439
FXUS66 KPDT 010000
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
500 PM PDT MON MAR 31 2025
UPDATED AVIATION DISCUSSION
SHORT TERM...TODAY THROUGH WEDNESDAY NIGHT
CURRENT RADAR SHOWS ISOLATED TO SCATTERED SHOWERS THROUGHOUT THE
CWA. AN OCCASIONAL THUNDER SHOWER IS POPPING UP AROUND THE
PENDLETON/LA GRANDE AREA ALL AFTERNOON AND WILL CONTINUE TO SEE
THOSE COME THROUGH FOR THE REST OF THE AFTERNOON. CAPE VALUES ARE
AROUND 500 J/KG TO SUPPORT SOME GRAUPEL/SMALL HAIL REPORTED IN THE
PENDLETON AND YAKIMA AREA EARLIER THIS AFTERNOON. SATELLITE SHOWS
BKN TO OVC SKIES ACROSS THE CWA, ALLOWING SOME FUEL TO DEVELOP
SCATTERED SHOWERS.
GOING FORWARD, HEAR ARE THE KEY MESSAGES THROUGH WEDNESDAY NIGHT:
1) LOW ELEVATION RAIN TO CONTINUE THROUGH TUESDAY AM. LIGHT
MOUNTAIN SNOW TO CONTINUE THROUGH WED PM.
2) PATTERN BECOMING MORE DRY AND WARMER AS WE HEAD THROUGH MID-
WEEK.
AN UPPER LEVEL TROUGH IS CURRENTLY PLACED OVER THE REGION WITH SW
SURFACE LEVEL WINDS, ALLOWING FOR MOISTURE ADVECTION TO ENTER THE
AREA. THIS IN RETURN IS BRINGING IN SCATTERED SHOWERS AND AN
OCCASIONAL THUNDERSTORM TO POP UP AND INCREASE MOUNTAIN SNOW
ACCUMULATIONS. PRECIPITATION IN THE LOWER VALLEYS WILL DROP OUT AS
THE OVER HEAD TROUGH MOVES TO THE EAST. ADDITIONAL MOUNTAIN SNOW
ACCUMULATIONS ARE NOT MUCH TO ISSUE ANY HIGHLIGHTS, WITH WA
CASCADES AND THE BLUE MOUNTAINS RECEIVING 2-4" (70-90%
CONFIDENCE), WITH THE OREGON CASCADES RECEIVING A SLIGHTLY HIGHER
AMOUNT OF 3-5" (60-80% CONFIDENCE).
A SECOND SYSTEM THAT'S ACCOMPANIED WITH ANOTHER SHORTWAVE WILL
PASS SHORTLY AFTER THE FIRST SYSTEM TUES PM, BUT WILL BE WEAKER
WITH LESS MOISTURE ATTACHED WITH LESS FAVORABLE WESTWARD WINDS.
THIS IS PRIMARILY A LIGHT MOUNTAIN SNOW EVENT WITH LOWER
ACCUMULATIONS THAN THE FIRST SYSTEM WITH NO MORE THAN AN
ADDITIONAL 3" OF ACCUMULATION (50-70% CONFIDENCE).
LONG TERM...TUESDAY THROUGH FRIDAY...KEY MESSAGES
- WARMEST TEMPERATURES OF 2025 WITH HIGHS 15-20 F ABOVE AVERAGE
WITH POTENTIAL FOR SITES TO APPROACH OR REACH THEIR DAILY
RECORD TUESDAY/WEDNESDAY.
- SLIGHT CHANCE OF THUNDERSTORMS IN THE EASTERN MOUNTAINS AND
EASTERN LOWER BASIN WITH RAIN LIKELY (>60 CHANCE) LATE
WEDNESDAY.
- REPEATED PRECIP CHANCES IN THE MOUNTAINS THURSDAY-FRIDAY WITH
HIGH MOUNTAIN RAIN MORE LIKELY THAN NOT CONTINUING IN THE EAST
THROUGH THURSDAY BEFORE SNOW LEVELS DROP.
- RISING RIVERS AND STREAMS BEGINNING WEDNESDAY WITH PEAKS
THURSDAY INTO FRIDAY, HOWEVER, POTENTIAL FOR RIVER FLOODING
IS LOW (< 30%)
LIMITED CHANGES IN EXPECTATIONS INTO MID WEEK. LARGE SCALE PATTERN
BEGINS WITH AN AMPLIFIED UPPER-LEVEL RIDGE ACROSS THE SOUTHWEST
CONUS INTO BRITISH COLUMBIA. ENSEMBLE GUIDANCE REMAINS IN GOOD
AGREEMENT WITH THIS STRONG RIDGE WITH EPS ENSEMBLE MEAN FORECAST
HEIGHTS IN EXCESS OF THE 99TH PERCENTILE ACROSS THE NORTHERN AND
CENTRAL ROCKIES THROUGH WEDNESDAY NIGHT. IT IS FORECAST TO
PROGRESS EAST WITH A DIGGING UPPER-LEVEL TROUGH EVOLVING UPSTREAM
IN THE EASTERN NORTH PACIFIC. A DRY PATTERN WILL BE IN PLACE WITH
WELL ABOVE NORMAL HIGHS EXPECTED, READINGS 15-20 DEGREES ABOVE
NORMAL, WITH MOST EXPECTED TO SEE THEIR FIRST 70 DEGREE DAY FOR
THE YEAR. TIGHT CLUSTERING SEEN IN RAW AND CALIBRATED GUIDANCE
THAT FURTHERS INCREASES CONFIDENCE IN THESE TEMPERATURES.
LIKEWISE, EPS EXTREME FORECAST INDEX DEPICTS VALUES OF 0.7-0.9 FOR
MAXT INDICATIVE OF A CLIMATOLOGICAL HIGH-END EVENT WITH MANY OF
ITS MEMBERS FORECASTING WELL ABOVE NORMAL HIGHS RELATIVE TO MODEL
CLIMATE. LASTLY, THERE WILL BE POTENTIAL TO BREAK DAILY HIGHS AT
SITES TUESDAY AND WEDNESDAY AS WELL.
ATTENTION TURNS TO THE UPSTREAM TROUGH DEEPENING WEDNESDAY
OFFSHORE THE COAST WITH ITS ASSOCIATED SURFACE LOW. CURRENT
CLUSTERING SHOWS MUCH OF ITS SPREAD IS TIED TO ITS STRENGTH OF ITS
EJECTING SHORTWAVE TROUGH. THE MOST LIKELY SCENARIO (~65%) IS NOT
AS PROGRESSIVE AND ARRIVES LATE WEDNESDAY/WEDNESDAY NIGHT
COMPARED TO THE MORE PROGRESSIVE OUTCOME (~20%). THAT SAID, THE
COMBINATION OF MILD DEW POINTS AND MARGINAL LAPSE RATES PAIRED
WITH MODEST INSTABILITY, WITH EVEN EPS SHOWING MEAN MUCAPES IN
EXCESS OF 1000 J/KG, SUPPORT SLIGHT CHANCE OF THUNDERSTORMS
WEDNESDAY AFTERNOON AND EVENING. CURRENT THINKING IS BEST FOCUS
FOR THUNDER CHANCES WILL BE ACROSS THE EASTERN MOUNTAINS AND
EASTERN BASIN. OTHERWISE, MUCH OF THE MOISTURE WILL BE ON A
SOUTHERLY PATHWAY INTO THE OR/WA CASCADES WITH LIMITED INLAND
PENETRATION LATE WEDNESDAY AND THURSDAY WITH RAIN EXPECTED TO
SPREAD AREA-WIDE BEGINNING LATE IN THE DAY. MEAN TROUGHING AND
CYCLONIC FLOW WILL THEN DOMINANT THURSDAY WITH THE UPPER TROUGH
OFF THE OFFSHORE COAST OF BC AND WA THAT WILL KEEP MOUNTAIN PRECIP
CHANCES IN PLACE.
OF NOTE, THE WARM AIR MASS AND HIGH SNOW LEVELS WILL RESULT IN
HIGH MOUNTAIN RAIN WEDNESDAY WITH RAIN-ON-SNOW ACROSS A SNOWPACK
THAT HAS CURRENT SWES % OF NORMAL AT 100-200% OR MORE. LATEST
SNOW DENSITIES AT SNOTEL SITES SHOW MOST BELOW 40%. THAT SAID,
RAINFALL AMOUNTS IN THE INTERIOR APPEAR AS A LIMITING FACTOR WITH
RAINFALL TOTALS IN THE EASTERN MOUNTAINS UNDER 0.75” THROUGH
THURSDAY. WHILE SNOW LEVELS START TO DROP LATE WEDNESDAY NIGHT-
EARLY THURSDAY, MUCH OF THE WATERSHEDS IN THE EASTERN MOUNTAINS
ARE FORECAST TO REMAIN BELOW THE SNOW LEVEL. WHEREIN EASTERN
MOUNTAINS WILL SEE SNOW LEVELS STILL 4.75-5.25 KFT BY LATE
THURSDAY BEFORE DROPPING BEFORE 4 KFT THURSDAY NIGHT. THE
COMBINATION OF RUNOFF, WARM TEMPERATURES, AND RAIN IS EXPECTED TO
PROMPT RISES ON AREA RIVERS AND STREAMS MID-LATE WEEK. LATEST
OFFICIAL FORECASTS HAVE RIVERS RISING WEDNESDAY WITH PEAKS
FORECAST THURSDAY INTO FRIDAY. THE POTENTIAL FOR RIVER FLOODING IS
LOW (< 30%) AT THIS TIME WITH JOHN DAY AT SERVICE CREEK SHOWING
THE HIGHEST RISES RELATIVE TO CATEGORIES BY THURSDAY. THIS ASPECT
BEARS MONITORING, ESPECIALLY TO SEE HOW TEMPERATURES AND QPF
EVOLVES IN TANDEM WITH THE SNOWPACK.
AVIATION...00Z TAFS
PREDOMINANTLY VFR CIGS/VSBYS AT ALL TAF
SITES FOR THE NEXT 24 HOURS. HOWEVER, BRIEF, LOCALIZED MVFR
CONDITIONS MAY ACCOMPANY CONVECTIVE SHOWERS THIS AFTERNOON AND
AGAIN TUESDAY AFTERNOON. WINDS WILL BE DIURNALLY DRIVEN,
DECREASING IN MAGNITUDE OVERNIGHT AT ALL SITES BEFORE RAMPING BACK
UP TUESDAY AFTERNOON. PLUNKETT/86
PRELIMINARY POINT TEMPS/POPS
PDT 34 55 38 53 / 10 10 20 10
ALW 36 54 39 53 / 10 10 20 20
PSC 36 60 38 59 / 10 10 10 0
YKM 33 58 33 58 / 10 10 0 0
HRI 34 59 38 58 / 10 10 10 0
ELN 36 55 36 54 / 30 10 0 0
RDM 27 51 29 49 / 20 20 10 0
LGD 27 49 32 47 / 40 30 40 20
GCD 27 48 31 46 / 40 40 50 20
DLS 35 58 40 55 / 10 10 10 10
PDT WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
SHORT TERM...95
LONG TERM....80
AVIATION...86
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