264
FXUS66 KPDT 270551
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
1051 PM PDT WED MAR 26 2025
AVIATION...06Z TAFS
VFR CONDITIONS FOR ALL SITES THROUGH THE
PERIOD. RADAR INDICATES ISOLATED THUNDERSTORMS NEAR YKM BUT NOT
NEAR ENOUGH TO WARRANT TS IN THE VICINITY. WINDS WILL BE STRONG
ENOUGH TO LIFT CEILINGS AND VIS AT VFR FOR THE WHOLE PERIOD.
SHOWERS AND RAIN RETURN TO DLS (20Z), PDT (17Z), RDM (22Z), BDN
(22Z), YKM (23Z), ALW (17Z), AND PSC (17Z). WINDS WILL BE FAIRLY
LIGHT UP TO 12 KNOTS EXCEPT AT BDN AND RDM UP TO 30 KNOTS AT 18Z.
SHORT TERM...TODAY THROUGH FRIDAY NIGHT...
KEY MESSAGES:
1. STRONG TO SEVERE THUNDERSTORMS POSSIBLE THROUGH THIS EVENING
*MARGINAL (1 OF 5) CATEGORY FOR SEVERE WEATHER*
2. THUNDERSTORM CHANCES RETURN FOR AREAS THURSDAY
3. RAIN SHOWERS LINGER THROUGH FRIDAY.
CURRENT RADAR AND VISIBLE SATELLITE IMAGERY SHOWING DISCRETE CELLS
BEGINNING TO DEVELOP ALONG AND WEST OF THE CASCADES UNDER MOSTLY
CLEAR SKIES. CUMULUS CLOUDS ARE BEGINNING TO ALSO DEVELOP ACROSS
CENTRAL OREGON AND AREAS OF THE JOHN DAY-OCHOCO HIGHLANDS AND THE
BLUE MOUNTAINS AS A STRONG UPPER LEVEL LOW PRESSURE AND ASSOCIATED
COLD FRONT APPROACH THE COAST. THIS SIGNIFICANT SYSTEM IS BREAKING
DOWN THE STRONG UPPER LEVEL RIDGE THAT BROUGHT WARM AND UNSEASONAL
WEATHER TO THE AREA OVER THE LAST COUPLE DAYS. THIS INCOMING
SYSTEM, COUPLED WITH A PRESENT UPPER LEVEL JET AND STRONG MOIST FLOW
ALOFT FROM THE SOUTH, WILL ATTRIBUTE TO THE POTENTIAL FOR STRONG
TO SEVERE THUNDERSTORMS TO OCCUR THROUGH THE EVENING TONIGHT. MEAN
CAPE OF 500-1000 J/KG, SHEAR OF 55-65 KTS, AND LAPSE RATES
BETWEEN 7-7.5 C/KM ARE PRESENT VIA THE HRRR, NSSL, NAM, AND ARW,
WHICH WILL PROVIDE ENOUGH ATMOSPHERIC FORCINGS TO PROMOTE ENHANCED
THUNDERSTORM DEVELOPMENT. THE ONLY INHIBITING FACTOR LOOKS TO BE
MOISTURE, WHICH IS A REMNANT FROM THE STRONG DEPARTING UPPER LEVEL
RIDGE THAT BROUGHT WARM AND DRY CONDITIONS EARLIER IN THE WEEK.
THIS MOISTURE, OR LACK THEREOF, WILL ALSO LEAD TO BETTER POTENTIAL
FOR STORM DEVELOPMENT BEING ALONG THE EAST SLOPES OF THE CASCADES
AND OVER WESTERN PORTIONS OF THE BASIN. THAT IS NOT TO SAY THAT
THE BASIN OR AREAS ALONG THE BLUE MOUNTAINS WILL NOT EXPERIENCE
STORM CELL DEVELOPMENT, BUT THE ATMOSPHERE WILL HAVE LESS PRIMING
TO DO FOR LOCATIONS FURTHER SOUTH AND WEST. THE PRIMARY CONCERNS
RELATED TO ANY DEVELOPING STORM CELLS WILL BE ASSOCIATED WITH
DAMAGING WINDS AND HAIL, WHICH IS ALSO MESSAGED BY THE STORM
PREDICTION CENTER AS OUR LOCATION IS WITHIN A MARGINAL (1 OUT OF
5) CATEGORY/RISK FOR SEVERE WEATHER. THUNDERSTORM CHANCES WILL
INCREASE THROUGH THE AFTERNOON, PEAKING BETWEEN 7 PM AND 11 PM.
RAIN AMOUNTS OF 0.01-0.10" WILL BE POSSIBLE OVER ANY DEVELOPING
STORM CELL, WITH 0.10-0.25" POSSIBLE ALONG THE EAST SLOPES OF THE
CASCADES WHERE MULTIPLE STORM CELLS COULD PASS OVER AN AREA.
BREEZY WINDS WILL ALSO BE EXPERIENCED ACROSS CENTRAL OREGON, JOHN
DAY-OCHOCO BASIN, AND THE SIMCOE HIGHLANDS AS SUSTAINED SOUTH-
SOUTHWEST WINDS OF 15-25 MPH WITH GUSTS UP TO 35 MPH ARE
POSSIBLE.
THE STRONG UPPER LEVEL RIDGE STAYS OFFSHORE THURSDAY AND BEGINS TO
SLOWLY PROPAGATE NORTH ALONG THE BRITISH COLUMBIA COAST THROUGH
THE EVENING AS A STOUT UPPER LEVEL SHORTWAVE SLIDES THROUGH THE
AREA. THIS SHORTWAVE WILL ALLOW FOR A SLIGHT CHANCE (15%) OF
THUNDERSTORMS TO DEVELOP, PRIMARILY ALONG THE EAST SLOPES OF THE
WASHINGTON CASCADES, SIMCOE HIGHLANDS, AND THE NORTHERN BLUE
MOUNTAINS THROUGH THE AFTERNOON. ATMOSPHERIC PARAMETERS ARE MUCH
LESS CONDUCIVE ON THURSDAY AS THE HREF ADVERTISES MEAN CAPE VALUES
OF 150-300 J/KG, SHEAR OF 35-45 KTS, AND LAPSE RATES OF 7.0-7.5
C/KM. TIMING LOOKS TO BEGIN AROUND 1 PM AND EXTEND UNTIL 11 PM,
PEAKING BETWEEN 2 PM AND 6 PM. THE MAIN CONCERNS WILL RESULT IN
DAMAGING WINDS AND HAIL, BUT CANNOT RULE OUT AN ISOLATE TORNADO.
WINDS WILL AGAIN BE BREEZY THROUGH CENTRAL OREGON, GRANDE RONDE
VALLEY, AND THE JOHN DAY-OCHOCO BASIN AS SUSTAINED SOUTHWEST WINDS
OF 20-25 MPH AND GUSTS UP TO 35 MPH WILL BE POSSIBLE.
AN ADDITIONAL SHORTWAVE SLIDES THROUGH THE AREA ON FRIDAY AS THE
UPPER LEVEL SYSTEM CONTINUES UP THE BRITISH COLUMBIA COAST TO
MERGE WITH THE STRONGER, PARENT LOW THAT IS LOCATED IN THE GULF OF
ALASKA. THIS SHORTWAVE WILL AGAIN PROMOTE WIDESPREAD SHOWERS
WITHOUT THE POTENTIAL FOR THUNDERSTORM ACTIVITY. LIGHT RAIN
CHANCES WILL PEAK THROUGH THE AFTERNOON AND SLOWLY DISSIPATE
THROUGH THE REMAINDER OF THE DAY. TEMPERATURES WILL CONTINUE TO
COOL DRASTICALLY ABOUT 10 DEGREES WEDNESDAY TO THURSDAY, AND
ANOTHER 3 TO 6 DEGREES THURSDAY TO FRIDAY, AS HIGHS PEAK IN THE
MID-50S ACROSS CENTRAL OREGON AND IN THE UPPER 50S TO LOW 60S
ACROSS THE LOWER COLUMBIA BASIN AND BLUE MOUNTAIN FOOTHILLS. 75
LONG TERM...SATURDAY THROUGH WEDNESDAY...ENSEMBLE GUIDANCE IS IN
GOOD AGREEMENT IN AN ACTIVE WEATHER PATTERN FOR THE PACNW THROUGH
THE MIDDLE OF NEXT WEEK, THOUGH DIFFERENCES IN DETAILS DO EMERGE
AFTER LATE MONDAY. OTHERWISE, WHILE THE PATTERN IS EXPECTED TO BE
ACTIVE, THE EFI (ECMWF EXTREME FORECAST INDEX) VALUES DON'T
INDICATE ANYTHING SIGNIFICANT, AND AR (ATMOSPHERIC RIVER) ENSEMBLE
PRODUCTS SHOW LOW MOISTURE TRANSPORT VALUES WHICH TRANSLATES TO
LIGHT TO LOCALLY MODERATE PRECIPITATION AMOUNTS.
ENSEMBLE GUIDANCE BEGINS IN GOOD AGREEMENT OF SHORTWAVE PASSAGE
SATURDAY BRINGING ANOTHER ROUND OF LIGHT MOUNTAIN SNOW WHILE
INTERMOUNTAIN VALLEYS AROUND OR BELOW 4KFT IN ELEVATION WILL SEE
RAIN IN THE AFTERNOON WITH A RETURN TO SNOW AFTER SUNSET. BEHIND
THE SHORTWAVE, A TRANSIENT RIDGE SLIDES ACROSS THE PACNW, BRINGING
WITH IT A BRIEF PERIOD OF DRY CONDITIONS INTO SUNDAY AFTERNOON.
BEHIND THE EXIT OF THE TRANSIENT RIDGE EARLY SUNDAY AFTERNOON,
AN UPPER SHORTWAVE TROUGH WILL ROUND AN UPPER LOW IN THE NORTHEAST
PACIFIC AND LIFT NORTH/NORTHEAST ACROSS THE PACNW THROUGH MONDAY.
THIS WILL INITIALLY RESULT IN WIDESPREAD LIGHT RAIN CHANCES BELOW
5KFT IN ELEVATION, WITH LIGHT SNOW OR RAIN/SNOW MIX ABOVE 5KFT IN
THE MOUNTAINS. AS THE SHORTWAVE TROUGH CONTINUES INLAND MONDAY,
LOCALLY BREEZY CONDITIONS WILL DEVELOP IN THE LOWER ELEVATIONS.
MONDAY THROUGH EARLY WEDNESDAY, ENSEMBLE GUIDANCE BECOMES SPLIT ON
THE EVOLUTION OF THE SYNOPTIC PATTERN, BUT DO AGREE THAT LIGHT TO
LOCALLY MODERATE MOUNTAIN SNOW AND LOWER ELEVATION RAIN CHANCES
WILL CONTINUE ACROSS THE FORECAST AREA. THROUGH THIS PERIOD,
ENSEMBLE CLUSTERING SOLUTIONS ARE SPLIT ABOUT 40/45% OF THE
ENSEMBLE MEMBERS (ECMWF, GFS, AND CANADIAN) ON WHETHER TO HAVE A
BROAD FLAT TROUGH SLIDE INLAND, OR TO KEEP TROUGHING CENTERED JUST
OFFSHORE THE PACNW. WHILE OVERALL MOISTURE SUPPORT IS SIMILAR
BETWEEN THE SCENARIOS, TEMPERATURES AND SNOW LEVELS WILL DIFFER.
FOR THE CASE OF THE UPPER TROUGH MOVING INLAND, COOLER
TEMPERATURES WITH LOWER SNOW LEVELS WILL RESULT IN MORE WIDESPREAD
LIGHT SNOW ACROSS THE MOUNTAINS AND INTERMOUNTAIN VALLEYS, WHILE
THE TROUGH OFFSHORE WILL KEEP CONDITIONS MORE MILD (COMPARABLY)
WITH LIGHT SNOW IN THE MOUNTAINS BUT RAIN OR RAIN/SNOW MIX IN THE
INTERMOUNTAIN VALLEYS. WHILE CONFIDENCE IN EITHER SOLUTION IS LOW
(20-30%) AT THIS TIME, CONFIDENCE IS MOD-HIGH (60-80%) IN
CONTINUED MOUNTAIN PRECIPITATION WITH PERIODIC LIGHT LOWER
ELEVATION RAIN SHOWERS THROUGH EARLY WEDNESDAY. LAWHORN/82
PRELIMINARY POINT TEMPS/POPS
PDT 50 65 48 61 / 10 40 40 50
ALW 52 65 49 60 / 20 40 50 60
PSC 52 65 49 63 / 30 60 40 20
YKM 48 61 44 58 / 60 40 50 20
HRI 50 66 48 64 / 20 60 40 30
ELN 46 59 41 56 / 70 50 50 40
RDM 44 60 40 55 / 50 30 40 20
LGD 47 64 44 53 / 20 40 30 70
GCD 47 63 41 53 / 20 30 20 70
DLS 50 62 46 59 / 80 60 70 60
PDT WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
SHORT TERM...75
LONG TERM....82
AVIATION...95
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