616  
FXUS66 KPDT 240520  
AFDPDT  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE PENDLETON OR  
1020 PM PDT MON APR 23 2018  
 
UPDATED AVIATION DISCUSSION  
   
SHORT TERM...TONIGHT AND TUESDAY
 
RIDGE OF HIGH PRESSURE WILL  
CONTINUE TO BUILD OVER THE REGION PROVIDING CLEAR SKIES AND PLEASANT  
SPRING WEATHER CONDITIONS. MINOR CHANGES MADE TO TEMPERATURES AND  
WINDS FOR TONIGHT AND TUESDAY IN EVENING FORECAST UPDATE.  
   
AVIATION...06Z TAFS
 
VFR CONDITIONS WITH CLEAR SKIES FOR  
NEXT 24 HOURS. LIGHT WINDS OVERNIGHT AT ALL TAF SITES. LIGHT WINDS  
TUESDAY BUT SOME SE 10-15KT WINDS AT KBDN AND KRDM.  
POLAN  
 

 
   
PREV DISCUSSION
 
/ISSUED 427 PM PDT MON APR 23 2018/  
 
SHORT TERM...TONIGHT THROUGH THURSDAY NIGHT...A RIDGE OF HIGH  
PRESSURE WILL CONTINUE TO SHIFT EASTWARD OVER THE INLAND NORTHWEST  
TONIGHT WITH MOSTLY CLEAR SKIES AND LIGHT WINDS EXPECTED. A TROUGH  
EXTENDING FROM AN UPPER LEVEL LOW OVER THE HUDSON BAY WILL GRAZE  
EASTERN WASHINGTON DURING THE DAY WEDNESDAY WEAKENING THE RIDGE  
SLIGHTLY AND ALLOWING SCATTERED MID TO UPPER LEVEL CLOUDINESS TO  
MAKE A BRIEF APPEARANCE. THE RIDGE WILL RESTRENGTHEN AS THE TROUGH  
DEPARTS WEDNESDAY AFTERNOON. UNDER HIGH PRESSURE AND MOSTLY CLEAR  
SKIES HIGH TEMPERATURES WILL BE ON AN INCREASING TREND THROUGH  
THURSDAY WHEN HIGHS IN THE LOWER ELEVATIONS WILL REACH THE UPPER  
70S TO LOWER 80S - 10 TO 15F ABOVE NORMAL FOR THIS TIME OF YEAR.  
FOCUS THEN TURNS TO THE CUT-OFF LOW OFF THE COAST FORECAST TO BE  
CENTERED NEAR 40N 135W BY THURSDAY MORNING. 12Z OPERATIONAL GFS IS  
SIGNIFICANTLY SLOWER BRINGING THIS FEATURE ONSHORE THAN THE ECMWF,  
CANADIAN, AND A FEW GFS ENSEMBLE MEMBERS KEEPING THE REGION MOSTLY  
DRY THROUGH FRIDAY. HAVE OPTED TOWARD A BLEND FAVORING THE SLOWER  
ECMWF/CANADIAN SOLUTION WHILE RETAINING AN EXISTING SLIGHT CHANCE  
OF SHOWERS/THUNDERSTORMS FOR CENTRAL/NORTH CENTRAL OREGON THURSDAY  
NIGHT/FRIDAY MORNING TO GIVE SOME WEIGHT TO THE FASTER GFS  
SOLUTION AS CONSIDERABLE UNCERTAINLY REMAINS. PECK  
 
LONG TERM...FRIDAY MORNING THROUGH MONDAY...THE BIG QUESTION FOR  
FRIDAY THROUGH THE WEEKEND IS JUST HOW QUICKLY THE MID-UPPER LEVEL  
RIDGE OF HIGH PRESSURE ALONG THE ROCKIES ON FRIDAY GIVES WAY TO A  
LARGE MID-LEVEL LOW PRESSURE SYSTEM, WHICH WILL BE NEAR 41N/129W  
FRIDAY MORNING. OVER THE PAST THREE DAYS THE EXTENDED MODELS HAVE  
PREDICTED THAT THE RIDGE WILL EVENTUALLY BREAK DOWN OVER THE  
FORECAST AREA DURING THE TIME FRAME OF FRIDAY AND SATURDAY. SOME OF  
THE MODELS FAVOR THE AFOREMENTIONED UPPER LEVEL LOW UNDERCUTTING THE  
RIDGE BY TAKING A MORE SOUTHERLY TRACK ACROSS NORTHERN CALIFORNIA  
AND THE GREAT BASIN, WHICH WOULD ALLOW WRAP AROUND MOISTURE TO BRING  
SHOWERS TO THE FORECAST AREA. AS SUCH THE FORECAST FOR FRIDAY  
THROUGH SUNDAY AFTERNOON IS FOR A CHANCE OF SHOWERS THROUGH THE  
WEEKEND. THE AIRMASS HAS MARGINAL INSTABILITY FRIDAY MORNING INTO  
FRIDAY EVENING FOR A SLIGHT CHANCE OF THUNDERSTORMS FROM DAYBREAK  
FRIDAY THROUGH FRIDAY EVENING. MONDAY LOOKS TO BE DRY DUE TO A DRIER  
AIRMASS MOVING INTO THE PACIFIC NORTHWEST ON THE HEELS OF A  
NORTHWEST FLOW ALOFT. POLAN  
 

 
   
PRELIMINARY POINT TEMPS/POPS
 
 
PDT 38 74 44 77 / 0 0 0 0  
ALW 39 76 47 79 / 0 0 0 0  
PSC 38 77 44 81 / 0 0 0 0  
YKM 40 75 45 79 / 0 0 0 0  
HRI 37 77 44 81 / 0 0 0 0  
ELN 37 71 43 76 / 0 0 0 0  
RDM 29 74 37 80 / 0 0 0 0  
LGD 35 68 40 74 / 0 0 0 0  
GCD 37 70 41 76 / 0 0 0 0  
DLS 42 78 47 82 / 0 0 0 0  
 

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

 
 

 
 
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