754
FXUS66 KPDT 120625
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
1125 PM PDT THU SEP 11 2025
AVIATION...06Z TAFS
SOME SHOWERS AND THUNDERSTORMS ARE
LINGERING OVER NORTHEAST OREGON AND SOUTHEAST WASHINGTON THIS
EVENING. MOST ACTIVITY IS EXPECTED TO REMAIN OVER THE BLUE
MOUNTAINS, BUT CONFIDENCE IN RAIN AT ALW WAS HIGH ENOUGH (50%) TO
INCLUDE A TEMPO GROUP THROUGH 10Z. CONFIDENCE IN THUNDER AT ALW
WAS TOO LOW (<30%) TO INCLUDE A MENTION. FARTHER SOUTH,
CONFIDENCE IS LOWER (10%) IN SHOWERS AND/OR THUNDER AT PDT. SUB-
VFR CONDITIONS ARE UNLIKELY, BUT POSSIBLE (<30% CONFIDENCE), WITH
THE AFOREMENTIONED ACTIVITY OVERNIGHT AT ALW/PDT.
SKIES ARE FORECAST TO BECOME MOSTLY CLEAR BY FRIDAY MORNING AT ALL
SITES, WITH VFR CONDITIONS LIKELY (>80% CONFIDENCE) THROUGH THE
REMAINDER OF THE VALID PERIOD.
MOSTLY LIGHT, DIURNALLY AND TERRAIN-DRIVEN WINDS OF 10 KTS OR LESS
ARE FORECAST FOR ALL SITES. PLUNKETT/86
PREV DISCUSSION
/ISSUED 117 PM PDT THU SEP 11 2025/
DISCUSSION...CURRENT SATELLITE AND RADAR IMAGERY SHOW SOME
ISOLATED STORMS BEGINNING TO DEVELOP OFF PORTIONS OF THE SOUTHERN
BLUES AND THE WALLOWAS THIS AFTERNOON, WITH SCATTERED CLOUD COVER
ACROSS NORTHEAST OR, AND PORTIONS OF SOUTHEAST WA.
TODAY THROUGH SATURDAY: AN UPPER LOW WILL CONTINUE TO PUSH ACROSS
THE EASTERN HALF OF THE PACNW TODAY AND SLOWLY PUSH EAST INTO THE
NORTHERN ROCKIES THROUGH FRIDAY NIGHT. HIGH-RES MEMBERS OF THE
HREF SHOW ANOTHER ROUND OF SCATTERED THUNDERSTORMS AND SHOWERS
DEVELOPING THROUGH THIS EVENING FROM CENTRAL OR UP TO SOUTHEAST
WA, WITH BEST CHANCES (20-40%) OF THUNDERSTORM ACTIVITY ACROSS THE
EASTERN MOUNTAINS. BY LATE TONIGHT, SHOWER/THUNDERSTORM ACTIVITY
WILL RETREAT TO FAR NORTHEAST OR AND SOUTHEAST WA, THEN WILL
DIMINISH BY LATE FRIDAY EVENING AS THE LOW PUSHES FURTHER EAST OF
THE REGION. PLENTY OF MOISTURE SUPPORT FROM THE UPPER LOW, MODEST
CAPE (250-750J/KG), AND MODEST LOWER TO MID LEVEL LAPSE RATES
ALLOW THUNDERSTORMS TO DEVELOP FAIRLY QUICKLY THROUGH THE
AFTERNOON, HOWEVER STORMS WILL BE SLOW MOVING AS STEERING FLOW IS
FAIRLY WEAK (10-15KTS) IN THE LOWER AND MID LEVELS. THESE
ATMOSPHERIC INGREDIENTS WILL ALLOW STORMS TO PRODUCE SOME GUSTY
OUTFLOW WINDS, SMALL HAIL, HEAVY RAIN, AND ABUNDANT LIGHTNING. THE
SLOW MOVING CELLS AND/OR TRAINING CELLS WITH HEAVY RAIN WILL
BRING A RISK OF FLASH FLOODING (AT LEAST 5%) TO RECENT BURN SCARS
ACROSS THE EASTERN MOUNTAINS. BY SATURDAY, DRIER CONDITIONS WILL
SETTLE INTO THE REGION AS TRANSIENT RIDGING SLIDES ACROSS THE
PACNW.
SATURDAY NIGHT THROUGH MONDAY: ENSEMBLE GUIDANCE IS IN GOOD
AGREEMENT OF AN UPPER TROUGH AND SURFACE COLD FRONT SWINGING
ACROSS THE PACNW THROUGH MONDAY, THOUGH ENSEMBLE MEMBERS (ECMWF,
GFS, AND CANADIAN) ARE SPLIT 50/50 ON WHETHER THE UPPER TROUGH
EXITS BY LATE MONDAY MORNING OR BY LATE MONDAY AFTERNOON. THE
UPPER TROUGH/COLD FRONT PASSAGE WILL PRODUCE A ROUND OF
SHOWERS WITH MOUNTAIN THUNDERSTORMS STARTING ACROSS THE CASCADE
CREST EARLY SUNDAY MORNING, THEN SPREADING EAST THROUGHOUT SUNDAY.
BEST PRECIPITATION CHANCES (60-80% MOUNTAINS AND 25-50% ELSEWHERE)
WILL BE ASSOCIATED WITH THE COLD FRONT PASSAGE SUNDAY MORNING AND
AFTERNOON, WITH DRYING CONDITIONS IN THE LOWER ELEVATIONS AND
CHANCES DECREASING IN THE MOUNTAINS (20-45%). ENSEMBLE GUIDANCE
ALSO DEPICTS THE TROUGH TAKING ON A NEGATIVE TILT AS IT COMES
ASHORE, WHICH WILL LEND ENOUGH INSTABILITY FOR SLIGHT CHANCES
(15-20%) OF ISOLATED THUNDERSTORMS ACROSS THE CASCADE CREST AND
EASTERN MOUNTAINS. BREEZY WEST WINDS (15-25MPH AND GUSTS 25-40MPH)
WILL ALSO DEVELOP SUNDAY AFTERNOON BEHIND THE COLD FRONT PASSAGE,
BUT WINDS WILL BE LIGHT TO LOCALLY BREEZY MONDAY(CONFIDENCE
50-80%).
TUESDAY THROUGH THURSDAY: ENSEMBLE GUIDANCE CONTINUES TO BE IN
GOOD AGREEMENT THAT UPPER LEVEL RIDGING WILL ONCE AGAIN SLIDE BACK
OVER THE PACNW TUESDAY, RESULTING IN DRYING CONDITIONS AREA WIDE.
BEHIND THE UPPER RIDGE, UPPER LEVEL TROUGHING EJECTING FROM A
LARGER TROUGH OVER THE ALEUTIAN ISLAND CHAIN WILL APPROACH THE
PACNW LATE TUESDAY, HOWEVER, ENSEMBLE GUIDANCE COMES INTO
DISAGREEMENT WITH THE LOCATION, STRENGTH, AND TIMING OF THE TROUGH
PASSAGE. ABOUT 60% OF ENSEMBLE MEMBERS FAVOR THE UPPER TROUGH
INLAND BY WEDNESDAY AFTERNOON, WHILE THE REMAINING 40% KEEP THE
TROUGH OFFSHORE. OF THE AFOREMENTIONED 60% OF MEMBERS, ONLY 20%
HAVE THE TROUGH CLIPPING THE PACNW WITH SHOWER ACTIVITY ACROSS THE
MOUNTAINS WHILE THE OTHER 40% KEEP THE TROUGH AND PRECIPITATION
FURTHER NORTH IN CANADA. AS FOR LATE WEDNESDAY INTO THURSDAY,
ENSEMBLE GUIDANCE DOES AGREE THAT SHORTWAVE TROUGHING WILL DEVELOP
OVER THE PACNW, THOUGH CONDITIONS LOOK TO REMAIN MOSTLY DRY,
EXCEPT FOR THE LOW POTENTIAL (15-20%) OF A SHOWER OR TWO OVER THE
WA CASCADE CREST. LAWHORN/82
PRELIMINARY POINT TEMPS/POPS
PDT 57 82 56 85 / 20 10 0 0
ALW 61 83 61 86 / 30 10 10 0
PSC 57 85 56 87 / 10 0 0 0
YKM 56 85 56 86 / 10 0 0 0
HRI 58 84 56 87 / 10 0 0 0
ELN 54 83 51 85 / 10 0 0 0
RDM 44 78 46 83 / 30 0 0 0
LGD 51 78 51 82 / 50 40 10 0
GCD 50 77 50 82 / 40 30 10 0
DLS 59 83 58 87 / 10 0 0 0
PDT WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
SHORT TERM...82
LONG TERM....82
AVIATION...86
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