177
FXUS66 KPDT 162129
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
229 PM PDT FRI MAY 16 2025
SHORT TERM...TONIGHT THROUGH SUNDAY NIGHT
KEY MESSAGES:
1. SHOWERS AND A 10-30% CHANCE OF THUNDERSTORMS TONIGHT THROUGH
SUNDAY.
2. BREEZY TO WINDY CONDITIONS THROUGH THE CASCADE GAPS AND ACROSS
PORTIONS OF THE COLUMBIA PLATEAU SATURDAY AND SUNDAY.
3. LIGHT SNOWFALL FOR MOUNTAIN PASSES SATURDAY NIGHT AND SUNDAY
MORNING.
TONIGHT, THE FIRST OF BACK-TO-BACK WAVES IS EXPECTED TO ARRIVE
FROM THE NORTHEAST PACIFIC (>90% CONFIDENCE). THIS WAVE IS
CURRENTLY VISIBLE ON WATER VAPOR IMAGERY WEST OF VANCOUVER ISLAND,
DIVING SOUTHEAST TOWARDS THE PACNW. THE SECOND VORTICITY MAXIMUM
LOCATED IN THE GULF OF ALASKA, IS NOT ADVERTISED BY ENSEMBLE NWP
TO ARRIVE UNTIL SATURDAY NIGHT THROUGH SUNDAY, AND IS THE MAIN
DRIVER OF UNCERTAINTY IN THE SHORT-TERM FORECAST; ITS TRACK WILL
HAVE IMPLICATIONS ON PRECIPITATION AND WIND.
SHOWER CHANCES WILL INCREASE TONIGHT, WITH SOME WEAK ELEVATED
INSTABILITY FACILITATING LOW-END CHANCES (10-15%) OF EMBEDDED
THUNDERSTORMS FOR PORTIONS OF CENTRAL AND EAST-CENTRAL OREGON,
MAINLY IN GRANT COUNTY.
AREA-WIDE SHOWER CHANCES WILL INCREASE SATURDAY THROUGH SATURDAY
NIGHT AS THE FIRST WAVE PROVIDES AMPLE FORCING, AND AS THE SECOND
WAVE DIGS SOUTHEAST INTO THE PACNW. HAVE MAINTAINED AN AREA-WIDE
SLIGHT CHANCE (15-24% PROBABILITY) TO CHANCE (25-35% PROBABILITY)
MENTION OF THUNDER IN THE FORECAST SATURDAY. BEST CHANCES OF
THUNDERSTORMS WILL BE OVER THE BLUE MOUNTAINS AND THEIR FOOTHILLS
AS WELL AS PORTIONS OF THE LOWER COLUMBIA BASIN DURING THE
AFTERNOON (25-35% PROBABILITY) .
DELVING INTO CLUSTERS OF ENSEMBLE SOLUTIONS DOES REVEAL SOME
UNCERTAINTY IN THE EVOLUTION OF THE SYSTEM AS THE TWO WAVES
INTERACT SATURDAY NIGHT THROUGH SUNDAY; ENSEMBLE MEMBERS ARE STILL
UNCERTAIN WHETHER THE SECOND WAVE WILL BECOME A SLOWER-MOVING
CLOSED LOW OVERHEAD LATE SATURDAY THROUGH SATURDAY NIGHT OR IF IT
WILL REMAIN A WEAKER OPEN WAVE TROUGH WITH A QUICKER EXIT THROUGH
SUNDAY.
WESTERLY WINDS WILL INCREASE IN MAGNITUDE SATURDAY AFTERNOON THROUGH
THE CASCADE GAPS AS CROSS-CASCADE PRESSURE DIFFERENCES INCREASE
AND A ROBUST LOW-LEVEL JET (35-45 KTS) SETS UP. NBM PROBABILITIES
OF EXCEEDING ADVISORY-LEVEL GUSTS (45 MPH) THROUGH THE EASTERN
COLUMBIA RIVER GORGE, KITTITAS VALLEY, AND WIND-PRONE PORTIONS OF
THE COLUMBIA BASIN/BLUE MOUNTAIN FOOTHILLS ARE ROUGHLY 40-70%.
SATURDAY NIGHT THROUGH SUNDAY, THE LIKELIHOOD OF REACHING
ADVISORY CRITERIA IS HIGH (60-95% CHANCE) THROUGH THE KITTITAS
VALLEY AND EASTERN COLUMBIA RIVER GORGE. MOREOVER, A LOW-MEDIUM
CHANCE (30-60%) OF WARNING-LEVEL WIND GUSTS (58 MPH OR GREATER)
IS ADVERTISED BY THE NBM FOR THE KITTITAS VALLEY. IN OTHER WIND-
PRONE PORTIONS OF THE COLUMBIA BASIN/BLUE MOUNTAIN FOOTHILLS, NBM
PROBABILITIES OF REACHING ADVISORY CRITERIA ARE MEDIUM-HIGH
(40-70%). DUE TO THE AFOREMENTIONED UNCERTAINTY IN THE PRECISE
TRACK OF THE SECOND WAVE, HAVE HELD OFF ISSUING ANY WIND
HIGHLIGHTS WITH THE AFTERNOON FORECAST PACKAGE.
LASTLY, WILL MENTION MEASURABLE SNOWFALL (0.1" OR GREATER) IS
MORE LIKELY THAN NOT (50-85% CHANCE) ACROSS MOUNTAIN PASSES
SATURDAY NIGHT THROUGH SUNDAY MORNING AS COLDER AIR ASSOCIATED
WITH THE TROUGH/CLOSED LOW SPREADS OVER THE REGION. IN FACT, NBM
PROBABILITIES PLACE MEDIUM (40-60%) CHANCES OF 1" OF SNOWFALL OR
MORE FOR THE HIGHER PASSES OF THE CASCADES AND BLUE MOUNTAINS.
HOWEVER, SNOW ACCUMULATION ON ROADWAYS MAY BE LIMITED DUE TO WARM
ANTECEDENT CONDITIONS. PLUNKETT/86
LONG TERM...MONDAY THROUGH FRIDAY
WESTERLY FLOW OVER THE AREA
WILL ALLOW FOR A WEAK SYSTEM TO MOVE ACROSS THE REGION ON
MONDAY. IT WILL BRING MAINLY LIGHT RAIN TO THE MOUNTAINS.
LINGERING MOISTURE IN THE WESTERLY FLOW WILL KEEP PRECIP CHANCES
IN THE MOUNTAINS ON TUESDAY.
THE REST OF THE EXTENDED PERIOD LOOKS TO BE DRY, WITH SOME
TRANSITORY RIDGING TUESDAY INTO WEDNESDAY AND MORE ZONAL FLOW
WEDNESDAY INTO THURSDAY THEN MORE RIDGING THURSDAY INTO THURSDAY
NIGHT.
MONDAY AND TUESDAY WILL SEE DIURNALLY BREEZY WINDS, WITH TUESDAY
POSSIBLY BREEZIER. WINDS WILL MAINLY BE IN THE 25 TO 30 MPH RANGE
IN THE NORMALLY GUSTY AREAS SUCH AS THE KITTITAS VALLEY, SIMCOE
HIGHLANDS, COLUMBIA BASIN AND FOOTHILLS OF THE BLUE MOUNTAINS.
ON MONDAY, NBM PROBABILITIES OF WIND GUSTS >= 25 MPH IS QUITE HIGH
GENERALLY 90 PERCENT OR GREATER IN THESE AREAS. HOWEVER, THE
PROBABILITIES OF WIND GUSTS >= 39 MPH IS 20 TO 50 PERCENT. ON
TUESDAY. NBM PROBABILITIES OF WIND GUSTS >= 25 MPH IS ABOUT THE
SAME AS MONDAY. HOWEVER, THE PROBABILITIES OF WIND GUSTS >= 39 MPH
IS A BIT HIGHER30 TO 60 PERCENT AND MUCH HIGHER IN THE KITTITAS
VALLEY (80 PERCENT).
AVIATION...18Z TAFS
VFR CONDITIONS ARE EXPECTED THROUGH THE DAY
TODAY AND INTO TONIGHT. BY EARLY SATURDAY MORNING, THERE COULD BE
SOME MVFR CONDITIONS AT BDN/RDM AS SHRA BEGINS TO MOVE IN.
OTHERWISE SHRA WILL IMPACT ALL SITES THROUGH THE PERIOD EXCEPT FOR
PSC, ALW WHERE THE BEST CHANCES OF SHRA WILL OCCUR AFTER 17/18Z.
WINDS WILL GENERALLY BE 10 KTS OR LESS EXCEPT AT PDT, WHERE WINDS
WILL GUST AROUND 20 KTS THIS AFTERNOON AND DLS WHO COULD SEE SOME
GUSTS IN THE 15 TO 20 KT RANGE AS WELL AND POSSIBLY HIGHER.
PRELIMINARY POINT TEMPS/POPS
PDT 48 64 43 62 / 20 90 70 30
ALW 49 64 44 61 / 10 80 90 40
PSC 48 69 45 69 / 10 70 60 10
YKM 49 69 41 67 / 30 70 10 0
HRI 49 69 44 67 / 20 80 50 20
ELN 47 65 41 61 / 40 80 20 0
RDM 42 62 34 57 / 30 80 20 10
LGD 42 58 39 54 / 30 90 90 50
GCD 43 56 36 52 / 70 100 80 30
DLS 51 68 46 64 / 30 60 10 10
PDT WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
SHORT TERM...86
LONG TERM....77
AVIATION...77
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