193
FXUS66 KPDT 190539
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
1039 PM PDT FRI SEP 18 2026
KEY MESSAGES
- WARMER AND DRIER TREND THROUGH THE WEEKEND.
- COOLER THROUGH WORKWEEK, SHOWERS POSSIBLE LATE IN THE WEEK.
DISCUSSION
CURRENT RADAR AND VISIBLE SATELLITE IMAGERY SHOWS LIGHT TO
MODERATE RETURNS AND BUILDING CLOUDS OVER WALLOWA, SOUTHERN
UNION, AND EASTERN GRANT COUNTIES. THIS IS IN RESPONSE TO A
SLOWLY DEPARTING UPPER LEVEL LOW PRESSURE SYSTEM MOVING INTO
SOUTHERN IDAHO THIS EVENING AS AN UPPER LEVEL RIDGE BUILDS IN
ITS WAKE. THE INCOMING HIGH PRESSURE IS KEEPING SKIES CLEAR
ACROSS THE COLUMBIA BASIN AND CENTRAL OREGON, BUT ALSO
ATTRIBUTES TO A POTENTIAL FOR THUNDERSTORMS DEVELOPING ALONG
THE BOUNDARY BETWEEN THE DEPARTING LOW AND INCOMING RIDGE.
TOWERING CUMULUS CLOUDS ARE CURRENTLY BEING OBSERVED ALONG THIS
BOUNDARY, AND IS EXPECTED TO LEAD TO ISOLATED THUNDERSTORMS
INTO THIS EVENING ACROSS WALLOWA, UNION, AND GRANT COUNTIES.
BOTH THE HREF AND REFS ALIGN WITH THUNDERSTORM POTENTIAL
EXTENDING UNTIL 8PM AS CAPE VALUES PEAK BETWEEN 200-400 J/KG
BEFORE 4PM. THE MAIN CONCERNS IN AND AROUND ANY STORM CELLS WILL
INCLUDE FREQUENT LIGHTNING, SMALL HAIL, AND BREEZY AND ERRATIC
OUTFLOW WINDS. ANY STORMS THAT DEVELOP SHOULD BE RATHER WET, AS
BOTH THE AI ECWMF AND GFS ENSEMBLES SHOWCASE PRECIPITABLE WATER
AMOUNTS OF 0.6-0.8" WHICH IS 120-140% OF NORMAL. RAIN AMOUNTS
WITHIN STORMS MAY REACH TO NEAR 0.20", AS LITTLE TO NO RAIN IS
EXPECTED OUTSIDE OF RAIN CORES.
THE UPPER LEVEL RIDGE CONTINUES TO BUILD AND SLOWLY SHIFT EAST
THROUGH THE WEEKEND, KEEPING SKIES SUNNY, CONDITIONS DRY, AND
TEMPERATURE WARMING AS UPPER LEVEL FLOW ENHANCES OUT OF THE
WEST-SOUTHWEST. HIGH TEMPERATURES WILL PEAK SUNDAY AND MONDAY,
REACHING INTO THE MID-80S ACROSS THE COLUMBIA BASIN AND CENTRAL
OREGON. AFTERNOON HUMIDITIES WILL ALSO DIVE INTO THE MID-TO
UPPER TEENS ACROSS CENTRAL OREGON AND THE JOHN DAY BASIN SUNDAY
AND PERSIST THROUGH THE WEEK.
GUIDANCE STRUGGLES WITH AGREEMENT TUESDAY ONWARD ASSOCIATED
WITH A PASSING UPPER LEVEL SHORTWAVE MOVING ACROSS SOUTH-CENTRAL
BRITISH COLUMBIA AHEAD OF A STRONGER SYSTEM THAT SLOWLY DROPS
ALONG THE BRITISH COLUMBIA COAST MID-TO LATE IN THE WEEK. THE
INITIAL SHORTWAVE IS EXPECTED TO BE WEAK, AND MERELY ADVECT A
SLIGHTLY COOLER AIRMASS INTO THE REGION. 47% OF ENSEMBLE MEMBERS
BRING LIGHT SHOWERS ACROSS THE CENTRAL WASHINGTON CASCADES,
WITH 26% OF MEMBERS EXTENDING LIGHT RAIN INTO HIGHER TERRAIN
ACROSS THE NORTHERN BLUE MOUNTAINS. THE MAIN CONSENSUS IS THAT
MOUNTAINS ARE TO STAY DRY, BUT WITH COOLER TEMPERATURES. THE
SECOND SYSTEM IS PLAGUED WITH TIMING CONCERNS, WITH 59% OF
ENSEMBLE MEMBERS ADVERTISING A SLOWER SYSTEM THAT BRINGS
MOISTURE ALONG THE CASCADES LATE THURSDAY BEFORE SLOWLY
EXTENDING ALONG THE EAST SLOPES AND INTO THE COLUMBIA BASIN
THROUGH FRIDAY AFTERNOON. THE SLOWER SCENARIO DOES ALLOW FOR
ADDITIONAL MOISTURE AND HIGHER OVERALL RAIN AMOUNTS FRIDAY AND
SATURDAY. 75
AVIATION /06Z TAFS THROUGH 06Z SUNDAY/
CONFIDENCE IS VERY HIGH (95% OR HIGHER) IN VFR CONDITIONS
THROUGH THE TAF PERIOD AT ALL SITES. ASIDE FROM SOME PERIODS
OF CIRRUS, SKIES ARE EXPECTED TO BE MOSTLY CLEAR. STUBBORNLY
BREEZY WINDS AT DLS SHOULD (90% CONFIDENCE) DECREASE IN
MAGNITUDE OVERNIGHT AS PRESSURE GRADIENTS SLACKEN. ELSEWHERE,
WINDS WILL BE PREDOMINANTLY 10 KTS OR LESS, DIURNALLY AND
TERRAIN-DRIVEN.
PRELIMINARY POINT TEMPS/POPS
PDT 47 78 48 82 / 0 0 0 0
ALW 53 79 53 82 / 0 0 0 0
PSC 51 82 51 84 / 0 0 0 0
YKM 52 82 53 83 / 0 0 0 0
HRI 51 81 50 84 / 0 0 0 0
ELN 50 78 50 79 / 0 0 0 0
RDM 39 79 42 83 / 0 0 0 0
LGD 47 79 47 82 / 0 0 0 0
GCD 46 80 48 84 / 0 0 0 0
DLS 54 85 56 87 / 0 0 0 0
PDT WATCHES/WARNINGS/ADVISORIES
WA...NONE.
OR...NONE.
DISCUSSION...95
AVIATION...86
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