744
FXUS66 KPDT 122257
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
357 PM PDT FRI SEP 12 2025
AVIATION...00Z TAFS
VFR CONDITIONS ARE FORECAST FOR ALL SITES
THROUGH THE VALID PERIOD. ASIDE FROM BREEZY WINDS IN THE AFTERNOON
AT DLS, LIGHT WINDS ARE FORECAST. MOSTLY CLEAR SKIES THIS
AFTERNOON WILL BECOME PARTLY CLOUDY (MID- AND HIGH-LEVEL CLOUD)
BY SATURDAY AFTERNOON AS A WEATHER SYSTEM APPROACHES FROM THE
PACIFIC. 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 56 84 58 72 / 0 0 10 60
ALW 60 85 62 73 / 10 0 0 60
PSC 55 87 58 75 / 0 0 0 50
YKM 56 86 58 74 / 0 0 10 50
HRI 56 87 59 74 / 0 0 10 60
ELN 52 84 54 71 / 0 0 10 50
RDM 46 82 50 66 / 0 0 30 60
LGD 51 82 53 69 / 10 0 0 70
GCD 50 82 53 70 / 10 0 10 60
DLS 57 85 61 73 / 0 0 20 60
PDT WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
SHORT TERM...82
LONG TERM....82
AVIATION...86
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