384
FXUS66 KPDT 210526
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
1026 PM PDT MON APR 20 2026
KEY MESSAGES
- LAST DAY OF DRY CONDITIONS BEFORE A COLD FRONT PASSAGE BRINGS
UNSETTLED WEATHER THROUGH THE REGION.
- THUNDERSTORM DEVELOPMENT POSSIBLE (10-25% CHANCES) TUESDAY
AND, TO A LESSER EXTENT, THROUGH WEDNESDAY MORNING.
- BREEZY TO LOCALLY WINDY CONDITIONS WEDNESDAY.
- SOME RIVERS WILL RUN HIGH INTO WEEKEND, RISING TO ACTION
STAGE BY WEDNESDAY NIGHT.
DISCUSSION
TODAY IS THE WARMEST DAY OF THE 7 DAY FORECAST PERIOD, AT LEAST
AS FAR AS THIS DETERMINISTIC FORECAST GOES. WIDESPREAD 70S AND
EVEN SOME LOW 80 DEGREE HIGHS ARE EXPECTED THIS AFTERNOON (LOW
80S IN CENTRAL OREGON, JOHN DAY, LOWER COLUMBIA AND KITTITAS
VALLEY). THE WARMED UP AIRMASS WILL COUPLE WITH PLENTY OF CLOUD
COVER OVERNIGHT, REMAINING MILD IN THE UPPER 40S TO AROUND 50
DEGREES IN THE NON MOUNTAINS ZONES BY EARLY TUESDAY MORNING.
WIDESPREAD PRECIPITATION WILL DEVELOP ACROSS THE AREA TUESDAY
AND WEDNESDAY WITH THE BULK OF THE PRECIPITATION FALLING ON
WEDNESDAY, ESPECIALLY IN THE FIRST HALF OF THE DAY. INTERESTINGLY
THE IVT/IVW PORTAL SHOWS A LINGERING SWATH OF 200 TO 300 KG/MS
THROUGH THE EASTERN COLUMBIA GORGE/FOOTHILL OF NRN BLUES BY 60
HOURS. CLUSTERS INDICATE THE GFS PRODUCING THE HIGHEST OVERALL
QPF AMOUNTS WHICH CAN EXCEED 3 INCHES IN THIS REGION OF THE SE
WA AND NE OR WHICH MAY HAVE IMPACTS ON AREA RIVERS SEE (HYDRO
SECTIONS). PRIOR TO MORE WIDESPREAD AND LOWER CAPE ENVIRONMENT
RAINS WILL BE A PERIOD OF CONVECTIVE POTENTIAL FOR TUESDAY
AFTERNOON AND LINGERING THROUGH LATE TUESDAY EVENING, SUPPORTED
BY NBM THUNDERSTORM CHANCES IN THE 15 TO 30% RANGE ACROSS THE
EASTERN MOUNTAINS (HIGHEST COVERAGE POTENTIAL ACROSS THE WALLOWA
COUNTY TUESDAY EVENING. AFTER THE BROADER UPPER TROUGH EXITS
TO THE EAST ON WEDNESDAY STRONGER WESTERLY BOUNDARY LAYER
MOMENTUM IS POISED TO CAUSE ABOUT 50-70% CHANCES FOR WIND GUSTS
TO 45 MPH OR MORE ACROSS THE SIMCOE HIGHLANDS AND OREGON
COLUMBIA BASIN WEDNESDAY AFTERNOON. FOLLOWING THE MIDWEEK
SYSTEM, ENSEMBLES FAVOR A RIDGE DEVELOPING OVER THE PAC NW
RESULTING IN A DRY AND WARMING PERIOD INTO WEEK 2. RUSSELL/71
AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/
VFR CONDITIONS TO
PREVAIL THROUGH THE PERIOD. AN UPPER LOW MOVING INTO THE REGION
WILL BRING RAIN SHOWER CHANCES TO NORTHERN SITES IN THE
AFTERNOON TOMORROW, WHILE SITES RDM/BDN WILL SEE INCREASING
CHANCES MID TO LATE MORNING TOMORROW. THERE IS A <20% CHANCE OF
THUNDER AT MOST SITES, AND GIVEN THE SHOWERY NATURE HAVE NOT
INCLUDED MENTION AT ANY SITE AT THIS TIME. WINDS WILL MOSTLY BE
LIGHT TONIGHT, THEN INCREASING TO 12-20KTS WITH GUSTS 20-30KTS
AT SITES DLS/PDT/YKM/ALW/PSC TOMORROW AFTERNOON, WITH WINDS
STARTING LATE MORNING AT SITE DLS. WINDS WILL BE MOSTLY 12KTS OR
LESS AT SITES RDM/BDN. LAWHORN/82
HYDROLOGY
AREA HAS UNDERGONE A WARM SPIKE IN RECENT DAYS WHICH CONTINUES
INTO TUESDAY, LEADING TO MELTING OF THE LIMITED AMOUNT OF SNOW
THAT IS ON THE NORTHERN BLUES/CASCADES CREST. THIS WILL LEAD TO
ELEVATED RIVER LEVELS PRIOR TO THE ONSET OF THE RAINS WHICH ARE
NBM MEAN IN EXCESS OF 2 INCHES ACROSS THE AREAS OF THE NORTHERN
BLUES, BY THURSDAY AFTERNOON (CASCADE CREST OF WA WILL BE
LIMITED TO AROUND A HALF INCH OF TOTAL QPF). BASED ON HEFS AT
THIS TIME, THESE RIVERS REMAIN BROADLY FORECAST BELOW THE MINOR
FLOOD STAGES, WHICH SUGGESTS A LESS THAN 10% CHANCE FOR MINOR
FLOODING WITH CURRENT SNOW MELTS AND RANGE OF QPF AS INPUT.
SEVERAL RIVERS INCLUDING THE NACHES AND GRANDE RONDE/WALLA WALLA
HAVE RIVER POINTS FORECAST TO REACH CLOSE TO OR EXCEED ACTION
STAGE BY WEDNESDAY NIGHT, AND FALL BY THE WEEKEND. RUSSELL/71
PRELIMINARY POINT TEMPS/POPS
PDT 47 72 44 53 / 10 40 90 90
ALW 53 73 45 52 / 0 20 90 100
PSC 49 78 49 63 / 0 10 70 80
YKM 50 76 50 65 / 10 20 50 40
HRI 48 74 46 58 / 0 20 80 80
ELN 48 70 45 56 / 10 30 50 40
RDM 44 61 36 53 / 20 50 50 40
LGD 44 74 41 47 / 0 40 100 100
GCD 44 69 39 47 / 10 70 100 90
DLS 53 66 49 59 / 20 30 40 60
PDT WATCHES/WARNINGS/ADVISORIES
WA...NONE.
OR...NONE.
DISCUSSION...95
AVIATION...82
HYDROLOGY...71
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