790
FXUS66 KPDT 232300
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
300 PM PST TUE DEC 23 2025
UPDATED AVIATION DISCUSSION
PREV DISCUSSION
/ISSUED 218 PM PST TUE DEC 23 2025/
KEY POINTS...
1. WIDESPREAD LOW ELEVATION RAIN TODAY THROUGH AFTERNOON
THROUGH WEDNESDAY MORNING
2. MOUNTAIN PASS SNOW THROUGH CHRISTMAS EVE
*SPS IN AFFECT*
3. BREEZY WINDS CHRISTMAS EVE
*SPS IN AFFECT 1 AM THROUGH 4 PM WEDNESDAY*
DISCUSSION
CURRENT SATELLITE SHOWS MOSTLY SKIES ACROSS
THE CWA. RADAR SHOWS A FEW RETURNS MOVING ACROSS THE COUNTIES
THROUGH THE CENTER OF THE CWA WITH GROUND OBSERVATIONS SHOWING 0.01-
0.04 INCHES OF RAIN ALONG THE LOWER ELEVATIONS AND NEAR 0.20 INCHES
ALONG SOME OF THE HIGHER ELEVATIONS THROUGH THE BLUES. RAIN IS
EXPECTED TO CONTINUE TO LINGER THROUGH TOMORROW AFTERNOON.
MODELS SHOW AN ACTIVE WEATHER PATTERN WITH AN ASSOCIATED ATMOSPHERIC
RIVER (AR) IS EXPECTED TO IMPACT THE CASCADES, MOST NOTABLY OVER THE
WASHINGTON CASCADES. MODERATE RAIN FAVORED, WITH AMOUNTS BETWEEN 0.5-
1 INCH (60-80% CONFIDENCE) AT THE CASCADE CREST WITH LESSER AMOUNTS
FOUND AT THE LOWER ELEVATIONS. LOWER ELEVATIONS WILL SEE UP TO 0.05
INCHES OF RAIN OVERNIGHT AND AGAIN INTO WEDNESDAY WITH 80-90%
CONFIDENCE. MODELS SHOW THE UPPER LEVEL LOW WITH THE AR TO MOVE JUST
ENOUGH TO PUSH THE BAND OF PRECIPITATION ACROSS THE OR PORTIONS OF
THE CWA MOVING FORM THE SOUTHEAST TO THE NORTHWEST BEFORE BECOMING
MOSTLY FOCUSED OVER THE CASCADES BY TONIGHT.
SNOW LEVELS WILL INCREASE TO NEAR 4500-5000 FEET TODAY AS THE MODELS
SHOW THE ATMOSPHERIC RIVER TO BE A BIT WARMER THAN ORIGINALLY
ANTICIPATED. SHORT TERM MODELS DO SHOW A SWATH OF SNOW ACCUMULATIONS
ACROSS THE WA CASCADES THROUGH THE EVENING WITH 60-80% PROBABILITIES
OF UP TO AN INCH OF SNOWFALL. HOWEVER, A SHOT OF COOLER AIR WILL
COME INTO THE AREAS WEDNESDAY NIGHT BRINGING THE SNOW LEVELS BACK
DOWN TO NEAR 3000-3500 WITH ANOTHER ACCUMULATION OF NEAR 1 INCH (30-
50%). HIGHEST AMOUNTS HAVE SINCE SHIFTED TO CHRISTMAS NIGHT INTO
FRIDAY MORNING WITH 70-90% PROBABILITIES OF 2-3 INCHES OF SNOWFALL.
MODELS CONTINUE TO SHOW A SURFACE LEVEL LOW TIGHTENING THE PRESSURE
GRADIENTS ACROSS THE REGION, ESPECIALLY THROUGH CENTRAL OR EASTWARD.
PRESSURE GRADIENT MODELS SHOW A TIGHTENING OF THE GRADIENTS OF NEAR
15 MB FROM CENTRAL OR ALONG THE JOHN-DAY OCHOCO HIGHLANDS AND
THROUGH THE EASTERN MOUNTAINS. THIS WILL LEAD TO BREEZY CONDITIONS
ACROSS THE AFOREMENTIONED AREAS. THIS SURFACE LOW WILL BRING SOUTH
WINDS OF 15 TO 25 MPH WITH GUSTS UP TO 30-40 MPH EXPECTED WITH
HIGHER WINDS NEARING 45 MPH ALONG THE HIGHER TERRAIN (70-90%
CONFIDENCE). THE SOUTH WINDS WILL CREATE A CROSS WIND ALONG THE I-84
CORRIDOR SO HIGH PROFILE TRUCKS SHOULD HEED CAUTION WHEN DRIVING THE
PASS.
SATURDAY ONWARDS, MODELS ARE IN DECENT AGREEMENT SHOWING A
PERSISTENT RIDGE MOVING IN OVER THE REGION. DRY CONDITIONS WILL
RETURN BEGINNING WITH SEASONAL TEMPERATURES. BY THE END OF THE
PERIOD, TEMPERATURES COULD BEGIN TO CREST TO NEARLY 10 DEGREES
ABOVE SEASONAL AVERAGE ALONG THE HIGHER TERRAIN AND THROUGH CENTRAL
OR AND THE JOHN-DAY BASIN (60-70% CONFIDENCE). WITH THAT SAID,
PATTERN RECOGNITION FOR THIS TIME OF YEAR SUGGESTS THAT WITH THE
UPPER LEVEL RIDGE LINGERING FOR A FEW DAY, WINTER TIME FOG WILL
SETTLE OVER THE REGION LATER IN THE PERIOD. 90
AVIATION...00Z TAFS
EVEN THOUGH THE FOG HAS LIFTED EARLIER,
THE LOW STRATUS LAYER WILL CONTINUE ACROSS KDLS THROUGH THE
REMAINING TAF PERIOD THUS MAKING VARY BETWEEN MVFR AND IFR
CONDITIONS. THE REMAINING SITES WILL BE IN VFR THIS AFTERNOON.
HOWEVER, THESE SITES WILL VARY BETWEEN MVFR AND LIFR DURING
EVENING HOURS AS THIS SYSTEM PROGRESSES. THIS WILL DECREASE VSBYS
AND/OR CIGS DUE TO LOW CLOUDS AND FOG/MIST. SLIGHT CHANCE (30%)
FOR KYKM TO RECEIVE SOME LIGHT RAIN/SNOW MIX OVERNIGHT. KALW COULD
DROP TO LIFR OVERNIGHT WHEN LOW CLOUDS ARRIVES ALONG WITH THE
NEXT SYSTEM. FOG MAY DEVELOP BRIEFLY AS WELL FOR KALW, BUT WILL
MONITOR THAT AREA IF MATERIALIZES. KPSC WILL BE VFR THROUGH THIS
TAF PERIOD, THOUGH WITH LIGHT RAIN LASTING FOR THE NEXT FEW HOURS
AS THIS SYSTEM PASSES. FEASTER/97
PRELIMINARY POINT TEMPS/POPS
PDT 34 55 35 49 / 40 30 20 30
ALW 37 54 39 49 / 50 40 30 50
PSC 35 52 32 46 / 60 30 10 40
YKM 33 46 29 43 / 90 70 10 40
HRI 33 53 33 46 / 60 30 20 30
ELN 30 42 27 39 / 80 80 10 60
RDM 30 51 29 50 / 40 40 10 10
LGD 38 51 38 49 / 20 40 40 50
GCD 39 52 36 50 / 10 50 40 60
DLS 38 51 36 45 / 80 70 30 50
PDT WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
SHORT TERM...90
LONG TERM....90
AVIATION...97
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