486
FXUS66 KPDT 231754
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
1054 AM PDT THU OCT 23 2025
UPDATED AVIATION DISCUSSION
AVIATION...18Z TAFS
ALL SITES WILL BE VFR THROUGHOUT THIS PERIOD.
KRDM/KBDN MAY SEE BREEZY WINDS TOMORROW MORNING FROM THE UPCOMING
FRONTAL PASSAGE. OTHERWISE, WINDS WILL BE LESS THEN 12KTS FOR ALL
SITES. FEASTER/97
PREV DISCUSSION
/ISSUED 419 AM PDT THU OCT 23 2025/
DISCUSSION
KEY MESSAGES:
1. WIDESPREAD RAIN FRIDAY AND SATURDAY,
2. MOUNTAIN SNOWFALL SATURDAY THROUGH MONDAY.
3. BREEZY WINDS FRIDAY TURNING WINDY SATURDAY INTO SUNDAY MORNING.
CURRENT RADAR AND INFRARED SATELLITE IMAGERY SHOWS DRY CONDITIONS
AS MID-TO HIGH LEVEL CLOUDS MOVE OVERHEAD FROM THE WEST-NORTHWEST.
THIS IS IN RESPONSE TO SOME LINGERING MOISTURE FROM THE
SHORTWAVE THAT PASSED THROUGH THE AREA WEDNESDAY EVENING. CLOUDS
WILL BRIEFLY CLEAR THIS AFTERNOON AS A WEAK RIDGE BUILDS IN FROM
THE SOUTH BEFORE SHIFTING EAST AS A ROBUST SYSTEM IN THE PACIFIC
STRENGTHENS AND APPROACHES THE COAST FRIDAY MORNING. BEFORE THIS
SYSTEM ARRIVES, AFTERNOON HUMIDITIES ACROSS CENTRAL OREGON WILL
DROP INTO THE MID-TO UPPER TEENS TODAY AND FRIDAY WITH MARGINAL
(40-50%) OVERNIGHT HUMIDITY RECOVERIES TONIGHT INTO FRIDAY
MORNING. FRIDAY DOES LOOK TO BE THE DRIER DAY, BUT EXCELLENT
(75-90%) OVERNIGHT HUMIDITY RECOVERIES SATURDAY MORNING AND
IMPROVED (+20-30%) MINIMUM HUMIDITIES DURING THE AFTERNOON.
THIS SYSTEM WILL BE SANDWICHED BETWEEN SHORTWAVES AND ACCOMPANIED
BY A SUBSTANTIAL ATMOSPHERIC RIVER (AR), WHICH WILL HELP PROVIDE
EFFICIENT MOISTURE TRANSPORT FRIDAY IN ORDER TO SET THE STAGE FOR
A SOGGY WEEKEND. THE INITIAL SHORTWAVE WILL PASS FRIDAY EVENING,
WITH THE MAIN SYSTEM PASSING MIDDAY SATURDAY AHEAD OF A
REINFORCING SHORTWAVE SUNDAY AFTERNOON. SHOWERS WILL BEGIN ALONG
THE WASHINGTON CASCADES FRIDAY MORNING, THEN WILL EXTEND ALONG THE
EAST SLOPES AND THE OREGON CASCADES IN THE AFTERNOON BEFORE
PUSHING INTO THE BASIN, FOOTHILLS, AND THE BLUE MOUNTAINS IN THE
EVENING. 0.25-0.40" OF RAIN IS EXPECTED ACROSS THE CASCADES,
0.15-0.30" OF RAIN ALONG THE EAST SLOPES OF THE CASCADES AND THE
BLUE MOUNTAINS, AND 0.05-0.15" OF RAIN ACROSS LOWER ELEVATIONS OF
THE COLUMBIA BASIN, CENTRAL OREGON, BLUE MOUNTAIN FOOTHILLS, AND
THE YAKIMA/KITTITAS VALLEYS ON FRIDAY. THE WETTEST DAY IS
EXPECTED TO COME ON SATURDAY AS RAIN AMOUNTS OF 0.50-0.75" ARE
LIKELY OVER THE CASCADES AND BLUE MOUNTAINS, 0.25-0.50" OF
RAINFALL ACROSS CENTRAL OREGON, BLUE MOUNTAIN FOOTHILLS, AND THE
GRANDE RONDE VALLEY, AND 0.05-0.15" OF RAIN LIKELY FOR LOWER
ELEVATIONS OF THE COLUMBIA BASIN AND THE YAKIMA/KITTITAS VALLEYS.
UPPER LEVEL FLOW BECOMES MORE ZONAL OR FROM THE WEST ON SUNDAY,
LEADING TO MORE OF A RAIN SHADOW EFFECT ACROSS SOUTH-CENTRAL
WASHINGTON AS RAIN AMOUNTS ARE EXPECTED TO STAY BELOW 0.06" OR
LESS FOR LOWER ELEVATIONS OF THE COLUMBIA BASIN AND THE
YAKIMA/KITTITAS VALLEYS. RAIN AMOUNTS OF 0.15-0.25" ARE MORE
LIKELY FURTHER SOUTH ACROSS CENTRAL OREGON AND THE BLUE MOUNTAIN
FOOTHILLS ON SUNDAY. SHOWERS BEGIN TO BE MORE CONFINED TO OUR
MOUNTAIN ZONES ON MONDAY AS A WEAK UPPER LEVEL RIDGE BUILDS SLOWLY
FROM THE SOUTH.
HIGH ELEVATION MOUNTAIN SNOWFALL WILL BEGIN FALLING FRIDAY EVENING
ASSOCIATED WITH THIS INCOMING SYSTEM, WITH SNOW LEVELS HOVERING
BETWEEN 4500-5000 FEET ON SATURDAY. AS A RESULT, SANTIAM AND WHITE
PASSES ARE EXPECTED TO RECEIVE 5-8 INCHES OF SNOWFALL SATURDAY,
WITH AN ADDITIONAL 7-11 INCHES ON SUNDAY AS SNOW LEVELS DROP TO
BETWEEN 3500-4000 FEET. THESE TWO-DAY SNOW ACCUMULATIONS WOULD
REACH EITHER ADVISORY OR ISOLATED AREAS OF WARNING CRITERIA, BUT
CONFIDENCE IN THESE SNOW TOTALS ARE STILL LACKING. THIS IS
PRIMARILY IN CONNECTION WITH ENSEMBLE MEMBERS AS 58% SUGGEST A
SLIGHTLY WEAKER PASSING TROUGH, WHICH WOULD RELATE TO SLIGHTLY
HIGHER SNOW LEVELS AND LESS SNOW AMOUNTS. HOWEVER, THIS IS THE
FIRST AR EVENT OF THE SEASON, WHICH IS USUALLY UNDER-REPRESENTED
BY GUIDANCE. IT IS EXPECTED THAT AN ELEVATION-BASED ADVISORY WILL
BE ISSUED SATURDAY THROUGH SUNDAY AS THE NBM SUGGESTS A 70-80%
CHANCE OF ADVISORY-LEVEL SNOW AMOUNTS ACROSS SANTIAM (5") AND
WHITE (6") PASSES, AND A 40-60% CHANCE OF WARNING-CRITERIA BEING
REACHED. SNOW AMOUNTS ARE LIKELY TO STAY JUST BELOW ADVISORY
CRITERIA OVER THE BLUE MOUNTAINS, WITH HIGHER TERRAIN PICKING UP A
48 HOUR TOTAL SATURDAY AND SUNDAY OF 3-6 INCHES (50-70%
CONFIDENCE). ANOTHER 2-4 INCHES OF SNOW ABOVE 4000 FEET IS
EXPECTED ON MONDAY BEFORE THE RIDGE BUILDS LATE MONDAY INTO
TUESDAY.
THE RIDGE THAT IS BRIEFLY BUILDING OVER THE REGION TODAY BEFORE
SHIFTING EAST, WILL ALLOW FOR A PRESSURE GRADIENT TO TIGHTEN
ACROSS THE COLUMBIA BASIN AS THE INCOMING SYSTEM NEARS THE AREA.
THIS WILL LEAD TO BREEZY WINDS FRIDAY AFTERNOON AND INTENSIFYING
INTO SATURDAY AS A VORTICITY MAXIMUM SURROUNDS THE TROUGH AXIS,
PEAKING IN THE MORNING AND AGAIN DURING THE EVENING AND OVERNIGHT
PERIOD INTO SUNDAY. SUSTAINED SOUTHWEST WINDS OF 15-25 MPH WITH
GUSTS UP TO 35 MPH ARE EXPECTED FRIDAY ACROSS THE EAST SLOPES OF
THE CASCADES, CENTRAL OREGON, GRANDE RONDE VALLEY, AND THE
SOUTHERN BLUE MOUNTAINS/FOOTHILLS. SOUTHWEST WINDS WILL INCREASE
TO BETWEEN 25-35 MPH WITH GUSTS OF UP TO 50 MPH ON SATURDAY
ACROSS THE AFOREMENTIONED AREAS. THE NBM SUGGESTS A 70-80% CHANCE
OF OCCURRENCE, WHICH WOULD WARRANT THE ISSUANCE OF A WIND
ADVISORY ON SATURDAY. CURRENT ENSEMBLE MEMBERS ARE CURRENTLY SPLIT
(50/50) IN REGARDS TO HOW TIGHT PRESSURE GRADIENTS BECOME ON
SATURDAY. THUS, THIS WILL NEED TO BE FURTHER ANALYZED AS THE EVENT
NEARS, BUT CURRENTLY DOES SEEM IN-LINE WITH THE 850MB WIND
FORECAST AS THEY ARE EXPECTED TO MIX DOWN TO THE SURFACE. 75
PRELIMINARY POINT TEMPS/POPS
PDT 66 43 67 45 / 0 0 10 70
ALW 65 48 67 48 / 0 0 10 80
PSC 65 42 64 44 / 0 0 10 60
YKM 63 43 63 38 / 10 0 60 70
HRI 66 43 64 44 / 0 0 10 70
ELN 60 39 57 33 / 10 10 60 80
RDM 68 40 67 38 / 0 0 30 80
LGD 64 41 66 44 / 0 0 10 70
GCD 67 42 69 44 / 0 0 0 70
DLS 67 48 64 46 / 10 10 70 90
PDT WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
SHORT TERM...75
LONG TERM....75
AVIATION...97
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