Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 100005 AAA
AFDPDT

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE PENDLETON OR
404 PM PST TUE FEB 9 2016

UPDATED AVIATION DISCUSSION

.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...00Z TAFS...VFR CONDITIONS WILL 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.

CONDITIONS AT KYKM WILL IMPROVE TO IFR BY AROUND 20Z-21Z TOMORROW.
CONDITIONS AT KPSC  WILL IMPROVE TO VFR BY 21Z.
CONDITIONS AT KRDM AND KBDN SHOULD IMPROVE TO VFR BY AROUND 16Z-17Z.

I KEPT KDLS, KPDT AND KALW AT VFR FOR THE NEXT 24 HOURS, AS GUIDANCE
SHOWED DOWNSLOPE DRAINAGE WINDS AND/OR MIXING IN THE BOUNDARY LAYER
IN COMBINATION WITH A DRIER BOUNDARY LAYER INITIALLY, SO 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 BASED IN NEW SCHEDULED TAF
ISSUANCES LATER THIS EVENING IF NEW 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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