002
FXUS66 KPDT 312155
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
255 PM PDT MON MAR 31 2025
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...18Z TAFS
LIMITED CONCERNS THE NEXT 24-HRS. LATEST OBS
SHOW LARGELY VFR WITH RADAR SHOWING ISOLATED-SCATTERED SHOWERS
LIFTING NE ACROSS THE LOWER BASIN TO THE EASTERN MOUNTAINS. THE
LATTER SEEING CONVECTIVE SNOWS IN THE HIGHER EASTERN MOUNTAINS WHERE
QUICK ACCUMULATIONS WHERE SEEN. ANOTHER ROUND OF SHOWERS ANTICIPATED
LARGELY OUTSIDE THE LOWER BASIN AND VICINITY WITH FOCUS MORE ON
CENTRAL OR BETWEEN 18-00Z IN TERMS OF TERMINALS. OTHERWISE, LOW-END
VFR CEILINGS (LESS THAN 7 KFT) ARE EXPECTED TO PREVAIL THOUGH CANNOT
RULE OUT MVFR WITH HEAVIER SHOWERS TODAY. MEANTIME, LIGHT BREEZES
WITH GUSTS GENERALLY AROUND 20 KTS, EXCEPT AT KDLS AND KYKM, WITH
WINDS LESSENING TONIGHT. ANOTHER UNSETTLED PERIOD EXPECTED TOMORROW
WITH LOW CHANCES (10-35%) OVER 18-00Z AS THE UPPER TROUGH CURRENTLY
OFFSHORE THE PACNW CROSSES THE REGION AND MOVES INTO THE CENTRAL
GREAT BASIN.
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...80
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