522  
FXUS66 KPDT 200551 CCA  
AFDPDT  
 
AREA FORECAST DISCUSSION...UPDATED  
NATIONAL WEATHER SERVICE PENDLETON OR  
1051 PM PDT THU OCT 19 2017  
 
UPDATED AVIATION DISCUSSION  
   
UPDATE
 
A COLD FRONT IS STRETCHED ACROSS THE COLUMBIA BASIN  
SOUTH TO CENTRAL OREGON AT THIS TIME AND WILL BE MOVING EAST  
THROUGH THE NIGHT. RAIN IS PICKING UP IN THE COLUMBIA BASIN WITH  
THE FRONT BUT AS EXPECTED IS TAPERING OFF ALONG THE CASCADES WHICH  
ALLOWED THE EXPIRATION OF THE FLASH FLOOD WATCH FOR THE EAST  
SLOPES OF THE WASHINGTON CASCADES. RAIN WILL BECOME LIGHT AND  
SHOWERY IN THE COLUMBIA BASIN AFTER THE FRONT PASSES IN THE NEXT  
FEW HOURS. SNOW LEVELS REMAIN AROUND 8000 FEET AHEAD OF THE FRONT  
BUT WILL BE DROPPING TO 4000-4500 FEET BEHIND THE FRONT BY  
TOMORROW MORNING. WINDS HAVE BEEN RUNNING TO 10 TO 15 MPH BUT  
INCREASING TO 15 TO 25 MPH FOR A HOUR OR TWO WITH THE FRONT.  
FORECAST IS IN GENERALLY GOOD SHAPE. MADE SOME MINOR ADJUSTMENTS  
TO POPS, TEMPERATURES AND WINDS. UPDATE ALREADY OUT. PERRY  
 

 
 
AVIATION...06Z TAFS...A COLD FRONT WILL SWEEP ACROSS THE FORECAST  
AREA TONIGHT AND EXIT TO THE EAST BY FRIDAY MORNING. THERE WILL BE  
SOME LOWER CIGS AND RAIN ACROSS THE EASTERN HALF OF THE AREA TONIGHT  
ASSOCIATED WITH THE FRONTAL PASSAGE WITH SOME BRIEF PERIODS OF MVFR  
CONDITIONS. AT TAF SITES, ONLY KALW AND KPDT WILL HAVE CONTINUE TO  
HAVE A CHANCE FOR MVFR CONDITIONS THROUGH 08Z. CEILINGS WILL BE  
SCATTERED TO BROKEN ABOVE 5000 FEET AGL TOMORROW WITH SHOWERS IN THE  
MOUNTAINS THOUGH TAF SITES SHOULD REMAIN DRY WITH THE POSSIBLE  
EXCEPTIONS OF SHOWERS AT KALW, KPDT KRDM AND KBDN. WINDS 10-20 KTS  
OVERNIGHT FOR MOST SITES THEN INCREASING TO 15-30 KTS BEHIND THE  
COLD FRONT TOMORROW MORNING AND AFTERNOON. PERRY  
 

 
   
PREV DISCUSSION
 
/ISSUED 226 PM PDT THU OCT 19 2017/  
 
SHORT TERM...TONIGHT THROUGH SUNDAY...MAIN WEATHER CHALLENGES ARE  
THE HEAVY RAINFALL ON RECENT BURN AREAS ALONG EAST SLOPES OF THE  
WASHINGTON CASCADES, STRONG WIND POTENTIAL ON SATURDAY, AND EARLY  
SEASON SNOW IN THE CASCADES AND BLUES. MODELS ARE IN GOOD  
AGREEMENT AND CONFIDENCE IS HIGH FOR AN EXTENDED WET PERIOD WITH  
BOUTS OF BREEZY TO LOCALLY STRONG WIND.  
 
MODERATE TO OCCASIONALLY HEAVY RAIN CONTINUES AS OF 21Z ALONG  
EAST SLOPES BURN AREAS. AS COOLER AIR ARRIVES AFTER THE FRONT,  
THERE SHOULD BE LESS MOISTURE TO WORK WITH AND RAINFALL WILL  
DECREASE TO JUST A FEW HUNDREDTHS PER HOUR. ANOTHER ROUND OF  
PACIFIC MOISTURE WILL PROVIDE HEAVIER RAINFALL TO THE EAST SLOPES  
LATE FRIDAY THROUGH EARLY SUNDAY, DECREASING SUNDAY AFTERNOON.  
THERE IS CURRENTLY A FLASH FLOOD WATCH IN EFFECT INTO THIS EVENING  
AND ANOTHER MAY NEED TO BE ISSUED FOR THIS WEEKEND. IN THE BURN  
AREAS, 2 TO 4 INCHES OF PRECIPITATION ARE POSSIBLE THIS WEEKEND.  
 
THE STRONG WIND FLOW ALOFT WILL OCCASIONALLY CAUSE VERY WINDY  
CONDITIONS AT THE SURFACE OVER THE NEXT 3 DAYS, BUT SPECIAL CONCERN  
IS FOR SATURDAY AFTERNOON AND NIGHT WHEN A TIGHT SURFACE PRESSURE  
GRADIENT WILL COUPLE WITH THE STRONG WINDS IN THE LOWER ATMOSPHERE  
ACROSS MAINLY OREGON AND WASHINGTON COUNTIES ON THE OREGON BORDER. A  
WIND ADVISORY MAY BE NEEDED IN THIS AREA LATER ON.  
 
REGARDING THE SNOW...COLD AIR WILL BE NEAR THE EAST SLOPES  
CASCADES FRIDAY NIGHT AND SATURDAY MORNING WHEN THE NEXT ROUND OF  
PACIFIC MOISTURE ARRIVES AHEAD OF A WARM FRONT. THE SNOW LEVEL  
WILL AROUND 3700 FEET AND A QUICK 3 TO 5 INCHES OF SNOW MAY FALL  
BEFORE THE WARMER AIR ARRIVES. THIS WILL LIKELY AFFECT THE LAPINE  
AND SUNRIVER AREAS AND ROADS LEADING OVER THE CASCADES IN  
DESCHUTES AND JEFFERSON COUNTIES. SINCE THIS IS AN PRE-SEASON  
EVENT BEFORE STUDDED TIRES ARE IN USE, THRESHOLDS ARE LOWER AND A  
WINTER WEATHER ADVISORY MAY BE NEEDED. THIS MAY ALSO BE TRUE FOR  
THE BLUE MOUNTAINS AROUND TOLLGATE AND SKI BLUEWOOD FOR LATER ON  
SATURDAY.  
 
LONG TERM...SUNDAY NIGHT THROUGH THURSDAY...SUNDAY NIGHT MOIST  
WESTERLY FLOW WILL TRANSITION TO DRIER NORTHWEST FLOW AS AN UPPER  
LEVEL RIDGE BEGINS TO DEVELOP OFFSHORE AND MOVE INLAND. RAIN WILL  
TAPER OFF SUNDAY NIGHT AND EARLY MONDAY. THE UPPER LEVEL RIDGE WILL  
SLOWLY SHIFT EAST OVER THE REGION MONDAY THROUGH TUESDAY FOR WARMER  
AND DRY CONDITIONS. THE UPPER LEVEL RIDGE WILL COLLAPSE ON WEDNESDAY  
ALLOWING A NORTHWEST FLOW TO BRING A FAST MOVING COLD FRONT THROUGH  
THE REGION AND A CHANCE OF PRECIPITATION. AN OFFSHORE UPPER LEVEL  
RIDGE WILL REBUILD BACK CLOSER TO THE COAST FOR A DRY NORTHWEST FLOW  
ON THURSDAY.  
 

 
   
PRELIMINARY POINT TEMPS/POPS
 
 
PDT 45 59 40 57 / 100 30 10 80  
ALW 48 61 44 57 / 100 30 20 80  
PSC 48 62 41 57 / 90 10 10 80  
YKM 41 59 36 52 / 40 20 20 80  
HRI 46 62 40 58 / 100 10 10 80  
ELN 37 56 35 48 / 40 20 20 80  
RDM 36 51 33 56 / 80 30 50 80  
LGD 43 51 37 46 / 90 50 30 90  
GCD 41 51 36 48 / 90 50 30 90  
DLS 46 61 43 56 / 60 20 40 80  
 

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

 
 

 
 
83/91/83  
 
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