003  
FXUS66 KPDT 211546  
AFDPDT  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE PENDLETON OR  
845 AM PDT THU OCT 21 2021  
   
SHORT TERM...TODAY THROUGH FRIDAY
 
THE TRANSITION TO A WET  
WEATHER PATTERN CONTINUES TODAY AS THE RIDGE OF HIGH PRESSURE OVER  
THE REGION IS RETREATING TO THE EAST. THIS IS IN RESPONSE TO AN  
UPPER LEVEL TROUGH OFF THE COAST DEEPENING AND SLOWLY MOVING  
EASTWARD. CURRENTLY THERE IS A COLD FRONT APPROACHING THE COAST THAT  
WILL SLOWLY MOVE EASTWARD OVER THE CASCADES THIS EVENING AND THEN  
ACROSS THE FORECAST AREA ON FRIDAY. NEW MODEL RUNS ARE SHOWING A  
SLIGHTLY SLOWER EASTWARD PROGRESSION OF THE FRONT OVERNIGHT AND  
FRIDAY SO UPDATED THE MORNING FORECAST TO REFLECT THIS. THIS INITIAL  
FRONT LOOKS LIKE IT WILL PRODUCE A QUARTER TO A THIRD OF AN INCH OF  
RAIN IN THE LOWER ELEVATIONS AND HALF AN INCH TO AROUND AN INCH IN  
THE MOUNTAINS.  
 

 
   
PREV DISCUSSION
 
/ISSUED 458 AM PDT THU OCT 21 2021/  
 
SHORT TERM...TODAY THROUGH SATURDAY NIGHT...IMPRESSIVE UPPER LOW  
OFF THE BC COAST WILL LIFT NEWD WHILE A SHORTWAVE TROUGH DIGS SEWD  
AND MOVES INLAND FRIDAY ACROSS NORTHERN CALIFORNIA AND OREGON.  
PRIMARY UNCERTAINTY TODAY IS THE AMOUNT OF QPF THAT WILL FALL  
ESPECIALLY WITH EASTWARD AND NORTHWARD EXTENT WITH THIS UPPER TROUGH  
WITH RAIN SPREADING EAST OF THE CASCADES THIS EVENING.  
THE ATMOSPHERIC RIVER ASSOCIATED WITH THIS STORM SYSTEM IS PROJECTED  
TO BE LESS PRONOUNCED THAN EARLIER ANTICIPATED AND IT MAY BE  
WEAKENING AS IT MOVES ACROSS EASTERN OREGON. THIS MAY CUT DOWN ON  
RAIN AMOUNTS OVER THE EASTERN PART OF THE FORECAST AREA ON FRIDAY.  
THERE ARE CONFLICTING SIGNALS IN THE AVAILABLE DATA WITH THE ECMWF  
EXTREME FORECAST INDEX (EFI) HIGHLIGHTING A CLIMATOLOGICALLY UNUSUAL  
PRECIPITATION EVENT FOR THIS TIME OF YEAR OVER CENTRAL AND NORTHEAST  
OREGON BUT SUCCESSIVE RUNS OF THE DETERMINISTIC NAM HAVE  
SIGNIFICANTLY WEAKENED THE BAND OF PRECIPITATION AS IT MOVES FROM  
CENTRAL INTO EASTERN OREGON. FOR NOW HAVE USED THE WPC QPF WHICH  
KEEPS .25 TO .60 INCH AMOUNTS IN THE LOWER ELEVATIONS AND .50 TO  
1.00 INCH AMOUNTS IN THE MOUNTAINS. THIS IS SIMILAR TO THE  
DETERMINISTIC NBM QPF. THE BEST BET TO REACH THESE TOTALS MAY END  
UP BEING IN CENTRAL OREGON WHERE THE IVT IS GREATEST. RAIN WILL  
GENERALLY TAPER OFF FRIDAY NIGHT BUT ANOTHER IMPULSE IS FORECAST TO  
MOVE ACROSS THE REGION ON SATURDAY AND SATURDAY NIGHT BRINGING  
MOSTLY LIGHT RAIN. IT WILL BE A WARM DAY TODAY WITH HIGHS MOSTLY IN  
THE 70S IN THE LOWER ELEVATIONS AND 60S IN THE MOUNTAINS...BUT  
TURNING COOLER FRIDAY AND SATURDAY WITH HIGHS IN THE MID 50S TO  
LOWER 60S EXCEPT MID 40S TO LOWER 50S MOUNTAINS. 78  
 
SUNDAY THROUGH WEDNESDAY. A CHALLENGE WILL BE WITH THE TIMING OF A  
SERIES OF WEATHER SYSTEMS THAT IS EXPECTED TO EFFECT THE TWO STATE  
AREA THROUGH THE EXTENDED.  
 
A STATIONARY AND INTENSE LOW PRESSURE SYSTEM OVER THE NE PAC SHOULD  
USHER ABUNDANT MOISTURE INTO THE TWO STATE AREA FOR THE LATTER PART  
OF THE WEEKEND. IN ADDITION PRESSURE GRADIENTS TIGHTEN AND BREEZY  
WINDS ARE POSSIBLE SUNDAY AND MONDAY. THE BULK OF THE PCPN DRIFTS  
AWAY LATER SUNDAY NIGHT BUT SHOWERS PERSIST INTO MONDAY. THE LOW  
PRESSURE SYSTEM OVER THE NE PAC MOVES INLAND MONDAY NIGHT KEEPING  
THE CLOUDS AND SHOWERS IN THE FORECAST. AS THE LOW PRESSURE MOVES  
AWAY FROM THE REGION TUESDAY MORNING ANOTHER WEATHER  
SYSTEM/DISTURBANCE QUICKLY FOLLOWS TUESDAY AFTERNOON AND INTO THE  
NIGHT. THE CONFIDENCE ABOUT THE TIMING AND STRENGTH OF THIS  
DISTURBANCE BEGINS TO LESSEN AS THE EOF/VARIANCE BEGINS TO INCREASE.  
AS THIS SYSTEM RAPIDLY MOVES EAST...DRIER CONDITIONS ARE LIKELY  
ALONG WITH BREEZY TO WINDY CONDITIONS POSSIBLE TUESDAY NIGHT AND  
WEDNESDAY. SNOW LEVEL REMAIN HIGH AND ABOVE 6K FEET WHILE  
TEMPERATURES REMAIN AROUND NORMAL THROUGH THE PERIOD.  
 
AVIATION DISCUSSION...MAINLY VFR CONDITIONS ARE EXPECTED TO PERSIST  
FOR THE NEXT 24 HOURS. MEANWHILE A WEATHER SYSTEM IS FORECAST TO  
MOVE INTO THE REGION TONIGHT AND EFFECT ALL TAF SITES WITH LOWERING  
CEILINGS. SHOWERS ARE FORECAST TO DEVELOP AT FIRST AT TAF SITES KRDM  
AND KBDN AND KYKM AFTER 22Z THEN THE REMAINDER OF THE TAF SITES  
AFTER 04Z. LCL MVFR CONDITIONS COULD BE APPROACHED IN HEAVIER SHOWERS.  
IN ADDITION BRIEF GUSTY WINDS BETWEEN 20 TO 25 KTS IS POSSIBLE AT  
TAF SITES KRDM AND KBDN AFTER 18Z.  
 

 
   
PRELIMINARY POINT TEMPS/POPS
 
 
PDT 73 49 59 40 / 0 40 90 20  
ALW 73 52 59 42 / 0 30 90 20  
PSC 69 54 60 45 / 0 50 90 10  
YKM 63 47 61 37 / 10 90 70 10  
HRI 71 51 62 42 / 0 50 90 10  
ELN 60 45 57 35 / 10 90 70 10  
RDM 70 44 57 36 / 10 100 70 20  
LGD 68 50 58 40 / 10 20 100 40  
GCD 71 49 61 38 / 10 30 90 20  
DLS 68 52 61 45 / 10 100 70 40  
 

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

 
 

 
 
SHORT TERM...91  
LONG TERM....91  
AVIATION...91  
 
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