616 
FXUS66 KPDT 212246
AFDPDT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
246 PM PST SAT NOV 21 2009

.SHORT TERM...TONIGHT THROUGH MONDAY...THOUGHTS HAVE CHANGED LITTLE 
FROM THE PREVIOUS OVERNIGHT SHIFT. MODELS REMAINED VERY CONSISTENT 
WITH THE PROGRESSION OF THE SYSTEM ACROSS THE AREA. WITH A COUPLE OF 
PRONOUNCED ISSUES DEALT WITH TODAY.

FIRST, DECIDED TO FOLLOW THE SURFACE LOW AS SHOWN BY THE NAM WITH 
THE 18Z GFS NOW LENDING THE CLOSEST SUPPORT OF RECENT RUNS. THIS 
GIVES A VERY TIGHT PRESSURE GRADIENT ACROSS MOST OF THE AREA AS THE 
SURFACE LOW TRACKS ACROSS THE WASHINGTON CASCADES AND THE LOWER 
COLUMBIA BASIN BEFORE LIFTING NORTHEAST LATER TOMORROW. THESE 
GRADIENTS, COMBINED WITH A VERY STABLE LOWER LEVEL AIR MASS, WILL 
GIVE A PROLONGED PERIOD OF STRONG WINDS ALOFT DOWN TOWARD THE 
SURFACE. WILL ISSUE NUMEROUS WIND ADVISORIES AND HIGH WIND WARNINGS 
AS A RESULT.

THE SECOND ISSUE DEALS WITH SNOWFALL. SNOW LEVEL WILL BE SOMEWHAT 
VARIABLE WITH A BRIEF PERIOD OF WARM AIR ADVECTION AS WARM DIFFLUENT 
AIR CROSSES THE CASCADES TONIGHT. THE WASHINGTON CASCADES WILL SEE 
SIGNIFICANT ACCUMULATIONS MAINLY TONIGHT WITH THE MAJOR PASSES 
IMPACTED. DO THINK MAINLY WESTERN AREAS WILL BEAR THE BRUNT AFTER 
THE COLD FRONT PASSES LATER TONIGHT AND SUNDAY. THE BLUE MOUNTAINS 
WILL START SEEING ACCUMULATIONS LATER TONIGHT AT THE HIGHER 
ELEVATIONS AND PASSES BUT SNOW LEVELS WILL DROP AND ACCUMULATION 
RATES WILL INCREASE MAINLY TOMORROW AFTER THE COLD FRONT PASSES AND 
A NORTHWESTERLY FLOW DEVELOPS. BOTH AREAS WILL SEE SIGNIFICANT 
BLOWING SNOW BUT DONT HAVE THE CONFIDENCE TO GO WITH A BLIZZARD 
WARNING, BUT IT BEARS WATCHING HOWEVER.

OTHER MOUNTAIN AREAS WILL SEE SNOW AND MAYBE SOME BLOWING AS WELL, 
BUT SHOULD STAY BELOW ADVISORY AMOUNTS. PRECIPITATION SHOULD BEGIN 
TAPERING OFF ACROSS THE WEST BY TOMORROW AFTERNOON AND GRADUALLY 
TAPER OFF ACROSS THE EAST TOMORROW EVENING. /JBONK


.LONG TERM...MONDAY NIGHT THROUGH SATURDAY...A WEAK SYSTEM WILL 
BREAK UP MONDAY NIGHT IT RIDES OVER A BUILDING UPPER LEVEL RIDGE. 
THE BUILDING RIDGE WILL MOVE SLOWLY EAST OVER THE PACIFIC NORTHWEST 
TUESDAY. THE DEPARTING SYSTEM WILL COMBINE WILL UPSLOPE FLOW IN THE 
MOUNTAINS TO KEEP A SLIGHT CHANCE OF SHOWERS IN NORTHEAST OREGON 
TUESDAY. ALSO...SLOPOVER PRECIPITATION MAY OCCUR NEAR THE CASCADES.  
SUBSIDENCE ASSOCIATED WITH THE RIDGE WILL PROVIDE LIGHT WINDS AND 
CLEARING SKIES WITH THE STRONG SURFACE INVERSIONS TUESDAY NIGHT. IN 
THE LOWER COLUMBIA BASIN PATCHY FOG AND FREEZING FOG WILL FORM AT 
NIGHT UNDER THE INVERSIONS AND KEEP DAYTIME TEMPERATURES WEDNESDAY 
BELOW NORMAL. AT HIGHER ELEVATIONS THE SURFACE INVERSIONS WILL BREAK 
DURING THE DAY AND WARMER AIR ALOFT ASSOCIATED WITH THE RIDGE WILL 
REACH THE SURFACE TO PRODUCE LARGE DIURNAL TEMPERATURE SPREADS. 
WEDNESDAY NIGHT THROUGH FRIDAY THERE ARE DRAMATIC DIFFERENCES 
BETWEEN THE GFS AND ECMWF MODELS EVEN THOUGH BOTH HAVE SOUTHWEST 
FLOW AT 500 MB. THE 0Z ECMWF HAS A MORE PROGRESSIVE PATTERN WITH A 
FRONT AT AN ANGLE TO THE 500 MB FLOW THAT WILL MOVE INTO EASTERN 
WASHINGTON AND OREGON AND FORM A DEFORMATION ZONE OVER THE BLUE 
MOUNTAINS THAT DROPS HALF AN INCH OF RAIN THURSDAY. THE 12Z GFS HAS 
THE FRONT PARALLEL TO THE 500 MB FLOW SO IT REMAINS OFFSHORE UNTIL 
FRIDAY. THE GFS ENSEMBLE RUNS SHOW 500 MB FLOW RUNNING TO BOTH 
EXTREMES WITH NO CLUSTERING. DECIDED TO MAKE LITTLE CHANGE TO 
EXISTING FORECAST WITH A CHANCE OF POPS MOST PLACES AND LIKELY POPS 
OVER THE MOUNTAINS. THINK ECMWF IS OVERBLOWN WITH AMOUNT OF 
PRECIPITATION UNLESS THE DEFORMATION BAND DOES SET UP...BUT DID 
TREND TOWARD IT BY KEEPING AT LEAST A CHANCE OF POPS ACROSS THE 
AREA. WHEN THE 12Z RUN OF THE ECMWF ARRIVED IT WAS SLOWER WITH NO 
DEFORMATION BAND...BUT IT STILL SUPPORTED THE FASTER ARRIVAL OF THE 
FRONT DURING THE DAY THURSDAY. BOTH MODELS HAD PRECIPITATION FRIDAY 
WITH THE GFS PUSHING THE FRONT THROUGH AND THE ECMWF MOVING THE 
UPPER LEVEL TROUGH THROUGH. WITH LOW CONFIDENCE DUE TO MODEL 
DIFFERENCES KEPT A LOW CHANCE POPS ACROSS THE AREA SATURDAY.  
COONFIELD 

&&

.AVIATION...18Z TAFS...VFR CONDITIONS WILL PREVAIL IN MOST AREAS 
THROUGH 03Z WITH SCATTERED TO BROKEN MID LEVEL CEILINGS. ANOTHER 
PACIFIC WEATHER SYSTEM WILL MOVE INTO THE AREA TONIGHT AND EARLY 
SUNDAY MORNING WITH RAIN AND MOUNTAIN SNOW INCREASING. THIS WILL 
CAUSE AREAS OF MVFR CONDITIONS. IFR WITH POSSIBLY EVEN LIFR 
CONDITIONS IN LOCAL AREAS WITH RAIN AND SNOW...ESPECIALLY NEAR ANY 
MOUNTAIN RANGES OR OVER THE CENTRAL OREGON PLATEAUS NEAR TAF SITE 
KRDM. WINDS OF 10 TO 20 KTS WITH GUSTS TO 30 KTS FROM THE SOUTHWEST 
WILL BE COMMON IN ALL AREAS TODAY. HOWEVER THE WINDS WILL INCREASE 
OVERNIGHT TONIGHT AS PRESSURE GRADIENTS TIGHTEN UP AHEAD OF THE NEXT 
WEATHER SYSTEM. DURING THAT TIME WINDS ARE EXPECTED TO INCREASE TO 
AT LEAST 15 TO 25 KTS WITH GUSTS TO 40 KTS OR POSSIBLY EVEN HIGHER 
INTO SUNDAY. 76


.PRELIMINARY POINT TEMPS/POPS...
PDT  41  47  31  43 /  80  70  10  10 
ALW  39  48  32  43 /  90  80  10  10 
PSC  37  51  30  44 /  90  50  10  10 
YKM  32  45  29  44 /  90  40  10  10 
HRI  38  49  29  45 /  80  50  10  10 
ELN  34  39  26  39 /  90  70  10  20 
RDM  35  45  24  47 /  80  40  10  10 
LGD  36  42  23  40 /  80  80  20  10 
GCD  34  41  21  44 /  70  60  10  10 
DLS  37  49  32  47 /  80  40  20  10 

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...HIGH WIND WARNING FROM 7 PM THIS EVENING TO 10 AM PST SUNDAY FOR 
     ORZ049-050.

     WINTER STORM WARNING FROM 10 PM THIS EVENING TO 7 PM PST SUNDAY 
     FOR ORZ502.

     HIGH WIND WARNING FROM 1 AM TO 4 PM PST SUNDAY FOR ORZ042.

     WIND ADVISORY FROM 10 PM THIS EVENING TO 1 PM PST SUNDAY FOR 
     ORZ043.

     WIND ADVISORY FROM 10 PM THIS EVENING TO 7 PM PST SUNDAY FOR 
     ORZ501-504.

     WINTER WEATHER ADVISORY FROM 10 PM THIS EVENING TO 7 PM PST 
     SUNDAY FOR ORZ503.

     WIND ADVISORY FROM 4 AM TO 4 PM PST SUNDAY FOR ORZ041-044.

WA...WINTER WEATHER ADVISORY FROM 7 PM THIS EVENING TO 4 PM PST 
     SUNDAY FOR WAZ501-502.

     WINTER STORM WARNING FROM 10 PM THIS EVENING TO 7 PM PST SUNDAY 
     FOR WAZ030.

     WIND ADVISORY FROM 10 PM THIS EVENING TO 7 PM PST SUNDAY FOR 
     WAZ029.

     WIND ADVISORY FROM 4 AM TO 4 PM PST SUNDAY FOR WAZ024-028.

&&

THREAT INDEX
SUNDAY : RED
MONDAY : GREEN
TUESDAY : GREEN

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

$$

87/76/76

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