415
FXUS66 KPDT 302248
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
348 PM PDT SUN AUG 30 2026
KEY MESSAGES
- DRYING AND WARMING TREND WILL CONTINUE THROUGH EARLY TUESDAY
AS UPPER LEVEL HIGH PRESSURE MOVES OVER THE REGION
- A SERIES OF UPPER LEVEL LOW PRESSURE SYSTEMS WILL BRING
PERIODS OF RAIN, BREEZY WESTERLY WINDS, AND ISOLATED
THUNDERSTORM CHANCES TUESDAY INTO FRIDAY
DISCUSSION
LITTLE TO TALK ABOUT THIS AFTERNOON AS SATELLITE
IMAGERY SHOWS SOME WISPS OF CIRRUS STREAMING EAST OF THE
CASCADES AND POCKETS OF DENSER SMOKE AROUND ACTIVE WILDFIRES IN
THE CASCADES AND ELKHORN CREST. AT THE SURFACE, WINDS HAVE
MAINLY BE LIGHT, THOUGH A FEW WEAK GUSTS HAVE DEVELOPED ACROSS
PORTIONS OF THE COLUMBIA BASIN.
TODAY THROUGH EARLY TUESDAY: WHILE TEMPERATURES WILL REMAIN
COOLER THAN NORMAL THIS AFTERNOON BEHIND YESTERDAY'S UPPER LOW
PASSAGE, AN UPPER LEVEL RIDGE SLIDING INTO THE PACNW WILL RESULT
IN ANOTHER WARM-UP THAT WILL PERSIST INTO TUESDAY. CONDITIONS
WILL REMAIN DRY UNDER THE HIGH PRESSURE ALOFT, WITH MOSTLY LIGHT
WINDS INTO EARLY TUESDAY.
BEHIND THE UPPER LEVEL RIDGE, AN UPPER SHORTWAVE TROUGH WILL
AMPLIFY SOUTHWARD OFFSHORE OUT OF THE GULF OF ALASKA, WITH
SOUTHERLY FLOW DEVELOPING OVER THE REGION BY TUESDAY MORNING.
TUESDAY AND INTO THE WEEKEND: CONFIDENCE REMAINS HIGH (75-85%)
THAT AN ACTIVE PERIOD OF WEATHER WILL BE IN STORE FOR THE
FORECAST AREA AS TWO LOW PRESSURE SYSTEMS IMPACT THE AREA.
TUESDAY AFTERNOON, THE AFOREMENTIONED SHORTWAVE TROUGH OFFSHORE
THE PACNW WILL LIFT NORTHEAST WITH SCATTERED RAIN SHOWERS
DEVELOPING ALONG THE CASCADES, CENTRAL OR, AND THE BLUES
MOUNTAINS THROUGH TUESDAY EVENING. THE DEEP SOUTHERLY FLOW AHEAD
OF THE TROUGH WILL RESULT IN WEAK INSTABILITY DEVELOPING OVER
THE AREA, THOUGH ISOLATED THUNDERSTORM CHANCES (10-20%) WILL BE
LIMITED TO FAR NORTHEAST OR TUESDAY AFTERNOON. THE APPROACHING
UPPER LOW WILL ALSO RESULT IN PRESSURE GRADIENTS TIGHTENING
ACROSS THE REGION, WITH BREEZY WESTERLY WINDS DEVELOPING IN THE
LOWER ELEVATIONS BY TUESDAY AFTERNOON. BREEZY WINDS WILL OVERLAP
WITH LOW RELATIVE HUMIDITY IN THE HARNEY BASIN, PROMOTING
ELEVATED FIRE WEATHER CONDITIONS ALONG THE SOUTHERN PERIPHERY OF
THE SOUTHERN BLUE MOUNTAINS AND CENTRAL OR FIRE WEATHER ZONES.
WEDNESDAY, THERE IS GOOD AGREEMENT AMONGST ENSEMBLE GUIDANCE
THAT THE UPPER TROUGH WILL LIFT NORTHEAST ACROSS THE PACNW,
PROVIDING THE BEST CHANCE OF WIDESPREAD RAIN SHOWERS ACROSS THE
MOUNTAINS AND LOWER ELEVATIONS THROUGH THE REMAINDER OF THE
PERIOD. DURING TRANSIT, THE UPPER TROUGH WILL TAKE ON A NEGATIVE
TILT THAT WILL PROMOTE ISOLATED TO WIDELY SCATTERED
THUNDERSTORMS DEVELOPING ACROSS THE BLUE MOUNTAINS IN THE
AFTERNOON AND EARLY EVENING. BREEZY WEST TO SOUTHWEST WINDS
WILL DEVELOP ACROSS THE LOWER ELEVATIONS THROUGHOUT WEDNESDAY,
BUT THE FIRE WEATHER THREAT WILL REMAIN LOW OWING TO COOLER
TEMPERATURES AND HIGHER RELATIVE HUMIDITY ACROSS THE AREA. THE
PROBABILITY OF WETTING RAINS (>0.1 INCHES) WILL BE 30-65% IN THE
LOWER ELEVATIONS, AND 70-90% IN THE MOUNTAINS FOR WEDNESDAY.
MEANWHILE, ENSEMBLE CLUSTER SOLUTIONS REMAIN IN GOOD AGREEMENT
THAT A POTENT UPPER LOW WILL DIVE SOUTH ALONG THE BC COASTLINE
AND ARRIVE OFFSHORE VANCOUVER ISLAND BY WEDNESDAY EVENING.
THURSDAY INTO SATURDAY, ENSEMBLE CLUSTER SOLUTIONS ARE IN
GENERAL AGREEMENT THAT THE UPPER LOW OFFSHORE THE PACNW WILL
CONTINUE TO IMPACT THE REGION WITH SHOWER ACTIVITY (ESPECIALLY
OVER THE CASCADES), BUT DIVERGE ON THE EVOLUTION OF THE UPPER
LOW IN REGARDS TO LOCATION AND TIMING. THE TWO MAIN SOLUTIONS
ARE FOR THE UPPER LOW TO MOVE INLAND AND ACROSS THE PACNW OR
STAY OFFSHORE THROUGH THE PERIOD. WHILE THERE IS AGREEMENT ON
THE FORMER OCCURRING, ENSEMBLE CLUSTER SOLUTIONS ARE SPLIT ON
THE TIMING OF UPPER LOW MOVING INLAND. AS WHAT THIS MEANS FOR
THE FORECAST, THE SOLUTIONS FAVORING THE UPPER LOW MOVING INLAND
WILL BRING LIGHT TO MODERATE RAIN SHOWERS TO PORTIONS OF THE
EASTERN MOUNTAINS AND THE BLUES; SOLUTIONS FAVORING THE UPPER
LOW OFFSHORE KEEP SHOWER CHANCES TIED TO THE CASCADE CREST AND
EAST SLOPES. WHILE CONFIDENCE REMAINS MODERATE (60-75%) IN RAIN
SHOWERS CONTINUING INTO THE WEEKEND, CONFIDENCE IS LOW (20-25%)
IN THE DETAILS AND TIMING. LAWHORN/82
AVIATION /00Z TAFS THROUGH 00Z TUESDAY/
VFR CONDITIONS PREVAIL WITH LIGHT AND VARIABLE WINDS THROUGH THE
FORECAST PERIOD. NO SUB-VFR CONDITIONS EXPECTED, EXCEPT A SMALL
CHANCE (5 TO 15 PERCENT) OF SOME SMOKE MAKING IT DOWN TO THE
SURFACE DURING THE OVERNIGHT TO EARLY MORNING HOURS FOR ALL TAF
SITES.
PRELIMINARY POINT TEMPS/POPS
PDT 44 86 51 83 / 0 0 0 0
ALW 50 89 57 85 / 0 0 0 0
PSC 49 89 54 88 / 0 0 0 0
YKM 54 86 59 87 / 0 0 0 0
HRI 49 88 55 86 / 0 0 0 0
ELN 47 81 54 82 / 0 0 0 10
RDM 41 87 46 80 / 0 0 0 40
LGD 44 89 52 87 / 0 0 0 10
GCD 47 92 54 87 / 0 0 0 0
DLS 55 88 62 81 / 0 0 0 0
PDT WATCHES/WARNINGS/ADVISORIES
WA...NONE.
OR...AIR QUALITY ALERT UNTIL NOON PDT MONDAY FOR ORZ041-505-506-
509>511.
DISCUSSION...82
AVIATION...95
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