Area Forecast Discussion
Issued by NWS Pendleton, OR

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000
FXUS66 KPDT 220239
AFDPDT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
733 PM PDT SUN SEP 21 2014

.SHORT TERM...UPPER LOW OVER NEVADA HAS SPREAD MID AND HIGH LEVEL
CLOUDS INTO THE FORECAST AREA TODAY. EXPECT THIS TO CONTINUE
OVERNIGHT WITH SKIES PARTLY TO MOSTLY CLOUDY. A SMALL AREA OF
INSTABILITY OVER CENTRAL OREGON RESULTED IN SCATTERED SHOWERS AND
THUNDERSTORMS OVER DESCHUTES COUNTY LATE AFTERNOON INTO EARLY
EVENING. THESE ARE NOW DISSIPATING WITH SUNSET. THE UPPER LOW WILL
DRIFT ACROSS IDAHO ON MONDAY. THIS COMBINED WITH AN APPROACHING
TROUGH ALONG THE COAST WILL KEEP SKIES PARTLY TO MOSTLY CLOUDY.
SCATTERED SHOWERS OR THUNDERSTORMS ARE POSSIBLE...MAINLY OVER THE
MOUNTAINS IN THE AFTERNOON. TEMPERATURES WILL BE 3-7 DEGREES COOLER
THAN TODAY.   94

&&

.PREV DISC... /ISSUED 335 PM PDT SUN SEP 21 2014/

SHORT TERM...TONIGHT THROUGH TUESDAY NIGHT...AN UPPER LEVEL TROUGH
OVER THE EASTERN PACIFIC WILL GRADUALLY DEEPEN AND SHIFT EAST
THROUGH THIS PERIOD. AS A RESULT, THE PACIFIC NORTHWEST WILL BE
UNDER AN UPPER LEVEL SOUTHWEST FLOW THROUGH THE PERIOD. CURRENTLY A
CUT OFF LOW IS OVER CENTRAL NEVADA. THIS LOW WILL MOVE INTO SOUTHERN
IDAHO THIS EVENING, THEN EAST TO WYOMING ON MONDAY. THIS LOW HAS
PUSHED VARYING AMOUNTS OF HIGH CLOUDINESS OVER THE AREA. IT HAS ALSO
CAUSED A SLIGHT INCREASE IN LOW LEVEL MOISTURE OVER THE MOUNTAINS OF
DESCHUTES, CROOK AND GRANT COUNTIES. A STRAY SHOWER MAY DEVELOP LATE
THIS AFTERNOON AND THIS EVENING OVER THESE MOUNTAINS. FOR NOW WILL
HOLD OFF ON ADDING A MENTION OF SHOWERS LATE THIS AFTERNOON AND
EVENING IN THESE AREAS, THOUGH LOCAL UPDATES MAY BE NEEDED. A WEAK
WAVE IS EXPECTED TO DRIFT NORTHEAST ACROSS THE REGION LATE TONIGHT
INTO MONDAY MORNING. THIS WAVE MAY CAUSE A FEW SHOWERS OVER THE
WALLOWA MOUNTAINS LATE TONIGHT INTO MONDAY MORNING. ALSO A FEW
SHOWERS MAY DEVELOP ALONG THE WASHINGTON CASCADE EAST SLOPES MONDAY
MORNING. ANOTHER WAVE IS EXPECTED TO MOVE ACROSS THE REGION MONDAY
AFTERNOON AND NIGHT. THIS WAVE WILL KEEP A FEW SHOWERS GOING NEAR
THE CASCADE CREST MONDAY AFTERNOON AND EVENING. INSTABILITY LOOKS TO
BE STRONG ENOUGH FOR A FEW THUNDERSTORMS TO DEVELOP FROM CROOK
COUNTY EAST TO GRANT COUNTY, AND NORTHEAST ACROSS THE BLUES, GRANDE
RONDE VALLEY AND WALLOWA COUNTY. SHOWERS MAY ALSO SPREAD INTO THE
BLUE MOUNTAIN FOOTHILLS MONDAY NIGHT. SHOULD ALSO SEE SHOWERS LINGER
OVER OUR EASTERN MOST ZONE LATE MONDAY NIGHT INTO TUESDAY MORNING. A
COLD FRONT ASSOCIATED WITH THE UPPER TROUGH WILL BEGIN TO MOVE
TOWARDS THE PACNW COAST TUESDAY INTO TUESDAY NIGHT. THIS FRONT WILL
SLOWLY PUSH CHANCES OF RAIN INTO THE CASCADE EAST SLOPES TUESDAY
AFTERNOON AND NIGHT. HIGH TEMPS WILL COOL A BIT EACH DAY THROUGH
TUESDAY, BUT WILL CONTINUE TO BE ABOVE SEASONAL VALUES. VARYING
AMOUNTS OF CLOUD COVER WILL KEEP LOW TEMPS SEASONALLY MILD. 90

LONG TERM...WEDNESDAY THROUGH SUNDAY.  THERE IS CONSIDERABLE
UNCERTAINTY IN THE EXTENDED FORECAST...ESPECIALLY THIS WEEKEND...DUE
TO THE DIFFERENCES IN THE MEDIUM RANGE MODELS. THE STRONG HIGH
PRESSURE RIDGE OVER THE PACIFIC NW WILL SHIFT EASTWARD IN RESPONSE
TO A DEVELOPING LOW OFFSHORE.  THE FORECAST AREA WILL BE UNDER A SW
FLOW ALOFT WEDNESDAY AND WEDNESDAY NIGHT...AND A SLOW MOVING PACIFIC
FRONT WILL GRADUALLY SPREAD PRECIPITATION EAST OF THE CASCADES
DURING THAT TIME.  ON THURSDAY...THE TROUGH WILL FORCE INTO WA/OR
WITH THE AXIS OF THE TROUGH JUST OFFSHORE. SCATTERED TO NUMEROUS
SHOWERS ARE FORECAST FOR THURSDAY.  LAPSE RATES WILL STEEPEN...AND
THERE COULD BE EMBEDDED THUNDERSTORMS OVER CENTRAL AND NORTHEAST
OREGON DURING THE AFTERNOON.  PRECIPITATION FROM THURSDAY NIGHT
THROUGH FRIDAY MORNING WILL MAINLY BE CONFINED TO THE CASCADES AND
THE EASTERN MOUNTAINS WITH ONLY A SLIGHT CHANCE ELSEWHERE.
INSTABILITY SHOWERS ARE POSSIBLE IN ALL AREAS ON FRIDAY BUT THE
THREAT OF THUNDERSTORMS IS MINIMAL AND ONLY OVER EASTERN WALLOWA
COUNTY.  THE BIGGEST UNCERTAINTY IN THE FORECAST IS OVER THE
WEEKEND.  THE ECMWF CONTINUES TO ADVERTISE THE DEEPENING OF THE
TROUGH INTO A CLOSED LOW OVER CALIFORNIA SATURDAY AND
SUNDAY...WRAPPING MOISTURE ACROSS EASTERN OREGON AND SOUTHEAST
WASHINGTON.  THE GFS CONTINUES TO ADVERTISE THE TROUGH SHIFTING
EASTWARD FOLLOWED BY HIGH PRESSURE FOR A DRY AND WARM WEEKEND.
THERE IS SIGNIFICANT SPREAD IN THE ENSEMBLES FROM BOTH THE GFS AND
ECMWF...SO WILL KEEP 20-30 PERCENT CHANCE OF PRECIPITATION IN OUR
SOUTHERN ZONES AND 10-20 PERCENT NORTH TO COMPROMISE BOTH SOLUTIONS.
WISTER

AVIATION...00Z TAFS...WINDS WILL BE AOB 15 KTS FOR THE NEXT 24
HOURS. CIRRUS CLOUDS HAVE DEVELOPED ACROSS CENTRAL AND NORTHEAST
OREGON AND WILL SPREAD NORTHWARD THIS EVENING. MID LEVEL ALTOCUMULUS
AND/OR ALTOSTRATUS CLOUDS WILL INCREASE OVERNIGHT. BY 06Z TONIGHT IN
CENTRAL OREGON AND 12Z MONDAY MORNING ELSEWHERE...THERE WILL BE
VARIABLE MID AND HIGH LEVEL CLOUDS WITH BKN-OVC CIGS AOA 10,000 FEET
AGL. WISTER

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  59  83  56  80 /   0  10  20  10
ALW  64  84  62  81 /   0  10  20  10
PSC  58  85  59  82 /   0  10  10   0
YKM  57  83  55  76 /   0  10  10  10
HRI  57  86  57  82 /   0  10  10   0
ELN  57  84  55  77 /   0  10  10  10
RDM  48  81  47  78 /   0  10  10  10
LGD  56  81  53  81 /   0  20  40  20
GCD  52  84  52  81 /  10  20  30  10
DLS  60  83  57  79 /   0  10  10  10

&&

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

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

$$

94





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