576
FXUS66 KPDT 161738
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
1038 AM PDT FRI MAY 16 2025
UPDATED FOR AVIATION
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.
PREV DISCUSSION
/ISSUED 309 AM PDT FRI MAY 16 2025/
SHORT TERM...TODAY THROUGH SUNDAY...SATELLITE IMAGERY TONIGHT
SHOWS A WEAK SHORTWAVE PUSHING LIGHT RAIN SHOWERS ACROSS THE
INTERMOUNTAIN PACNW, WITH SKIES GRADUALLY CLEARING ACROSS THE
WESTERN THIRD OF THE FORECAST AREA.
THE SHORTWAVE WILL EXIT THE REGION LATER THIS MORNING, WITH THE
BULK OF SHOWER ACTIVITY DIMINISHING AREA-WIDE. LIGHT OROGRAPHIC
SHOWERS WILL CONTINUE ACROSS THE CASCADES, BLUES, AND WALLOWAS
THROUGH THIS AFTERNOON AS A NORTHWEST FLOW ALOFT DEVELOPS BEHIND
THE SHORTWAVE EXIT. BY THIS EVENING, A BRIEF DRY PERIOD WILL
DEVELOP AS FLOW ALOFT TURNS MORE ZONAL, THEN TO THE SOUTHWEST
AHEAD OF AN UPPER TROUGH APPROACH.
TONIGHT, AN UPPER TROUGH WILL ARRIVE TO THE PACNW, THE FIRST IN A
SERIES OF UPPER LOW PRESSURE FEATURES THAT WILL IMPACT THE REGION.
SHOWER CHANCES ALONG THE CASCADES AND THE EASTERN MOUNTAINS WILL
INCREASE THROUGH THE OVERNIGHT HOURS INTO TOMORROW MORNING AS THE
TROUGH MOVES INLAND. WEAK ELEVATED INSTABILITY WITH MODEST MID-
LEVEL LAPSE RATES WILL DEVELOP OUT AHEAD OF THE TROUGH AXIS
TONIGHT, ALLOWING SLIGHT CHANCES (AROUND 15%) OF ISOLATED
THUNDERSTORMS TO DEVELOP MAINLY OVER THE MOUNTAINOUS TERRAIN OF GRANT
AND EASTERN CROOK COUNTIES.
THE UPPER TROUGH WILL CONTINUE TO DIVE SOUTHEAST INTO THE GREAT
BASIN SATURDAY MORNING, ALLOWING THE NEXT UPPER TROUGH TO DIVE
ACROSS THE PACNW SATURDAY THROUGH SUNDAY. GUIDANCE DOES INDICATE
THAT THE UPPER TROUGH WILL DEVELOP INTO A CLOSED LOW OVER THE
PACNW DURING IT'S SOUTHEASTWARD DESCENT, THOUGH THERE ARE MINOR
DIFFERENCES IN THE TIMING AND POSITION OF THE CLOSED LOW.
NONETHELESS, THE SECOND UPPER LOW FEATURE WILL CONTINUE TO BRING
SHOWER ACTIVITY AREA-WIDE THE FIRST HALF OF SATURDAY, WITH SHOWER
ACTIVITY DIMINISHING ACROSS THE LOWER ELEVATIONS AS THE UPPER LOW
MOVES OVERHEAD THROUGH SATURDAY NIGHT AND SUNDAY MORNING. DURING
THE DAY SATURDAY, INCREASING SURFACE BASED INSTABILITY(200-500
J/KG) AND MODEST LOW TO MID LEVEL LAPSE RATES WILL RESULT IN
ISOLATED TO WIDELY SCATTERED THUNDERSTORM CHANCES (15-30%) MIXING
IN WITH SHOWERS ACROSS THE FORECAST AREA SATURDAY AFTERNOON
THROUGH THE LATE EVENING (CONFIDENCE 50-70%). THROUGH SATURDAY
NIGHT, THERE IS A 65-90% CHANCE FOR RAIN ACCUMULATIONS OF 0.25
INCHES ACROSS THE MOUNTAIN ZONES, INCLUDING THE GRANDE RONDE
VALLEY...55-85% CHANCE FOR 0.1 INCHES IN THE LOWER ELEVATIONS.
WINDS WILL INCREASE THROUGH THE CASCADE GAPS AND INTO PORTIONS OF
THE COLUMBIA BASIN AND CENTRAL OR AS COLD AIR ADVECTION UNDER THE
UPPER TROUGH/LOW PASSAGES WILL RESULT IN A STRENGTHENING OF THE
CROSS-CASCADE SURFACE PRESSURE GRADIENT. WINDS SATURDAY WILL
INCREASE TO 20-30MPH WITH GUSTS UP TO 40MPH THROUGH THE CASCADE
GAPS, AND 15-25MPH WITH GUSTS UP TO 35MPH ELSEWHERE IN THE LOWER
ELEVATIONS (CONFIDENCE 70-80%).
SUNDAY, RAIN/SNOW SHOWERS WILL MAINLY BE CONFINED TO THE CASCADES,
BLUES, AND WALLOWA COUNTY AS THE UPPER LOW CONTINUES TO PUSH
SOUTHEAST. BY SUNDAY LATE AFTERNOON AND EVENING, SHOWER ACTIVITY
WILL DIMINISH ACROSS THE AFOREMENTIONED AREAS AS THE UPPER LOW
CROSSES INTO THE GREAT BASIN TO THE SOUTHEAST. SURFACE WINDS WILL
CONTINUE TO STRENGTHEN SUNDAY, WITH A 75-90% CHANCE THAT WIND
GUSTS WILL REACH OR EXCEED 45MPH THROUGH THE KITTITAS VALLEY AND
A 60-75% CHANCE THROUGH THE EASTERN COLUMBIA RIVER GORGE.
ELSEWHERE IN THE LOWER ELEVATIONS, WINDS WILL CONTINUE TO BE
15-25MPH WITH GUSTS UP TO 35MPH (CONFIDENCE 65-80%). LAWHORN/82
LONG TERM...MONDAY THROUGH FRIDAY...MODELS KEY IN ON A RELATIVELY
PROGRESSIVE PATTERN NEXT WORK WEEK, ALBEIT ONE WITHOUT MUCH IN THE
WAY OF SIGNIFICANT SENSIBLE WEATHER IMPACTS AS THE SYNOPTIC PATTERN
LOOKS TO BE ZONAL IN NATURE. AS A RESULT, THE WEATHER THREATS NEXT
WEEK LOOK TO BE COMPRISED OF BREEZY DOWNSLOPE WINDS, SLIGHT CHANCE
TO CHANCE POPS FOR OUR MOUNTAIN ZONES, AND GENERALLY SEASONABLE
TEMPERATURES, SAVE FOR EARLY MONDAY MORNING WHEN NORTHERLY FLOW
TRAILING A DEPARTING SYSTEM MAY MAKE FOR A POTENTIAL OVERNIGHT
FREEZE ACROSS SOME OF OUR ELEVATED VALLEY ZONES.
THE SYNOPTIC PATTERN EVOLVES AS THUS: A LOW DIGGING INTO THE FOUR
CORNERS REGION WILL MAKE FOR NORTHERLY FLOW HEADING INTO MONDAY,
LEADING TO A CHILLY MORNING AS CENTRAL OREGON, THE GRANDE RONDE
VALLEY, AND THE WALLOWA VALLEY ALL STAND TO SEE A CHANCE OF FREEZING
TEMPERATURES (20-30%, 10-20%, AND 50-60%, RESPECTIVELY). FLOW ALOFT
THEN TURNS ZONAL, BEFORE A SHORTWAVE DEVELOPS OFF THE PACIFIC COAST
TUESDAY INTO WEDNESDAY, INTRODUCING A SLIGHT AMOUNT OF INSTABILITY,
ENOUGH TO TRIGGER LOW-END THUNDERSTORM CHANCES (10-20%) FOR THE
EASTERN MOUNTAINS TUESDAY AFTERNOON, BUT THE THREAT LOOKS TO BE
ISOLATED GIVEN THE LACK OF MOISTURE ADVECTION WITH THIS SHORTWAVE.
MODELS START TO DIVERGE WEDNESDAY ONWARD, WITH ENSEMBLES GENERALLY
SUGGESTING A RETURN TO ZONAL CONDITIONS AND THUS BENIGN WEATHER FOR
THE REST OF THE PERIOD, HOWEVER THE DETERMINISTIC GFS AND ECMWF DO
SUGGEST THE POSSIBILITY OF SHORTWAVES EMBEDDED WITHIN THE ZONAL FLOW
THAT COULD LEAD TO AT LEAST SLIGHT WIDESPREAD POPS FOR THE FORECAST
AREA. GIVEN THAT ENSEMBLE GUIDANCE DOESN'T CURRENTLY REFLECT THIS,
HOWEVER, CONFIDENCE IN THIS OCCURRING IS LOW.
SUCH PATTERNS GENERALLY LEAD TO BREEZY CONDITIONS DOWNSLOPE OF THE
CASCADES, SO EXPECT THE CASCADE GAPS AND EAST SLOPES TO SEE
RECURRING DAYS OF GUSTS OVER 25 MPH SO LONG AS WE REMAIN UNDER ZONAL
FLOW. SOME ENSEMBLE MEMBERS SUGGEST HIGH PRESSURE BUILDING IN BY THE
TAIL END OF THE PERIOD, WHICH COULD LEAD TO A WARMING TREND, HOWEVER
OTHER MEMBERS INSIST ON KEEPING AT LEAST A WEAK ZONAL PATTERN IN
PLACE. CONFIDENCE IN THE FORECAST WEDNESDAY AND BEYOND REMAINS LOW
(30-40%). EVANS/74
AVIATION...12Z TAFS...VFR CONDITIONS EXPECTED THROUGH THE PERIOD.
LIGHT RAIN WILL END EARLY THIS MORNING, LEAVING US WITH PARTIALLY
CLEARING SKIES DURING THE DAY AT SCT-BKN 5-10 KFT. CLOUDS WILL BUILD
BACK IN THIS EVENING, BECOMING OVC AT 10-15 KFT BY NIGHTFALL. WINDS
WILL GENERALLY BE W TO SW, EXCEPT NW FOR DLS, BDN, AND RDM, AT LESS
THAN 15 KTS. EVANS/74
PRELIMINARY POINT TEMPS/POPS
PDT 66 48 65 43 / 20 20 80 70
ALW 64 50 64 44 / 50 10 80 90
PSC 71 49 71 45 / 10 10 70 60
YKM 71 50 69 42 / 10 20 70 10
HRI 71 48 70 45 / 10 20 80 50
ELN 66 47 65 42 / 10 40 80 20
RDM 66 42 61 34 / 0 30 70 20
LGD 59 43 58 39 / 40 20 90 90
GCD 62 43 56 37 / 10 60 100 80
DLS 68 51 68 46 / 10 30 60 10
PDT WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
SHORT TERM...82
LONG TERM....74
AVIATION...77
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page