361
FXUS66 KPDT 041709
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
1009 AM PDT MON MAY 4 2026
KEY MESSAGES
- WARM AND ABOVE NORMAL TEMPERATURES PERSIST THROUGH THE WEEK.
- DRY CONDITIONS THROUGH THE WORKWEEK.
- SLIGHT CHANCE FOR MOUNTAIN SHOWERS FRIDAY.
DISCUSSION
CURRENT RADAR AND INFRARED SATELLITE IMAGERY SHOWS DRY
CONDITIONS UNDER MOSTLY CLEAR SKIES. THIS IS IN RESPONSE TO AN
UPPER LEVEL RIDGE ENCROACHING IN FROM THE COAST THAT WILL KEEP
SKIES SUNNY AND TEMPERATURES WELL ABOVE NORMAL. HIGH
TEMPERATURES ACROSS THE LOWER COLUMBIA BASIN, BLUE MOUNTAIN
FOOTHILLS, CENTRAL OREGON, AND THE YAKIMA/KITTITAS VALLEYS
SHOULD BE SLIGHTLY WARMER (+1-2 DEGREES) FROM SUNDAY.
TEMPERATURES WILL COOL 2 TO 5 DEGREES ON TUESDAY DUE TO
NORTHERLY FLOW ALOFT BECOMING MORE ENHANCED AND EXTENDING INTO
THE YUKON AND NORTHWEST TERRITORY PROVINCES. HIGH TEMPERATURES
REBOUND BACK INTO THE UPPER 80S TO LOW 90S ACROSS THE LOWER
COLUMBIA BASIN, GORGE, BLUE MOUNTAIN FOOTHILLS, CENTRAL OREGON,
AND THE YAKIMA/KITTITAS VALLEYS ON WEDNESDAY. THIS IS A RESULT
OF A WEAK SHORTWAVE THAT SUPPRESSES THE UPPER LEVEL RIDGE TO
BRING MORE UPPER LEVEL FLOW FROM THE WEST, AS ADVERTISED BY BOTH
THE ECMWF AND GFS AI ENSEMBLES. THE BEST CHANCE FOR ANY HIGH
TEMPERATURE RECORDS BEING BROKEN WILL BE IN YAKIMA TODAY, WITH
THE CURRENT FORECAST BEING TWO DEGREES SHY (88/90) SET BACK IN
1966. THE NBM SUGGESTS THERE TO BE A 28% CHANCE OF TYING THE
RECORD AND A 7% CHANCE OF BREAKING IT.
THE CONTINUED PRESENCE OF THE UPPER LEVEL RIDGE ACROSS THE
PACIFIC NORTHWEST WILL KEEP CONDITIONS DRY AND HUMIDITIES RATHER
LOW. THIS IS CLEARLY VISIBLE ACROSS OUR OREGON ZONES WHEN
VIEWING THE HOT-DRY-WINDY INDEX (HDWI), WHICH SHOWS 75-95 MEDIAN
PERCENTILES EXCEEDED FROM CLIMATOLOGY OVER THE LAST 30 YEARS.
AFTERNOON HUMIDITIES HAVE DROPPED INTO THE LOW TEENS ACROSS
CENTRAL OREGON AND THE JOHN DAY BASIN OVER THE LAST 3 DAYS, WITH
AREAS OF THE LOWER COLUMBIA BASIN, BLUE MOUNTAIN FOOTHILLS,
UNION COUNTY, AND THE YAKIMA VALLEY EXPERIENCING MINIMUM
HUMIDITIES IN THE TEENS ON SUNDAY. THESE CONDITIONS ARE EXPECTED
TO IMPROVE THROUGH TUESDAY ASSOCIATED WITH NORTHERLY FLOW
ALOFT, HOWEVER THE DOWNWARD TREND RETURNS BEGINNING WEDNESDAY.
AFTERNOON HUMIDITIES ARE EXPECTED TO BOTTOM-OUT THURSDAY AND
DROP INTO THE LOW TO MID-TEENS ACROSS CENTRAL OREGON, JOHN DAY
BASIN, LOWER COLUMBIA BASIN, GORGE, BLUE MOUNTAIN FOOTHILLS, AND
THE YAKIMA VALLEY. HUMIDITIES LOOK TO MODERATE ON FRIDAY AS
ENSEMBLE MEMBERS SUGGEST AN INCOMING UPPER LEVEL TROUGH CLIPPING
THE REGION, BUT GUIDANCE HINTS AT THE RIDGE REBUILDING AND
DROPPING HUMIDITIES THROUGH THE WEEKEND.
ENSEMBLE MEMBERS ARE IN FAIRLY GOOD AGREEMENT RELATED TO AN
INCOMING UPPER LEVEL SHORTWAVE FRIDAY, THAT SPINS OFF ITS
PARENT LOW PRESSURE THAT IS LOCATED OFF THE GULF OF ALASKA. THE
SHORTWAVE IS EXPECTED TO SUPPRESS THE UPPER LEVEL RIDGE THAT SET
UP EARLIER IN THE WEEK, WHICH EFFECTIVELY SHEARS THE SHORTWAVE
NORTH AND INTO BRITISH COLUMBIA. 86% OF ENSEMBLE MEMBERS KEEP
PRECIPITATION CONFINED TO OUR CASCADE AND BLUE MOUNTAIN ZONES,
WITH 35% OF MEMBERS SUGGESTING ONLY PRECIPITATION OVER THE
CASCADE CREST. GUIDANCE HAS TRENDED TOWARD A DRIER SOLUTION OVER
THE LAST 24 HOURS, WHICH MAY CONTINUE. THE MORE DRY CLUSTER
ENSEMBLES (1 AND 3) CONSIST OF 76% AND 75% OF ECMWF AND CMC
MEMBERS, WITH 40% OF GFS MEMBERS ADVERTISING SHOWERS EXTENDING
INTO LOWER ELEVATIONS OF THE BASIN AND ALONG THE BLUE MOUNTAIN
FOOTHILLS. EVEN WITH THIS WETTER CLUSTER SCENARIO (14% CHANCE),
RAIN AMOUNTS ARE EXPECTED TO STAY BELOW A WETTING RAIN (0.10").
DEPENDING ON THE STRENGTH OF THE INCOMING SHORTWAVE AND HOW
EFFECTIVE IT IS IN BREAKING THE RIDGE DOWN, THERE IS A SLIGHT
CHANCE (10%) OF ISOLATED AFTERNOON/EVENING THUNDERSTORMS ACROSS
GRANT, UNION, AND WALLOWA COUNTIES ON FRIDAY. NOT ONLY WILL
THIS POTENTIAL BE RELATED TO SHORTWAVE STRENGTH, BUT ALSO THE
TIMING OF THE SHORTWAVE COINCIDING WITH PEAK AFTERNOON HEATING.
THE ECWMF HAS SLOWED THE SHORTWAVE PASSING TO LATER IN THE
EVENING OVER THE PAST TWO MODEL RUNS (18Z AND 0Z), WHICH IS ALSO
SUGGESTED VIA THE LREF SHOWING A PASSING OVER THE CASCADES IN
THE EARLY AFTERNOON AND BETWEEN 7PM-9PM ACROSS GRANT, UNION, AND
WALLOWA COUNTIES USING A 567MB THRESHOLD IN RELATION TO THE
500MB HEIGHT TIMING PRODUCT. THUS, SHOWERS OUTSIDE THE CASCADES
AND ISOLATED THUNDERSTORMS ACROSS OUR EASTERN ZONES ON FRIDAY
IS CURRENTLY AN UNLIKELY SCENARIO (10%). 75
AVIATION /18Z TAFS THROUGH 18Z TUESDAY/
VFR CONDITIONS WILL PERSIST THROUGH THE FORECAST PERIOD. BREEZY
WINDS OF 15-25KTS ARE EXPECTED FOR KDLS/KRDM/KBDN/KYKM AFTER 19Z
AND WILL PERSIST THROUGH 05-07Z. ELSEWHERE, WINDS WILL BE 10KTS
OR LESS. CIGS WILL BE 25 KFT TO SKC. 90
PRELIMINARY POINT TEMPS/POPS
PDT 83 51 78 50 / 0 0 0 0
ALW 82 54 78 54 / 0 0 0 0
PSC 89 54 84 51 / 0 0 0 0
YKM 88 56 84 54 / 0 10 0 0
HRI 87 53 83 51 / 0 0 0 0
ELN 83 51 79 50 / 0 10 0 0
RDM 81 43 78 43 / 0 0 0 0
LGD 78 49 74 47 / 0 0 0 0
GCD 79 46 75 45 / 0 0 0 0
DLS 85 56 84 56 / 0 0 0 0
PDT WATCHES/WARNINGS/ADVISORIES
WA...NONE.
OR...NONE.
DISCUSSION...75
AVIATION...90
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