000 
FXUS66 KPDT 190418
AFDPDT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
800 PM PST WED DEC 18 2013

.SHORT TERM...AN UPPER LEVEL TROUGH AND COLD FRONT ARE MOVING 
THROUGH THE REGION THIS EVENING. EXPECT SOME LINGERING CLOUDS AND 
RAIN/SNOW SHOWERS FOR A WHILE THEN CLEARING LATER TONIGHT. AN UPPER 
RIDGE BUILDS IN FOR A SHORT TIME THURSDAY WITH CLEAR TO PARTLY 
CLOUDY SKIES. THE AIRMASS WILL BE MUCH COLDER AND HIGHS WILL ONLY BE 
IN THE 20S AND 30S. MID AND HIGH LEVEL CLOUDS WILL BE INCREASING 
THURSDAY NIGHT AS A WARM FRONT APPROACHES. THIS FRONT WILL MOVE 
THROUGH FRIDAY WITH SNOW...CHANGING OVER TO RAIN IN SOME LOCATIONS 
DURING THE DAY. SIGNIFICANT SNOW ACCUMULATIONS ARE EXPECTED OVER THE 
CASCADES AND NORTHEAST OREGON MOUNTAINS. STRONG WINDS ALOFT WILL 
ALSO CREATE BREEZY TO WINDY CONDITIONS. A NORTHWEST FLOW WILL 
CONTINUE TO PRODUCE SNOW OVER THE BLUES AND CASCADES INTO FRIDAY 
NIGHT. 94

&&

.PREV DISC... /ISSUED 229 PM PST WED DEC 18 2013/ 

SHORT TERM...TONIGHT THROUGH SATURDAY NIGHT...A WEAK DISTURBANCE 
WILL CLIP THE AREA TONIGHT AND BRING SNOW LEVELS DOWN TO THE SURFACE 
ACROSS ALL ZONES.  SNOWFALL WILL MAINLY BE OVER THE MOUNTAINS OF 
NORTHEAST OREGON...BUT THE FOOTHILLS OF THE BLUE MOUNTAINS MAY SEE A 
DUSTING TO AN INCH IN SOME AREAS.  HIGH PRESSURE WILL BEGIN TO BUILD 
IN BEHIND THE PREVIOUS SYSTEM AND DRY AIR WILL INTRUDE LATE TOMORROW 
MORNING INTO THE AFTERNOON.  PROGRESSIVE NORTHWEST FLOW WILL KEEP 
TEMPERATURES QUITE CHILLY AS HIGHS WILL STRUGGLE TO BE ABOVE 
FREEZING FOR THE LOWER ELEVATIONS...AND IN THE 20S FOR THE 
MOUNTAINS.  ALTHOUGH IT WILL BE COLD...THERE WILL AT LEAST BE A 
BREAK IN THE PRECIPITATION TOMORROW AS WE AWAIT THE NEXT SYSTEM ON 
FRIDAY AND INTO THE WEEKEND.  

FRIDAY ONWARD...A COMPLEX WEATHER SYSTEM WILL INVADE THE AREA THIS 
WEEKEND.  SNOW LEVELS WILL START OFF QUITE LOW FROM THE PREVIOUS 
SYSTEM...AND WILL GRADUALLY RAISE THROUGH THE WEEKEND.  AS NORTHWEST 
FLOW CONTINUES OVER THE AREA ON FRIDAY...A SURGE OF MOISTURE WILL 
ACCOMPANY IT.  TIMING OF THE ARRIVAL OF THIS MOISTURE HAS BEEN QUITE 
TRICKY...AS IT WILL AFFECT CERTAIN AREAS THAT COULD SEE SNOW 
CHANGING OVER TO RAIN...VERSUS NO SNOW AT ALL ON FRIDAY MORNING.  
THIS IS MAINLY FOCUSED ALONG THE FOOTHILLS OF THE BLUE MOUNTAINS.  
IF THE LATEST NAM SOLUTION FOLLOWS THROUGH...SOME OF THE AREAS ALONG 
THE FOOTHILLS OF THE BLUES COULD HAVE AN INCH OR TWO OF SNOW ON THE 
GROUND FOR THE FRIDAY MORNING COMMUTE.  

BY LATE FRIDAY MORNING THE WARM AIR ADVECTION WILL START TO MOVE 
INTO THE FORECAST AREA FROM THE WEST.  THIS IS DUE TO WARM AIR ALOFT 
MIXING DOWN FROM A STRONG MID AND UPPER LEVEL JET.  THESE WINDS WILL 
LIKELY RAINSHADOW OUT ANY PRECIPITATION CHANCE ACROSS THE BASIN AND 
GORGE AREAS.  IT IS POSSIBLE THAT SOME OF THE WINDS MAY NOT REACH 
THE SURFACE ACROSS THE WASHINGTON BASIN AREA.  IF PRECIPITATION WERE 
TO DEVELOP OVER THIS AREA AND THE COLD AIR REMAINS TRAPPED DUE TO 
THE LACK OF MIXING...THEN WILL HAVE TO CONSIDER THE POSSIBILITY OF 
MIXED PRECIPITATION IN THE FORM OF SLEET OR FREEZING RAIN.
  
ELSEWHERE...THE FOOTHILLS WILL MIX OUT THE COLD AIR AND IT SHOULD 
CHANGE TO RAIN SHOWERS BY LATE FRIDAY MORNING.  THE NORTHERN BLUE 
MOUNTAINS LOOK TO TAKE A BIT LONGER TO WARM UP AND SHOULD NOT CHANGE 
OVER TO RAIN UNTIL SOMETIME MID TO LATE SATURDAY MORNING.  DUE TO 
THE ABUNDANT PRECIPITATION EXPECTED TO FALL ACROSS THE NORTHEAST 
MOUNTAINS FRIDAY INTO SATURDAY...WILL BE ISSUING A WINTER STORM 
WATCH FOR SEVERAL NORTHEAST ZONES.  PLEASE REFER TO PRODUCT 
PDXWSWPDT FOR FURTHER DETAILS.  

WILL NEED TO KEEP AN EYE ON THE WINDS THAT WILL MIX OUT THE COLD 
AIR...AS WIND SPEEDS MAY BE STRONG ENOUGH TO REQUIRE HIGHLIGHTS 
FRIDAY INTO SATURDAY. WEBER 

LONG TERM...SUNDAY THROUGH WEDNESDAY...MODELS ARE SOMEWHAT IN 
AGREEMENT TO BEGIN THE EXTENDED BUT DIVERGE OVER TIME. INITIALLY 
MODELS PLACE US UNDER A FLAT RIDGE WITH SOME MOISTURE CLIPPING THE 
NORTHERN PORTION OF THE FORECAST AREA IN A WEST TO NORTHWEST FLOW. 
THIS WILL RESULT IN SOME PRECIPITATION CHANCES FOR THE CASCADES AND 
NORTHEAST MOUNTAINS BUT GENERALLY DRY FOR THE REST OF THE FORECAST 
AREA. MODELS BEGIN TO DIVERGE ON MONDAY AS THE GFS CONTINUES A FLAT 
RIDGE OVER THE REGION THROUGH THE EXTENDED PERIOD WHILE THE EUROPEAN 
DEVELOPS A TROUGH MOVING INTO WESTERN CANADA AND THE NORTHERN 
PACIFIC NORTHWEST. BY TUESDAY THE EUROPEAN BEGINS TO DIG THIS TROUGH 
INTO THE NORTHERN ROCKIES AND THEN IT SETTLES SOUTH INTO THE GREAT 
BASIN ON WEDNESDAY. OBVIOUSLY THE EUROPEAN WOULD WOULD TEND TO BE A 
COLDER SOLUTION WITH A MORE LIKELY SCENARIO FOR PRECIPITATION BUT 
WOULD LIKE TO SEE A LITTLE MORE MODEL AGREEMENT BEFORE BUYING OFF ON 
THE OVERALL EUROPEAN SOLUTION. THUS CONFIDENCE LEVEL FOR THE 
EXTENDED FORECAST IS LOW AT THIS POINT.  

AVIATION...0Z TAFS...A WEAK COLD FRONT WILL PASS OVER AND EXIT THE 
REGION THIS EVENING WITH VERY LITTLE IMPACT TO TAF SITES. EXPECT 
THIS TO BE A DRY FRONTAL PASSAGE FOR THE MOST PART WITH MAINLY VFR 
CONDITIONS. CLEARING WILL BEGIN TO TAKE PLACE BEHIND THE FRONTAL 
PASSAGE. WINDS WILL BE 5-15 KNOTS THIS EVENING THEN DECREASING 
OVERNIGHT.  

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  23  32  20  38 /  30  10  10  50 
ALW  26  34  23  37 /  30  10  10  50 
PSC  22  35  19  36 /  10   0  10  40 
YKM  22  36  20  37 /  10   0  10  50 
HRI  23  35  20  39 /  20   0  10  40 
ELN  21  35  20  37 /  10   0  20  50 
RDM  17  30  14  39 /  40  10  10  40 
LGD  23  28  19  31 /  50  20  10  80 
GCD  21  30  15  34 /  60  10  10  80 
DLS  28  41  24  40 /  10   0  20  50 

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...WINTER STORM WATCH FROM FRIDAY MORNING THROUGH SATURDAY MORNING 
     ORZ502.

     WINTER STORM WATCH FROM FRIDAY MORNING THROUGH LATE FRIDAY NIGHT 
     ORZ503.

     WINTER STORM WATCH FROM FRIDAY MORNING THROUGH SATURDAY MORNING 
     ORZ049-050.

WA...WINTER STORM WATCH FROM FRIDAY MORNING THROUGH SATURDAY MORNING 
     WAZ030.

&&

THREAT INDEX
THURSDAY : GREEN
FRIDAY : YELLOW
SATURDAY : YELLOW

GREEN: NONE OR LIMITED NEED FOR WATCHES, WARNINGS, OR ADVISORIES.
YELLOW: A FEW WATCHES, WARNINGS, OR ADVISORIES POSSIBLE OR IN EFFECT.
RED: NUMEROUS WATCHES, WARNINGS, OR ADVISORIES POSSIBLE OR IN EFFECT.

FOR ADDITIONAL WEATHER INFORMATION, CHECK OUR WEB SITE AT...
WWW.WEATHER.GOV/PENDLETON

$$

94/