Area Forecast Discussion
Issued by NWS Pendleton, OR

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000
FXUS66 KPDT 210525
AFDPDT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
1025 PM PDT MON OCT 20 2014

UPDATED AVIATION DISCUSSION

.SHORT TERM...TONIGHT AND TUESDAY...A COLD FRONT IS SLOWLY WORKING
ITS WAY WEST TO EAST ACROSS THE FORECAST AREA. CURRENTLY IT
STRETCHES FROM THE HANFORD AREA SOUTH TO SOUTHERN OREGON.
PRECIPITATION ALONG THE FRONT IS BEING ENHANCED BY A SHORTWAVE
COMING ONTO THE SOUTHWEST COAST OF OREGON. THIS FRONT WILL SLOWLY
MOVE EASTWARD OVERNIGHT AND THEN EXIT THE AREA EARLY TUESDAY. WILL
SEE RAIN SHIFT EASTWARD WITH THE FRONT THUS HAVE INCREASED CHANCE OF
PRECIPITATION ACROSS THE EASTERN HALF OF THE FORECAST AREA FOR THE
REST OF TONIGHT. WITH THE FRONT EXITING EARLY TUESDAY WILL SEE
SHOWERS ON THE DECREASE OVER FAR EASTERN OREGON TO JUST A SLIGHT
CHANCE BY AFTERNOON. REST OF THE FORECAST AREA WILL BE PARTLY CLOUDY
AND COOL FOLLOWING THE FRONTAL PASSAGE.

.AVIATION...06Z TAFS...MAINLY VFR CONDITIONS EXPECTED AT ALL TAF
SITES THROUGH THE PERIOD...WITH SOME LCL MVFR CONDITIONS POSSIBLE AT
TIMES OVERNIGHT...ESPECIALLY AT KALW AND KPDT DUE TO RAIN SHOWERS. A
TROUGH PASSAGE OVERNIGHT WILL USHER IN SOME WESTERLY WINDS TUESDAY
OF 10 TO 20 KNOTS ALONG WITH DECREASING LOW AND MID LEVEL CLOUDS.
ANOTHER SYSTEM WILL APPROACH LATE TUESDAY ONCE AGAIN INCREASING MID
AND HIGH LEVEL CLOUDS.

&&

.PREV DISC... /ISSUED 450 PM PDT MON OCT 20 2014/

SHORT TERM...TONIGHT THROUGH THURSDAY. TWO UPPER LEVEL SYSTEMS WILL
IMPACT THE FORECAST AREA DURING THE SHORT TERM.  THE FIRST UPPER
LEVEL TROUGH IS OFFSHORE...AND A SOUTH FLOW ALOFT AHEAD OF THE
SYSTEM IS PREVENTING THE TROUGH FROM SHIFTING EASTWARD.  THE TROUGH
IS SPLITTING WITH THE STRONGEST ENERGY OFF THE SW OREGON COAST.
PRECIPITATION HAS DEVELOPED IN THE EASTERN VALLEYS OF THE CASCADES
AND WILL GRADUALLY SPREAD ACROSS THE FORECAST AREA OVERNIGHT.  DUE
TO THE STRONGEST ENERGY TO THE SOUTH...THE SOUTHERN BLUES AND JOHN
DAY-OCHOCO HIGHLANDS WILL LIKELY RECEIVE 0.1"-0.25" OF RAIN
OVERNIGHT.  THE TROUGH WILL SWING TO THE NORTHEAST AS IT MOVES INTO
IDAHO EARLY TUESDAY MORNING...AND SIMILAR PRECIPITATION AMOUNTS ARE
FORECAST OVER THE NORTHERN BLUES AND WALLOWAS.  THERE WILL BE A
BREAK BETWEEN SYSTEMS TUESDAY AND TUESDAY EVENING BEFORE THE NEXT
UPPER LEVEL SYSTEM MOVES ONSHORE TUESDAY NIGHT.  THIS SYSTEM IS
CURRENTLY STRENGTHENING BETWEEN 140-150W OVER THE GULF OF
ALASKA...AND WATER VAPOR LOOPS CLEARLY SHOW A SIGNIFICANT MOISTURE
TAP FROM THE REMAINS OF TYPHOON VONGFONG. RAIN WILL ALSO BE SLOW TO
SPREAD EASTWARD...AS THE UPPER LEVEL FLOW IS PARALLEL TO THE
FRONT...AND WILL EVENTUALLY DEVELOP OVER ALL AREAS BY WEDNESDAY
NIGHT.  A COLD FRONT WITH THE SYSTEM WILL LOWER SNOW LEVELS DOWN TO
6000-6500 FEET ALONG THE CASCADES THURSDAY.  48-HOUR PRECIPITATION
AMOUNTS FROM WEDNESDAY MORNING THROUGH FRIDAY MORNING ARE AROUND
0.25"-0.75" WITH THE HEAVIEST AMOUNTS IN THE MOUNTAINS.  WISTER

LONG TERM...THURSDAY NIGHT THROUGH MONDAY NIGHT...THE PERIOD STARTS
OFF RATHER WET AND UNSETTLED ACROSS THE AREA. BOTH THE 20/12Z ECMWF
AND 20/12Z GFS AGREE THAT A PLUME OF DEEP...SUBTROPICAL MOISTURE
ALONG WITH A STRONG UPPER LEVEL JET WILL BE POINTED AT THE PAC NW
DURING THIS PERIOD. THIS WILL LEAD TO PLENTY OF CLOUDS AND A GOOD
CHANCE FOR RAIN...OR SNOW ABOVE 5000 TO 7000 FEET THURSDAY NIGHT
INTO EARLY FRIDAY. BY LATE FRIDAY INTO SATURDAY A DEVELOPING UPPER
LEVEL LOW SHOULD TURN THE FLOW MORE SOUTHERLY...PERHAPS LEADING TO A
SHORT BREAK IN THE ACTIVE WEATHER. BY SATURDAY NIGHT INTO SUNDAY THE
UPPER LEVEL DISTURBANCE MOVES OVER THE REGION BRINGING INCREASES
CHANCES FOR SHOWERS AND COOLER TEMPERATURES. SNOW LEVELS SHOULD ALSO
LOWER TO BETWEEN 5000 TO 6000 FEET DURING THIS TIME. FOLLOWING THIS
SYSTEM...WHAT APPEARS TO BE A RATHER WEAK AND TRANSIENT UPPER LEVEL
RIDGE WILL TRY TO BUILD BACK INTO THE AREA ON MONDAY. HIGH
TEMPERATURES ARE FORECAST TO BE RIGHT AROUND AVERAGE FOR THIS TIME
OF YEAR THROUGHOUT THE PERIOD...WITH LOW TEMPERATURES RUNNING NEAR
TO SLIGHTLY ABOVE AVERAGE DUE TO THE INCREASED CLOUD COVER/MOISTURE.
77



&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  47  65  44  67 /  90  20  10  50
ALW  51  65  48  66 / 100  20  10  40
PSC  49  67  46  65 /  90  10  10  60
YKM  43  62  44  59 /  20  10  30  80
HRI  47  67  44  66 /  90  10  10  60
ELN  44  63  44  57 /  20  10  60  90
RDM  37  60  40  63 /  20  10  10  60
LGD  44  58  39  60 /  90  60  10  30
GCD  43  57  40  63 /  90  20  10  20
DLS  49  66  47  62 /  20  10  30  80

&&

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

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

$$

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