967
FXUS66 KPDT 301012
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
312 AM PDT MON MAR 30 2026
KEY MESSAGES
- COOLER, BELOW NORMAL TEMPERATURES EARLY IN THE WEEK
- LINGERING SHOWERS TODAY ACROSS CENTRAL OREGON
- MOUNTAIN SNOW, WIDESPREAD SHOWERS, AND BREEZY WINDS MIDWEEK
DISCUSSION
CURRENT RADAR AND INFRARED SATELLITE IMAGERY SHOWS LIGHT RETURNS
ACROSS THE OREGON CASCADES UNDER PARTLY TO MOSTLY CLOUDY SKIES.
THIS IS IN RESPONSE TO THE SLOWLY DEPARTING COLD FRONT
ASSOCIATED WITH A PASSING UPPER LEVEL SHORTWAVE TROUGH LOCATED
ALONG THE CANADIAN BORDER. THE COOLER AIR BEHIND THE COLD FRONT
WILL DROP HIGH TEMPERATURES 5-10 DEGREES FROM SUNDAY. SKIES
WILL CLEAR THROUGH THE MORNING AND EARLY AFTERNOON, SETTING UP A
RATHER CHILLY MONDAY NIGHT/TUESDAY MORNING AS EFFICIENT
RADIATIONAL COOLING WILL BRING MORNING TEMPERATURES INTO THE
UPPER 20S ACROSS THE LOWER COLUMBIA BASIN, BLUE MOUNTAIN
FOOTHILLS, AND CENTRAL OREGON. HIGH TEMPERATURES WILL REBOUND
SLIGHTLY TUESDAY INTO THE LOW TO MID-50S, BUT STILL WILL BE 5-7
DEGREES BELOW NORMAL.
ECMWF AND GFS AI ENSEMBLES ARE IN AGREEMENT WITH A STRENGTHENING
UPPER LEVEL TROUGH OFFSHORE AS A SURFACE LOW PRESSURE DEVELOPS
OVER NORTHERN CALIFORNIA LATER TODAY INTO TUESDAY. THESE
FEATURES WILL KEEP LIGHT SHOWER CHANCES OVER CENTRAL OREGON AND
THE JOHN DAY BASIN TODAY (45-55%) AND TUESDAY (30-60%), WITH
SNOW LEVELS HOVERING BETWEEN 3500-4500 FEET BOTH DAYS. MINIMAL
SNOW AMOUNTS ARE EXPECTED, WITH A 60-65% CHANCE OF 48 HOUR SNOW
TOTALS OF 1 INCH OR MORE ACROSS SANTIAM PASS THROUGH TUESDAY VIA
THE NBM. THE BETTER CHANCES FOR RAIN AND SNOW WILL COME ON
TUESDAY AS MID-TO UPPER LEVEL SUPPORT IS PRESENT DUE TO THE
OFFSHORE UPPER TROUGH PASSING THROUGH THE AREA. AS A RESULT, A
SLIGHT CHANCE (~15%) OF ISOLATED THUNDERSTORMS WILL BE POSSIBLE
ACROSS EASTERN DESCHUTES, SOUTHERN CROOK, AND SOUTHERN GRANT
COUNTIES TUESDAY AFTERNOON. THE NAMNEST, HRRR, AND NSSL ALL
INDICATE THE POTENTIAL FOR ISOLATED, DISCRETE THUNDERSTORMS
TUESDAY BETWEEN 2 PM AND 8 PM, WITH RAIN AMOUNTS AT OR EXCEEDING
A WETTING RAIN (0.10" OR GREATER).
ENSEMBLES ARE IN GOOD AGREEMENT RELATED TO AN INCOMING UPPER
LEVEL LOW PRESSURE STRENGTHENING OVER THE GULF OF ALASKA
TUESDAY, PASSING THROUGH THE PACIFIC NORTHWEST WEDNESDAY AND
THURSDAY. THIS SYSTEM WILL BRING A RETURN TO SUBSTANTIAL SNOW
AMOUNTS ACROSS THE CASCADES THROUGH THE PERIOD, WITH THE
POTENTIAL OF 48 HOUR SNOW TOTALS OF 10-15 INCHES OVER SANTIAM
PASS AND 5-8 INCHES OVER SNOQUALMIE AND WHITE PASSES. THE BLUE
MOUNTAINS ARE ALSO EXPECTED TO PICK UP 4-8 INCHES DURING THIS
TIMEFRAME. HOWEVER, UNCERTAINTY IN THE UPPER LOW'S PATH AND
STRENGTH IS PRESENT, WHICH DIRECTLY RELATES TO SNOW AMOUNTS AND
MOISTURE EFFICIENCY AND TRANSPORT OVER THE CASCADE CREST.
CURRENTLY, 30-45% OF MEMBERS SUGGEST WINTER STORM WARNING SNOW
AMOUNTS BEING MET ACROSS THE OREGON CASCADES (8 INCHES OR MORE),
WITH THE NBM ADVERTISING AN 80-90% CHANCE. IT IS WORTH NOTING
THAT THE NBM ALSO INCURS AN OVERALL SPREAD OF 7 INCHES RELATED
TO 48 SNOW TOTALS WEDNESDAY THROUGH THURSDAY. WILL HOLD OFF ON
ISSUING ANY WINTER WATCH PRODUCTS DUE TO THIS UNCERTAINTY, BUT A
WINTER PRODUCT (WARNING OR ADVISORY) IS VERY LIKELY (>80%)
ACROSS THE OREGON CASCADES DURING THIS TIMEFRAME. WINTER WEATHER
ADVISORIES ARE ALSO EXPECTED ALONG THE WASHINGTON CASCADES AND
THE NORTHERN BLUE MOUNTAINS MIDWEEK, AS THE NBM SHOWS A 55-70%
OF 6 INCHES OF SNOWFALL WEDNESDAY THROUGH THURSDAY.
A VORTICITY MAXIMUM WILL ALSO BE ASSOCIATED WITH THE PASSING
UPPER LEVEL LOW PRESSURE WEDNESDAY AFTERNOON AND EVENING, WHICH
MAY LEAD TO A SLIGHT CHANCE (10-20%) OF ISOLATED THUNDERSTORMS.
BOTH THE NAM AND GFS SHOWCASE MUCAPE OF 200-300J/KG AND 30-40KT
SHEAR ACROSS CENTRAL OREGON, NORTH-CENTRAL OREGON, JOHN DAY
BASIN, GRANDE RONDE VALLEY, AND BLUE MOUNTAINS/FOOTHILLS. 74% OF
LREF ENSEMBLES INDICATE THESE CONVECTIVE PARAMETERS, WHICH
ALIGN WITH THE POTENTIAL FOR ISOLATED, DISCRETE THUNDERSTORM
DEVELOPMENT PRIMARILY BETWEEN 2 PM AND 8 PM WEDNESDAY. RAIN
AMOUNTS OF 0.15-0.35" ARE EXPECTED IN THESE AREAS AS A 70-90%
CHANCE OF A WETTING RAIN (0.10" OR MORE) IS INDICATED BY THE
NBM.
UPPER LEVEL RIDGING RETURNS LATE THURSDAY THROUGH EARLY
SATURDAY, BRINGING A RETURN TO WARMER AND DRIER CONDITIONS.
ENSEMBLES THEN HINT AT ANOTHER UPPER LEVEL SHORTWAVE PASSING
SUNDAY AS A BROAD TROUGH APPROACHES THE BRITISH COLUMBIA AND
WASHINGTON COASTS EARLY NEXT WEEK. 75
AVIATION /12Z TAFS THROUGH 12Z TUESDAY/
VFR CONDITIONS CURRENTLY ACROSS ALL SITES, WHICH WILL STAY THE
COURSE THROUGH THE PERIOD. THE ONLY EXCEPTION WILL BE MVFR
CONDITIONS FOR KRDM/KBDN EARLY THIS MORNING AS CEILINGS DROP TO
AROUND 2KFT. ELSEWHERE, CEILINGS STAY AROUND 25KFT WITH
WIDESPREAD LIGHT WINDS OF LESS THAN 10KTS. 75
PRELIMINARY POINT TEMPS/POPS
PDT 50 28 51 37 / 10 10 10 20
ALW 50 31 52 40 / 10 0 10 20
PSC 56 29 57 38 / 0 0 0 0
YKM 53 28 55 34 / 0 0 0 0
HRI 54 28 54 37 / 0 0 10 10
ELN 48 26 50 31 / 0 0 0 0
RDM 49 29 54 35 / 30 20 20 10
LGD 48 26 54 36 / 40 10 40 50
GCD 48 32 55 37 / 70 40 70 60
DLS 57 32 56 40 / 0 10 10 20
PDT WATCHES/WARNINGS/ADVISORIES
WA...NONE.
OR...NONE.
DISCUSSION...75
AVIATION...75
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