586
FXUS66 KPDT 180942
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
242 AM PDT SUN MAY 18 2025
SHORT TERM...TODAY THROUGH TUESDAY
OVERNIGHT SATELLITE IMAGERY
SHOWS CLEARING TAKING PLACE AS AN UPPER-LEVEL TROUGH EXITS OUR CWA
AND DIGS TOWARD THE FOUR CORNERS REGION. THIS WILL LEAVE US UNDER A
DRY NW FLOW PATTERN ALOFT, LEADING TO A COOL DAY TODAY WITH HIGH
TEMPS AS LOW AS 15 DEGREES BELOW AVERAGE, AS WELL AS SOME LIGHT POPS
ACROSS OUR HIGH MOUNTAIN ZONES. EXPECTATION IS THAT THE BULK OF THE
RAINFALL ASSOCIATED WITH YESTERDAY'S SYSTEM IS OVER WITH, BUT THE
FLOW PATTERN ALOFT IS AMPLIFIED ENOUGH TO TRIGGER AT LEAST SOME
LIGHT OROGRAPHIC PRECIP THROUGH THE DAY. NBM GUIDANCE WANTS TO PUT
IN SOME SLIGHT THUNDER CHANCES ACROSS THE EASTERN MOUNTAINS OF
OREGON, BUT GIVEN THE COOLER AIRMASS MOVING IN, REDUCING SNOW LEVELS
TO THE 4000-4500 FT RANGE AND INHIBITING INSTABILITY, AM THINKING
THAT WE'LL ONLY REALISTICALLY SEE LIGHT SHOWERS ACROSS THE MOUNTAINS
TODAY.
WITH THIS TRANSITION FROM YESETDAY'S TROUGH TO AN AMPLIFIED NW TO
ZONAL FLOW PATTERN, WINDS WILL PICK UP, ESPECIALLY THROUGH THE
CASCADE GAPS AND ALONG EXPOSED RIDGETOPS THROUGH THE FORECAST AREA.
ALREADY SEEING GUSTS ECLIPSE 40 MPH EARLY THIS MORNING ALONG THESE
RIDGETOPS, WITH THE GAPS EXPECTED TO SEE THEIR STRONGEST WINDS AFTER
DAYBREAK. GUIDANCE DID SEEM TO TREND DOWN, HOWEVER, JUST FROM
LOOKING AT LATEST NBM GUSTS AS WELL AS UW WRF VALUES FOR THE
KITTITAS VALLEY AND THE COLUMBIA RIVER GORGE, WITH BOTH EXPECTED TO
SEE GUSTS IN THE 30-40 MPH RANGE TODAY. WILL OPT TO LEAVE THE
KITTITAS'S WIND ADVISORY IN PLACE, BUT SHOULD NOTE THAT IT LOOKS TO
BE AN EDGE CASE WITH SUSTAINED WINDS MORE LIKELY TO VERIFY THAN
GUSTS. ELSEWHERE, EXPECT GUSTS IN THE 20-30 MPH RANGE, STRONGER
DOWNSLOPE OF THE SOUTHERN BLUES AND EAST SLOPES OF THE CASCADES,
MAINLY OUT OF THE WEST AND NORTHWEST.
A SHORTWAVE EMBEDDED WITHIN THE AMPLIFIED FLOW ALOFT WILL DELIVER
ANOTHER ROUND OF LIGHT PRECIP TO THE FORECAST AREA DURING THE DAY
MONDAY, BUT THIS LOOKS TO BE A QUICK-HITTING SYSTEM WITH RAINFALL
AMOUNTS GENERALLY LESS THAN A TENTH OF AN INCH OUTSIDE OF OUR HIGH
MOUNTAIN ZONES AND THE GRANDE RONDE VALLEY. THERE, PROBABILISTIC
GUIDANCE GENERALLY SUGGESTS ABOUT A 60-70% CHANCE FOR LIQUID PRECIP
OVER A TENTH OF AN INCH. HEADING INTO TUESDAY, THE PATTERN ALOFT
STARTS TO BECOME ZONAL, WHICH WILL PROVIDE THE HIGH MOUNTAINS WITH
PERSISTENT LIGHT POPS (20-30%) THROUGH MUCH OF THE WEEK, WITH
TEMPERATURES WARMING BACK UP TO MORE SEASONABLE VALUES. UNDER SUCH A
PATTERN, THE LOWLANDS WILL REMAIN DRY, WITH WINDS REMAINING ELEVATED
THROUGH THE CASCADE GAPS AND EAST SLOPES AS WELL. EVANS/74
LONG TERM...WEDNESDAY THROUGH SUNDAY
ENSEMBLES CONTINUE TO KEEP
US UNDER A RELATIVELY BENIGN ZONAL FLOW PATTERN UNTIL AROUND FRIDAY,
WHEN BOTH THE CONSENSUS ACROSS ENSEMBLE MEMBERS AND DETERMINISTIC
GUIDANCE IS TO BRING IN A NEGATIVELY TILTED TROUGH THAT COULD SPAWN
SHOWERS AND ISOLATED THUNDERSTORMS TO THE FORECAST AREA. GUIDANCE IS
SPLIT ON JUST HOW STRONG THIS SYSTEM COULD BE, AND JUST HOW MUCH
MOISTURE ADVECTION THE CWA COULD SEE, BUT THE PATTERN IS FAVORABLE
FOR AT LEAST THE MOUNTAINS TO RECEIVE SHOWERS AND POSSIBLY STORMS,
ESPECIALLY ACROSS THE EASTERN MOUNTAINS OF OREGON.
STARTING AROUND LATE SATURDAY ONWARD, ENSEMBLES AND BOTH THE
DETERMINISTIC GFS AND ECMWF HINT AT RIDGING BUILDING OVER THE PACNW,
LASTING THROUGH AT LEAST THE START OF NEXT WORK WEEK. UNCERTAINTY
REMAINS ON THE STRENGTH AND POSITION OF THE RIDGE, BUT THE NBM DOES
SEEM TO PICK UP ON THIS TREND, AS IT SUGGESTS HIGH TEMPS CLIMBING
BACK INTO THE 80S BY THE TAIL END OF THE PERIOD. THAT LEAVES FRIDAY
INTO SATURDAY BEING THE MAIN PERIOD OF CONCERN FOR SENSIBLE WEATHER,
DEPENDING ON HOW THAT POTENTIAL TROUGH SHAPES UP ACROSS SUBSEQUENT
MODEL RUNS. EVANS/74
AVIATION...12Z TAFS
VFR CONDITIONS EXPECTED, WITH THE MAIN
IMPACTS EXPECTED THROUGH THE PERIOD BEING GUSTY WINDS ACROSS ALL
SITES. MOST SITES WILL SEE GUSTS IN THE 20-30 KT RANGE, MAINLY OUT
OF THE W AND NW, WHILE GUSTS COULD ECLIPSE 30 KTS AT TIMES DURING
THE DAY FOR DLS AND PDT. WINDS ARE EXPECTED TO BACK DOWN BY
NIGHTFALL, BECOMING LIGHT AND TERRAIN-DRIVEN. CIGS GENERALLY SCT-BKN
AT 5-10 KFT, WITH SOME HIGH CLOUDS PREVAILING AS WELL, BEFORE SOME
SLIGHT CLEARING TAKES PLACE IN THE EVENING. EVANS/74
PRELIMINARY POINT TEMPS/POPS
PDT 61 39 67 44 / 10 10 70 20
ALW 60 42 65 46 / 20 10 70 30
PSC 68 40 71 43 / 0 0 50 10
YKM 65 39 69 40 / 0 0 30 0
HRI 66 42 71 45 / 0 0 50 10
ELN 60 38 64 41 / 10 0 40 10
RDM 58 34 65 35 / 0 0 20 0
LGD 53 33 62 42 / 20 20 60 60
GCD 55 32 65 39 / 30 10 60 50
DLS 63 44 66 47 / 10 0 20 0
PDT WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...WIND ADVISORY FROM 8 AM THIS MORNING TO 8 PM PDT THIS EVENING
FOR WAZ026.
SHORT TERM...74
LONG TERM....74
AVIATION...74
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