682
FXUS66 KPDT 091737 AAA
AFDPDT
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE PENDLETON OR
1037 AM PDT FRI MAY 9 2025
UPDATED AVIATION DISCUSSION
AVIATION...18Z TAFS
VFR CONDITIONS EXPECTED THROUGH THE
PERIOD. EXPECT SCT-BKN HIGH CLOUDS AT OR ABOVE 20K FEET AGL AND
LIGHT TERRAIN-DRIVEN WINDS LESS THAN 12 KTS OVER THE NEXT 24
HOURS. PERRY/83
PREV DISCUSSION
/ISSUED 341 AM PDT FRI MAY 9 2025/
SHORT TERM...TODAY THROUGH SUNDAY NIGHT...
KEY MESSAGES;
1. BREEZY AFTERNOON WINDS SATURDAY AND SUNDAY.
2. ISOLATED THUNDERSTORMS POSSIBLE SUNDAY AFTERNOON/EVENING.
CURRENT RADAR AND INFRARED SATELLITE IMAGERY SHOWS DRY CONDITIONS
AS SPOTTY HIGH CLOUDS PASS OVER THE REGION FROM THE WEST-
SOUTHWEST. THIS IS A RESULT OF BUILDING UPPER LEVEL TROUGH FROM
THE SOUTHEAST, WITH SOUTHWEST FLOW ALOFT PROVIDING A SLIGHT
INCREASE IN MOISTURE IN THE FORM OF UPPER LEVEL CLOUDS. THESE
FEATURES WILL ALSO LEAD TO A 10 DEGREE INCREASE IN HIGH
TEMPERATURES TODAY AS THEY REBOUND BACK INTO THE UPPER 70S TO LOW
80S ACROSS THE LOWER COLUMBIA BASIN, BLUE MOUNTAIN FOOTHILLS,
GORGE, AND CENTRAL OREGON. AFTERNOON HUMIDITIES WILL IMPROVE
SLIGHTLY OVER WASHINGTON AS THE SOUTHWEST FLOW ALOFT SETS UP OVER
OUR NORTHERN ZONES, BUT WILL DECREASE IN THE LOW-TEENS ACROSS
CENTRAL OREGON ASSOCIATED WITH THE BUILDING RIDGE.
AN UPPER LEVEL TROUGH WILL BE APPROACHING THE COAST TONIGHT AS THE
RIDGE TO OUR SOUTHEAST BEGINS TO SUPPRESS TO OUR SOUTHEAST. A
WEAK SHORTWAVE WILL SLIDE UP THE BACKSIDE OF THE RIDGE ON SATURDAY
TO ALLOW FOR PERIODS OF LIGHT SHOWERS TO OCCUR ACROSS THE
WASHINGTON CASCADES AND NORTHERN BLUE MOUNTAINS AFTER 5 PM. LITTLE
ACCUMULATIONS OF LESS THAN 0.03" WILL OCCUR, PRIMARILY AT HIGHER
ELEVATIONS ABOVE 4,000 FEET. THE BIGGER IMPACT WILL COME IN THE
FORM OF BREEZY AFTERNOON/EVENING WINDS DUE TO A DEVELOPING
PRESSURE GRADIENT ALONG THE CASCADES. THIS WILL LEAD TO SUSTAINED
WEST-NORTHWEST WINDS OF 20-30 MPH WITH GUSTS REACHING UP TO 40 MPH
ACROSS THE SIMCOE HIGHLANDS, GORGE, SOUTHERN BLUE MOUNTAIN
FOOTHILLS, AND KITTITAS VALLEY. CONFIDENCE IN THESE VALUES IS HIGH
(70-80%) AS THE NBM ADVERTISES A 70-90% CHANCE OF GUSTS REACHING
35 MPH OR GREATER AND A 40-60% CHANCE OF GUSTS REACHING 40 MPH OR
GREATER OVER THE AFOREMENTIONED AREAS. THE UPPER LEVEL TROUGH WILL
BRIEFLY MOVE ONSHORE OVER THE OREGON COAST ON SUNDAY BEFORE
DIGGING SOUTH ALONG THE NORTHERN CALIFORNIA COAST INTO MONDAY.
THIS WILL BRING ANOTHER ROUND OF BREEZY WINDS TO THE SAME AREAS AS
ON SATURDAY, BUT SUSTAINED WEST-NORTHWEST WINDS OF ONLY 15-25 MPH
WITH GUSTS OF UP TO 35 MPH ARE EXPECTED DUE TO A WEAKER GRADIENT
ALONG THE CASCADES. THE GFS, NAM, AND SREF ALL INDICATE A PRESSURE
GRADIENT OF 6-7.5 MB SATURDAY, DECREASING TO 4.5-6.5 MB ON
SUNDAY. THIS DECREASE IN WINDS IS ALSO SHOWCASED BY THE NBM AS
PROBABILITIES OF GUSTS REACHING 35 MPH OR GREATER ON SUNDAY IS
50-70% AND 40 MPH OR GREATER IS 30-50%.
AS THE TROUGH MOVES SLIGHTLY ONSHORE AND MORE EFFECTIVELY ERODES
THE BACKSIDE OF THE DEPARTING UPPER LEVEL RIDGE, INSTABILITY WILL
DEVELOP ALONG THE BOUNDARY TO PROMOTE THE DEVELOPMENT OF ISOLATED
THUNDERSTORMS ALONG THE JOHN DAY HIGHLANDS NORTHEAST INTO THE
NORTHERN BLUES AND WALLOWA/UNION COUNTIES SUNDAY AFTERNOON AND
EVENING. THE NAM, ECMWF, GFS, AND NBM SUGGEST CAPE VALUES BETWEEN
150-350 J/KG. THE ECMWF, GFS, AND NAM ALSO ADVERTISE SHEAR OF
40-50 KTS WITH THE NAM AND GFS HINTING AT LOW-LEVEL LAPSE RATES
OF 7-8 C/KM. THESE PARAMETERS DO SUGGEST THE POTENTIAL FOR THE
DEVELOPMENT OF ISOLATED AFTERNOON AND EVENING THUNDERSTORMS ON
SUNDAY, BUT DIFFERENCES ARE STILL PRESENT IN REGARDS TO THE
STRENGTH OF THE INCOMING SYSTEM AND HOW FAR INLAND IT IS ABLE TO
PROGRESS. CURRENTLY, 51% OF ENSEMBLE MEMBERS HINT AT A STRONGER
AND FURTHER INLAND PUSH OF THE TROUGH WHICH WOULD CORRELATE TO
INCREASED CAPE VALUES AND A BETTER POTENTIAL FOR THUNDERSTORM
DEVELOPMENT. THE OTHER 49% OF MEMBERS SUGGEST A WEAKER TROUGH OR
STRONGER INFLUENCING RIDGE, LESSENING THE AMOUNT OF CAPE IN THE
ENVIRONMENT. SO AT THIS TIME THE THUNDERSTORM THREAT IS MARGINAL
(40-60%), BUT IT IS WORTH NOTING AS IT IS THE MORE PROBABLE
SOLUTION. THE MAIN CONCERNS FOR ANY DEVELOPING STORM CELLS WOULD
BE PERIODS OF HEAVY RAINFALL, LIGHTNING, AND GUSTY WINDS. FOR
AREAS INCURRING ISOLATED THUNDERSTORMS, A WETTING RAIN (0.10" OR
GREATER) DOES LOOK LIKELY AS THE NBM SHOWS A 75-85% OF OCCURRENCE.
75
LONG TERM...MONDAY THROUGH FRIDAY...MAIN FEATURE OF THE PERIOD
CONTINUES TO BE A BROAD TROUGH DROPPING IN FROM THE GULF OF ALASKA
AND ENVELOPING THE FORECAST AREA THROUGH THE FIRST STRETCH OF THE
WORK WEEK. THE CENTER OF THE LOW WILL BE OVERHEAD ON MONDAY, SO
WHILE THE AXIS OF THE MOST FAVORABLE MOISTURE ADVECTION WILL FALL TO
OUR SOUTH AND EAST, THE INSTABILITY PROVIDED BY THE SYSTEM WILL
STILL MAKE FOR WIDESPREAD SHOWER CHANCES ACROSS THE CWA, WITH
ISOLATED THUNDERSTORMS POSSIBLE OVER THE EASTERN MOUNTAINS AS WELL.
CAPE IS NOT SUPER FAVORABLE FOR CONVECTIVE DEVELOPMENT AT ONLY A
COUPLE HUNDRED J/KG, BUT THE SW FLOW ALOFT PROVIDED BY THE TROUGH
SHOULD STILL HELP TO CREATE AT LEAST A SLIGHT CHANCE (15-20%) FOR AN
ISOLATED CELL TO FORM OVER THE EASTERN MOUNTAINS.
SIMILAR CONDITIONS WILL PREVAIL ON TUESDAY AS THE LOW IS SLOW TO
MEANDER OUT OF OUR FORECAST AREA. MORE OF THE MOISTURE WILL BE
WRAPAROUND IN NATURE, SO TUESDAY WON'T BE QUITE AS WET AS MONDAY,
BUT SIMILAR THUNDERSTORM CHANCES (15-20%) WILL ARISE ACROSS THE
EASTERN MOUNTAINS. OVERALL, NBM PROBABILISTIC GUIDANCE DEPICTS ABOUT
A 55-65% CHANCE FOR THE EASTERN MOUNTAINS AND CASCADE CRESTS TO SEE
OVER 0.25 INCHES OF PRECIP FROM THIS SYSTEM FROM MONDAY TO WEDNESDAY
MORNING, WITH ABOUT A 30-40% CHANCE FOR THE BASIN, CENTRAL OREGON,
AND ADJACENT VALLEYS OF SEEING OVER A TENTH OF AN INCH. THIS IS ON
TOP OF WHAT IS EXPECTED TO OCCUR ON SUNDAY. THE BASIN WILL LARGELY
BE SPARED FROM THE WETTEST OF WHAT THIS SYSTEM HAS TO OFFER, GIVEN
HOW THE DRY CENTER OF THE LOW IS EXPECTED TO TRACK RIGHT OVERHEAD,
BUT EXPECTATION IS THAT THE MOUNTAINS WILL STILL SEE A NICE DOSE OF
MOISTURE FROM THIS LOW. EXPECT GUSTY CONDITIONS THROUGH THE CASCADE
GAPS ON MONDAY AND TUESDAY AFTERNOON AS WELL, WITH ABOUT A 60-70%
CHANCE FOR GUSTS TO EXCEED 40 MPH BOTH DAYS.
A MORE BENIGN PICTURE IS BEING PAINTED BY ENSEMBLE GUIDANCE
WEDNESDAY ONWARD, WITH THE MAIN SOLUTIONS BEING EITHER ZONAL FLOW OR
WEAK NW FLOW. THE LATTER WOULD PROVIDE FOR SLIGHT CHANCES (20-30%)
FOR SHOWERS OVER THE MOUNTAINS, WITH DRY CONDITIONS ELSEWHERE. TEMPS
ARE EXPECTED TO GRADUALLY TREND UPWARD ONCE THE EARLY WEEK LOW
DEPARTS OUR REGION AS WELL. EVANS/74
PRELIMINARY POINT TEMPS/POPS
PDT 79 51 77 50 / 0 0 0 10
ALW 80 54 78 52 / 0 0 0 20
PSC 82 52 83 50 / 0 0 0 10
YKM 80 51 77 48 / 0 0 0 10
HRI 82 52 79 51 / 0 0 0 10
ELN 78 47 71 45 / 0 0 0 0
RDM 82 46 76 43 / 0 0 0 10
LGD 83 50 78 48 / 0 0 10 20
GCD 85 49 81 46 / 0 0 10 10
DLS 81 51 74 50 / 0 0 0 10
PDT WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
SHORT TERM...75
LONG TERM....74
AVIATION...83
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