034
FXUS66 KPDT 200514
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
914 PM PST WED FEB 19 2025
AVIATION UPDATE
AVIATION...06Z TAFS...PRECIPITATION HAS MOVED OUT OF ALL TERMINALS.
NO MORE PRECIP EXPECTED FOR ANY SITES FOR THE REMAINDER OF THE
TAF PERIOD. BIG CONCERNS THIS PERIOD WILL BE LOW CEILINGS PASSING
THROUGH YKM/ALW/PSC. PSC/ALW HAVE BEEN FLIPPING BETWEEN IFR AND
MVFR FOR THE LAST SEVERAL HOURS AND EXPECT WITH HIGH CONFIDENCE
(80-90%) THAT CEILINGS WILL STAY AT OR BELOW MVFR STANDARDS
OVERNIGHT. YKM HAS BEEN MORE STABLE AT MVFR FOR THE LAST SEVERAL
HOURS AND EXPECT CEILINGS TO DROP TO IFR BY 09Z WITH MEDIUM
CONFIDENCE (30-50%). REST OF TERMINALS ARE IN VFR STATUS AND WILL
REMAIN SO FOR THE REMAINDER OF THE PERIOD.
PREV DISCUSSION
/ISSUED 749 PM PST WED FEB 19 2025/
UPDATE...LATEST WATER VAPOR IMAGERY SHOWS A COMPACT UPPER
TROUGH/LOW MOVING SEWD AND AWAY FROM THE FORECAST AREA THIS
EVENING. SNOW HAS TAPERED OFF ALONG THE CASCADES AND RECENTLY
CANCELLED THE WINTER WEATHER ADVISORIES THAT WERE IN EFFECT THERE.
LEFT THE NORTHERN BLUES ADVISORIES UP FOR A LITTLE WHILE LONGER
AS SCATTERED MOSTLY LIGHT SNOW SHOWERS CONTINUE. LATEST SPC HREF
GREATLY DIMINISHES THE SNOW SHOWERS AFTER 06-07Z SO WILL MONITOR
THE TRENDS THE REST OF THE EVENING TO SEE IF THESE HIGHLIGHTS CAN
BE LOWERED AS WELL. OTHERWISE THE CURRENT FORECAST IS ON TRACK
AND MADE ONLY A FEW MINOR ADJUSTMENTS TO THE OVERNIGHT POP GRIDS.
78
PREV DISCUSSION... /ISSUED 304 PM PST WED FEB 19 2025/
SHORT TERM...TODAY THROUGH FRIDAY NIGHT...
KEY MESSAGES:
1. CONTINUED MOUNTAIN SNOW THROUGH THURSDAY MORNING.
*WINTER WEATHER ADVISORIES ACTIVE*
2. BREEZY WINDS OVERNIGHT INTO THURSDAY MORNING.
3. LIGHT MOUNTAIN SNOW RETURNS FRIDAY AFTERNOON.
CURRENT RADAR AND VISIBLE SATELLITE IMAGERY SHOWING LIGHT TO
MODERATE RETURNS ALONG THE CASCADES AND NORTHERN BLUE MOUNTAINS AS
A FRONTAL SYSTEM CONTINUES TO PASS THROUGH THE AREA UNDER MOSTLY
CLOUDY TO CLOUDY SKIES. THIS IS IN RESPONSE TO AN UPPER LEVEL
TROUGH THAT IS CONTINUING TO PASS THROUGH THE AREA BEFORE EXITING
TO OUR SOUTHEAST THURSDAY MORNING. LIGHT RAIN WILL LINGER ALONG
THE BLUE MOUNTAIN FOOTHILLS THROUGH THE EVENING AS PRECIPITATION
BECOMES MORE CONFINED ALONG OUR MOUNTAIN ZONES, KEEPING LIGHT TO
MODERATE SNOWFALL OCCURRING - PRIMARILY ABOVE 4000 FEET. AN
ADDITIONAL 2 TO 6 INCHES OF SNOW IS EXPECTED IN THESE AREAS, WITH
THE HIGHEST OVER THE OREGON CASCADES AND THE NORTHERN BLUE
MOUNTAINS. THUS, A WINTER WEATHER ADVISORY IS IN EFFECT UNTIL 4 AM
THURSDAY MORNING OVER THESE AREAS. CONFIDENCE IN THESE SNOW
AMOUNTS IS HIGH (80%) AS THE NBM SUGGESTS A 70-90% CHANCE OF 3
INCHES OF SNOW OR MORE, WITH A 25-45% CHANCE OF RECEIVING 6 INCHES
OF SNOW OR MORE (SANTIAM PASS AND NORTHERN BLUE MOUNTAINS NORTH OF
INTERSTATE 84).
THE FRONTAL SYSTEM HAS ALSO ALLOWED A PRESSURE GRADIENT TO SET UP
ALONG THE BLUE MOUNTAINS, PROVIDING BREEZY WINDS ALONG THE BLUE
MOUNTAIN FOOTHILLS AND THE GRANDE RONDE VALLEY. WINDS HAVE
SLACKENED OFF CONSIDERABLY FROM EARLIER IN THE DAY, ESPECIALLY
ALONG THE FOOTHILLS OF THE NORTHERN BLUE MOUNTAINS. HOWEVER, WIND
GUSTS OF 20-30 MPH OUT OF THE NORTH ARE STILL BEING OBSERVED IN
THE GRANDE RONDE VALLEY, SPECIFICALLY ACROSS LADD AND PYLES
CANYONS. THESE VALUES ARE EXPECTED TO PERSIST OVER THE NEXT
TWO TO THREE HOURS, BUT WILL CONTINUE TO DECREASE THROUGH THE
EVENING AS THE PRESSURE GRADIENT LOOSENS. THIS IS OBSERVED VIA
GFS, NAM, AND SREF GUIDANCE WHICH ADVERTISES CURRENT GRADIENTS OF
3 MB DROPPING TO LESS THAN 1 MB BETWEEN 5 PM AND 6 PM. FURTHER
CONFIDENCE IS GLEANED THROUGH THE NBM, WHICH SUGGESTS ONLY A 10%
CHANCE OF WIND GUSTS REACHING 15 MPH OR GREATER BY 5 PM, DROPPING
TO BELOW 5% BY 6 PM.
AN UPPER LEVEL RIDGE PUSHES ONSHORE LATE THURSDAY MORNING AND
MOVES OVER THE AREA THROUGH THE EVENING AND EARLY MORNING HOURS ON
FRIDAY AHEAD OF AN UPPER LEVEL SHORTWAVE THAT BRINGS LIGHT
MOUNTAIN SNOW CHANCES BACK INTO THE FORECAST. LIGHT SNOW WILL
IMPACT THE WASHINGTON CASCADES FRIDAY AFTERNOON, THEN MOVES OVER
THE OREGON CASCADES, BLUE MOUNTAINS, AND THE JOHN DAY-OCHOCO
HIGHLANDS THROUGH THE LATE AFTERNOON AND EVENING. LIMITED MOISTURE
WILL BE ASSOCIATED WITH THIS SHORTWAVE, WITH ONLY 1-2 INCHES
EXPECTED AT HIGHER ELEVATIONS ABOVE 4500 FEET. THIS CORRESPONDS
WITH THE NBM, AS A 30-60% CHANCE OF 1 INCH OF SNOW OR MORE IS
ADVERTISED ALONG THE WASHINGTON CASCADES ABOVE 4500 FEET AND ONLY
A 10% CHANCE OF 1 INCH OF SNOW OR MORE OVER THE NORTHERN BLUE
MOUNTAINS ABOVE 4500 FEET. 75
LONG TERM...SATURDAY THROUGH WEDNESDAY...
BOTTOM LINE UP FRONT
1) WET AND WARMER WEATHER ON THE WAY
2) SOME HYDROLOGIC INCREASES FOR RIVERS
OVERALL THE LONG TERM WILL BE QUITE ACTIVE IN THE SYNOPTIC REALM.
THE PERIOD WILL BEGIN WITH WESTERLY FLOW WITH RAIN ALONG THE EASTERN
SLOPES OF THE CASCADES, FOOTHILLS OF THE BLUES WITH MOUNTAIN SNOW
ABOVE 4500 FEET. A WEEK TRANSIENT RIDGE WILL THEN MOVE OVERHEAD
SATURDAY NIGHT BRINGING SNOW LEVELS TO ABOVE 7000 FEET AND
WIDESPREAD RAIN THROUGH MONDAY NIGHT. THE LEADING EDGE OF AN UPPER
LEVEL TROUGH WILL THEN MAKE ITS WAY ONSHORE LATE MONDAY NIGHT
BRINGING INCREASED CHANCES OF THROUGH TUESDAY BEFORE YET ANOTHER
RIDGE MOVES OVERHEAD DRYING THE REGION OUT.
MODELS ARE IN RELATIVELY FIRM AGREEMENT WITH THE OVERALL PATTERNS
THROUGH THE LONG TERM PERIOD WITH THE CLUSTERS SHOWING THE MAIN
VARIANCES TO BE WITH THE AMPLITUDE OF EACH SYSTEM. LOOKING AT
ENSEMBLES GUIDANCE, OVER 40-70% OF THE ENSEMBLES SHOW THE CASCADES
WILL RECEIVE NEAR 0.30 INCHES OF RAIN SATURDAY, 40-60% OF THE
ENSEMBLES SHOW THE BLUES WILL GET 0.15-2 INCHES WHILE THE BASIN AND
CENTRAL OR WILL SEE NEAR 0.10 INCHES. ENSEMBLES THEN SHOW MORE
SIGNIFICANT RAIN MONDAY AS THE SYSTEM WRAPS UP WITH AN ATMOSPHERIC
RIVER BRINGING CHANCES OF 0.30 INCHES OF RAIN AND HIGHER TO THE
MOUNTAINS, EAST SLOPES AND FOOTHILLS WHILE THE REMAINDER OF THE
REGION WILL SEE 20-40% CHANCES OF 0.20-0.25 INCHES. CHANCES DECREASE
AGAIN MONDAY AFTERNOON TO 20-40% AGREEMENT TO AMOUNTS OF 0.20 IN THE
MOUNTAINS AND A LIGHT RAIN ACROSS THE LOWER ELEVATIONS AND CENTRAL
OR. TUESDAY MUCH OF THE PRECIPITATION WILL BE LOCKED ALONG THE
MOUNTAINS WITH SNOW ELEVATIONS DROPPING TO 4500 FEET. SNOW AMOUNTS
ALONG THE CRESTS WILL BE LIGHT. MODERATE-HIGH CONFIDENCE IN THE
OVERALL FORECAST.
TEMPERATURES THROUGH THE LONG TERM WILL DEFINITELY BE WARMER WITH
OVER 80% OF THE RAW ENSEMBLES SHOWING TEMPERATURES TO BE ABOVE 50
BEGINNING SATURDAY THROUGH CENTRAL & NORTH CENTRAL OR, THE GORGE,
FOOTHILLS OF THE BLUES AND THE LOWER AND MID COLUMBIA BASIN. SUNDAY
SHOWS TEMPERATURES TO BE A FEW DEGREES COOLER WITH OVER 80% OF THE
ENSEMBLES SHOWING MID TO HIGH 50S FOR THE AFOREMENTIONED AREAS BUT
EXTENDING ACROSS THE ENTIRE BASIN AND INTO JOHN-DAY BASIN AS WELL.
MONDAY WILL BE THE DAY WITH THE HIGHEST TEMPERATURES WITH 60-80% OF
THE ENSEMBLES SHOWING MID TO UPPER 50S ACROSS THE SAME LOCATIONS.
THE REMAINING DAYS CONTINUE TO SHOW HIGH CONFIDENCE THOSE SAME
LOCATIONS WILL SEE TEMPERATURES IN THE 50S. EFI IS SIGNALING THESE
TEMPERATURES TO BE ABOVE SEASONAL AVERAGE AND WHEN COMPARING AGAIN
PAST CLIMATE DATA FOR THE REGION, UP TO 10 DEGREES ABOVE THE
SEASONAL AVERAGE.
LASTLY, WITH ALL THE WARMER AIR, HIGHER SNOW LEVELS AND EXCESS
RAINFALL, THERE ARE SOME RIVERS FORECASTING TO RISE TO JUST BELOW
ACTION STAGE. MOST OF THE RIVERS AFFECTED ARE ALONG THE EAST SLOPES
OF THE CASCADES WHILE ONLY ONE LOCATION ALONG THE BLUES. REGARDLESS,
WE WILL CONTINUE TO CLOSELY MONITOR ALL RIVERS IN THE FORECAST AREA.
BENNESE/90
PRELIMINARY POINT TEMPS/POPS
PDT 32 47 27 46 / 40 10 0 0
ALW 33 45 30 44 / 70 10 0 10
PSC 30 47 29 43 / 20 0 0 10
YKM 28 45 28 42 / 20 10 10 10
HRI 31 48 28 46 / 30 0 0 10
ELN 30 44 28 41 / 20 10 10 20
RDM 25 47 25 51 / 20 10 10 10
LGD 29 42 21 41 / 80 20 0 0
GCD 26 40 23 46 / 60 10 0 0
DLS 36 49 33 47 / 30 10 10 10
PDT WATCHES/WARNINGS/ADVISORIES
OR...WINTER WEATHER ADVISORY UNTIL 4 AM PST THURSDAY FOR ORZ502.
WA...WINTER WEATHER ADVISORY UNTIL 4 AM PST THURSDAY FOR WAZ030.
SHORT TERM...78
LONG TERM....90
AVIATION...95
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