891
FXUS66 KPDT 210928
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
228 AM PDT WED MAY 21 2025
SHORT TERM...TODAY THROUGH FRIDAY
MODELS CONTINUE TO EVOLVE WITH
REGARDS TO HOW THEY DEPICT A SERIES OF WAVES EXPECTED TO TREK
THROUGH THE FORECAST AREA THROUGH THE END OF THE WORK WEEK.
WEDNESDAY WILL GENERALLY BE QUIET AS A BRIEF TRANSITORY RIDGE RIDES
OVER THE PACNW, BEFORE A SHORTWAVE TROUGH MOVES IN LATE IN THE
EVENING THROUGH THE OVERNIGHT HOURS HEADING INTO THURSDAY. ANOTHER
WEAKER SHORTWAVE WILL MOVE THROUGH THE AREA ON FRIDAY, HOWEVER
MODELS NOW DEPICT OUR CWA BEING CAUGHT IN THE DRY SLOT OF THIS
SYSTEM, SO IMPACTS LOOK TO BE LIMITED. THIS IS A REVERSE OF WHAT
MODELS HAD INITIALLY BEEN HINTING AT - NOW THE WEDNESDAY NIGHT INTO
THURSDAY SYSTEM LOOKS TO BE THE WETTEST OF THE TWO.
LOOKING AT CAMS, ARRIVAL OF PRECIPITATION WITH THIS FIRST SYSTEM
APPEARS TO BE AROUND 10 PM, HOWEVER SOME MEMBERS OF THE HREF DO SHOW
A LIGHT LEADING EDGE OF RAIN SWEEPING THROUGH THE FORECAST AREA FROM
THE SOUTHWEST A LITTLE EARLIER. EITHER WAY, THE BULK OF THE SHOWER
ACTIVITY LOOKS TO ARRIVE DURING THE OVERNIGHT HOURS, LASTING INTO
EARLY MORNING THURSDAY. MOISTURE ONCE LOOKED TO TRAVEL PRIMARILY
THROUGH THE OREGON HALF OF THE FORECAST AREA, BUT NOW APPEARS TO BE
MORE WIDESPREAD. THAT BEING SAID, MODELS STILL SHOW LIMITED QPF FOR
THE LOWER WA BASIN AND THE YAKIMA/KITTITAS VALLEYS, WITH THE
HEAVIEST AMOUNTS CONCENTRATED OVER THE EASTERN MOUNTAINS. BY
THURSDAY AFTERNOON, MOISTURE TREKS OVER WALLOWA COUNTY AND STARTS TO
PICK UP ON SOME INSTABILITY, HOWEVER SHOULD NOTE THAT MODEL
PARAMETERS FOR CONVECTION AREN'T TOO EXCITING, SO EXPECT ONLY A LOW-
END (10-20%) THREAT FOR T-STORMS, AGAIN CONCENTRATED PRIMARILY OVER
THE WALLOWAS, BEFORE DRY CONDITIONS PREVAIL BY THE EVENING.
FRIDAY'S TROUGH HAS DEVELOPED A BIT MORE OF AN AMPLITUDE, WHICH
LEAVES THE INTERMOUNTAIN WEST CAUGHT MORE IN THE DRY SLOT OF THE
SYSTEM. COULD STILL SEE SOME SHOWERS AND ISOLATED T-STORMS FORM OVER
THE EASTERN MOUNTAINS DURING THE DAY FRIDAY, BUT POPS (15-25%) ARE
MUCH MORE SCALED BACK COMPARED TO WHAT THEY WERE OVER PREVIOUS RUNS.
THUS, FOR AREA-WIDE PRECIP, THE WEDNESDAY NIGHT INTO THURSDAY SYSTEM
WILL LIKELY BE THE CENTER OF ATTENTION, WITH CONVECTIVE BANDING
WITHIN THE WAVE RESULTING IN PERHAPS ANOTHER ROUND OF WETTING RAINS
FOR THE EASTERN MOUNTAINS OF OREGON. EVANS/74
LONG TERM...SATURDAY THROUGH WEDNESDAY
CONFIDENCE HAS BEEN SHAKY
OVER THE LAST FEW DAYS WITH REGARDS TO THE SYNOPTIC PATTERN NEXT
WORK WEEK. ALL BETS ARE SOLID ON A WARM AND DRY HOLIDAY WEEKEND WITH
HIGH PRESSURE OVERHEAD, WITH HIGHS ON SUNDAY AND EVEN MONDAY
POTENTIALLY REACHING THE 90S IN THE LOWER BASIN (NBM PROBABILISTIC
SUGGESTS A 20-30% CHANCE). ENSEMBLE GUIDANCE, HOWEVER, CONTINUES TO
DIVERGE GREATLY ON WHAT HAPPENS BEYOND THIS SPELL OF HIGH PRESSURE.
MOST MEMBERS STILL SEEM TO LEAN TOWARDS INTRODUCING SW FLOW ALOFT OF
SOME KIND INTO THE PACNW, ALBEIT OF VARYING DEGREES OF STRENGTH,
WHILE A MINORITY HOLDS ON TO A CONTINUATION OF BENIGN CONDITIONS, BE
IT IN THE FORM OF HIGH PRESSURE PERSISTING OR THE FLOW PATTERN ALOFT
BEING TOO WEAK TO SPURN ANY SIGNIFICANT WEATHER.
SHOULD NOTE THAT, ACROSS THE DETERMINISTIC GUIDANCE, THE GFS FAVORS
A MORE BENIGN PATTERN WITH A CUTOFF LOW DIVING TO OUR SOUTH, LEAVING
US UNDER DRY HIGH PRESSURE, WHILE THE ECMWF SWINGS THROUGH A
NEGATIVELY-TILTED TROUGH ASSOCIATED WITH A BROAD PARENT LOW CENTERED
OVER THE NORTH PACIFIC. THE FORMER SOLUTION SUGGESTS A BETTER CHANCE
OF OUR LOWLANDS REACHING THE 90S, WHILE THE LATTER SUGGESTS AREA-
WIDE SHOWERS AND THUNDERSTORMS. OVERALL FORECAST CONFIDENCE REMAINS
LOW-MODERATE (30-40%), BUT SO LONG AS MOST ENSEMBLE MEMBERS LEAN
TOWARD SW FLOW, MESSAGING WILL RESTRICT WARM AND DRY CONDITIONS TO
THE WEEKEND ALONE, WITH A RELATIVELY UNCERTAIN FORECAST BEYOND THAT.
EVANS/74
AVIATION...12Z TAFS
VFR CONDITIONS EXPECTED. SKIES WILL START OUT
MOSTLY CLEAR IN THE MORNING, BEFORE A BKN-OVC DECK AROUND 20 KFT
BUILDS IN BY THE AFTERNOON AHEAD OF AN APPROACHING WEATHER SYSTEM.
RAINFALL IS EXPECTED TO HOLD OFF UNTIL THE OVERNIGHT HOURS HEADING
INTO THURSDAY, BUT CIGS WILL CONTINUE TO TREND DOWNWARD IN THE
MEANTIME, BECOMING LESS THAN 10 KFT FOR MOST SITES BY NIGHTFALL.
WINDS WILL START OUT LIGHT AND TERRAIN-DRIVEN IN THE EARLY MORNING,
BEFORE SHIFTING THROUGHOUT THE DAY - FIRST TO THE WEST IN THE
AFTERNOON, AND THEN N/NE BY THE LATE EVENING. WINDS GENERALLY LESS
THAN 12 KTS. EVANS/74
PRELIMINARY POINT TEMPS/POPS
PDT 69 47 67 45 / 0 50 50 0
ALW 69 49 67 47 / 0 40 60 0
PSC 72 50 71 45 / 0 30 30 0
YKM 70 50 69 45 / 0 30 20 0
HRI 72 49 71 46 / 0 40 30 0
ELN 68 46 65 44 / 0 20 20 0
RDM 70 43 63 36 / 10 30 20 0
LGD 66 45 63 40 / 0 50 70 10
GCD 71 44 66 39 / 0 50 50 10
DLS 72 51 68 46 / 0 40 30 0
PDT WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
SHORT TERM...74
LONG TERM....74
AVIATION...74
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