Area Forecast Discussion
Issued by NWS Pendleton, OR

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853
FXUS66 KPDT 092244
AFDPDT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
143 PM PST TUE FEB 9 2016

.SHORT TERM...TONIGHT THROUGH FRIDAY...THE UPPER LEVEL RIDGE OVER
THE REGION IS BEGINNING TO WEAKEN AS WEATHER SYSTEMS OFF THE COAST
BUMP UP AGAINST IT. THE RIDGE WILL SLOWLY FLATTEN OVER THE NEXT
COUPLE OF DAYS ALLOWING A SOUTHWEST FLOW ALOFT TO BRING SOME
MOISTURE INTO THE REGION STARTING AS CLOUDS OVERNIGHT AND WEDNESDAY.
THERE WILL BE SOME LIGHT PRECIPITATION SPREADING INTO WESTERN
WASHINGTON AND OREGON ON WEDNESDAY EVENTUALLY REACHING THE
WASHINGTON CASCADES WEDNESDAY NIGHT AND THURSDAY. THE UPPER LEVEL
RIDGE WILL FINALLY BREAK DOWN ON FRIDAY ALLOWING A COLD FRONT TO
PUSH THROUGH THE FORECAST AREA FRIDAY INCREASING THE CHANCE OF
PRECIPITATION FOR THE ENTIRE AREA. SNOW LEVELS WILL REMAIN HIGH SO
EXPECTING MAINLY RAIN THROUGH FRIDAY.


.


.LONG TERM...FRIDAY NIGHT THROUGH TUESDAY...PRESSURE PATTERN ALOFT
ACROSS NORTHEAST PACIFIC AND THE PACIFIC NORTHWEST BECOMES VERY
PROGRESSIVE WITH A SERIES OF PACIFIC WEATHER SYSTEMS TRACKING
EASTWARD THROUGH THE REGION THROUGH THE PERIOD. AS SUCH SNOW LEVELS
WILL BE UNSEASONABLY HIGH RESULTING IN PRECIPITATION BEING IN THE
FORM OF RAIN EACH DAY. THE FIRST UPPER LEVEL TROUGH APPROACHES THE
CASCADES FRIDAY NIGHT AND THEN SWEEPS A STRONG COLD FRONT THROUGH
THE FORECAST AREA ON SATURDAY. TIGHTENING SURFACE PRESSURE GRADIENTS
ACCOMPANYING THE COLD FRONT WILL PRODUCE BREEZY CONDITIONS BEGINNING
SOON AFTER DAYBREAK ON SATURDAY MORNING WITH BREEZY WINDS CONTINUING
THROUGH SATURDAY AFTERNOON. THE UPPER LEVEL TROUGH EXITS INTO
IDAHO/MONTANA SATURDAY AFTERNOON FOLLOWED BY A FLAT UPPER LEVEL
RIDGE OF HIGH PRESSURE BUILDING OVER THE PACIFIC NORTHWEST SATURDAY
NIGHT, WHICH WILL USHER IN A WARM FRONT AND ATTENDANT WARM AIR
OVERRUNNING RAIN FOR SATURDAY NIGHT, WHICH THEN PERSISTS THROUGH
SUNDAY AFTERNOON. AS THE RIDGE AMPLIFIES SUNDAY NIGHT AND MONDAY...
GEORGE WASHINGTON`S BIRTHDAY...SINKING AIR ASSOCIATED WITH THE RIDGE
WILL YIELD DRY CONDITIONS AT LOWER ELEVATIONS AND A LOW CHANCE OF
RAIN OVER THE HIGHER MOUNTAINS. MONDAY NIGHT AND TUESDAY THE RIDGE
WILL STILL BE OVER THE INTERIOR PACIFIC NORTHWEST FOR DRY CONDITIONS
IN CENTRAL OREGON AND EAST CENTRAL OREGON, BUT WITH A LOW CHANCE OF
RAIN IN THE MOUNTAINS ON TUESDAY.  POLAN


&&

.AVIATION...VFR CONDITIONS WILL BE CONTINUE THROUGH THIS EVENING.
THEN A STRENGTHENING INVERSION WILL TRAP AND INCREASE MOISTURE IN
THE BOUNDARY LAYER PRODUCING LOW CIGS AND FOG DUE TO INCREASING
AREAL COVERAGE OF LOW STRATUS AND FOG IN THE LOWER COLUMBIA BASIN
AND ADJACENT VALLEYS BEGINNING AROUND MIDNIGHT AND CONTINUING WELL
PAST DAYBREAK ON WEDNESDAY. AS SUCH CONDITIONS ARE EXPECTED TO
DETERIORATE AT KYKM, KPSC, KRDM AND KBDN BECOMING VLIFR AT KRDM AND
KBDN, WITH KPSC AND KYKM BECOMING LIFR.

I KEPT KDLS, KPDT AND KALW AT VFR FOR THE NEXT 24 HOURS, AS GUIDANCE
SHOWED DOWNSLOPE DRAINAGE WINDS YIELDING MIXING IN COMBINATION WITH
A DRIER BOUNDARY LAYER INITIALLY, THESE FACTORS SHOULD WORK AGAINST
FORMATION OF FOG AND LOW STRATUS CLOUDS AT THOSE TAF SITES TONIGHT.
IF VISIBILITY DOES LOWER TO 5-6SM WITH LOCALIZED MVFR CONDITIONS AT
KDLS, KPDT AND KALW, THESE SITES WILL BE AMENDED OR THEIR FORECAST
UPDATED WITH NEW SCHEDULED TAF ISSUANCES LATER TODAY IF MODEL
FORECAST GUIDANCE CHANGES.

SURFACE WINDS LESS THAN 10 KTS FOR THE NEXT 24 HOURS.  POLAN


&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  30  46  34  50 /   0   0   0  10
ALW  31  46  35  50 /   0   0   0  10
PSC  28  47  32  47 /   0   0   0  10
YKM  29  50  32  48 /   0   0  10  20
HRI  28  46  33  49 /   0   0   0  10
ELN  20  34  27  37 /   0   0  10  20
RDM  28  60  32  59 /   0   0   0  10
LGD  34  46  34  47 /   0   0   0   0
GCD  33  56  33  52 /   0   0   0  10
DLS  32  50  37  50 /   0   0  10  20

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...AIR STAGNATION ADVISORY UNTIL 10 AM PST SATURDAY FOR ORZ041-044-
     050-502-503-505-507-508-510.

WA...AIR STAGNATION ADVISORY UNTIL 10 AM PST SATURDAY FOR WAZ024-
     026>029-520-521.

&&

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

$$

91/99/99



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