770
FXUS66 KPDT 011739
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
1039 AM PDT TUE SEP 1 2026
KEY MESSAGES
- A SERIES OF UPPER LEVEL LOW PRESSURE SYSTEMS WILL BRING
PERIODS OF RAIN, BREEZY WESTERLY WINDS, AND ISOLATED
THUNDERSTORM CHANCES THROUGH FRIDAY.
DISCUSSION
UPPER RIDGING AT 500 MB WILL SHIFT TO A SOUTHWESTERLY FLOW
ALOFT TODAY AS AND EASTERN PACIFIC TROUGH SHIFTS TOWARD THE
WA/OR COAST. THE EC/GFS/HIRES MODELS ALL SHOW THE LEAD SHORTWAVE
SPREADING INTO NRN CA TONIGHT AND NORTHWARD TOWARD THE SNAKE
RIVER BY MIDDAY WEDNESDAY. TEMPERATURES TODAY LOOK COOLER BY
ABOUT 5 TO 10 DEGREES ACROSS THE GAPS, CENTRAL OREGON AND WARMER
BY ABOUT 5 DEGREES ACROSS THE YAKIMA VALLEY AND PARTS OF THE
COLUMBIA BASIN OF WASHINGTON. MORE SKY COVER IS EXPECTED TODAY
AHEAD OF A CHANGING SYNOPTIC PATTERN, HOWEVER SOME PERIODS OF
SUN ARE FORECAST BY NBM TRANSITIONING THROUGH THE AFTERNOON.
BREEZY TO WINDY WESTERLY SURFACE WINDS ACROSS THE CENTRAL OREGON
ZONES, EASTERN COLUMBIA GORGE, SIMCOE HIGHLANDS AND THE
KITTITAS VALLEY CAN LINGER INTO THE EVENING AND OVERNIGHT GIVEN
THE SURFACE PRESSURE GRADIENTS. THE BREEZY WINDS, SHIFT WEST
SOUTHWEST THROUGH LATE WEDNESDAY AS THE INITIAL SHORTWAVE
SPREADS EAST OF THE REGION AND THE PARENT UPPER PACIFIC LOW
MOVES ONSHORE THURSDAY NIGHT.
THE PATTERN WILL BRING A TRANSITION TO WET CONDITIONS FOR
MIDWEEK. FOR THIS AFTERNOON, THE HREF CALIBRATED 4-HR
PROBABILITY OF THUNDER IS LIMITED TO A 10 TO 25 PERCENT CHANCE
RANGE BETWEEN ABOUT 20Z AND 03Z OVER EASTERN WALLOWA COUNTY AND
EVEN LOWER CHANCES FOR THE SAME GEOGRAPHIC AREA ON WEDNESDAY
AFTERNOON, SO A LOW CONFIDENCE FORECAST OF ISOLATED DRY
THUNDERSTORMS. PRECIPITATION CHANCES INCREASE FROM THERE AS THE
48 HOUR EXPECTED NBM PRECIPITATION WOULD PUT ABOUT ONE THIRD TO
THREE QUARTERS OF AN INCH OF RAIN BY WEDNESDAY
OVERNIGHT/THURSDAY MORNING. THE EXTENDED PERIOD OF THE FORECAST
LOOKS NEAR TO COOLER THAN NORMAL AND WETTER THAN NORMAL AS THE
AFOREMENTIONED UPPER LOW LINGERS OVER THE PAC NW AND INTERIOR NW
THROUGH AROUND TUESDAY OR WEDNESDAY OF NEXT WEEK.
AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/
VFR CONDITIONS CONTINUE THROUGH THE TAF PERIOD, BUT CONFIDENCE
IN STAYING VFR GOES DOWN AS WE HEAD INTO TOMORROW MORNING, AS A
WEATHER SYSTEM CONTINUES TO PUSH INTO THE AREA. BREEZY WINDS
THROUGH MOST OF THE SITES WITH PEAKS OCCURRING SOMETIME THIS
AFTERNOON INTO THE EVENING HOURS. RAIN CHANCES OF 15-30% START
ENTERING THE PICTURE AT 15Z AT ALW/PDT/PSC WITH NO ANTICIPATED
THUNDERSTORMS EXPECTED. WE'LL SEE THE SYSTEM START TO IMPACT
MOST/ALL TAF SITES WITH MODERATE TO HEAVY RAIN STARTING WITH THE
00Z TAFS, BUT FOR NOW WE CAPTURED THE TAIL END OF THE DRY
PERIOD WITH THE 18Z TAFS.
PRELIMINARY POINT TEMPS/POPS
PDT 83 48 75 45 / 10 10 50 80
ALW 84 54 76 50 / 10 10 50 90
PSC 87 56 79 50 / 10 0 30 60
YKM 88 55 75 50 / 10 0 30 50
HRI 87 55 77 50 / 10 10 40 60
ELN 84 49 71 44 / 0 10 30 60
RDM 80 43 65 40 / 10 10 80 90
LGD 86 48 73 47 / 20 30 70 90
GCD 88 48 73 46 / 10 10 60 100
DLS 81 57 72 53 / 0 0 80 90
PDT WATCHES/WARNINGS/ADVISORIES
WA...AIR QUALITY ALERT UNTIL 10 AM PDT WEDNESDAY FOR WAZ026-522-523.
OR...AIR QUALITY ALERT UNTIL NOON PDT WEDNESDAY FOR ORZ041-505-506-
509>511.
DISCUSSION...71
AVIATION...95
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