Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 270531 AAA
AFDPDT

AREA FORECAST DISCUSSION...UPDATE
NATIONAL WEATHER SERVICE PENDLETON OR
931 PM PST MON JAN 26 2015

UPDATED AVIATION DISCUSSION

.UPDATE...LOW STRATUS AND WIDESPREAD FOG REMAINS OVER THE LOWER
COLUMBIA BASIN AND ADJACENT VALLEYS TONIGHT. OBSERVATIONS HAVE
SHOWN VERY LITTLE VARIATION IN VISIBILITY OR CEILING HEIGHTS...SO
NO ADJUSTMENTS WERE NECESSARY WITH THE WEATHER GRIDS TONIGHT INTO
TOMORROW. A DENSE FOG ADVISORY REMAINS IN EFFECT UNTIL NOON
TUESDAY AS A RESULT. BREEZY CONDITIONS HAVE CONTINUED IN THE
SOUTHERN GRANDE RONDE VALLEY WITH SOME WIND GRID ADJUSTMENTS TO
ACCOUNT FOR LATEST OBSERVATIONS. OTHERWISE...CURRENT FORECAST IS
ON TRACK. BIEDA

.AVIATION...06Z TAFS...LOW STRATUS AND FOG WILL CONTINUE THRU 28/03Z
FOR KDLS...KPDT...KYKM...KALW AND KPSC.  AS A RESULT...LIFR TO IFR
CONDITIONS WILL PREVAIL AT THE AFOREMENTIONED TAF SITES.  KRDM AND
KBDN WILL HAVE CIG AOA 10K FT AGL AS MID AND UPPER LEVEL CLOUDS MOVE
IN AHEAD OF AN UPPER LOW AND PASSING TROUGH.  BEST CHANCE OF PCPN IS
EXPECTED ALONG THE CASCADES...WITH VERY LITTLE CHANCE AT TAF SITES.
PASSING WEATHER SYSTEMS WILL HELP FLATTEN THE RIDGE AND ERODE THE
INVERSION SOME WITH WESTERLY WINDS BTWN 5 TO 10 KTS ACROSS WESTERN
PORTION OF THE LOWER COLUMBIA BASIN.  THE FOG MAY BECOME BANKED
AGAINST THE BLUE MOUNTAINS AND KEEP KALW UNDER LIFR TO IFR
CONDITIONS AS A RESULT.  BIEDA

&&

.PREV DISC... /ISSUED 340 PM PST MON JAN 26 2015/

SHORT TERM...TONIGHT THROUGH THURSDAY...CURRENT RIDGE OF HIGH
PRESSURE OVER THE REGION WILL WEAKEN AND FLATTEN ON TUESDAY. THIS
FLAT RIDGE WILL REMAIN OVER THE REGION WEDNESDAY AND THURSDAY WITH
SOME CLOUDS PASSING OVERHEAD BUT NOT MUCH PRECIPITATION THREAT. THE
FLATTENING RIDGE WILL ALLOW SOME COOLER AIR ALOFT BACK INTO THE
REGION WHICH WILL WEAKEN THE INVERSION AND BRING COOLER TEMPERATURES
BACK TO THE AREAS THAT HAVE BEEN EXPERIENCING RECORD WARMTH. EXPECT
THE FOG AND LOW CLOUDS THROUGHOUT THE LOWER COLUMBIA BASIN TO
CONTINUE OVERNIGHT AND INTO TUESDAY AND POTENTIALLY INTO WEDNESDAY
BEFORE SEEING SOME IMPROVEMENT. MEANWHILE DENSE FOG ADVISORIES HAVE
BEEN ISSUED OR EXTENDED THROUGH NOON TUESDAY. THE WEAKENING HIGH
PRESSURE WILL ALSO WEAKEN THE PRESSURE GRADIENT OVER NORTHEAST
OREGON THAT IS PRODUCING THE VERY WINDY CONDITIONS IN THE SOUTHERN
GRANDE RONDE VALLEY. AS SUCH WILL LET THE WIND ADVISORY EXPIRE AT
THREE WITH DECREASING WINDS THROUGH THE EVENING AND OVERNIGHT.

LONG TERM...THURSDAY NIGHT THROUGH MONDAY NIGHT...THE PERIOD STARTS
OFF WITH AN UPPER LEVEL RIDGE SITUATED ALONG THE WEST COAST...THIS
WILL KEEP CONDITIONS DRY ACROSS THE CWA...WITH PATCHY AREAS OF FOG
AND FREEZING FOG EXPECTED THURSDAY NIGHT THROUGH SUNDAY IN THE
LOWER BASINS. FOR SATURDAY NIGHT THROUGH MONDAY NIGHT MODEL GUIDANCE
IS IN GOOD AGREEMENT THAT THE UPPER RIDGE WILL GRADUALLY BREAK DOWN
YIELDING A MUCH MORE ZONAL/MOIST FLOW FOR THE PAC NW. GUIDANCE IS
ALSO IN GOOD AGREEMENT THAT SEVERAL PERIODS OF PRECIPITATION WILL
AFFECT THE AREA DURING THIS TIME. WITH THE POTENTIAL FOR A STRONGER
SOUTHWESTERLY FLOW DECIDED TO TAKE OUT ANY MENTION OF FOG BY
MONDAY...THINKING THAT IT WOULD FINALLY BE SCOURED OUT OF THE LOWER
BASINS. AT THIS TIME SNOW LEVELS LOOK TO REMAIN FAIRLY HIGH AOA 4500
FEET AS 850MB TEMPERATURES HOVER BETWEEN 0 TO +5 CELSIUS NORTH AND
+3 TO +8  CELSIUS SOUTH. AT TIMES SNOW LEVELS MAY LOWER ENOUGH FOR
SOME SNOW TO FALL...MAINLY IN THE NORTH AND NORTHEASTERN PART OF THE
CWA. WINDS SHOULD BE LIGHT THROUGH THE FIRST HALF OF THE
EXTENDED...BEFORE INCREASING OUT OF THE SOUTH AND SOUTHWEST BY
SUNDAY AND MONDAY UP TO 10-20 MPH. WILL NEED TO WATCH FOR THE
POTENTIAL OF STRONGER WINDS IN THE GRANDE RONDE VALLEY IF THE
SOUTHERLY GRADIENT MATERIALIZES AS ADVERTISED BY TODAY`S GUIDANCE.
OVERALL TEMPERATURES ARE FORECAST TO BE NEAR OR SLIGHTLY ABOVE
AVERAGE FOR THE LOWER ELEVATIONS AND BASINS...AND ABOUT 10 DEGREES
ABOVE AVERAGE FOR THE MOUNTAINS AND HIGHER PLATEAUS INCLUDING MUCH
OF CENTRAL OREGON. 77

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  32  38  35  40 /   0   0   0   0
ALW  34  39  35  41 /   0   0  10  10
PSC  36  41  34  42 /   0   0   0   0
YKM  31  36  30  38 /   0   0  10   0
HRI  35  40  35  42 /   0   0  10   0
ELN  32  39  32  39 /   0  10  10   0
RDM  38  60  34  55 /   0   0   0  10
LGD  37  51  36  49 /   0   0  10  10
GCD  35  54  35  51 /   0  10  10  10
DLS  37  45  38  45 /  10  10  10  10

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...DENSE FOG ADVISORY UNTIL NOON PST TUESDAY ORZ041-044-507-508-510.

WA...DENSE FOG ADVISORY UNTIL NOON PST TUESDAY WAZ024-026>029-521.

&&

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

$$

98/77/98








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