473 
FXUS66 KPDT 211743 AAA
AFDPDT

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE PENDLETON OR
943 AM PST SAT NOV 21 2009

UPDATED AVIATION DISCUSSION

.UPDATE...RELATIVELY FEW CHANGES MADE TO TODAY'S FORECAST WITH
PRIMARY FOCUS BEING DIRECTED ON THE APPROACHING SYSTEM AFFECTING
TONIGHT AND TOMORROW. AN EARLY LOOK AT THE 12Z RUNS SHOW RATHER
GOOD CONTINUITY FROM THE NAM AND GFS REGARDING POSITION OF THE
SURFACE LOW SO WILL NEED TO WORK OUT THE DIFFERENCES AND RELATIVE
IMPACTS. AS PREVIOUSLY STATED, THE SPECIFIC TRACK OF THE LOW WILL
DETERMINE THE DIFFERENCE BETWEEN ADVISORY AND WARNING AMOUNTS AND
WIND SPEEDS. RECENTLY RELEASED PRECIPITATION ESTIMATES FROM
NESDIS INDICATE AVAILABLE MOISTURE AND RAIN RATES ARE LESS THAT
HAVE BEEN SEEN WITH THE MOST RECENT SYSTEM SO MAY BE LEANING
TOWARD THE OVERALL DRIER NAM QPF, BUT THIS MODEL STILL BRINGS
SIGNIFICANT QPF TO THE NORTHERN BLUE MOUNTAINS AFTER A BRIEF
PERIOD OF MODERATE PRECIP MAINLY TO THE WASHINGTON PORTION OF THE
CWA. /JBONK

&&

.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

&&

.PREV DISCUSSION... /ISSUED 300 AM PST SAT NOV 21 2009/ 

SHORT TERM...TODAY THROUGH SUNDAY...THE BACK SIDE OF A VERY SHARP 
AND DEEP UPPER TROUGH CONTINUES TO MOVE ACROSS THE REGION EARLY THIS 
MORNING. THE ENERGY DIGGING DOWN THE BACK SIDE OF THE TROUGH IS 
KEEPING A FEW SHOWERS...MOSTLY SNOW...GOING OVER PORTIONS OF THE 
AREA...ESPECIALLY ALONG AND JUST EAST OF THE CASCADES. AS THIS 
TROUGH EXITS THE AREA THIS MORNING SHOULD SEE THESE SHOWERS WIND 
DOWN FURTHER...TO MAINLY A FEW ALONG THE CASCADE CREST. A POTENT 
SYSTEM IS CURRENTLY TAKING SHAPE OUT ALONG 150W THIS MORNING. THIS 
SYSTEM WILL SWING ACROSS THE REGION LATE TONIGHT AND ON SUNDAY. 
THERE IS A CHANCE THAT A SURFACE LOW WILL FORM OFF THE NORTHWEST 
OREGON COAST LATE TONIGHT AND THEN MOVE EAST ACROSS WASHINGTON STATE 
SUNDAY. THERE IS SOME UNCERTAINTY AS TO THE TRACK OF THIS SURFACE 
LOW AS SOME DATA POINTS TO IT SWINGING MORE NORTHEASTWARD THROUGH 
WESTERN WASHINGTON INTO BRITISH COLUMBIA. THE TRACK OF THIS SURFACE 
LOW WILL DETERMINE THE WEATHER CONDITIONS OVER OUR AREA SUNDAY. IF 
THE LOW MOVES INTO THE INTERIOR NORTHWEST AS SOME DATA SUGGESTS THEN 
WE WOULD SEE STRONG WINDS OVER CENTRAL OREGON...THE BLUE MOUNTAIN 
FOOTHILLS...THE GRANDE RONDE VALLEY AND WALLOWA COUNTY. ALSO THERE 
WOULD BE SIGNIFICANT PRECIP OVER MANY AREAS AS THE SYSTEM MOVES 
THROUGH. ALSO THERE WOULD BE WESTERLY UPSLOPE FLOW BEHIND THE 
SYSTEM. A QUICK CUT OFF OF PRECIP IN THE LEE OF THE CASCADES DUE TO 
THE WEST FLOW WOULD LIMIT SNOW ALONG THE CASCADE EAST SLOPE ZONES. 
MEANWHILE THE UPSLOPE FLOW INTO THE BLUE MOUNTAINS WOULD ALLOW 
CONSIDERABLE POST SYSTEM SNOW ACCUMULATIONS. THE ALTERNATE SOLUTION 
REDUCES THE WIND RISK ACROSS THE AREA...AND ALTERS THE FOCUS OF 
PRECIP AND SNOW ACCUMULATIONS AWAY FROM THE BLUES AND TO THE 
WASHINGTON CASCADE EAST SLOPES. AT THIS TIME WILL SIDE WITH THE 
SOLUTIONS (NAM AND EUROPEAN) THAT ADVERTISE THE SURFACE LOW TRACKING 
EAST INTO THE INTERIOR NORTHWEST. AS SUCH WILL ISSUE WIND AND WINTER 
STORM WATCHES FOR THE AREAS MENTIONED ABOVE THAT WOULD BE AFFECTED 
BY THE EASTERLY TRACK. WILL ONLY GO WITH WATCHES THOUGH DUE TO THE 
CONTINUED UNCERTAINTY. 90 

LONG TERM...SUNDAY NIGHT THROUGH NEXT SATURDAY...A WEATHER SYSTEM 
WILL BE DEPARTING THE FORECAST AREA SUNDAY NIGHT WHILE AN UPPER 
RIDGE BUILDS OVER THE REGION. THIS WILL PUSH MOST OF THE MOISTURE 
WITH ANY NEW SYSTEMS THAT TRY TO MOVE INTO THE PACIFIC NORTHWEST UP 
INTO SW CANADA AND EXTREME NW WASHINGTON. AS A RESULT OUR FORECAST 
AREA WILL SEE MOSTLY DRY CONDITIONS WITH JUST ISOLATED TO SCATTERED 
SHOWERS IN THE MOUNTAINS. THIS SCENARIO WILL PERSIST THROUGH 
THURSDAY. THERE WILL BE PATCHY FOG DEVELOPMENT IN THE USUAL LOW 
AREAS OF THE LOWER COLUMBIA BASIN AND ESPECIALLY ALONG THE LARGER 
RIVERS SUCH AS THE COLUMBIA...YAKIMA AND SNAKE RIVERS. A PACIFIC 
TROUGH WILL THEN MOVE INTO THE REGION AGAIN ON FRIDAY AND FRIDAY 
NIGHT BRINGING ANOTHER CHANCE OF RAIN AND MOUNTAIN SNOW. THERE IS 
CONSIDERABLE MODEL DIFFERENCES THAT FAR OUT IN THE EXTENDED PERIOD 
SO WILL NOT MAKE ANY CHANGES TO THE CURRENT FORECAST WHICH IS 
ALREADY REPRESENTATIVE FOR THAT SYSTEM. 88 

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  48  37  47  31 /  10  80  70  10 
ALW  49  38  48  32 /  10  80  70  10 
PSC  52  36  51  30 /  10  80  50  10 
YKM  49  32  48  29 /  10  80  40  10 
HRI  50  35  49  29 /  10  80  50  10 
ELN  46  32  45  26 /  20  80  50  10 
RDM  44  34  45  24 /  20  70  40  10 
LGD  43  36  43  22 /  20  80  80  20 
GCD  42  33  42  21 /  10  70  60  10 
DLS  50  37  49  32 /  20  80  40  20 

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...HIGH WIND WATCH FROM LATE TONIGHT THROUGH SUNDAY AFTERNOON FOR 
     ORZ501-504.

     WINTER STORM WATCH FROM LATE TONIGHT THROUGH SUNDAY AFTERNOON 
     FOR ORZ502.

     HIGH WIND WATCH FROM THIS EVENING THROUGH SUNDAY MORNING FOR 
     ORZ042-043.

     HIGH WIND WATCH FROM 7 PM PST THIS EVENING THROUGH SUNDAY 
     MORNING FOR ORZ049-050.

WA...HIGH WIND WATCH FROM LATE TONIGHT THROUGH SUNDAY AFTERNOON FOR 
     WAZ029.

     WINTER STORM WATCH FROM LATE TONIGHT THROUGH SUNDAY AFTERNOON 
     FOR WAZ030.

&&

THREAT INDEX
TODAY : RED
SUNDAY : RED
MONDAY : 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

National Weather Service Glossary of Abbreviations

Expanded Version (without abbreviations)