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AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
1028 AM PDT THU SEP 18 2014

UPDATED AVIATION DISCUSSION

.UPDATE...THE CURRENT FORECAST REMAINS ON TRACK WITH JUST A FEW 
MINOR ADJUSTMENTS TO THE TODAY AND THIS EVENING PERIOD.  HAVE MADE 
SOME MINOR ADJUSTMENTS TO THE HIGHS TODAY...MAINLY ACROSS THE 
WESTERN PORTION OF THE CWA.  

EXPECT WINDY CONDITIONS ALONG THE KITTITAS VALLEY AND THE COLUMBIA 
RIVER GORGE TODAY...WITH THE BASIN AND FOOTHILL AREAS BEING BREEZY.  
EXPECT 20 MPH GUSTING TO 30 MPH FOR THE GORGE AND THE KITTIAS 
VALLEY...WITH 15 MPH GUSTING 25 MPH ELSEWHERE ACROSS THE BASIN.  
WINDS SHOULD BEGIN TO PICK UP AFTER NOON TODAY...AND ARE EXPECTED TO 
BE STRONGEST AROUND 5 PM DIMINISHING AFTER MIDNIGHT. 

HAVE ALSO PULLED BACK ON POPS TO GO MOSTLY SLIGHT CHANCE EAST OF THE 
CASCADE CREST.  THE SPLIT FLOW WILL CUT OFF MOST OF THE MOISTURE 
FROM THE TROUGH THAT WILL PROGRESS SOUTH ALONG THE CALIFORNIA COAST 
TODAY INTO TONIGHT.  SLIGHT CHANCE UPSLOPE SHOWERS CAN BE EXPECTED 
ACROSS THE NORTHEAST MOUNTAINS TODAY AND THIS EVENING.  HAVE 
MENTIONED SLIGHT CHANCE THUNDER ACROSS THE NORTHEAST MOUNTAINS 
THROUGH 5 PM...AS IT STILL CAN'T BE RULED OUT.  BUT ONCE THE WEST 
NORTHWEST FLOW SETS IN THIS EVENING...INSTABILITY WILL BE VERY 
LIMITED.  SO HAVE PULLED BACK ON THE THUNDER POTENTIAL TO JUST THE 
EAGLE CAPS...SOUTHERN GRANT...CROOK...AND DESCHUTES COUNTY FROM 5 TO 
8 PM THIS EVENING. WEBER 

.AVIATION...18Z TAFS...VFR CONDITIONS ARE EXPECTED TO PERSIST 
THROUGH THE NEXT 24 HOURS. THERE MAY BE SOME LIGHT SHOWERS AROUND 
THE REGION TODAY WITH THE REMOTE POSSIBILITY OF A THUNDERSTORM AT 
KRDM AND KBDN IN THE AFTERNOON AND EVENING...THEN PARTIAL CLEARING 
OVERNIGHT. WESTERLY WINDS WILL BE INCREASE SLIGHTLY TODAY AT 10 TO 
20 MPH THEN DECREASE OVERNIGHT. 

&&

.PREV DISC... /ISSUED 255 AM PDT THU SEP 18 2014/ 

SHORT TERM...TODAY THROUGH SATURDAY NIGHT...AN UPPER LEVEL TROUGH 
IS NEAR THE COAST AS IT SLOWLY SHIFTS EASTWARD. THE TROUGH IS 
SPLITTING AS IT MOVES INLAND WITH THE NORTHERN SECTION IN WASHINGTON 
AND THE SOUTHERN SECTION IN CALIFORNIA. THERE ARE TWO BANDS OF 
PRECIPITATION ON RADAR AND MODELS. ONE IS NEAR THE CASCADES ON THE 
EAST SIDE OF THE TROUGH AXIS AND THE SECOND ONE IS IN EASTERN GRANT 
COUNTY...WALLOWA COUNTY...AND BAKER COUNTY. HRRR SHOWS THE FIRST 
BAND REMAINING IN CENTRAL/NORTH CENTRAL OREGON AND CENTRAL 
WASHINGTON THIS MORNING. THE SECOND BAND IS ASSOCIATED WITH A JET 
STREAK. HRRR SHOWS THIS BAND REMAINING SEPARATE AND MOVING NORTHEAST 
OUT OF THE OREGON BY 16Z. THE MORNING FORECAST HAS THE TWO SEPARATE 
BANDS...THEN THE FIRST BAND WILL SPREAD ACROSS CENTRAL TO NORTHEAST 
OREGON AS THE TROUGH AXIS MOVES ACROSS EASTERN WASHINGTON AND OREGON 
THIS AFTERNOON. THE BEST INSTABILITY WILL MOVE FROM CENTRAL TO 
NORTHEAST OREGON WHERE THE DIFFLUENCE FROM THE SPLITTING TROUGH IS 
ADDED TO THE INSTABILITY AHEAD OF THE TROUGH. ISOLATED THUNDERSTORMS 
MAY DEVELOP IN THIS REGION DURING THE AFTERNOON AND EARLY EVENING. 
THE TROUGH AXIS WILL BE IN IDAHO BY 6Z/2300 PDT WITH RAIN SHOWERS 
ENDING EXCEPT FOR OROGRAPHIC SHOWERS NEAR THE CASCADE CREST. FRIDAY 
AND SATURDAY THE UPPER LEVEL RIDGE WILL BUILD OVER THE PACIFIC 
NORTHWEST WITH CLEARING SKIES AND WARMING DAYTIME TEMPERATURES. 
COONFIELD 

LONG TERM...SUNDAY THROUGH WEDNESDAY...00Z MODEL RUNS INDICATE VERY 
SIMILAR SOLUTIONS OVER FORECAST AREA AND NORTHEAST PACIFIC WITH A 
MID/UPPER LEVEL RIDGE OF HIGH PRESSURE CONTINUING OVER THE PACIFIC 
NORTHWEST SUNDAY AND MONDAY. MODELS SHOW CONSISTENT SOLUTIONS FOR 
TUESDAY AS WELL WITH THE RIDGE MOVING EAST INTO THE NORTHERN PLAINS 
BY DAYBREAK TUESDAY AS THE NEXT LONGWAVE TROUGH SPREADS EASTWARD TO 
130-140W. THE GFS IS MORE PROGRESSIVE IN TAKING THE AXIS OF AN OPEN 
LONGWAVE TROUGH TO 132W BY TUESDAY AFTERNOON WHEREAS THE ECMWF KEEPS 
THE LOWEST HEIGHTS IN THE OVERALL TROUGH NEAR 140W WHERE A CLOSED 
LOW WITH MUCH LOWER HEIGHTS DEVELOPS IN THE ECMWF SOLUTION. BOTH GFS 
AND ECMWF SHOW A VERY WEAK DISTURBANCE MOVING THROUGH FORECAST AREA 
MONDAY NIGHT AND TUESDAY SO I HAVE INCREASED POPS A TAD TO SLIGHT 
CHANCE FOR POSSIBLE ISOLATED LIGHT SHOWERS IN THE BLUE MOUNTAINS 
MONDAY NIGHT AND TUESDAY. THE TROUGH APPROACHES THE COAST TUESDAY 
NIGHT AND SPREADS INCREASING CLOUDS, MOISTURE, AND RAIN TO THE 
CASCADES JUST BEFORE DAYBREAK ON WEDNESDAY. THE PRECIPITATION 
SPREADS ACROSS FORECAST AREA WEDNESDAY MORNING. AS ALREADY 
MENTIONED, THE GFS IS FASTER IN TERMS OF BRINGING THE TROUGH AXIS TO 
THE COAST BY LATE WEDNESDAY MORNING WHILE THE ECMWF KEEPS THE TROUGH 
AXIS WELL OFFSHORE. THIS PHASING DIFFERENCE BETWEEN THE TWO MODELS 
ON WEDNESDAY WITH RESPECT TO THE PLACEMENT OF THE TROUGH AXIS 
RESULTS IN THE ECMWF TAKING LONGER TO SPREAD RAIN TO THE BLUE 
MOUNTAINS UNTIL LATE WEDNESDAY NIGHT OR THURSDAY MORNING. AS SUCH 
HAVE LOWER CONFIDENCE IN POP FORECAST FOR WEDNESDAY IN THE EASTERN 
SECTIONS OF FORECAST AREA.  POLAN



&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  80  55  80  52 /  20  10   0   0 
ALW  83  61  80  57 /  20  10   0   0 
PSC  85  57  85  51 /  10  10   0   0 
YKM  80  56  84  54 /  20  10   0   0 
HRI  83  55  85  48 /  10  10   0   0 
ELN  80  57  83  52 /  20  10   0   0 
RDM  76  43  79  40 /  20  20   0   0 
LGD  81  51  79  44 /  20  10   0   0 
GCD  78  49  81  47 /  20  10   0   0 
DLS  78  58  83  52 /  30  10   0   0 

&&

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

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

$$

89/99/99




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