173
FXUS66 KPDT 282343
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
443 PM PDT MON APR 28 2025
UPDATED FOR AVIATION
SHORT TERM...TODAY THROUGH WEDNESDAY...WITH THE RIDGE OVER THE
PACNW, WARM DRY CONDITIONS CONTINUE THROUGH THIS LATE AFTERNOON.
AS THE SHORTWAVE TROUGH BEGIN CLIPPING ACROSS THE FORECAST AREA
THIS EVENING INTO TONIGHT, THE FRONTAL SYSTEM WILL ARRIVE WITH
LIGHT SHOWERS AT THE WA/OR CASCADES FIRST (>35% CHANCE) AND THEN
NORTHERN BLUES INCLUDING YAKIMA VALLEY AND COLUMBIA BASIN (<20%
CHANCE). HOWEVER WITH THE MARINE STRATUS LAYER STILL PRESENT AND
TIGHTEN SURFACE PRESSURE GRADIENTS, LOCALLY WINDY CONDITIONS
(25-35 MPH) WILL REMAIN OVER THE GORGE, SOUTHERN BLUE MOUNTAINS-
FOOTHILLS, AND KITTITAS VALLEY.
WIDESPREAD SHOWERS DEVELOP TOMORROW EARLY MORNING AS THE FRONTAL
SYSTEM PASSES THROUGH. LIGHT QPF AMOUNTS (0.10" OR LESS) FOR MOST
OF THE FORECAST AREA BUT THE NORTHERN BLUES MAY REACH UP TO
0.35". WIND GUSTS OF 45 MPH WITH SUSTAINED WINDS AT 25-35 MPH WILL
DEVELOP AT KITTITAS VALLEY WITH THE MARINE STRATUS LAYER
CONTINUING TO LINGER AND TIGHTEN SURFACE PRESSURE GRADIENTS, WHICH
HAS WARRANTED FOR A WIND ADVISORY TOMORROW FROM 2PM TO 8PM PDT.
OTHERWISE, WINDS WILL REMAIN GUSTY AT 30-40 MPH THROUGH THE EARLY
EVENING FOR THE GORGE AND SOUTHERN BLUE MOUNTAINS-FOOTHILLS (>60%
CHANCE). LATER EVENING INTO NIGHT, WINDS WILL THEN DECREASE AS THE
TROUGH MOVES OUT OF THE AREA. BY WEDNESDAY, WARM AND DRY
CONDITIONS WITH LIGHT WINDS RETURN AS THE RIDGE BUILDS OVER THE
PACNW. TEMPERATURES REMAIN NEAR TO ABOVE NORMAL FOR THIS TERM.
FEASTER/97
LONG TERM...THURSDAY THROUGH MONDAY...
KEY MESSAGES:
1. ISOLATED THUNDERSTORMS POSSIBLE FRIDAY AFTERNOON AND EVENING.
2. WIDESPREAD RAIN AND MOUNTAIN SNOW FRIDAY AFTERNOON INTO SATURDAY.
3. BREEZY AFTERNOON CONDITIONS FRIDAY THROUGH SUNDAY.
THE EXTENDED PERIOD IS CHARACTERIZED BY INITIAL UPPER LEVEL RIDGING
AHEAD OF A SIGNIFICANT UPPER LEVEL TROUGH THAT WILL APPROACH FRIDAY
BEFORE PASSING THROUGH THE PACIFIC NORTHWEST OVER THE WEEKEND. THIS
WILL BRING WIDESPREAD RAIN FRIDAY INTO SATURDAY, BREEZING AFTERNOON
CONDITIONS FRIDAY ONWARD, AND COOLER TEMPERATURES OVER THE WEEKEND.
FLOW ALOFT FROM THE SOUTH AND AN INCOMING UPPER LEVEL TROUGH THAT IS
NEGATIVELY-TILTED WILL ALLOW FOR INSTABILITY TO DEVELOP ACROSS
CENTRAL OREGON, EAST SLOPES OF THE CASCADES, BLUE MOUNTAIN
FOOTHILLS, AND PORTIONS OF THE COLUMBIA BASIN FRIDAY AFTERNOON AND
EVENING. THE NBM AND GFS BOTH ADVERTISE CAPE VALUES BETWEEN 100-300
J/KG, WITH THE GFS HIGHLIGHTING SHEAR OF 35 KTS AND LOW-LEVEL LAPSE
RATES OF AROUND 8 C/KM. THESE PARAMETERS WOULD ALLOW FOR ISOLATED,
DISCRETE THUNDERSTORM CELLS, WITH THE MAIN IMPACTS RELATED TO
LIGHTNING, PERIODS OF HEAVY RAINFALL, AND GUSTY AND ERRATIC WINDS.
THE INCOMING SYSTEM WILL ALLOW FOR WIDESPREAD RAINFALL AND HIGH
ELEVATION SNOW ABOVE 4500 FEET TO OCCUR ACROSS CENTRAL OREGON FRIDAY
AFTERNOON, BEFORE EXTENDING ACROSS THE ENTIRE AREA AFTER 5 PM. LIGHT
RAIN WILL THEN CONTINUE OVERNIGHT AND INTO SATURDAY MORNING AS RAIN
AMOUNTS REACH INTO THE 0.40-0.50" RANGE ACROSS THE BLUE AND CASCADE
MOUNTAINS, 0.30-0.40" THROUGH CENTRAL OREGON AND THE JOHN DAY BASIN,
0.15-0.25" OVER THE BLUE MOUNTAIN FOOTHILLS, AND 0.03-0.15" ACROSS
THE LOWER COLUMBIA BASIN. CONFIDENCE IN THESE RAIN AMOUNTS IS
MODERATE (50-60%), AS 69% OF ENSEMBLES RAIN AMOUNTS ARE NEAR TO
SLIGHTLY ABOVE (0.01-0.03") THE CURRENT FORECAST. THE POTENTIAL FOR
INCREASING RAIN AMOUNTS ARE PRIMARILY FOCUSED ALONG THE BLUE
MOUNTAINS, JOHN DAY BASIN, AND WALLOWA COUNTY, WHICH IS RELATED TO A
DEEPER AND STRONGER INCOMING UPPER LEVEL TROUGH. THE SYSTEM WILL
CONTINUE DIVING SOUTH INTO CALIFORNIA SATURDAY, WHICH WILL CONFINE
PRECIPITATION TO AREAS ALONG THE BLUE MOUNTAINS AND EAST WITH
HIGHEST RAIN AMOUNTS EXPECTED OVER WALLOWA COUNTY AND THE NORTHERN
BLUE MOUNTAINS WITH 0.25-0.35" OF RAIN LIKELY. ADDITIONAL RAIN
AMOUNTS SATURDAY EVENING THROUGH SUNDAY MORNING WILL REACH 0.15-
0.25" OVER THE JOHN DAY BASIN, AND 0.05-0.15" ACROSS THE NORTHERN
BLUE MOUNTAIN FOOTHILLS. CONFIDENCE IN THESE RAIN AMOUNTS IS MUCH
LESS AS ENSEMBLE CLUSTERS ARE IN DISAGREEMENT IN HOW DEEP, STRONG,
AND BROAD THE DROPPING UPPER LEVEL TROUGH IS AS IT PROCEEDS THROUGH
NORTHERN CALIFORNIA. UPPER LEVEL RIDGING AND HIGH PRESSURE RETURNS
SUNDAY EVENING INTO MONDAY, BUT LOOKS TO STRUGGLE TO EXTEND OVER
WALLOWA COUNTY AND OVER HIGHER TERRAIN OF THE JOHN DAY-OCHOCOS AND
BLUE MOUNTAINS - KEEPING LIGHT RAIN INTO EARLY MONDAY MORNING.
THE APPROACHING UPPER LEVEL TROUGH FRIDAY WILL ERODE THE SLOWLY
DEPARTING RIDGE, TIGHTENING ISOBARS AND CREATING A PRESSURE GRADIENT
ALONG THE CASCADES. BREEZY WEST-NORTHWEST SUSTAINED WINDS OF 20-25
MPH WITH GUSTS UP TO 40 MPH WILL BE POSSIBLE ACROSS THE EAST SLOPES
OF THE WASHINGTON CASCADES, SOUTHERN BLUE MOUNTAIN FOOTHILLS,
SIMCOE HIGHLANDS, AND THE KITTITAS VALLEY FRIDAY, SATURDAY, AND
SUNDAY DURING THE AFTERNOON/EVENING. WINDS ARE EXPECTED BE HIGHEST
ON SATURDAY, AS THERE IS A 50-70% CHANCE OF ADVISORY-LEVEL WIND
GUSTS (45 MPH OR GREATER) ACROSS THE KITTITAS VALLEY AND THE
SOUTHERN BLUE MOUNTAIN FOOTHILLS EACH DAY. ENSEMBLE CLUSTERS ARE IN
FAIRLY GOOD AGREEMENT REGARDING WINDS WITH 59% OF ENSEMBLE MEMBERS
HINTING AT SLIGHTLY LOWER VALUES THAN THE FORECAST SATURDAY AND
SUNDAY. 75
AVIATION...00Z TAFS...VFR CONDITIONS ARE EXPECTED THROUGH THE TAF
PERIOD. RA IS EXPECTED MAINLY AT PDT AND ALW FOR A TIME TUESDAY
MORNING. OTHERWISE, THE MAIN CONCERN WILL BE GUSTY WINDS THROUGH
THE EVENING AT DLS, PDT, RDM AND ALW. WINDS WILL GUST AGAIN ON
TUESDAY AT DLS, PDT, ALW AND PSC. WINDS WILL GUST MAINLY IN THE 20
TO 25 KT RANGE.
PRELIMINARY POINT TEMPS/POPS
PDT 49 67 41 70 / 20 60 0 0
ALW 49 65 43 69 / 20 80 0 0
PSC 49 73 41 74 / 20 70 0 0
YKM 49 71 39 74 / 20 10 0 0
HRI 49 71 41 73 / 20 70 0 0
ELN 48 65 40 72 / 30 10 0 0
RDM 41 63 32 70 / 10 20 0 0
LGD 44 60 36 67 / 20 80 0 0
GCD 42 60 35 69 / 10 70 0 0
DLS 50 67 41 74 / 20 30 0 0
PDT WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...WIND ADVISORY FROM 2 PM TO 8 PM PDT TUESDAY FOR WAZ026.
SHORT TERM...97
LONG TERM....75
AVIATION...77
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