135  
FXUS66 KPDT 190032  
AFDPDT  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE PENDLETON OR  
530 PM PDT FRI SEP 18 2020  
   
SHORT TERM
 
SATELLITE INDICATES UPPER LEVEL LOW JUST BEGINNING TO  
PUSH INTO CASCADES. SHOWERS AND A FEW STORMS ARE EVIDENT IN RADAR  
AND SATELLITE, PRIMARILY ALONG CASCADE CREST AND WESTWARD AT THIS  
TIME, THOUGH THE ACTIVITY IS BEGINNING TO ENCROACH INTO US-97  
CORRIDOR. THIS EVENING THROUGH TONIGHT, ISOLATED STORMS ARE  
EXPECTED TO CONTINUE. THIS ACTIVITY WILL FOCUS ON WHERE  
INSTABILITY IS MARGINAL TO DECENT AND LIFT FROM UPPER LOW IS  
EXPECTED TO TRACK, MOSTLY IN OREGON AND POSSIBLY INTO SOUTHERN  
CASCADES OF WASHINGTON. PRIMARY RISKS WILL BE SOME GUSTY OUTFLOW  
WINDS, LOCALLY INTENSE LIGHTNING, AND POSSIBLE FLOODING SHOULD A  
CELL FAVORABLY TRACK OVER A BURN SCAR AREA. OUTSIDE OF CONCERNS  
FOR BURN SCAR FLOODING, PRECIPITATION TOTALS LOOK BENEFICIAL,  
RANGING FROM NEARLY A QUARTER INCH OR MORE ALONG CASCADE CREST AND  
EVENTUALLY PORTIONS OF WALLOWA MTNS TO A TENTH INCH OR SO FOR  
LARGE PORTION OF BLUE/OCHOCO MTNS AND UPPER FOOTHILLS OF BLUE  
MTNS TO POSSIBLY ONLY A TRACE FOR DRIER PORTIONS OF MID-COLUMBIA  
REGION. WINDS MAY BECOME A TOUCH BREEZY THROUGH GORGE AND EAST  
SLOPES OF WASHINGTON CASCADES AS THE SURFACE BOUNDARY WORKS ACROSS  
THE REGION LATE THIS EVENING. OVERNIGHT, STORM CHANCES LINGER FOR  
SOUTHERN BLUE MTNS AND WALLOWA. TOMORROW MORNING, SHOWERS TAPER  
OFF FOR BLUE MTNS AND EVENTUALLY FAR EAST OREGON AS SYSTEM MOVES  
OUT. UPPER LEVEL NW FLOW TOMORROW SHIFTS MORE WESTERLY ON SUNDAY  
WITH COOLER TEMPERATURES AND DRYING CONDITIONS. CONFIDENCE IS HIGH  
WE WILL SEE BLUE SKIES BY SUNDAY, THOUGH NARROW PLUMES OF SMOKE  
MAY STILL TRACK OVER LOCAL AREAS.  
   
LONG TERM...MONDAY THROUGH FRIDAY
 
MONDAY WILL START OFF UNDER  
AN ACTIVE UPPER LEVEL PATTERN, WITH THE FLOW REGIME GENERALLY WEST  
TO WEST SOUTHWEST THROUGH THE EXTENDED PERIOD. MODELS IN FAIRLY  
GOOD AGREEMENT THAT A SHORTWAVE WILL PASS OVER THE FORECAST AREA  
MONDAY WITH LOCALLY BREEZY CONDITIONS IN THE COLUMBIA GORGE AND  
SOME DEVELOPMENT OF MID TO HIGH LEVEL CLOUD COVER OVER THE  
FORECAST AREA. BEHIND THE SHORTWAVE EXIT TUESDAY, A WEAK REX BLOCK  
PATTERN WILL PASS OVER THE FORECAST AREA WITH DRY CONDITIONS AND  
SEASONABLY COOL TEMPERATURES. EARLY WEDNESDAY, THE NEXT SYSTEM  
ARRIVES IN THE FORM OF SLOW MOVING FRONTAL BOUNDARY SWINGING  
AROUND AN UPPER LEVEL LOW OVER THE GULF OF ALASKA. FRONTAL  
BOUNDARY WILL STALL AS IT INTERACTS WITH THE CASCADES WEDNESDAY,  
AND FINALLY CROSS THE FORECAST AREA OVERNIGHT WEDNESDAY INTO  
THURSDAY WITH CHANCE TO SLIGHT CHANCE RAIN SHOWERS ACROSS THE  
FORECAST AREA, AND LOCALLY BREEZY CONDITIONS DEVELOPING IN THE  
AFTERNOON AND EVENING AHEAD OF AND BEHIND THE FRONTAL BOUNDARY.  
BEHIND THE FRONTAL BOUNDARY, A SHORTWAVE TROUGH WILL ROUND THE  
LARGER UPPER LOW THURSDAY AND CROSS THE FORECAST AREA OVERNIGHT  
THURSDAY INTO FRIDAY. MODELS ARE IN FAIRLY GOOD AGREEMENT WITH THE  
SCALE AND TIMING OF THIS LATE WORK WEEK SYSTEM, AND INDICATE A  
CONTINUATION OF NOCTURNAL RAIN SHOWERS THURSDAY NIGHT/FRIDAY  
MORNING, WITH LOCALLY BREEZY WINDS IN THE AFTERNOON FRIDAY.  
LAWHORN/82  
 

 
 
AVIATION...00Z TAFS. SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS  
WILL MOVE ACROSS THE REGION THIS EVENING DECREASING OVERNIGHT.  
WESTERLY WINDS WILL BE INCREASING AND WILL CLEAR MUCH OF THE SMOKE  
FROM THE TAF SITES.  
 

 
   
PRELIMINARY POINT TEMPS/POPS
 
 
PDT 51 74 48 75 / 30 10 0 0  
ALW 54 75 51 76 / 40 10 10 0  
PSC 57 78 53 78 / 20 0 0 0  
YKM 53 75 48 76 / 20 0 0 0  
HRI 55 78 50 78 / 20 0 0 0  
ELN 51 71 48 74 / 30 10 10 0  
RDM 43 70 39 76 / 40 10 0 0  
LGD 48 69 44 74 / 60 30 10 0  
GCD 47 70 43 78 / 60 20 0 0  
DLS 57 75 54 79 / 20 10 0 0  
 

 
   
PDT WATCHES/WARNINGS/ADVISORIES
 
 
OR...NONE.  
WA...NONE.  

 
 

 
 
SHORT TERM...76  
LONG TERM....82  
AVIATION...94  
 
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