916  
FXUS66 KPDT 172334  
AFDPDT  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE PENDLETON OR  
320 PM PST SUN DEC 17 2017  
   
SHORT TERM...TONIGHT THROUGH WEDNESDAY
 
ONE WEAK WAVE IN NORTHWEST  
FLOW ALOFT HAS EXITED TO THE EAST EARLY THIS AFTERNOON, WITH ANOTHER  
IMPULSE CLIPPING SOUTHERN WA/NORTHERN OR THIS AFTERNOON/EVENING.  
RADAR SHOWS AREAS OF RAIN AND MOUNTAIN SNOW, WITH SNOW LEVELS RISING  
TO 3000-4000 FEET ACROSS THE EASTERN MOUNTAINS. EXPECT CHANCES OF  
PRECIPITATION TO CONTINUE THROUGH TUESDAY AS SEVERAL WAVES IN  
WESTERLY FLOW ALOFT CLIP THE AREA, WITH A SURFACE COLD FRONT  
ENTERING THE AREA ON TUESDAY. THE GREATEST POPS WILL BE USED ACROSS  
THE IMMEDIATE CASCADE CREST AND THE NORTHEAST MOUNTAINS, WHERE  
LIKELY TO CATEGORICAL POPS WILL BE USED. THE LOWER ELEVATIONS WILL  
SEE SIGNIFICANTLY LOWER COVERAGE, WITH CHANCE POPS FOR THE FOOTHILLS  
AND SLIGHT CHANCE POPS TO DRY WEATHER FOR THE BASIN DOWN TO THE  
DESCHUTES PLATEAU. SNOW LEVELS IN THE 4000-6000 FEET RANGE CAN BE  
EXPECTED THROUGH TUESDAY, THUS EXPECT ANY SNOW ACCUMULATIONS AT PASS  
LEVELS TO REMAIN UNDER ADVISORY CRITERIA. LOW LEVEL WINDS WILL  
BECOME BREEZY AND FROM THE SW ON MONDAY/TUESDAY, ALLOWING FULL  
SCOURING OF THE PREVIOUSLY COLD AIRMASS. MILD TEMPERATURES WILL  
RESULT, WITH HIGHS IN THE LOWER ELEVATIONS IN THE UPPER 40S TO MID  
50S, WITH LOWS IN THE UPPER 30S/LOWER 40S. EXPECT MAINLY 40S FOR  
HIGHS IN THE MOUNTAINS EARLY WEEK WITH LOWS GENERALLY IN THE 20S TO  
LOWER 30S.  
 
TUESDAY NIGHT/WEDNESDAY...COOLER AIR BEGINS TO WORK INTO THE REGION  
BEHIND A COLD FRONT, WITH SNOW LEVELS FALLING TO 2500-3500 FEET  
TUESDAY EVENING, FALLING FURTHER TO 1500-2500 FEET BY WEDNESDAY.  
WITH THE UPPER TROUGH AXIS MOVING ACROSS THE INTERIOR PACIFIC  
NORTHWEST, WILL CONTINUE HIGH POPS FOR THE FOOTHILLS AND MOUNTAINS  
WITH MAINLY LIKELY POPS. THINK ALL LOCATIONS WILL RECEIVE SOME  
PRECIP WITH CHANCE POPS FOR MOST LOWER ELEVATION LOCATIONS. PRECIP  
AMOUNTS DO NOT LOOK VERY HIGH, 0.05-0.15 INCHES FOR THE LOWER  
ELEVATIONS, WITH 0.25-0.50 FOR THE HIGHER ELEVATIONS. GIVEN THE  
COOLER AIR AND LOWER SNOW LEVELS, THIS WILL YIELD UNDER ADVISORY  
ACCUMULATIONS FOR THE MOUNTAINS, WITH PERHAPS A DUSTING OR SO FOR  
THE FOOTHILLS. LOWS TUESDAY NIGHT WILL RANGE FROM 30-35 FOR THE  
LOWER ELEVATIONS WITH 20S IN THE MOUNTAINS. HIGHS WEDNESDAY WILL BE  
SIGNIFICANTLY COOLER THAN MONDAY/TUESDAY, WITH UPPER 30S/LOWER 40S  
FOR THE LOWER ELEVATIONS AND 30-35 FOR THE MOUNTAINS.  
   
LONG TERM
 
WEDNESDAY NIGHT THROUGH FRIDAY NIGHT. MODELS IN GOOD  
AGREEMENT FOR THIS PERIOD. UPPER LOW WILL BE EXITING THE REGION  
WED NIGHT. LIGHT SNOW WILL LINGER INTO THE EVENING OVER THE  
NORTHEAST MOUNTAINS WITH CLOUDY SKIES. OTHERWISE THE REMAINDER OF  
THE FORECAST AREA WILL HAVE GRADUAL CLEARING OVERNIGHT. UPPER  
LEVEL RIDGE OVER THE REGION THURSDAY WITH PARTLY CLOUDY SKIES AND  
COOLER TEMPERATURES. AN UPPER LEVEL TROUGH AND STRONG COLD FRONT  
WILL THEN MOVE THROUGH THE AREA LATE THU NIGHT INTO FRIDAY. THIS  
WILL BRING A PERIOD OF SNOW ESPECIALLY ALONG THE COLD FRONTAL  
BOUNDARY. MUCH COLDER TEMPERATURES WILL FOLLOW FRI NIGHT INTO THE  
WEEKEND. 94  
 
SATURDAY AND SUNDAY...A SUBSTANTIAL PUSH OF COLD AND DRY AIR WILL  
ENTER THE REGION SATURDAY MORNING YIELDING BREEZY TO LOCALLY WINDY  
CONDITIONS ACROSS THE LOWER COLUMBIA BASIN AS A SIGNIFICANT PORTION  
OF WINDS 35-45 MPH AT 2000-3000 FT AGL MIXES TO THE SURFACE. WINDS  
WILL GRADUALLY SLACKEN THROUGH SUNDAY MORNING. HIGHS TEMPERATURES ON  
SATURDAY AND SUNDAY WILL BE IN THE LOWER 20S TO LOWER 30S, 10 TO 15  
DEGREES BELOW NORMALS. UNDER PARTLY CLOUDY SKIES, LOWS WILL DROP  
INTO THE UPPER TEENS IN THE LOWER COLUMBIA BASIN AND UPPER SINGLE  
DIGITS IN THE SOUTHERN HIGHLANDS ON SATURDAY NIGHT. WITH LIGHTER  
WINDS EXPECTED ON CHRISTMAS EVE TEMPERATURES WILL DROP VERY QUICKLY  
AFTER SUNSET ESPECIALLY IN THOSE AREAS WITH SNOW COVER. NEAR TO  
BELOW ZERO IN THE SOUTHERN HIGHLANDS AND MOUNTAINS, UPPER SINGLE  
DIGITS TO LOWER TEENS IN THE FOOTHILLS, AND LOWER TO MID TEENS IN  
THE LOWER COLUMBIA BASIN. AT THIS TIME IMPACTS TO CHRISTMAS TRAVEL  
APPEAR TO BE MINIMAL OUTSIDE OF THE LOW TEMPERATURES. 74  
 

 
   
AVIATION
 
00Z TAFS. CEILINGS TONIGHT INTO MONDAY MAINLY 040-080  
WITH A MID LEVEL CLOUD DECK AT 100-150. A FRONT MOVING SLOWLY  
SOUTHWARD INTO THE REGION MONDAY WILL BRING AN INCREASE IN RAIN  
SHOWERS LATE MORNING INTO THE AFTERNOON FOR THE COLUMBIA BASIN TAF  
SITES. BDN RDM LIKELY TO REMAIN DRY. WINDS 5-10KT TONIGHT AND 5-15KT  
MON. 94  
 

 
   
PRELIMINARY POINT TEMPS/POPS
 
 
PDT 38 53 39 54 / 20 30 30 20  
ALW 40 53 41 53 / 30 50 50 50  
PSC 41 55 42 53 / 20 10 30 40  
YKM 35 50 36 49 / 10 20 30 40  
HRI 38 54 39 53 / 10 10 20 20  
ELN 35 47 35 44 / 20 20 40 50  
RDM 32 50 33 51 / 10 0 10 30  
LGD 35 44 37 45 / 40 30 30 20  
GCD 37 47 37 49 / 10 10 10 10  
DLS 41 53 41 52 / 10 30 20 40  
 

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

 
 

 
 
80/94/94/74  
 
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