448
FXUS66 KPDT 031121
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
421 AM PDT THU SEP 3 2026
KEY MESSAGES
- PERIODIC SHOWER CHANCES (35-85%) ACROSS THE MOUNTAIN ZONES
WILL CONTINUE THROUGH THE WEEKEND, WITH LOWER CHANCES IN THE
LOWER ELEVATIONS
- ISOLATED THUNDERSTORM CHANCES (15-25%) WILL DEVELOP ACROSS
CASCADES, BLUES, AND WALLOWA COUNTY TODAY AND FRIDAY
- BELOW NORMAL TEMPERATURES THROUGH EARLY NEXT WEEK, WITH
POTENTIAL FOR FREEZING TEMPERATURES IN MOUNTAIN VALLEYS
TONIGHT AND FRIDAY NIGHT
DISCUSSION
WATER VAPOR SATELLITE IMAGERY TONIGHT SHOWS A
SHORTWAVE TROUGH LIFTING NORTHEAST ACROSS THE INTERMOUNTAIN
PACNW, WHILE AN UPPER LOW OFFSHORE IS SWINGING SOUTHEAST TOWARDS
THE COAST. THE SHORTWAVE TROUGH PASSAGE THIS MORNING HAS
RESULTED IN LIGHT TO MODERATE RAINFALL CONTINUING ACROSS THE
EASTERN HALF OF THE FORECAST AREA. THIS ACTIVITY WILL DIMINISH
IN THE LOWER ELEVATIONS OVER THE NEXT COUPLE OF HOURS AS THE
SHORTWAVE LIFTS INTO ID, WITH LIGHT SHOWERS CONTINUING ACROSS
THE MOUNTAINS.
TODAY THROUGH THIS WEEKEND, THE PACNW WILL BE UNDER THE
INFLUENCE OF THE UPPER LEVEL LOW CURRENTLY OFFSHORE, WITH
ANOTHER COUPLE ROUNDS OF RAIN SHOWERS IN THE LOWER ELEVATIONS,
WITH MORE PERSISTENT CHANCES ACROSS THE MOUNTAINS (CONFIDENCE
70-90%). TEMPERATURES ACROSS THE REGION WILL BE NEARLY 10-15
DEGREES BELOW AVERAGE EACH DAY, WITH AFTERNOON HIGH TEMPERATURES
AT THEIR LOWEST IN THE MID 60S AND LOW 70S TODAY AND FRIDAY
(CONFIDENCE 80-90%). BY THIS AFTERNOON, THE UPPER CLOSED LOW
WILL PARK ITSELF OVER THE PACNW, WITH THE CENTER OF THE LOW
REMAINING WEST OF THE CASCADE CREST THROUGH SATURDAY BEFORE
SLIDING EAST SUNDAY INTO MONDAY(CONFIDENCE 75-85%). DURING THIS
TIME, PERSISTENT RAIN SHOWER CHANCES (30-60%) WILL REMAIN OVER
THE CASCADES AND EASTERN MOUNTAINS EACH DAY, WITH SHORTWAVE
IMPULSES FRIDAY/SATURDAY AND THE LOW PASSAGE SUNDAY/MONDAY
PRODUCING LIGHT RAIN CHANCES (15-40%) IN THE LOWER ELEVATIONS.
ISOLATED THUNDERSTORMS WILL BE POSSIBLE OVER THE MOUNTAINS
TODAY AND FRIDAY AS WEAK INSTABILITY DEVELOPS IN THESE AREAS
WITH ADDITIONAL SUPPORT FROM THE COLD CORE OF THE LOW ALOFT. AS
FOR PRECIPITATION AMOUNTS, THE CASCADES AND BLUES WILL SEE 0.1
TO 0.25 INCHES OF DAILY PRECIP (CONFIDENCE 70-90%), WITH
LOCALLY HIGHER AMOUNTS WHERE THUNDERSTORMS DEVELOP.
SUNDAY INTO MONDAY, ENSEMBLE AND DETERMINISTIC MEMBERS SHOW THE
UPPER CLOSED LOW BEGINNING TO PUSH EAST, WITH THE LOW OVER THE
FORECAST AREA DURING THE DAY SUNDAY. WHILE LIGHT TO MODERATE
RAIN SHOWERS ARE FORECAST ACROSS THE AREA, THE UPPER LOW BEING
OVERHEAD AND WEAK INSTABILITY DEVELOPING WILL ALSO RESULT IN
SLIGHT CHANCES (15-25%) OF ISOLATED THUNDERSTORMS FOCUSED ACROSS
CENTRAL OR AND THE EASTERN MOUNTAINS SUNDAY AFTERNOON AND
EVENING. BY MONDAY EVENING, WHAT IS LEFT OF THE UPPER LEVEL LOW
WILL HAVE PUSHED EAST OF THE REGION, WITH SHOWERS DIMINISHING
AREA WIDE.
TUESDAY AND WEDNESDAY, ENSEMBLE MEMBERS ARE IN GOOD AGREEMENT OF
WEAK SPLIT FLOW DEVELOPING OVER THE PACNW AS WEAK ZONAL FLOW
DEVELOPS TO THE NORTH AND TROUGHING TO THE SOUTH. THIS WILL
RESULT IN MOSTLY DRY CONDITIONS, LIGHT WINDS, AND NEAR NORMAL
TEMPERATURES ACROSS THE REGION (CONFIDENCE 40-50%). LAWHORN/82
AVIATION /12Z TAFS THROUGH 12Z FRIDAY/
VFR CONDITIONS TO
PREVAIL THROUGH THE PERIOD. UPPER LEVEL LOW PRESSURE SYSTEM
IMPACTING THE REGION WILL PRODUCE A CHANCE (25-35%) OF LIGHT
RAIN SHOWERS AT MOST SITES BETWEEN 22Z-06Z, EXCEPT AT SITES
YKM/PSC WHERE CHANCES ARE MUCH LOWER THROUGH THE PERIOD. CIGS
MAY LOWER DOWN TO AROUND 5KFT WITH PRECIPITATION, WITH VSBY
REMAINING ABOVE 6 MILES IN PRECIPITATION. WINDS WILL BE LIGHT,
12KTS OR LESS, THROUGH THE PERIOD. LAWHORN/82
PRELIMINARY POINT TEMPS/POPS
PDT 68 42 68 43 / 10 40 30 10
ALW 69 46 68 47 / 20 40 30 20
PSC 73 43 73 43 / 0 10 20 10
YKM 70 45 71 47 / 10 10 20 10
HRI 71 43 71 43 / 0 20 10 20
ELN 66 40 66 41 / 30 20 40 20
RDM 64 31 63 32 / 20 40 50 60
LGD 66 41 66 39 / 80 80 60 40
GCD 63 39 65 39 / 80 70 40 30
DLS 70 47 72 48 / 30 30 20 30
PDT WATCHES/WARNINGS/ADVISORIES
WA...NONE.
OR...NONE.
DISCUSSION...82
AVIATION...82
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