338
FXUS66 KPDT 272315
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
315 PM PST SAT DEC 27 2025
KEY MESSAGES
- FOG CONCERNS AS A HIGH PRESSURE RIDGE BUILDS THROUGH MID-WEEK.
- PRECIPITATION CHANCES WITH LIGHT MOUNTAIN SNOW RETURN THURSDAY
ONWARD.
DISCUSSION
CURRENT RADAR AND SATELLITE IMAGERY SHOW LIGHT
RETURNS MAINLY OVER PORTIONS OF UMATILLA AND UNION COUNTIES, WHICH
IS DUE TO THE OROGRAPHIC LIFT FROM THE POST-FRONTAL SYSTEM. THESE
RETURNS IS ASSOCIATED LIGHT SNOW ALONG WITH MIST AND BREEZY WINDS,
MAINLY ALONG AND SOUTH OF CABBAGE HILL EARLIER TODAY. SURFACE
OBSERVATIONS ALSO SHOWED PRECIP AMOUNTS OF 0.10 INCH OR LESS FALLEN
AT UNION COUNTY, JOSEPH STATE AIRPORT (KJSY) AND OTHER MOUNTAIN
AREAS. WEBCAMS ARE NOW SHOWING IMPROVED VSBYS ACROSS THE
AFOREMENTIONED AREA. FOR THE REST OF TODAY, SCATTERED TO BROKEN HIGH
CLOUDS WILL BE LEFT BEHIND AS THE UPPER TROUGH EXITS FURTHER
EASTWARD WITH THE UPPER RIDGE MOVING IN. LIGHT SNOW MAY LINGER FOR
THE CREST OF WA/OR CASCADES TONIGHT FROM THE APPROACHING LIGHT
RETURNS, BUT CHANCES ARE LOW (<20%).
A HIGH PRESSURE SYSTEM WILL THEN ENTER THE PACNW SUNDAY THROUGH
WEDNESDAY. HOWEVER, FOG WILL BE THE MAIN HIGHLIGHT FOR THESE DAYS
DURING MORNING AND OVERNIGHT HOURS. WITH NEAR TO BELOW FREEZING
NIGHTTIME TEMPERATURES AND DEWPOINTS, THERE IS A GOOD CHANCE (>50%)
THAT FREEZING FOG COULD ALSO DEVELOP. VISIBILITIES MAY BE AFFECTED,
BUT WITH LOWER CONFIDENCE (<20%) OF 3 STATUE MILES OR LOWER BASED ON
THE NBM. IN ADDITION TO THAT, AIR STAGNATION COULD BE A CONCERN FOR
MONDAY THROUGH WEDNESDAY WITH THE MIXING HEIGHTS BELOW 1.5 KFT
DURING MORNING AND AFTERNOON HOURS AND TRANSPORT WINDS LESS THAN
10KTS. FOR NOW, WE WILL MONITOR FOR THAT AND SEE IF AN ADVISORY WILL
BE NEEDED. WINDS WILL BE LIGHT ACROSS THE FORECAST AREA WITH SOME
BREEZES OVER THE MOUNTAINS.
THURSDAY ONWARD IS WHEN PRECIP WILL RETURNS WITH AN APPROACHING
TROUGH. THE CASCADES WILL SEE SHOWERS BEFORE BECOMING MORE
WIDESPREAD WITH LIGHT RAIN FOR THE LOW ELEVATIONS WITH MOUNTAINS
RAIN/SNOW MIX TO ALL SNOW. QPF AMOUNTS MAY EXCEED TO 0.10 INCH OR
HIGHER ALONG THE CASCADES AND OTHER MOUNTAIN AREAS BUT LESS FOR THE
LOW ELEVATIONS. THERE SEEMED TO BE A TIMING DISAGREEMENT WITH THE
FRONTAL SYSTEM COMING THURSDAY. THE EURO HAS BEEN FAVORING AN EARLY
ONSET OF THE SYSTEM WHEREAS CANADIAN HAS IT COME IN LATER THURSDAY
AND FRIDAY FOR GFS, MAKING IT CHALLENGING ON WHEN THE SYSTEM WILL
ACTUALLY ARRIVE. FEASTER/97
AVIATION...00Z TAFS.
VFR CONDITIONS CURRENTLY AREA-WIDE WITH
STRATOCU ACROSS CENTRAL AND NORTHEAST OR AND CLEARING ACROSS SOUTH
CENTRAL WA. A DISTURBANCE EMBEDDED IN THE PERIPHERY OF A BUILDING
RIDGE WILL MOVE IN TONIGHT PROMPTING INCREASING SKY COVER. THE MAIN
AVIATION CONCERNS REVOLVE AROUND FOG AND LOW STRATUS OVERNIGHT-EARLY
TOMORROW AS PRECIP CHANCES ARE CONFINED TO THE CREST OF THE CASCADES
AND UPPER SLOPES.
LIGHT WINDS AND LIMITED MIXING EXPECTED TONIGHT, HOWEVER, MUCH DRIER
AIR THAN ANTICIPATED IS IN PLACE WITH DEW POINTS IN THE TEENS IN THE
BASIN AND FOOTHILLS. WHILE THERE IS ADDED MOISTURE IN THE WAY FROM
RECENT RAINFALL OVER THE LAST 36 HOURS, THIS DRIER AIR MASS IN
TANDEM WITH INCREASING CLOUDS AND WARM GROUND BASED ON SOIL
TEMPERATURES IS LOWERING THE OVERALL THREAT. AS SUCH, FORECAST
FAVORS MORE STRATUS THAN FOG PRESENTLY AS THIS SETUP WILL MORE
LIKELY DELAY OR LIMIT ANY FOG DEVELOPMENT. CURRENTLY HAVE LEFT
VISIBILITY RESTRICTIONS OUT BEYOND 6SM AND EMPHASIS ON POTENTIAL
MVFR-IFR CEILINGS WITH STRATUS. HIGHEST CONFIDENCE IN KPDT, KDLS,
AND KALW.
PRELIMINARY POINT TEMPS/POPS
PDT 26 38 24 35 / 10 10 0 0
ALW 26 36 26 35 / 10 10 0 0
PSC 24 36 23 35 / 10 10 0 0
YKM 21 36 22 36 / 10 0 0 0
HRI 25 38 23 35 / 10 10 0 0
ELN 19 31 21 32 / 10 0 0 0
RDM 20 40 21 43 / 10 0 0 0
LGD 24 36 23 38 / 10 10 0 0
GCD 23 38 24 43 / 10 0 0 0
DLS 31 40 29 38 / 20 0 0 0
PDT WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
DISCUSSION...97
AVIATION...80
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