400
FXUS66 KPDT 131750
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
1050 AM PDT SAT SEP 13 2025
AVIATION...18Z TAFS
MOSTLY CLEAR SKIES THIS MORNING WILL
BECOME SCT-BKN (MID- AND HIGH-LEVEL CLOUD) BY THIS EVENING AS A
WEATHER SYSTEM APPROACHES FROM THE PACIFIC. BKN-OVC SKIES ARE THEN
FORECAST OVERNIGHT THROUGH SUNDAY MORNING, AND ALL SITES HAVE A
30-50% CHANCE OF RAIN SHOWERS ALONG AND AHEAD OF A COLD FRONTAL
PASSAGE. THUNDER CHANCES ARE LOW (15% OR LESS), BUT CANNOT RULE
OUT ISOLATED EMBEDDED THUNDERSTORMS WITHIN THE BROADER REGION OF
SHOWERS.
THE OVERNIGHT TIMING OF THE COLD FRONTAL PASSAGE REDUCES
CONFIDENCE IN TAF DETAILS TO MEDIUM (40-60%) DUE TO UNCERTAINTY IN
WINDS, AND OF COURSE EXACT TIMING/LOCATION OF SHOWERS.
ADDITIONALLY, SUB-VFR CONDITIONS MAY OCCUR IN SHOWERS AND/OR
THUNDERSTORMS, BUT CONFIDENCE WAS TOO LOW (<30%) TO INCLUDE ANY
MENTION IN THE 18Z TAFS. PLUNKETT/86
PREV DISCUSSION
/ISSUED 143 PM PDT FRI SEP 12 2025/
DISCUSSION...SATELLITE IMAGERY THIS AFTERNOON SHOWS LEFT OVER
CLOUD COVER FROM OVERNIGHT AND MORNING SHOWERS MOVING ACROSS FAR
EASTERN OR AND SOUTHEASTERN WA. OTHERWISE, SCATTERED CUMULUS
FIELDS ARE DEVELOPING OVER THE HIGH ELEVATION RIDGES OF THE
EASTERN MOUNTAINS, WITH RADAR HAVING PICKED UP A WEAK SHOWER OR
TWO MOVING SOUTH FROM THE WALLOWA MOUNTAINS.
TODAY THROUGH SATURDAY: AN UPPER LOW THAT HAS FUELED SHOWERS AND
THUNDERSTORMS ACROSS THE AREA THE PAST SEVERAL DAYS HAS MOVED OFF
INTO THE ID THIS MORNING, WITH THE FORECAST AREA ON THE NORTHERLY
FLOW SIDE OF THE LOW. THIS WILL RESULT IN MOST OF THE SHOWER AND
THUNDERSTORM ACTIVITY BEING FOCUSED ACROSS FAR SOUTHEASTERN WA,
WALLOWA COUNTY, AND THE MOUNTAINOUS TERRAIN IN UMATILLA AND GRANT
COUNTIES THROUGH THIS EVENING. MUCH LIKE PREVIOUS DAYS, MODEST
CAPE (250-750 J/KG), AND MODEST LOWER TO MID LEVEL LAPSE RATES
WILL ALLOW THUNDERSTORMS TO DEVELOP FAIRLY QUICKLY (PULSE) THROUGH
THE AFTERNOON, HOWEVER STORMS WILL BE SLOW MOVING AS STEERING
FLOW IS FAIRLY WEAK (10-15 KTS) IN THE LOWER AND MID LEVELS. THIS
WILL RESULT IN SOME STORMS PRODUCING TORRENTIAL RAINFALL, SMALL
HAIL, AND FREQUENT LIGHTNING. 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. 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 30-50% 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 (15-25%) OF ISOLATED TO
WIDELY SCATTERED THUNDERSTORMS ACROSS THE CASCADE CREST,
CENTRAL/NORTH CENTRAL OR, AND EASTERN MOUNTAINS. BREEZY WEST WINDS
(15-25 MPH AND GUSTS 25-40 MPH) 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 CONTINUES TO BE IN
DISAGREEMENT WITH THE LOCATION, STRENGTH, AND TIMING OF THE TROUGH
PASSAGE THROUGH THURSDAY. THE MAIN IMPACTS WILL BE FELT FROM THE
LOCATION/STRENGTH OF THE TROUGH, AS SOME ENSEMBLE MEMBERS HAVE THE
TROUGH SWING UP INTO BC AND CLIP THE CENTRAL WA CASCADES WITH
LIGHT SHOWERS, WHILE OTHER MEMBERS SHOW THE TROUGH SWINGING INLAND
OVER THE PACNW WITH SHOWER ACTIVITY ALONG THE NORTHERN OREGON AND
WASHINGTON CASCADES. BETWEEN THESE TWO SOLUTIONS, THE FURTHER
SOUTH TRAJECTORY OF THE UPPER TROUGH WOULD ALSO RESULT IN A COOLER
AIRMASS SETTLING INTO THE REGION WHILE THE FURTHER NORTH SOLUTION
WOULD RESULT IN SOME COOLING, BUT NOT TO THE SAME DEGREE.
CURRENTLY, CONFIDENCE IN SHOWER ACTIVITY RETURNING TO THE WA
CASCADES IS MODERATE (65-75%) FOR WEDNESDAY AND THURSDAY, WITH LOW
CONFIDENCE (25-35%) ACROSS THE OREGON CASCADES. OTHERWISE, THERE
IS GOOD AGREEMENT THAT DRIER CONDITIONS WILL PERSIST IN THE LOWER
ELEVATIONS WITH LOW CHANCES OF SHOWERS IN THE BLUES AS WELL.
(CONFIDENCE 50-60%). LAWHORN/82
PRELIMINARY POINT TEMPS/POPS
PDT 84 58 72 50 / 0 10 80 30
ALW 86 62 72 54 / 0 10 70 40
PSC 87 58 75 51 / 0 10 70 20
YKM 87 56 75 48 / 0 20 60 10
HRI 87 59 74 51 / 0 20 80 20
ELN 84 53 71 47 / 0 20 60 20
RDM 82 51 68 38 / 0 50 60 10
LGD 82 53 67 44 / 0 10 80 50
GCD 82 52 68 42 / 0 20 80 30
DLS 86 61 74 51 / 0 50 70 10
PDT WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
SHORT TERM...82
LONG TERM....82
AVIATION...86
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page