131
FXUS66 KPDT 220544
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
1044 PM PDT MON SEP 21 2026
KEY MESSAGES
- SHOWER AND ISOLATED THUNDERSTORM CHANCES TUESDAY.
- BREEZY WINDS TUESDAY AND FRIDAY.
- WIDESPREAD SHOWERS AND ISOLATED STORMS RETURN LATE THURSDAY.
DISCUSSION
CURRENT RADAR AND VISIBLE SATELLITE IMAGERY SHOWS DRY CONDITIONS
UNDER MOST SUNNY SKIES AS HIGH LEVEL CLOUDS BEGIN TO MOVE IN
FROM THE SOUTHWEST. THIS IS IN RESPONSE TO THE UPPER LEVEL RIDGE
THAT KEPT CONDITIONS SUNNY AND WARM, CONTINUING TO DEPART TO OUR
EAST AS A WEAK UPPER LEVEL SHORTWAVE MOVES ONSHORE OVER CENTRAL
BRITISH COLUMBIA. INCREASING CLOUD COVER IS EXPECTED THROUGH
THE REMAINDER OF THE DAY, WITH HIGH TEMPERATURES REACHING INTO
THE MID-80S ACROSS THE COLUMBIA BASIN, GORGE, BLUE MOUNTAIN
FOOTHILLS, AND CENTRAL OREGON. THE PASSING OF THIS SYSTEM ON
TUESDAY WILL PROVIDE A 10-15% CHANCE OF LIGHT SHOWERS AND
ISOLATED THUNDERSTORMS, PRIMARILY ACROSS EASTERN GRANT, SOUTHERN
UNION, AND SOUTHERN WALLOWA COUNTIES. RAIN AMOUNTS WILL BE
MINIMAL AS BOTH THE HREF AND NBM ADVERTISE ONLY A 20-40% CHANCE
OF MEASURABLE RAINFALL (0.01" OR GREATER) OVER THE
AFOREMENTIONED AREAS. THE HREF AND REFS ALSO SHOW THE POTENTIAL
FOR ISOLATED THUNDERSTORMS, PRIMARILY BETWEEN THE HOURS OF 1PM
AND 7PM WITH SURFACE CAPE OF 200-300 J/KG AND 20-25 KNOT SHEAR
PRESENT. PRIMARY CONCERNS RELATED TO ANY DEVELOPING
THUNDERSTORMS WILL BE FREQUENT LIGHTNING AND BREEZY OUTFLOW
WINDS.
THE SYSTEM WILL ALSO LEAD TO A PRESSURE GRADIENT FORMING ALONG
THE CASCADES, PRODUCING BREEZY WINDS ALONG THE COLUMBIA GORGE,
BLUE MOUNTAIN FOOTHILLS, AND KITTITAS VALLEY THOUGH MUCH OF THE
DAY - PEAKING IN THE EARLY TO MID-AFTERNOON HOURS. THE GFS AND
NAM FORECAST A PRESSURE GRADIENT OF 7-8MB BETWEEN PAINE FIELD
AND PASCO, PRODUCING WEST-NORTHWEST WINDS OF 20-25 MPH WITH
GUSTS OF 30-35 MPH. CONFIDENCE IS HIGH (70-90%) IN THESE WIND
VALUES AS THE NBM SHOWCASES A 45-55% CHANCE OF MAXIMUM WIND
GUSTS OF 35 MPH OR GREATER OVER THESE AREAS. WINDS WILL SUBSIDE
TUESDAY NIGHT AS THE SYSTEM EXITS TO OUR EAST, BUT WILL RETURN
WITH A MORE ROBUST SYSTEM THURSDAY AFTERNOON AND EXTEND THROUGH
FRIDAY. THURSDAY'S WIND CONCERNS WILL BE MORE FOCUSED ACROSS
CENTRAL OREGON AND THE COUNTIES OF UNION AND WALLOWA AS A
PRESSURE GRADIENT IS EXPECTED TO DEVELOP ALONG THE BLUE
MOUNTAINS. SOUTH WINDS OF 15-20 MPH WITH GUSTS OF AROUND 30 MPH
WILL BE POSSIBLE. FRIDAY'S ELEVATED WINDS WILL BE MORE
ASSOCIATED WITH THE INCOMING UPPER LEVEL SHORTWAVE, PROVIDING
BREEZY CONDITIONS ACROSS THE COLUMBIA GORGE/BASIN, BLUE MOUNTAIN
FOOTHILLS, AND KITTITAS VALLEY. WEST-NORTHWEST WINDS OF 20-25
MPH WITH GUSTS OF 30-35 MPH WILL AGAIN BE POSSIBLE AND LIKELY
WILL INCLUDE MORE AREAS OF THE BASIN AND FOOTHILLS.
THIS SECOND, MORE ROBUST SYSTEM LATE IN THE WEEK WILL ALSO
BRING WITH IT AMPLE MOISTURE AS IT STRENGTHENS AND DIGS SOUTH
ALONG THE WEST COAST. AI ECMWF AND GFS ENSEMBLES SUGGEST
PRECIPITABLE WATER OF 0.8-0.9", WHICH IS 130-150% OF NORMAL.
NBM GUIDANCE STILL STRUGGLES WITH TIMING AND STRENGTH AS
INDICATED WITH 48 HOUR RAIN AMOUNTS OF LESS THAN A WETTING RAIN
(0.10" OR LESS) FOR THE MAJORITY OF THE AREA, WITH THE
EXCEPTION OF THE CASCADES AND HIGHER TERRAIN OVER THE BLUE
MOUNTAINS. THIS MIRRORS THE NBM OF 48 HOURS AGO, BEFORE IT
SHIFTED TO A MUCH WETTER SCENARIO JUST 24 HOURS AGO. LREF
GUIDANCE HAS BEEN MORE STABLE OVER THE PAST 24 TO 48 HOURS, WITH
91% OF ENSEMBLE MEMBERS HIGHLIGHTING WIDESPREAD MEASURABLE RAIN
AND 47% OF MEMBERS SUGGESTING WIDESPREAD WETTING RAIN ACROSS THE
AREA. THUS, THE SCENARIO OF MOUNTAIN ZONES ACQUIRING A WETTING
RAIN AND LOWER ELEVATIONS OF THE BASIN AND FOOTHILLS STAYING
BELOW 0.10" RAIN AMOUNTS THURSDAY AND FRIDAY IS MORE PROBABLE.
EMBEDDED ISOLATED THUNDERSTORMS MAY ALSO BE POSSIBLE FRIDAY
AFTERNOON, BUT CURRENT CONFIDENCE IS LACKING DUE TO GUIDANCE
ONLY SUGGESTING CAPE VALUES OF 50-100 J/KG. THIS WILL NEED TO BE
MONITORED AS THE EVENT NEARS. 75
AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/
VFR CONDITIONS ARE FORECAST AT ALL SITES THROUGH THE TAF PERIOD.
MID/HIGH CLOUD COVER WILL PREVAIL THROUGH THE NIGHT AND MUCH OF
TUESDAY, WITH SOME BREAKS BY LATER AFTERNOON. WESTERLY WINDS
WILL INCREASE IN MAGNITUDE TUESDAY MORNING AT DLS/PDT/ALW, WITH
BREEZY WINDS FOLLOWING AT RDM/BDN IN THE AFTERNOON.
PRELIMINARY POINT TEMPS/POPS
PDT 52 76 45 74 / 0 0 0 0
ALW 58 77 52 75 / 0 0 0 0
PSC 55 80 48 77 / 0 0 0 0
YKM 54 79 48 74 / 0 0 0 0
HRI 56 78 49 76 / 0 0 0 0
ELN 50 70 43 69 / 0 0 0 0
RDM 45 75 38 73 / 0 0 0 0
LGD 52 79 44 77 / 0 0 0 0
GCD 51 80 44 79 / 0 0 0 0
DLS 56 74 51 77 / 0 0 0 0
PDT WATCHES/WARNINGS/ADVISORIES
WA...NONE.
OR...NONE.
DISCUSSION...75
AVIATION...21/86
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