575  
FXUS66 KPDT 202123  
AFDPDT  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE PENDLETON OR  
123 PM PST THU FEB 20 2020  
   
SHORT TERM
 
 
TONIGHT THROUGH SATURDAY...THE LONG PERSISTENT RIDGE OF HIGH  
PRESSURE OVER THE REGION IS STARTING TO SLOWLY BREAK DOWN AND MOVE  
EASTWARD. AS IT DOES, THE FLOW WILL BECOME MORE ZONAL OVER THE  
AREA, HIGH CLOUDS WILL INCREASE THROUGH FRIDAY AND A WEAK AND DRY  
TROUGH WILL MOVE OVER THE AREA ON FRIDAY AS WELL. THEN, BY  
SATURDAY CLOUDS WILL CONTINUE TO LOWER AND THICKEN AS AN AREA OF  
LOW PRESSURE WILL APPROACH THE REGION FROM THE NORTHWEST. IT LOOKS  
LIKE ANY PRECIPITATION FROM THIS SYSTEM WILL WAIT UNTIL AFTER THE  
SHORT TERM PERIOD FOR MOST AREAS, THOUGH SOME LIGHT RAIN OR RAIN  
AND SNOW CAN NOT BE RULED OUT OVER THE CASCADE CREST AND THE  
EXTREME NORTHWESTERN AREAS BY LATE SATURDAY AFTERNOON/SATURDAY  
EVENING. SNOW LEVELS WILL INITIALLY BE FAIRLY HIGH, MAINLY  
3000-4000 FT NORTH AND 3500-4500 FEET SOUTH.  
 
FRIDAY MORNING STILL LOOKS COLD (THOUGH PROBABLY NOT AS COLD AS  
THE LAST FEW), AND WITH INCREASING CLOUDINESS, SATURDAY MORNING  
WILL LIKELY BE ON AVERAGE 4 TO 5 DEGREES WARMER. HIGHS THE FRIDAY  
WILL BE A COUPLE OF DEGREES ABOVE NORMAL AND ON SATURDAY, SHOULD  
BE EVEN A BIT WARMER THAN FRIDAY.  
   
LONG TERM
 
 
SUNDAY...SYSTEM IS STILL ON TRACK TO IMPACT THE REGION LATE  
SATURDAY NIGHT INTO MONDAY. FROM A SYNOPTIC VIEW, NORTH PACIFIC  
ENERGY WILL MOVE NE TOMORROW NIGHT INTO SATURDAY WHERE IT IS  
EXPECTED TO INTERACT WITH A MODEST TROUGH DIGGING SOUTH INTO THE  
GULF OF ALASKA. IN GENERAL, MODELS AGREE ON A MEDIUM STRENGTH  
ORGANIZED LOW PEAKING IN STRENGTH ALONG THE BRITISH COLUMBIA COAST  
SATURDAY NIGHT BEFORE WEAKENING AS IT MOVES INLAND ON SUNDAY.  
WHERE MODELS SEEM TO DISAGREE MOST IS IN TIMING, THE STRENGTH OF A  
WARM NOSE NUDGING ACROSS THE INLAND NORTHWEST, AND IN TOTAL QPF  
FOR THE SYSTEM. THESE DISAGREEMENTS IN DETAILS MAY BE RELATED TO  
PHASING ISSUES WITH THE MARITIME PACIFIC ENERGY AND THE ARCTIC  
TROUGH. SOME MODELS OR RUNS HAVE ADVERTISED A FASTER, OPEN WAVE  
SYSTEM WITH MODEST QPF BUT A LIMITED WARM NOSE WHILE THE TREND WE  
ARE SEEING TODAY, PARTICULARLY FROM THE 12Z GFS, IS FOR A SLOWER  
SYSTEM WITH HIGHER QPF BUT ALSO WARMER TEMPS/HIGHER SNOW LEVELS.  
DESPITE THE CONTINUED UNCERTAINTY IN DETAILS, THE BROAD STROKES OF  
THE SYSTEM ARE CLEAR: INCREASED MOISTURE AND CLOUD COVER WILL  
BEGIN PRECIPITATING ALONG THE WASHINGTON CASCADE CREST BY SUNDAY  
MORNING. WINDS WILL BE BREEZY IN THE GRANDE RONDE VALLEY AS  
SOUTHERLY WINDS ARE CHANNELED INTO THE LOW. SNOW IS LIKELY TO  
BEGIN IN THE BLUE MOUNTAINS BY SUNDAY AFTERNOON WHILE THE BASIN  
HOLDS ONTO RAIN CHANCES SUNDAY INTO SUNDAY NIGHT. SNOW LEVELS  
BEGIN QUITE HIGH LATE SATURDAY INTO SUNDAY, RANGING FROM 3000FT IN  
THE WA CASCADES TO NEAR 4000 IN THE BLUE MTNS, BUT THESE WILL  
GRADUALLY FALL THROUGH THE DAY SUNDAY TO 2000FT BY MONDAY. MOST  
MOUNTAIN PASSES ARE LIKELY TO EXPERIENCE AT LEAST MINOR IMPACTS  
FROM ACCUMULATING SNOW. A FRONTAL PASSAGE WILL INCREASE WINDS  
THROUGH THE COLUMBIA BASIN, CENTRAL OREGON, AND THE KITTITAS  
VALLEY ON SUNDAY.  
 
MONDAY THROUGH FRIDAY...PRECIP CHANCES DWINDLE FOR THE BASIN ON  
MONDAY WHILE MORE UNSTABLE AIRMASS BEHIND THE FRONT CONTINUES TO  
PROMOTE SNOW FOR THE BLUE AND WALLOWA MOUNTAINS THROUGH MUCH OF THE  
DAY. A RIDGE BUILDS IN TUESDAY YIELDING CLEAR AND COOL CONDITIONS.  
IT'S NOT CLEAR WHEN THIS RIDGE BREAKS DOWN NEXT WEEK AS SOME MODEL  
SOLUTIONS MAINTAIN SOME AMOUNT OF MID LEVEL RIDGING THROUGH MUCH OF  
THE WEEK WHILE OTHERS FLATTEN THE FLOW INTO MORE WESTERLY WINDS,  
WHICH WOULD PROMOTE SOME CLOUD COVER AND POSSIBLE HIGH MOUNTAIN  
SNOW. REGARDLESS, THE MID-WEEK PERIOD OF NEXT WEEK IS EXPECTED TO  
HOLD RELATIVELY BENIGN WEATHER.  
 

 
   
AVIATION
 
 
00Z TAFS...VFR CONDITIONS WILL CONTINUE THROUGH THE TAF PERIOD AND  
BEYOND. WINDS WILL GENERALLY BE LIGHT, THOUGH A BRIEF WIND GUST IN  
THE 10 TO 15 KT RANGE CAN NOT BE RULED OUT THROUGH THIS EVENING.  
OTHERWISE, MAINLY INCREASING HIGH CLOUDS ARE EXPECTED.  
 

 
   
PRELIMINARY POINT TEMPS/POPS
 
 
PDT 29 52 33 54 / 0 0 0 0  
ALW 30 51 35 55 / 0 0 0 0  
PSC 29 50 34 54 / 0 0 0 0  
YKM 28 49 33 53 / 0 0 0 0  
HRI 30 52 33 55 / 0 0 0 0  
ELN 27 44 31 49 / 0 0 0 0  
RDM 28 55 30 56 / 0 0 0 0  
LGD 23 41 28 49 / 0 0 0 0  
GCD 24 46 29 53 / 0 0 0 0  
DLS 31 51 35 55 / 0 0 0 0  
 

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

 
 

 
 
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