737
FXUS66 KPDT 221738
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
938 AM PST SAT FEB 22 2025
UPDATED AVIATION DISCUSSION
AVIATION...18Z TAFS
VFR CONDITIONS EXPECTED DURING MOST OF THE
DAY. LIGHT SHOWERS IN THE BASIN WILL LET UP BY THE EARLY
AFTERNOON, LEAVING SITES WITH SCT-BKN MID-LEVEL CLOUDS, BEFORE AN
ATMOSPHERIC RIVER BRINGS WIND AND RAIN TO ALL SITES STARTING THIS
EVENING. RAIN IS EXPECTED TO ENCOMPASS ALL SITES BY 03Z AT THE
LATEST. WINDS WILL BE STRONGEST AT THE FOOTHILLS OF THE MOUNTAINS,
EXCEPT FOR DLS, WITH RAIN EXPECTED TO PERSIST THROUGH MUCH OF THE
WEEKEND, ALBEIT INTERMITTENTLY. GUSTS COULD REACH 30 KTS AT SOME
SITES, WITH STRONGER WINDS EXPECTED DURING THE DAY TOMORROW. DURING
RAIN, CIGS WILL BECOME OVC AND DROP TO 3-6 KFT FOR MOST SITES.
WITH GUSTY WINDS EXPECTED, LLWS IS POSSIBLE AT SOME SITES, WITH
MENTIONS INCLUDED AT PDT AND PSC, BUT DID SCALE BACK ON LLWS FROM
PREVIOUS TAFS, AS WINDS DO LOOK TO BE MORE UNIDIRECTIONAL ACROSS
MODELS THAN PREVIOUSLY THOUGHT. EVANS/74
PREV DISCUSSION
/ISSUED 423 AM PST SAT FEB 22 2025/
SHORT TERM...TODAY THROUGH MONDAY...SATELLITE AND RADAR IMAGERY
TONIGHT SHOW A WEAK SHORTWAVE AND FRONTAL BOUNDARY PUSHING THE
LAST OF VERY LIGHT PRECIPITATION ACROSS FAR EASTERN WA/OR, WITH
SOME LIGHT SHOWERS DEVELOPING JUST WEST OF THE CASCADE CREST.
OTHERWISE, POCKETS OF CLEAR SKY ALONG THE CASCADE EAST SLOPES
SHOWS AREA OF LOW STRATUS, WITH SHALLOW FOG IN PORTIONS OF THE
YAKIMA/KITTITAS VALLEYS.
THE SHORTWAVE TROUGH AND ATTENDANT FRONT WILL EXIT THE PACNW EARLY
THIS MORNING, SETTING UP WARM AIR ADVECTION UNDER A WEST
SOUTHWEST FLOW ALOFT. THE FORECAST AREA WILL SEE A BRIEF BREAK IN
PRECIPITATION INTO THE EARLY AFTERNOON. OTHERWISE, SNOW LEVELS
WILL BE ON THE RISE BEHIND THE SYSTEM EXIT, WITH SNOW LEVELS
EXPECTED TO RISE TO ABOVE 6KFT BY MID-AFTERNOON.
LATE THIS AFTERNOON THE NEXT SHORTWAVE WILL ARRIVE TO THE REGION
WHILE ACCOMPANIED BY A WEAK TO MODERATE ATMOSPHERIC RIVER (AR) AND
SURFACE WARM FRONT. A MILD AND MOIST AIRMASS WILL FILTER IN BEHIND
THE WARM FRONT PASSAGE TONIGHT, RESULTING IN SNOW LEVELS RISING TO
ABOVE 7KFT ACROSS THE FORECAST AREA. THIS WILL FACILITATE MOSTLY RAIN
BELOW THE HIGHEST MOUNTAIN PEAKS ALONG THE CASCADE CREST AND
EASTERN MOUNTAINS THROUGH SUNDAY. ONCE AGAIN, THERE HAS BEEN
LITTLE CHANGE SINCE 24 HOURS AGO AMONGST GUIDANCE, WITH THE
EXPECTATION THAT THERE WILL BE PLENTY OF MOISTURE TO WORK WITH AS
THE AR WITH THIS SYSTEM WILL BE CENTERED ALONG THE 45TH PARALLEL.
BOTH THE GFS AND ECMWF IVT ENSEMBLE SUITES SHOW CLOSE TO A 100%
CHANCE OF IVT VALUES GREATER THAN 250 KG/M/S MAKING IT EAST OF
THE CASCADE CREST. VAPOR TRANSPORT AT THIS MAGNITUDE WILL RESULT
IN ENOUGH MOISTURE FOR MODERATE TO HEAVY PRECIPITATION
ACCUMULATIONS ALONG THE CASCADE CREST AND THE INTERIOR NORTHERN
BLUES, WITH LIGHT TO LOCALLY MODERATE ACCUMULATIONS IN THE LOWER
ELEVATIONS THROUGH SUNDAY AFTERNOON. SUNDAY EVENING, THE NEXT
SHORTWAVE TROUGH IS EXPECTED TO QUICKLY PASS THROUGH THE PACNW AND
EXIT BY MONDAY MORNING, WITH THE AR EFFECTIVELY ENDING EARLY
SUNDAY NIGHT. THE NBM 48-HR PROBABILITIES ENDING MONDAY MORNING
FOR PRECIPITATION ACCUMULATIONS SHOWS A 95-100% CHANCE ALONG THE
CASCADE CREST/EAST SLOPES AND A 70-90% CHANCE ALONG THE INTERIOR
NORTHERN BLUES FOR 1 INCH OF RAIN ACCUMULATIONS. LOOKING AT 2
INCHES OR GREATER, CHANCES ARE BETWEEN 70-90% ALONG THE CASCADE
CREST, WITH A 25-45% CHANCE ALONG THE HIGHER TERRAIN OF THE
INTERIOR NORTHERN BLUES. IN THE LOWER ELEVATION, THERE IS A
60-80% CHANCE OF 0.25 INCHES OF RAIN ACROSS CENTRAL/NORTH CENTRAL
OR, AND THE YAKIMA/KITTITAS VALLEYS; THERE IS A 70-90% CHANCE
ALONG THE BLUE MOUNTAIN FOOTHILLS, GRANDE RONDE/WALLOWA VALLEYS;
THERE IS A 50-70% CHANCE ACROSS THE REMAINDER OF THE LOWER
ELEVATION ZONES.
BREEZY TO LOCALLY WINDY CONDITIONS WILL ALSO DEVELOP THIS
AFTERNOON AHEAD OF THE SHORTWAVE TROUGH AND WARM FRONT ARRIVAL
THIS EVENING. SURFACE PRESSURE GRADIENTS BETWEEN THE BLUE
MOUNTAIN FOOTHILLS TO THE LOWER TREASURE VALLEY WILL INCREASE TO
AROUND 10-12MB THIS EVENING AND OVERNIGHT, FACILITATING THE
STRONGEST WINDS (GUSTS BETWEEN 45-55MPH) THROUGH THE GRANDE RONDE
VALLEY AND ALONG THE BLUE MOUNTAIN FOOTHILLS THROUGH SUNDAY
MORNING (CONFIDENCE 70-90%). FROM CENTRAL OR TO THE COLUMBIA
BASIN, LOCALLY BREEZY SOUTHWEST WINDS WILL ALSO DEVELOP TONIGHT.
THERE WILL BE A BRIEF PERIOD LATE TOMORROW MORNING INTO THE
AFTERNOON WHERE WINDS WILL DECREASE BEHIND THE SHORTWAVE PASSAGE
IN THE LOWER ELEVATIONS, HOWEVER A DEVELOPING MODEST LOW TO MID
LEVEL JET WILL SETUP OVER THE COLUMBIA BASIN. BY LATE SUNDAY
AFTERNOON, WINDS WILL ONCE AGAIN INCREASE ACROSS THE AREA AS THE
NEXT SHORTWAVE TROUGH ARRIVES AND THE LOWER TO MID LEVEL JET WINDS
BEGIN TO MIX DOWN. THIS WILL RESULT IN BREEZY TO LOCALLY WINDY
CONDITIONS (25-50MPH GUSTS) ACROSS THE LOWER ELEVATIONS THROUGH
SUNDAY EVENING, WITH WINDS DECREASING BY MONDAY MORNING.
EARLY MONDAY MORNING, A BRIEF WINDOW OF DRY CONDITIONS WILL
DEVELOP ACROSS THE FORECAST AREA AS A TRANSIENT RIDGE MOVES ACROSS
THE PACNW. HOWEVER, BY MID MORNING HOURS, A WARM FRONT WILL LIFT
NORTH ACROSS THE FORECAST AREA THROUGH THE AFTERNOON, FOLLOWED BY
THE ARRIVAL OF A COMPACT AND STRONG UPPER TROUGH MONDAY EVENING
THROUGH OVERNIGHT HOURS. SNOW LEVELS WILL LOWER TO BETWEEN 4KFT TO
6KFT (WEST TO EAST GRADIENT), ALLOWING FOR MODERATE SNOW
ACCUMULATIONS ON UPPER ELEVATION RIDGES ABOVE 5.5KFT, WITH LIGHT
SNOW DOWN TO PASS LEVEL IN THE CASCADES. OTHERWISE, MODERATE
(0.25-0.5 INCHES) RAIN ACCUMULATIONS WILL BE POSSIBLE ALONG THE
MID TO LOWER CASCADE SLOPES AND THE EASTERN MOUNTAINS. LIGHT TO
LOCALLY MODERATE (0.1-0.25 INCHES) RAIN ACCUMULATIONS. WINDS WILL
AGAIN BE A CONCERN MONDAY WITH THE FRONTAL PASSAGE AND
REDEVELOPMENT OF A LOW TO MID LEVEL JET ACROSS THE COLUMBIA BASIN.
WIND GUSTS WILL INCREASE ACROSS THE LOWER ELEVATIONS TO 25-40MPH,
WITH LOCALLY 40-50MPH IN WIND PRONE AREAS ALONG THE BLUE MOUNTAIN
FOOTHILLS, CENTRAL/NORTH CENTRAL OR, AND RIDGES IN THE COLUMBIA
BASIN.
WITH THE EXPECTED RAINFALL AND SUBSEQUENT SNOWMELT/RUNOFF IN THE
MOUNTAINS, AREA RIVERS AND STREAMS WILL BEGIN TO RISE SUNDAY, AND
ARE CURRENTLY FORECAST TO PEAK DURING MONDAY. AT THE MOMENT, MOST
RIVERS ARE EXPECTED TO REMAIN WITHIN BANKFULL THROUGH SUNDAY,
THOUGH THE NACHES, YAKIMA, KLICKITAT, WALLA WALLA, AND UMATILLA
RIVERS WILL BEGIN TO REACH OR JUST EXCEED BANKFULL BY EARLY NEXT
WEEK. SMALLER STREAMS WILL ALSO SEE RISES, AND THOSE STREAMS THAT
HAVE NOT BEEN CLEARED OF DEBRIS MAY SEE MINOR FLOODING INTO
ADJACENT LOW LYING AREAS. LAWHORN/82
LONG TERM...TUESDAY THROUGH FRIDAY NIGHT...
OVERVIEW: A WEAKENING UPPER-LEVEL LOW PRESSURE SYSTEM WILL LIKELY
(>90% CONFIDENCE) BECOME AN OPEN-WAVE TROUGH AS IT PASSES OVER THE
FORECAST AREA TUESDAY. PRECIPITATION CHANCES DIMINISH THROUGH THE
DAY TUESDAY AS AN UPPER-LEVEL RIDGE OF HIGH PRESSURE BUILDS OVER THE
PACNW. THE FORECAST AREA WILL THEN LIKELY (~75% CHANCE) STAY DRY
THROUGH FRIDAY WITH TEMPERATURES RUNNING 5-10 DEGREES ABOVE NORMAL.
UNCERTAINTY/HYDRO: WEDNESDAY THROUGH FRIDAY, ENSEMBLE CLUSTER
ANALYSIS INDICATES ROUGHLY 25% OF MEMBERS SUGGEST A GLANCING BLOW
FROM A WEAK SHORTWAVE TROUGH; THIS SCENARIO WOULD BRING LIGHT
PRECIPITATION TO THE MOUNTAINS. EITHER WAY, HYDROLOGIC CONCERNS
SHOULD LESSEN THROUGH THE PERIOD WITH NO SIGNIFICANT PRECIPITATION
FORECAST.
WINDS: WIDESPREAD BREEZY TO WINDY, LOCALLY VERY WINDY, WESTERLY
WINDS ARE FORECAST TO SLACKEN THROUGH THE DAY TUESDAY. BREEZY
SOUTHERLY WINDS ARE THEN FORECAST WEDNESDAY INTO THURSDAY THROUGH
THE GRANDE RONDE VALLEY AND ALONG THE BASE OF THE BLUE MOUNTAINS.
CONFIDENCE IN ADVISORY-LEVEL WINDS WEDNESDAY/THURSDAY IS LOW (<40%),
WHILE CONFIDENCE IN ADVISORY-LEVEL WINDS TUESDAY MORNING IS MEDIUM-
HIGH (40-80%) FOR CENTRAL/NORTH-CENTRAL OR, THE BLUE MOUNTAIN
FOOTHILLS, SIMCOE HIGHLANDS, AND COLUMBIA BASIN. PLUNKETT/86
PRELIMINARY POINT TEMPS/POPS
PDT 60 47 61 43 / 20 70 80 60
ALW 53 45 57 42 / 30 90 90 80
PSC 58 45 62 41 / 10 70 70 50
YKM 49 40 57 36 / 40 70 70 50
HRI 59 47 63 42 / 10 60 70 50
ELN 46 37 52 33 / 50 80 70 50
RDM 59 46 61 40 / 20 60 60 40
LGD 45 37 48 37 / 30 80 90 80
GCD 52 40 53 38 / 10 80 80 50
DLS 54 45 58 43 / 60 90 90 80
PDT WATCHES/WARNINGS/ADVISORIES
OR...WIND ADVISORY FROM 4 PM THIS AFTERNOON TO 7 AM PST SUNDAY FOR
ORZ049-507-508.
WA...NONE.
SHORT TERM...82
LONG TERM....86
AVIATION...74
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