964
FXUS66 KPDT 202352
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
352 PM PST THU FEB 20 2025
SHORT TERM...TODAY THROUGH SUNDAY NIGHT
KEY MESSAGES:
1. WIDESPREAD RAIN AND MOUNTAIN SNOW FRIDAY RETURNING SATURDAY.
2. BREEZY WINDS FRIDAY AND SATURDAY.
3. WARMING TEMPERATURES THROUGH THE WEEKEND.
CURRENT RADAR AND VISIBLE SATELLITE IMAGERY SHOWING VERY LIGHT
RETURNS ALONG THE EAST SLOPES OF THE WASHINGTON CASCADES UNDER
MOSTLY CLEAR SKIES. THESE RETURNS ARE NOT PRODUCING RAINFALL AS
THE LOWER LEVELS OF THE ATMOSPHERE ARE DRY ENOUGH TO ALLOW THE
MOISTURE TO EVAPORATE BEFORE REACHING THE GROUND SURFACE, AS
INDICATED BY HUMIDITIES OF 50-70% OVER THESE AREAS. HIGH LEVEL
CLOUDS ARE BEGINNING TO INFILTRATE INTO THE AREA, WHICH IS IN
RESPONSE TO A WEAK UPPER LEVEL SHORTWAVE RIDING OVER THE PRESENT
UPPER LEVEL RIDGE. THIS UPPER LEVEL RIDGE WILL FLATTEN AND SHIFT
TO OUR EAST TO ALLOW SOUTHWEST FLOW ALOFT TO TAKE HOLD AS
AN ADDITIONAL SHORTWAVE MOVES OVER THE AREA FRIDAY AFTERNOON AND
EVENING BEFORE A MORE SUBSTANTIAL SHORTWAVE FOLLOWS SATURDAY
EVENING THROUGH SUNDAY. THE SOUTHWEST FLOW ALOFT WILL INCREASE
SNOW LEVELS ON FRIDAY FROM 2000-3000 FEET IN THE MORNING TO
5000-6000 FEET BY THE EVENING. THIS WILL KEEP SNOWFALL AT
ELEVATIONS ABOVE 4000 FEET AS 1-3 INCHES OF SNOW IS EXPECTED
FRIDAY, BEGINNING OVER THE WASHINGTON CASCADES IN THE AFTERNOON
AND EXTENDING OVER THE OREGON CASCADES AND BLUE MOUNTAINS BY THE
EVENING. CONFIDENCE IN THESE SNOW AMOUNTS IS MODERATE (50-60%) AS
THE NBM SUGGESTS A 40-80% CHANCE OF 1 INCH OF SNOW OR MORE ACROSS
THESE MOUNTAIN ZONES. LIGHT RAINFALL WILL BE IMPACTING THE BASIN
AFTER 4 PM AND EXTEND INTO THE EARLY MORNING HOURS ON SATURDAY AS
0.01-0.05" OF RAIN IS EXPECTED. CONFIDENCE IN THESE RAIN AMOUNTS
IS MODERATE (60-70%) AS THE NBM SHOWS A 25-50% CHANCE OF
MEASURABLE RAIN (0.01" OR GREATER) ACROSS LOWER ELEVATIONS OF THE
COLUMBIA BASIN (TRI-CITIES AND HERMISTON) AND A 40-65% CHANCE OF
MEASURABLE RAINFALL (0.01" OR GREATER) ALONG THE BLUE MOUNTAIN
FOOTHILLS. LIGHT MOUNTAIN SNOWFALL WILL PERSIST THROUGH SATURDAY
MORNING BEFORE TRANSITIONING TO RAIN OVER THE AFTERNOON AND
EVENING AS THE NEXT SHORTWAVE MOVES OVER THE AREA. SOUTHWEST FLOW
ALOFT WILL ENHANCE WITH THIS SECOND SHORTWAVE TO ALLOW SNOW LEVELS
TO INCREASE TO BETWEEN 7000-8000 FEET SATURDAY AND SUNDAY. THIS
WILL LEAD TO RAIN AMOUNTS ACROSS THE CASCADES OF 1.5-2 INCHES OF
SATURDAY AFTERNOON THROUGH SUNDAY AND 1-1.5 INCHES OF RAIN OVER
THE NORTHERN BLUE MOUNTAINS. CONFIDENCE IN THESE AMOUNTS IS HIGH
(70-80%) AS THE NBM ADVERTISES A 75-95% CHANCE OF 1.5 INCHES OF
RAIN ACROSS THE CASCADES AND A 60-80% CHANCE OF 1 INCH OR MORE
RAIN OVER THE NORTHERN BLUE MOUNTAINS. CENTRAL OREGON IS EXPECTED
TO RECEIVE AROUND 0.25" SATURDAY AFTERNOON THROUGH SUNDAY, WITH
THE BLUE MOUNTAIN FOOTHILLS PICKING UP 0.20-0.50", AND LOWER
ELEVATIONS OF THE BASIN RECEIVING 0.05-0.15".
THE INITIAL SHORTWAVE ON FRIDAY AND THE REINFORCING SHORTWAVE ON
SATURDAY WILL ALSO ALLOW A PRESSURE GRADIENT TO SET UP ALONG THE
BLUE MOUNTAINS AS SURFACE HIGH PRESSURE LINGERS TO OUR SOUTHEAST.
THIS WILL PROVIDE ELEVATED WINDS ACROSS THE GRANDE RONDE VALLEY
FRIDAY AFTERNOON AND INCLUDING THE BLUE MOUNTAINS/FOOTHILLS
SATURDAY NIGHT INTO SUNDAY MORNING. GUSTS OF UP TO 30 MPH OUT OF
THE SOUTH WILL BE POSSIBLE FRIDAY AFTERNOON AND EARLY EVENING OVER
THE GRANDE RONDE VALLEY, WITH GUSTS REACHING UP TO 35 MPH
SATURDAY EVENING INTO SUNDAY MORNING. DOWNSLOPING WINDS ALONG THE
BLUE MOUNTAINS WILL LEAD TO GUSTS REACHING AROUND 40 MPH BETWEEN 7
PM SATURDAY AND 1 AM SUNDAY. CONFIDENCE IN FRIDAY'S WINDS OVER
THE GRANDE RONDE VALLEY IS HIGH (75%) AS THE NBM SUGGESTS A 60-80%
CHANCE OF GUSTS REACHING 35 MPH OR GREATER, WITH THE NAM, GFS,
AND SREF HINTING AT A 7-9 MB GRADIENT BETWEEN MEACHAM (KMEH) AND
ONTARIO (KONO) - WHICH IS INDICATIVE OF GUSTS REACHING BETWEEN
35-40 MPH. THE NAM, SREF, AND GFS INDICATE A STRONGER PRESSURE
GRADIENT BETWEEN THESE LOCATIONS SATURDAY EVENING INTO THE EARLY
MORNING HOURS OF SUNDAY MORNING, WITH VALUES BETWEEN 8-11 MB -
WHICH DOES APPROACH THE 11 MB ADVISORY THRESHOLD. PRESSURE
GRADIENTS BETWEEN MEACHAM (KMEH) AND PENDLETON (KPDT) ARE ALSO
ELEVATED SATURDAY EVENING INTO SUNDAY MORNING, BUT ONLY THE GFS
INDICATES BORDERLINE ADVISORY VALUES OF 6 MB. THE NBM DOES SHOW
AREAS INDICATING A 50-60% CHANCE OF ADVISORY LEVEL WIND GUSTS (45
MPH OR GREATER) BETWEEN ATHENA AND MILTON-FREEWATER, BUT THE
MAJORITY OF THE FOOTHILLS ARE BELOW A 30% CHANCE. THUS, CONFIDENCE
AT THIS TIME IS LOW TO MODERATE (30-50%) IN ADVISORY- LEVEL WINDS
EFFECTING THE NORTHERN BLUE MOUNTAIN FOOTHILLS, WITH EVEN LOWER
CHANCES (20-40%) OVER THE GRANDE RONDE VALLEY.
DUE TO PERSISTENT SOUTHWEST FLOW ALOFT, TEMPERATURES WILL BE
TRENDING WARMER THROUGH THE WEEKEND AS HIGH TEMPERATURES REACH
INTO THE MID-40S FRIDAY, MID-TO UPPER 50S SATURDAY, AND LOW TO
MID-60S OVER LOWER ELEVATIONS OF THE BASIN. THESE WEEKEND HIGH
TEMPERATURES ARE 10 TO 15 DEGREES ABOVE NORMAL. LOW TEMPERATURES
WILL ALSO STAY ABOVE FREEZING FRIDAY NIGHT INTO SATURDAY MORNING,
WHICH WILL CONTINUE INTO THE EXTENDED PERIOD. 75
LONG TERM...MONDAY THROUGH THURSDAY
BOTTOM LINE UP FRONT
1) MODERATE MOUNTAIN RAIN/SNOW, LIGHT LOWLAND RAIN TO START
2) WARMER AND DRIER CONDITIONS RETURN BY MIDWEEK
3) HYDROLOGICAL CONCERNS FROM SUNDAY & MONDAYS SYSTEM
MODELS SHOW THAT LATE SUNDAY ANOTHER SHORTWAVE TROUGH IS EXPECTED TO
BRIEFLY TRAVERSE ACROSS THE PACNW AND EXIT THE REGION BY MONDAY
MORNING. THIS WILL BE THE END OF THE ATMOSPHERIC RIVERS THAT
INFLUENCES THE REGION FROM THE SHORT TERM INTO THE LONG TERM. THE 48-
HR RAW ENSEMBLE PROBABILITIES ENDING MONDAY MORNING FOR
PRECIPITATION ACCUMULATIONS SHOWS A 90-100% CHANCE ALONG THE CASCADE
CRESTS, THE EAST SLOPES SHOW 60-90% PROBABILITIES, 40-70% ALONG THE
INTERIOR NORTHERN BLUES FOR 1 INCH OF RAIN ACCUMULATIONS. THE 48-HR
RAW ENSEMBLES PROBABILITIES FOR 2 INCHES OR GREATER, SHOW
PROBABILITIES ARE BETWEEN 70-90% ALONG THE CASCADE CRESTS, WITH LESS
THAN 10% ALONG THE CRESTS OF THE NORTHERN BLUES. LOWER ELEVATIONS
SHOW THERE IS GENERALLY A 40-60% CHANCE OF 0.25 INCHES OF RAIN
ACROSS CENTRAL & NORTH CENTRAL OR, THE YAKIMA/KITTITAS/GRANDE RONDE
VALLEYS, AND ALONG THE NORTHERN BLUE MOUNTAIN FOOTHILLS AND LESS
THAN 30-40% PROBABILITY ACROSS THE REMAINDER OF THE LOWER ELEVATION
ZONES. MONDAY NIGHT INTO TUESDAY NIGHT, MODELS SHOW YET ANOTHER WET
SHORTWAVE SYSTEM MAKING ITS WAY BRIEFLY ACROSS THE REGION EXITING BY
TUESDAY NIGHT. THIS SYSTEM WILL BRING MORE PRECIPITATION ALONG WITH
IT WITH 70-90% PROBABILITIES OF ANOTHER 1 INCH OF RAIN FOR THE
CRESTS OF THE CASCADES, 50% FOR THE CRESTS ON THE NORTHERN BLUES.
AGAIN THE LOWER ELEVATIONS SHOW THERE IS A 30-40% CHANCE OF 0.25
INCHES OF RAIN ACROSS CENTRAL & NORTH CENTRAL OR, THE
YAKIMA/KITTITAS/GRANDE RONDE VALLEYS, AND ALONG THE NORTHERN BLUE
MOUNTAIN FOOTHILLS, AND LESS THAN 30-40% PROBABILITY ACROSS THE
COLUMBIA BASIN. THERE IS ONLY 30-50% PROBABILITIES THE CASCADE
CRESTS WILL SEE 2 INCHES DURING THIS SHORTWAVE SYSTEM.
THE SOUTHWESTERLY FLOW ASSOCIATED WITH THESE UPPER LEVEL SHORTWAVES
AS WELL AS THE SURFACE WARM FRONTS ASSOCIATED WITH THEM WILL BRING
WARMER TEMPERATURES ACROSS THE REGION. COMPARING THE CURRENTLY
FORECASTED TEMPERATURES AGAINST THE CLIMATE DATA TEMPERATURES FOR
THIS TIME OF YEAR, THESE TEMPERATURES ARE ANYWHERE FROM 5 TO 10
DEGREES ABOVE NORMAL FOR THE LOWER AND MID ELEVATIONS AND 2 TO 5
DEGREES ABOVE NORMAL FOR THE HIGHER TERRAINS. EFI IS ALSO SHOWING
TEMPERATURES ARE ABOVE NORMAL FOR THIS TIME IN THE SEASON WITH
TEMPERATURES AVERAGING IN THE UPPER 50S TO LOW 60S IN LOWER
ELEVATIONS, LOW TO MID 50S ALONG THE MID ELEVATIONS AND IN THE UPPER
30 TO MID 40S THROUGH THE HIGHER TERRAINS ON MONDAY. AFTER MONDAY
TEMPERATURES ARE STILL AVERAGING ABOVE NORMAL WITH TEMPERATURES IN
THE 50S ALONG THE LOWER TERRAINS, HIGH 40S TO LOW 50S ALONG THE MID
ELEVATIONS AND MID 30S TO LOW 40S FOR THE HIGHER TERRAINS.
CONFIDENCE IS HIGH (<80%) WITH TEMPERATURES THAT ARE FORECASTED FOR
THE LONG TERM.
LASTLY AND MOST IMPORTANTLY, THERE ARE SOME HYDROLOGICAL CONCERNS
THAT ARE POPPING UP FROM ALL THE WARM TEMPERATURES AND
PRECIPITATION. RIVERS THROUGH THE YAKIMA, NACHES, KLICKITAT AND THE
LOWER YAKIMA RIVER BASINS WILL SEE RISES IN THE RIVERS WITHIN
NEARING BANKFULL WITH THE NACHES AT CLIFFDELL FORECASTED TO BREAK
ABOVE BANKFULL BY MONDAY AFTERNOON DUE TO THE MELT WATER AND EXCESS
RAIN. A HYDROLOGIC OUTLOOK HAS BEEN ISSUED AND WE WILL CONTINUE TO
CLOSELY MONITOR THE RIVER FORECASTS ANS WORK WITH THE RIVER CENTERS
AS THE DAY DRAWS CLOSER. IN THE MEANTIME, BE PREPARED AND CONTINUE
TO REMAIN VIGILANT AND CHECK THE WEBSITE FOR UPDATED INFORMATION
REGARDING THE RIVERS. BENNESE/90
AVIATION...00Z TAFS
ALL TAF SITES WILL REMAIN VFR THROUGH THE
PERIOD WITH THE EXCEPTION OF YKM AND PSC SEEING MVFR AND LIFR
RESPECTIVELY. HOWEVER, CONFIDENCE IN THE TIMING OF THE LOW CLOUDS IS
LOW/MODERATE (20-40%). OTHERWISE, THE PERIOD WILL BE CALM WITH WINDS
BELOW 12 KTS. BENNESE/90
PRELIMINARY POINT TEMPS/POPS
PDT 28 47 37 59 / 0 0 30 30
ALW 30 44 36 54 / 0 10 40 40
PSC 29 44 34 57 / 0 10 30 20
YKM 29 42 32 52 / 10 10 30 30
HRI 29 45 35 59 / 0 10 20 20
ELN 30 41 32 47 / 10 30 40 50
RDM 26 52 34 58 / 0 10 20 10
LGD 22 41 32 44 / 0 0 30 30
GCD 24 47 33 51 / 0 0 30 20
DLS 34 47 37 54 / 0 20 30 50
PDT WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
SHORT TERM...75
LONG TERM....90
AVIATION...90
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