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AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
800 PM PDT MON AUG 31 2015

.SHORT TERM...TONIGHT THROUGH WEDNESDAY AFTERNOON...SATELLITE WATER
VAPOR IMAGERY LOOP SHOWS A LONG WAVE TROUGH CENTERED ALONG 130W
WITH A SERIES OF DISTURBANCES MOVING THROUGH THE LONG WAVE
MID/UPPER LEVEL CYCLONIC CIRCULATION ASSOCIATED WITH THE LONG WAVE
TROUGH. THE FIRST ONE MOVING THROUGH SOUTHERN BC IS DRAGGING MID
AND HIGH CLOUDS ACROSS THE CWA THIS EVENING. ANOTHER ONE IS POISED
TO ROUND THE BASE OF THE LONG WAVE TROUGH NEAR 131W AND HAS A
DRIER AIR MASS ASSOCIATED WITH IT, AND YET ANOTHER ONE, THE
STRONGEST BY FAR, NEAR 57N/141W IN THE EASTERN GULF OF ALASKA. THE
LAST DISTURBANCE WILL DROP DOWN THE WESTERN FLANK OF THE LONG WAVE
TROUGH OVER THE NEXT 36 HOURS, THUS DIGGING THE LONG WAVE TROUGH
FARTHER SOUTH AND ALLOWING WEAK DYNAMIC LIFT TO ENTER THE FORECAST
AREA ON WEDNESDAY IN COMBINATION WITH OROGRAPHIC LIFT OVER THE
HIGHER MOUNTAINS FOR A CHANCE OF SHOWERS DURING THE DAY ON
WEDNESDAY IN THE BLUE MOUNTAINS AND ALONG THE EAST SLOPES OF THE
CASCADES. DRY CONDITIONS WILL PERSIST ELSEWHERE FOR TONIGHT
THROUGH WEDNESDAY AFTERNOON.  POLAN

&&

.PREVIOUS DISCUSSION... /ISSUED 212 PM PDT MON AUG 31 2015/ 

SHORT TERM...TONIGHT THROUGH THURSDAY...A BROAD UPPER LEVEL 
TROUGH OVER THE PACIFIC NORTHWEST WITH A WESTERLY FLOW WILL KEEP 
MOST OF THE FORECAST AREA DRY EXCEPT FOR SOME SHOWERS ALONG THE 
CASCADE CREST THROUGH TUESDAY. THEN SOME ENERGY DROPPING INTO THE 
TROUGH WILL LEAD TO THE TROUGH DIGGING SOUTHWARD TUESDAY NIGHT AND 
WEDNESDAY. THIS WILL PUSH A COLD FRONT TROUGH THE FORECAST AREA WITH 
A BAND OF PRECIPITATION ASSOCIATED WITH IT TUESDAY NIGHT AND 
WEDNESDAY. THE PRECIPITATION IS LIKELY TO SKIP OVER THE LOWER 
ELEVATIONS BUT THE MOUNTAINS COULD END UP SEEING SOME LIGHT 
ACCUMULATIONS. BY THURSDAY THE UPPER LEVEL TROUGH IS SETTLING OVER 
THE REGION BUT THERE IS SOME MODEL UNCERTAINTY. HAVE INDICATED A 
TREND TOWARDS MORE SHOWER ACTIVITY THURSDAY BELIEVING THE INCREASED 
INSTABILITY ASSOCIATED WITH THE TROUGH WILL LEAD TO A BETTER CHANCE 
OF PRECIPITATION ACROSS MOST OF THE FORECAST AREA. HIGH TEMPERATURES 
WILL BEGIN TO COOL ON WEDNESDAY AND BY THURSDAY WILL BE 10 TO 15 
DEGREES BELOW NORMAL. 

LONG TERM...THURSDAY NIGHT THROUGH MONDAY...ACTIVE WEATHER 
PATTERN THROUGH PERIOD AND MODELS NOT IN AGREEMENT BEGINNING 
SUNDAY. UPPER LEVEL LOW PRESSURE AREA TO DROP SOUTH FROM BC INTO PAC 
NW ON FRIDAY. THAT MUCH MODELS AGREE UPON.  THIS WILL BRING 
UNSETTLED...COOLER...AND SHOWERY CONDITIONS INTO ALL AREAS FOR 
FRIDAY AND SATURDAY. ENOUGH INSTABILITY FOR THUNDERSTORMS FRIDAY.
BY SUNDAY...GFS OPENS UPPER LOW INTO A WAVE AND EJECTS INTO IDAHO AND
MONTANA...WHILE GFS/CANADIAN HAVE STRONG JET LEVEL WINDS DIVING 
SOUTH ON WEST SIDE OF LOW AND KEEPING IT ANCHORED OVER SOUTHERN 
OREGON FOR ABOUT 12-18 HOURS LONGER BEFORE MOVING EAST.
SO WITH THIS IN MIND I HAVE KEPT CHANCE POPS GOING LONGER ACROSS 
EASTERN ZONES...ESPECIALLY WALLOWA COUNTY TO ACCOUNT FOR POSSIBLE 
WRAPAROUND MOISTURE AFTER LOW MOVES INTO ID/MT. IF EC/CANADIAN 
MODELS PROVE CORRECT...SIGNIFICANT PRECIPITATION COULD OCCUR.  FOR 
NOW WILL JUST INCREASE POPS UNTIL MODELS COME INTO AGREEMENT. 

AVIATION...00Z TAFS...VFR CONDITIONS TO PREVAIL WITH GENERALLY DRY 
WESTERLY FLOW ALOFT AND ONLY SCT200 AND LIGHT SFC WINDS EXCEPT
G20 AT KDLS TIL 05Z.

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  52  79  55  72 /   0   0  20  20 
ALW  59  80  60  75 /   0   0  20  20 
PSC  58  83  58  76 /   0   0  10  10 
YKM  51  75  51  71 /  10  10  10  10 
HRI  55  81  57  75 /   0   0  10  10 
ELN  53  77  52  71 /  10  10  20  20 
RDM  42  78  46  70 /   0   0  10  10 
LGD  48  82  48  71 /   0   0  10  20 
GCD  46  85  48  72 /   0   0  10  20 
DLS  59  80  58  75 /   0  10  20  20 

&&

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

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

$$

99/91/79

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