499  
FXUS66 KPDT 281753  
AFDPDT  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE PENDLETON OR  
953 AM PST MON NOV 28 2022  
   
UPDATED AVIATION DISCUSSION
 
VFR CONDITIONS AT KDLS/KYKM/KPSC  
AND WILL REMAIN VFR THROUGH THE PERIOD. MVFR CONDITIONS AT  
KPDT/KRDM/KALW AND HAVE BEEN INTERMITTENT AS THE PRECIPITATION  
MOVES OVERHEAD AND SLOWLY OUT OF THE REGION. THESE TAF SITES  
SHOULD RETURN TO VFR CONDITIONS THIS AFTERNOON AS THE ISOLATED  
SHOWERS MOVE THROUGH. KBDN IS LIFR CURRENTLY WITH 1/4SM VIS DUE TO  
SNOW, BUT SHOULD ALSO RETURN TO VFR CONDITIONS THIS BY THIS  
AFTERNOON. BENNESE/90  
 

 
   
PREV DISCUSSION
 
/ISSUED 859 AM PST MON NOV 28 2022/  
 
UPDATE...UPPER TROUGH DIGGING SOUTHEAST ACROSS THE REGION WILL  
SHIFT EAST OF THE AREA THIS EVENING. ALREADY SEEING SOME CLEARING  
SKIES EAST OF THE CASCADES THIS MORNING. SNOW IS TAPERING OFF OVER  
THE EAST SLOPES BUT WILL CONTINUE INTO THE AFTERNOON OVER THE  
EASTERN MOUNTAINS BUT DECREASE IN INTENSITY. LITTLE ADDITIONAL  
ACCUMULATION IS EXPECTED OVER THE EAST SLOPES BUT 1-2 INCHES OF  
SNOW IS PROBABLE OVER THE EASTERN MOUNTAINS. SNOW WILL END ALL  
AREAS TONIGHT AS A TEMPORARY RIDGE BUILDS INTO THE AREA. 78  
 
PREV DISCUSSION... /ISSUED 232 AM PST MON NOV 28 2022/  
 
SHORT TERM...TODAY THROUGH WEDNESDAY NIGHT...THE SHORT TERM  
CONTINUES TO BE ACTIVE, FOR AT LEAST THROUGH TODAY. A WINTER STORM  
CONTINUES TO MOVE ACROSS THE REGION AND FORECAST AREA THIS  
MORNING. CURRENTLY, THE RADAR IS SHOWING PRECIPITATION CONTINUING  
TO MOVE ACROSS THE CASCADES AND ALSO THE EASTERN AND NORTHEAST  
MOUNTAINS. HOWEVER, THERE SEEMS TO BE LESS PRECIPITATION COVERAGE  
THAN PREVIOUSLY FORECASTED, ESPECIALLY OVER THE LOWER ELEVATIONS.  
THE NBM V4.1 24 HOUR SNOWFALL AMOUNT PROBABILITIES ENDING AT 00Z  
THIS AFTERNOON CONTINUES TO SHOW A HIGH PROBABILITY OF STORM  
TOTAL WARNING SNOW AMOUNTS OVER THE CASCADES (BOTH OR AND WA), AND  
ALSO OVER THE BLUE MOUNTAINS. WEB CAMERAS DO SHOW SNOW FALLING IN  
THESE AREAS. THE NBM V4.1 PROBABILITIES OF 24 HOUR SNOWFALL  
AMOUNTS OF GREATER THAN 6 INCHES ARE IN THE 70 TO 90 PERCENT  
CHANCE RANGE OVER THE CASCADES AND BLUE MOUNTAINS. IT IS ALSO  
SHOWING PROBABILITIES OF ADVISORY AMOUNTS (24 HOUR SNOWFALL  
AMOUNTS GREATER THAN 4 INCHES) IN THE SAME PERCENTAGE RANGE FOR  
THE OCHOCO-JOHN DAY HIGHLANDS. HOWEVER, IT IS NOT SHOWING AS MUCH  
OF A PROBABILITY OF MORE THAN 4 INCHES, ENDING AT 00Z TODAY, OVER  
WALLOWA COUNTY. IT DOES SHOW A HIGH PROBABILITY (MOSTLY 70-90  
PERCENT) OF GREATER THAN 2 INCHES OVER WALLOWA COUNTY. RADAR  
IMAGERY IS NOT SHOWING MUCH PRECIPITATION OVER WALLOWA COUNTY,  
THOUGH THE RADAR BEAM TYPICALLY HAS A PROBLEM SEEING LOW ALTITUDE  
ECHOES OVER WALLOWA COUNTY DUE TO BEAM BLOCKAGE FROM THE BLUE  
MOUNTAINS. CAMERAS OVER WALLOWA COUNTY DO SHOW SNOW IS FALLING IN  
SOME AREAS OVER WALLOWA COUNTY. ALSO, THERE WAS A REPORT EARLIER  
OF 4.5 INCHES NEAR JOSEPH, WHICH IS IN THE HEART OF WALLOWA  
COUNTY. STILL HAVE HIGH CONFIDENCE THAT ADVISORY AMOUNTS WILL  
STILL BE MET IN BOTH WALLOWA COUNTY AND THE OCHOCO-JOHN DAY  
HIGHLANDS BY 00Z THIS AFTERNOON.  
 
THE WINTER STORM WARNINGS FOR BOTH THE OR AND WA CASCADES END AT  
18Z THIS MORNING. IT MAY NEED TO BE EXTENDED IF THE STREAM OF  
SNOWFALL, CURRENTLY SEEN ON RADAR, CONTINUES BEYOND 18Z, WITH THE  
EXPECTATION OF ADDITIONAL ACCUMULATIONS. THIS IS ESPECIALLY TRUE  
FOR THE OR CASCADES. THE WARNINGS AND ADVISORIES FOR THE EASTERN  
AND NORTHEAST MOUNTAINS ALL END AT 00Z TODAY, WHICH STILL LOOKS  
GOOD. STORM TOTAL QPF AMOUNTS BY THE NBM AND WPC, AS WELL AS THE  
SHORT RANGE DETERMINISTIC AND ENSEMBLE MODELS, SHOW THAT THE SNOW  
WILL DECREASE ENOUGH BY 00Z TO WARRANT THE ENDING OF THE WARNINGS  
AND ADVISORIES THERE AT 00Z THIS AFTERNOON.  
 
ELSEWHERE ACROSS THE FORECAST AREA, SNOW, OR A MIX OF RAIN AND  
SNOW IS STILL EXPECTED THROUGH THIS MORNING, AND POSSIBLY INTO  
THE AFTERNOON. HOWEVER, ACCUMULATIONS WILL BE VERY LIGHT, IF ANY,  
AND MOSTLY LESS THAN AN INCH WHERE THERE IS ANY ACCUMULATION.  
SOME AREAS, SUCH AS THE LOWER COLUMBIA BASIN WILL LIKELY NOT HAVE  
ANY SNOW ACCUMULATIONS AT ALL, THOUGH THERE COULD BE SOME LIGHT  
SNOW OR A MIX OF RAIN AND SNOW THERE THIS MORNING.  
 
TEMPERATURES ARE NOT AS COLD AS PREVIOUSLY EXPECTED BY THIS TIME.  
MOST LOWER ELEVATION AREAS ARE STILL SHOWING TEMPERATURES MOSTLY IN  
THE 30S TO NEAR 40. HOWEVER, SOME LOCATIONS, SUCH AS AT KPSC IS  
SHOWING A CURRENT TEMPERATURE OF 28 DEGREES. THIS IS LIKELY DUE  
TO SOME CLEARING THERE. HIGH TEMPERATURES TODAY FOR THE LOWER  
ELEVATIONS ARE EXPECTED TO BE IN THE 30S, WITH MOSTLY 20S IN THE  
MOUNTAINS.  
 
THIS CURRENT WEATHER SYSTEM WILL MOVE TO THE SOUTHEAST, WITH A  
LARGE UPPER TROUGH CONTINUING TO DIG OVER THE REGION WITH A  
NORTHWEST TO NORTH FLOW ALOFT. THIS WILL BRING IN COLDER AIR  
TONIGHT AND TUESDAY, WITH HIGH TEMPERATURES IN THE UPPER 20S TO  
MID 30S IN THE LOWER ELEVATIONS, AND MOSTLY LOWER TO MID 20S IN  
THE MOUNTAINS. TUESDAY WILL BE A DRY DAY, EXCEPT FOR POSSIBLE  
LINGERING LIGHT SNOW FLURRIES OVER THE MOUNTAINS.  
 
THE NEXT WEATHER SYSTEM IS THEN FORECAST TO BRING SNOW BACK TO THE  
CASCADES AGAIN BY TUESDAY EVENING, WHICH WILL SPREAD TO THE  
EASTERN AND NORTHEAST MOUNTAINS BY EARLY WEDNESDAY MORNING. WARM  
AIR ADVECTION IN A SOUTHWEST FLOW ALOFT BY WEDNESDAY AFTERNOON  
WILL CAUSE SNOW LEVELS TO RISE AND CHANGE THE SNOW OVER TO RAIN  
IN THE LOWER ELEVATIONS, AS WELL AS CENTRAL/NORTH CENTRAL OR. THE  
MOUNTAINS WILL POSSIBLY SEE SIGNIFICANT AMOUNTS OF SNOW AGAIN  
FROM THIS NEXT SYSTEM. HOWEVER, CONFIDENCE IS NOT YET HIGH ENOUGH  
TO ISSUE ANY WINTER WEATHER HIGHLIGHTS FOR THE MOUNTAIN AT THIS  
TIME.  
 
THERE WILL BE LOCALLY BREEZY WINDS ACROSS MOST OF THE FORECAST  
AREA TODAY, WHICH WILL DIMINISH THIS EVENING AND THEN REMAIN LIGHT  
THROUGH TUESDAY NIGHT. AFTER THAT, WINDS WILL INCREASE AGAIN ON  
WEDNESDAY WITH THE APPROACH OF THE NEXT WEATHER SYSTEM. THIS WILL  
ESPECIALLY BE THE CASE OVER THE CASCADES AND THE EASTERN/NORTHEAST  
MOUNTAINS. THESE WINDS WILL BE SOUTHWESTERLY AHEAD OF THE NEXT  
UPPER TROUGH THAT WILL BE MOVING INTO THE REGION, WHICH WILL BRING  
IN WARMER AIR, CAUSING MAINLY RAIN FOR THE LOWER ELEVATIONS. 88  
 
LONG TERM...THURSDAY THROUGH MONDAY...A COUPLE OF UPPER-LEVEL  
SYSTEMS THREATEN THE FORECAST AREA THROUGH THE PERIOD. GUIDANCE  
SUGGESTING MAINLY THURSDAY AND EARLY SATURDAY LOOK TO BE THE BEST  
THREATS FOR AREA-WIDE PRECIP, WITH THE OVERALL TREND IN THE FORECAST  
LOOKING TO BE TOWARD COLDER TEMPERATURES DUE TO THE NORTHWESTERLY  
ORIGIN OF THESE SYSTEMS.  
 
PRECIP TYPE WILL BE A CHALLENGE FOR THURSDAY'S SYSTEM, AS ZONAL TO  
SW FLOW ALOFT HEAD OF THE POSITIVELY-TILTING TROUGH AS IT APPROACHES  
FROM THE BC COAST WILL WARM THINGS UP ACROSS THE LOWER ELEVATIONS  
THROUGH THURSDAY, BUT THIS SYSTEM LOOKS TO DEEPEN OVERHEAD AS ITS  
AXIS APPROACHES THE FORECAST AREA, MEANING COLD AIR ADVECTION AS THE  
TROUGH PULLS IN COLDER AIR FROM THE NORTH. NBM SNOW LEVELS AS A  
RESULT ARE PRETTY BORDERLINE FOR SNOW IN THE LOWER ELEVATIONS, WITH  
AROUND 2000-2500 FT FROM CENTRAL OR UP THROUGH THE EASTERN  
MOUNTAINS, AROUND 1000 FT FOR THE GORGE AND LOWER BASIN, AND LESS  
THAN 700 FT FOR THE YAKIMA/KITTITAS VALLEYS NORTH AND NORTHWESTWARD.  
ENSEMBLES SUGGEST, GIVEN THE ORIENTATION OF THIS SYSTEM, THAT THE SW  
FLOW AHEAD OF THIS SYSTEM WILL BE MOST PROMINENT ACROSS OR,  
RESULTING IN THE HIGHER SNOW LEVELS, WHILE CAA WILL BE STRONGER IN  
WA, RESULTING IN BETTER CHANCES FOR SNOW. QPF ENSEMBLES HAVE TRENDED  
WETTER WITH THURSDAY'S SYSTEM, BUT POTENTIAL IMPACTS WILL DEPEND  
HEAVILY ON THE ENVIRONMENTAL TEMPERATURE PROFILE ACROSS THE LOWER  
ELEVATIONS. THE TIMING OF PRECIP (AROUND EARLY TO LATE MORNING  
THURSDAY) ALSO COMPLICATES THE FORECAST. FOR NOW, WILL SAY THAT  
CONFIDENCE IS HIGH (>70%) FOR ANOTHER HEAVY SNOW EVENT FOR THE  
MOUNTAINS, PARTICULARLY FOR THE BLUES, WITH SIMILAR CONFIDENCE FOR  
SOME KIND OF PRECIP OUTSIDE THE MOUNTAINS, BUT LOW CONFIDENCE (<20%)  
ON EXACT AMOUNTS AND POTENTIAL ACCUMULATIONS.  
 
GUIDANCE THEN HAS THE SYSTEM ABSORBED BY A PRECEDING TROUGH COMING  
IN FROM THE GULF OF ALASKA, FURTHER ENHANCING THE POTENTIAL FOR CAA  
ACROSS THE PACNW. ENSEMBLES IN STRONG AGREEMENT ON THIS, WITH SOME  
SLIGHT DISAGREEMENT ON TIMING, BUT OVERALL FOCUSED ON THE EARLY  
MORNING SATURDAY TIMEFRAME. JUST HOW MUCH THIS SYSTEM DEEPENS WILL  
IMPACT THE POTENTIAL PRECIP FORECAST, AS THE LOW CENTERED RIGHT OVER  
THE CWA, AS SUGGESTED BY SOME ENSEMBLE MEMBERS, WOULD MEAN A COLDER,  
DRIER FORECAST OVERALL. THAT BEING SAID, THE CONSENSUS ACROSS  
GUIDANCE ON THE MERE PRESENCE OF THIS SYSTEM SUGGESTS MODERATE  
CONFIDENCE (40-60%) IN ANOTHER MOUNTAIN SNOW EVENT, BUT WILL HAVE TO  
SEE WHERE THIS SYSTEM TRENDS ACROSS FUTURE MODEL RUNS TO MAKE A  
DETERMINATION ON THE POTENTIAL FOR LOWER-ELEVATION PRECIP. WILL SAY  
CONFIDENCE IS LOW TO MODERATE (20-40%) ON PRECIP CHANCES OUTSIDE THE  
MOUNTAINS SATURDAY, REFLECTED BY THE NBM'S POPS ACROSS OUR NON-  
MOUNTAIN ZONES.  
 
THE OVERALL TREND OF NW FLOW WITH SOME KIND OF TROUGHING OVERHEAD  
CONTINUES BEYOND THE WEEKEND, MEANING MUCH OF THE BEGINNING OF  
DECEMBER LOOKS TO SEE COLDER THAN AVERAGE TEMPERATURES. TEMPERATURE  
SPREADS ACROSS ENSEMBLE MEMBERS ARE RELATIVELY LARGE, AS EXPECTED  
NEARLY A WEEK OUT, BUT LOOKING LIKE WIDESPREAD LOWS IN THE TEENS TO  
20S ARE LIKELY BY THE TAIL END OF THE EXTENDED PERIOD. EVANS/74  
 
AVIATION...12Z TAFS...EXPECTING MOSTLY VFR CONDITIONS THROUGH THE  
PERIOD. ONLY EXCEPTION WOULD BE A CHANCE FOR LIGHT SNOW SHOWERS,  
PRIMARILY FOR RDM/BDN/PDT THIS MORNING. ANY SHOWERS ARE EXPECTED TO  
BE OF MINIMAL IMPACT, WITH ACCUMULATIONS LIGHT AND MVFR CONDITIONS  
AT THE WORST. DRY CONDITIONS WILL PREVAIL DURING THE DAY MONDAY,  
WITH MOSTLY W/NW WINDS LESS THAN 10 KTS AND LOW CIGS, BKN-OVC AROUND  
4-8 KFT. EVANS/74  
 

 
   
PRELIMINARY POINT TEMPS/POPS
 
 
PDT 35 17 32 24 / 50 10 0 20  
ALW 36 18 33 25 / 50 20 0 20  
PSC 38 20 31 25 / 20 10 0 30  
YKM 39 15 28 18 / 20 0 0 60  
HRI 39 22 34 25 / 30 10 0 20  
ELN 35 12 26 18 / 30 10 0 70  
RDM 36 16 36 25 / 60 10 0 20  
LGD 32 13 28 21 / 70 10 0 20  
GCD 31 13 31 22 / 80 20 0 30  
DLS 44 26 37 30 / 50 20 30 70  
 

 
   
PDT WATCHES/WARNINGS/ADVISORIES
 
 
OR...WINTER WEATHER ADVISORY UNTIL 4 PM PST THIS AFTERNOON FOR ORZ050-  
506.  
 
WINTER STORM WARNING UNTIL 4 PM PST THIS AFTERNOON FOR ORZ502-  
503.  
 
WA...WINTER STORM WARNING UNTIL 4 PM PST THIS AFTERNOON FOR WAZ030.  
 

 
 

 
 
SHORT TERM...78  
LONG TERM....74  
AVIATION...90  
 
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