROM 2000-3000 FEET OVER
THE WASHINGTON CASCADES TO 3500-4000 FEET OVER THE BLUE MOUNTAINS
AND EASTERN OREGON MOUNTAINS TO 5000-6500 FEET OVER THE OREGON
CASCADES. BY BY THURSDAY AFTERNOON, SNOW LEVELS WILL RISE TO
BETWEEN 3000 TO 4000 FEET IN THE WASHINGTON CASCADES, 4500-5000
FEET IN THE BLUE MOUNTAINS AND THE EASTERN OREGON MOUNTAINS AND
OVER 6000 FEET IN THE OREGON CASCADES. SNOW LEVELS WILL CONTINUE
TO RISE FURTHER THROUGH FRIDAY UNTIL THE TROUGH MOVES ONSHORE, AT
WHICH POINT THEY WILL BEGIN TO FALL. BY SATURDAY NIGHT INTO SUNDAY
MORNING, SNOW LEVELS WILL BE BACK TO BELOW 3000 FEET IN THE
WASHINGTON CASCADES AND BELOW 4000 FEET VIRTUALLY EVERYWHERE
ELSE.
SO, FOR MOST OF THE PERIOD, MAINLY RAIN WILL BE EXPECTED, EXCEPT
AT THE HIGHER ELEVATIONS, DURING THE SATURDAY INTO SUNDAY PERIOD
SOME LIGHT ACCUMULATIONS OF SNOW COULD BE SEEN IN THE MOUNTAINS.
AVIATION...
12Z TAFS...VFR CONDITIONS ARE EXPECTED THROUGH THE DAY TODAY AND
INTO EARLY TONIGHT, WITH LIGHT WINDS, GENERALLY LESS THAN 10 KTS.
FOR THE OVERNIGHT TONIGHT PERIOD INTO TUESDAY MORNING, GUIDANCE
SUGGESTS, THAT FOG COULD START TO DEVELOP, ESPECIALLY AT
PDT/ALW/YKM/PSC. NOT ALL OF THESE SITES MAY SEE IT BUT SOME MAY.
AND THERE ALSO COULD END UP BEING LOW CLOUDS AS WELL. FOR RIGHT
NOW, WILL INDICATE MVFR VSBYS IN FOG, BUT IT COULD END UP BEING
LOWER DEPENDING ON HOW THINGS DEVELOP. MODERATE CONFIDENCE (40-60
PERCENT) AT BEST.
PRELIMINARY POINT TEMPS/POPS
PDT 34 21 36 21 / 0 0 0 0
ALW 34 24 35 25 / 0 0 0 0
PSC 34 22 36 21 / 0 0 0 0
YKM 36 21 37 21 / 0 0 0 0
HRI 34 23 35 22 / 0 0 0 0
ELN 32 20 34 20 / 0 0 0 0
RDM 42 20 46 20 / 0 0 0 0
LGD 38 26 41 29 / 0 0 0 0
GCD 43 25 46 26 / 0 0 0 0
DLS 38 27 38 26 / 0 0 0 0
PDT WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
SHORT TERM...99
LONG TERM....99
AVIATION...71
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