516
FXUS66 KPDT 101034
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
334 AM PDT THU SEP 10 2026
KEY MESSAGES
- BREEZY WINDS AND DRY CONDITIONS TODAY - ELEVATED FIRE WEATHER
- ISOLATED THUNDERSTORMS SATURDAY
- WIDESPREAD SHOWERS SATURDAY THROUGH SUNDAY MORNING
DISCUSSION
SHORT TERM
CURRENT RADAR AND INFRARED SATELLITE IMAGERY SHOWS DRY
CONDITIONS AS HIGH LEVEL CLOUDS STREAM ACROSS THE KITTITAS
VALLEY AND INTO THE COLUMBIA BASIN FROM THE NORTH. THIS IS IN
RESPONSE TO AN APPROACHING UPPER LEVEL TROUGH AND ASSOCIATED
WEAK COLD FRONT THAT WILL MOVE INTO THE AREA THIS AFTERNOON.
THE SYSTEM WILL PROVIDE AN INCREASE IN CLOUD COVER, SLIGHTLY
COOLER AFTERNOON TEMPERATURES, LIGHT EVENING SHOWERS OVER THE
NORTHERN BLUE MOUNTAINS/FOOTHILLS, AND BREEZY CONDITIONS ACROSS
THE COLUMBIA GORGE, SIMCOE HIGHLANDS, AND THE KITTITAS VALLEY.
THE OVERALL TREND IN BOTH THE LIGHT RAINFALL AND BREEZY WINDS
HAVE DECREASED OVER THE PAST 24 TO 48 HOURS AS GUIDANCE HAS
TRENDED TOWARD A WEAKER COLD FRONT, UPPER LEVEL SHORTWAVE, AND
PRESSURE GRADIENT DEVELOPING ALONG THE CASCADES. SUSTAINED
WEST-NORTHWEST WINDS OF 15-25 MPH WITH GUSTS OF UP TO 40 MPH
WILL BE POSSIBLE ACROSS THE AFOREMENTIONED AREAS, WITH GUSTS OF
20-25 MPH EXPECTED OVER LOWER ELEVATIONS OF THE COLUMBIA BASIN,
BLUE MOUNTAIN FOOTHILLS, AND CENTRAL OREGON. WINDS PEAK BETWEEN
1PM AND 5 PM. ADVISORY-LEVEL WINDS ARE NOT ANTICIPATED AS THE
NBM SUGGESTS ONLY A 6% CHANCE ACROSS ELLENSBURG, WHICH IS DOWN
FROM 9% YESTERDAY AND 22% ON TUESDAY. HOWEVER, FIRE WEATHER
CONCERNS ARISE AS AFTERNOON HUMIDITIES ARE PROJECTED TO DROP
BACK INTO THE MID-TEENS ACROSS CENTRAL OREGON AND THE JOHN DAY
BASIN. WINDS ARE EXPECTED TO BE JUST SHY OF CRITICAL VALUES AT
LOWER ELEVATIONS WHERE HUMIDITIES ARE LOWEST, BUT MAY STILL LEAD
TO FIRE SPREAD CONCERNS THROUGH THE AFTERNOON AND EARLY
EVENING. DUE TO THE PRESENT DRY AIRMASS, RAIN AMOUNTS ARE
EXPECTED TO BE MINIMAL AND ONLY 0.01-0.05" AT HIGHER ELEVATIONS
THROUGH THE BLUE MOUNTAINS AFTER 5PM. THE HREF AND NBM BOTH
HIGHLIGHT A 10-30% CHANCE OF MEASURABLE RAINFALL (0.01") OVER
THESE AREAS, WITH HIGHEST AMOUNTS IN AND AROUND THE TOLLGATE
AREA.
THE TROUGH BROADENS TONIGHT INTO FRIDAY MORNING AS A STRONG
UPPER LEVEL SHORTWAVE PUSHES OFFSHORE JUST NORTH OF VANCOUVER
ISLAND AND STRENGTHENS TO A LOW PRESSURE SYSTEM AS IT CONTINUES
ITS DESCENT. IT REACHES THE WASHINGTON AND OREGON COASTS EARLY
SATURDAY BEFORE MOVING ONSHORE AND INTO THE REGION SATURDAY
EVENING INTO SUNDAY MORNING. THE DEVELOPING SOUTHWEST FLOW AND
EFFICIENT MOISTURE SUPPLY FROM ANOTHER CLOSED LOW PRESSURE
SYSTEM LOCATED IN THE EASTERN PACIFIC, WILL INITIATE SHOWERS
ALONG THE CASCADE AND EASTERN MOUNTAINS SATURDAY AFTERNOON
BEFORE BECOMING WIDESPREAD AFTER 5PM. GUIDANCE IS IN GOOD
AGREEMENT WITH THIS FEATURE, AND HAS TRENDED SLOWER AND WETTER
IN THE PREVIOUS 24-48 HOURS - WHICH IS DIRECTLY RELATED TO THE
STRENGTH OF THE CLOSED LOW OVER THE EASTERN PACIFIC. THIS SLOWER
PROGRESSION OF THE INCOMING SYSTEM WILL PROVIDE A SLIGHT GAP
BETWEEN THIS SYSTEM AND THE EXITING SYSTEM BRINGING TODAY'S
BREEZY CONDITIONS TO THE AREA. THIS GAP WILL ALLOW A TRANSIENT
RIDGE OF HIGH PRESSURE TO DEVELOP BETWEEN THESE TWO SYSTEMS,
WHICH WILL KEEP HUMIDITIES AT LOWER ELEVATIONS RATHER DRY AND IN
THE 30-40% RANGE EARLY SATURDAY AFTERNOON. AS A RESULT, RAIN
AMOUNTS ACROSS LOWER ELEVATIONS OF THE COLUMBIA BASIN/GORGE,
CENTRAL OREGON, AND BLUE MOUNTAIN FOOTHILLS MAY STRUGGLE TO
REACH A WETTING RAIN (0.10" OR GREATER). HIGHER ELEVATIONS ARE
EXPECTED TO RECEIVE A WETTING RAIN (60-70% CHANCE VIA THE NBM),
WITH UP TO 0.50" OVER THE CASCADE CREST AND WALLOWA COUNTY. THE
DEVELOPING RIDGE WILL ALSO LEAD TO THE POTENTIAL FOR ISOLATED
THUNDERSTORMS TO DEVELOP THROUGH THE AFTERNOON AND EVENING
ACROSS THE EAST SLOPES OF THE CASCADES, JOHN DAY BASIN, AND THE
BLUE MOUNTAINS (15-25% CHANCE). THE MAIN THUNDERSTORM CONCERNS
INCLUDE GUSTY OUTFLOW WINDS, FREQUENT LIGHTNING, AND BRIEF
DOWNPOURS AS BOTH THE AI ECWMF AND GFS ENSEMBLES SUGGEST
PRECIPITABLE WATER AMOUNTS OF 0.88-0.98" - WHICH IS 125-155% OF
NORMAL. 75
LONG TERM
DURING THE DAY ON SUNDAY, MODELS ARE IN GOOD
AGREEMENT THAT RAIN CHANCES WILL START TO DECREASE THROUGHOUT
THE DAY AS THE CLOSED UPPER LOW MOVES INTO THE REGION. LATEST
LREF CLUSTERS SHOW THAT THIS SOLUTION IS SUPPORTED BY AROUND 75%
OF THE MEMBERS. DUE TO THE SLOWING TREND MENTIONED EARLIER, THE
PRECIP WILL LIKELY LINGER THROUGH THE MORNING HOURS AND INTO
THE AFTERNOON. CURRENT NBM PROBABILITIES FOR MEASURABLE PRECIP
(>0.01 IN) DURING THE MORNING ARE HIGHEST IN THE BLUE AND THE
WALLOWA MOUNTAINS WITH PROBABILITIES BETWEEN 70-80%. ELSEWHERE
IN THE CWA, PROBABILITIES ARE GENERALLY BETWEEN 40-50%. THE
EXCEPTION IS IN THE LEE OF THE CASCADES SOUTH OF I-84, WHERE THE
NBM HAS PROBABILITIES BETWEEN 5-20%. MOST OF THE REGION WILL
HAVE A GOOD CHANCE OF SEEING A WETTING RAIN (>0.1IN) FROM THIS
SYSTEM WITH PROBABILITIES FROM THE NBM BETWEEN 50-60% FOR LOWER
ELEVATIONS AND 80-90% IN HIGHER ELEVATIONS. LATEST MODEL
GUIDANCE DOES DEVELOP VERY SMALL AMOUNTS OF INSTABILITY DURING
THE DAY ON SUNDAY OVER THE HIGHER TERRAIN SO AN ISOLATED
THUNDERSTORM COULD DEVELOP (10-20%).
IT IS WORTH NOTING THAT THERE HAS BEEN AN INCREASE IN SUPPORT SINCE
THE LAST RUN OF THE LREF FOR AN OUTLIER SCENARIO WHERE THE TROUGH
DOESN'T COME ASHORE UNTIL MIDDAY SUNDAY. CURRENTLY ONLY AROUND 12%
OF THE MEMBERS SUPPORT THIS SOLUTION (THE VAST MAJORITY OF THEM COME
FROM THE GEPS ENSEMBLE). IN THIS SOLUTION, THE RAIN CHANCES DON'T
COME IN UNTIL SUNDAY (INSTEAD OF SATURDAY) AND THE OVERALL
QPF AMOUNTS ARE LOWER.
AFTER SUNDAY, MODELS INDICATE WEAK LARGE SCALE TROUGHING TO BE
PRESENT WITH THE POSSIBILITY OF A WEAK CUTOFF LOW FORMING OFF THE
COAST OF CALIFORNIA. HOWEVER, GIVEN THE QUIET NATURE OF THE UPPER-
LEVEL FLOW, IMPACTS SEEM LIMITED AT THIS TIME WITH TEMPERATURES
RUNNING AROUND OR SLIGHTLY BELOW NORMAL (1-6F).
AVIATION /12Z TAFS THROUGH 12Z FRIDAY/
VFR CONDITIONS CURRENTLY ACROSS ALL SITES, WHICH WILL STAY THE
COURSE THROUGH THE PERIOD. AN INCOMING SYSTEM WILL LEAD TO
BREEZY WINDS OF 15-25KTS ACROSS MOST SITES, AND INCREASING
BROKEN TO OVERCAST CLOUD COVER WITH CEILINGS OF 25KFT THIS
AFTERNOON AND EVENING. WINDS SHOULD TAPER OFF AS CLOUDS SLOWLY
BREAK TOWARD THE END OF THE PERIOD. 75
PRELIMINARY POINT TEMPS/POPS
PDT 84 48 72 49 / 0 20 0 0
ALW 84 54 73 53 / 0 10 0 0
PSC 87 52 76 50 / 0 0 0 0
YKM 82 50 71 52 / 0 0 0 0
HRI 87 52 76 49 / 0 10 0 0
ELN 74 46 68 47 / 0 0 0 0
RDM 85 44 74 40 / 0 0 0 0
LGD 86 48 75 45 / 0 20 0 0
GCD 86 49 76 47 / 0 0 0 0
DLS 83 54 75 54 / 0 0 0 0
PDT WATCHES/WARNINGS/ADVISORIES
WA...NONE.
OR...NONE.
SHORT TERM...75
LONG TERM...26
AVIATION...75
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