Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 181855 AAA
AFDPDT

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE PENDLETON OR
1050 AM PST THU DEC 18 2014

UPDATED AVIATION DISCUSSION

.SHORT TERM...MORNING UPDATE...THE AIR MASS ACROSS THE BASIN
CONTINUES TO BECOME INCREASINGLY MIXED DUE TO THE PASSAGE OF WEAK
SYSTEMS. FOG IS PATCHY AT MOST ACROSS THE BASIN THIS MORNING, AND
EXPECT SOME PATCHES TO LINGER THROUGH THE DAY. STILL COVERAGE IS NOT
EXPECTED TO BECOME WIDESPREAD IN ANY AREA, THUS DO NOT EXPECT ANY
NEW FOG ADVISORIES AT THIS TIME. ALSO WILL ALLOW THE AIR STAGNATION
ADVISORY TO CONTINUE TO IT`S CURRENT EXPECTED END TIME TOMORROW
MORNING. ANOTHER WEAK SYSTEM IS MOVING THROUGH THE REGION AND WILL
CONTINUE TO PRODUCE SPOTTY SHOWERS. A MORE VIGOROUS SYSTEM IS
APPROACHING THE COAST. EXPECT TO SEE AN INCREASE IN SHOWER CHANCES
OVER CENTRAL AND NORTH-CENTRAL OREGON THIS AFTERNOON, AND INCREASED
POPS. THIS SYSTEM WILL MOVE ACROSS THE AREA TONIGHT, BRINGING PRECIP
TO MOST LOCATIONS. SNOW LEVELS LOOK TO MAINLY RUN BETWEEN 4000 AND
5000 FEET WITH THIS SYSTEM, THOUGH THEY COULD BE AS LOW AS 2500 FEET
OVER WESTERN KITTITAS COUNTY. 90

.AVIATION...18Z TAFS...MVFR CONDITIONS WILL OCCUR AT KYKM AND KDLS
DUE TO LOW STRATUS. CONDITIONS SHOULD IMPROVE THIS AFTERNOON. AN
APPROACHING WEATHER SYSTEM WILL START TO SPREAD RAIN AFTER 03Z/19TH
TO ALL TAF SITES. CONDITIONS WILL DETERIORATE A FEW HOURS AFTER
03Z/19TH TO IFR/MVFR, WITH SOME LIFR UNDER MODERATE TO HEAVY RAIN.
WINDS WILL BE AOB 10 KTS THROUGHOUT THE TAF PERIOD.  POLAN

&&

.LONG TERM...PREVIOUS DISCUSSION...AN ACTIVE WEATHER PATTERN IS
EXPECTED DURING THE FORECAST PERIOD WITH SEVERAL STORM SYSTEMS SET
TO IMPACT THE AREA. A 150 KT ZONAL JET IS EXPECTED TO LINE UP WITH
THE PACIFIC NORTHWEST SUNDAY AND MONDAY. THE RIGHT JET EXIT
REGION...SYNONYMOUS WITH SINKING AIR...IS PRESENTLY PROGGED TO BE
OVER THE CWA SUNDAY AND MONDAY WITH THE POTENTIAL FOR A LEE SIDE
TROUGH TO SETUP DOWNWIND OF THE CASCADES. THEREFORE...CONCERN EXISTS
FOR A HIGH WIND EVENT BUT TIMING FROM RECENT MODEL RUNS HAS DELAYED
THE POTENTIAL START OF THE EVENT TO SUNDAY NIGHT INTO MONDAY. WILL
CONTINUE TO MONITOR OR THE POTENTIAL FOR HIGH WINDS ACROSS THE CWA
AND HAVE CHANGED THE FORECAST TO INDICATE STRONGEST WIND POTENTIAL
INTO MIDDAY SUNDAY INTO EARLY MONDAY TIMEFRAME. THE OTHER ITEM OF
NOTE DURING THE UPCOMING WEEKEND IS THE POTENTIAL FOR A STEADY
STREAM OF MOISTURE INTO THE AREA WITH RAINFALL SATURDAY NIGHT THRU
MONDAY THAT CAN BE HEAVY AT TIMES. QPF TOTALS COULD BE IN EXCESS OF
2 INCHES IN THE MOUNTAINS WITH BETWEEN A QUARTER TO HALF AN INCH IN
LOW LYING AREAS. GIVEN THE STRONG WINDS AND A WARM FRONT EXPECTED TO
MOVE IN SUNDAY...TEMPERATURES WILL RISE INTO THE MID 40S TO LOWER
50S IN THE COLUMBIA BASIN AND UPPER 30S TO MID 40S ALONG THE HIGHER
ELEVATIONS. THIS WILL TRANSLATE TO A MOSTLY RAIN PRECIPITATION
EVENT...THOUGH SNOW MAY STILL FALL ALONG THE HIGHEST MOUNTAIN PEAKS.

A LONGWAVE RIDGE WILL SETUP OFF THE PACIFIC COAST MONDAY NIGHT
BRINGING A NORTHWEST FLOW TO THE AREA. SHORTWAVE TROUGHS WILL STILL
RIDE OVER THE RIDGE INTO THE REGION BRINGING A CHANCE OF
PRECIPITATION FAVORING THE HIGHER ELEVATIONS THROUGH EARLY
WEDNESDAY. A TROUGH ORIGINATING FROM THE GULF OF ALASKA AND BRITISH
COLUMBIA IS PROGGED TO MOVE SOUTHEAST INTO OUR REGION WEDNESDAY WITH
A SHOT OF ARCTIC AIR EXPECTED. THIS WILL DROP TEMPERATURES 10
DEGREES ON WEDNESDAY...CHRISTMAS EVE...WITH THE POSSIBILITY OF SNOW
LEVELS DROPPING DOWN TO THE COLUMBIA BASIN FLOOR.

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  42  33  43  35 /  10  60  70  20
ALW  43  35  44  37 /  10  60  80  20
PSC  44  34  46  36 /  10  60  70  10
YKM  41  33  44  32 /  20  70  60  10
HRI  43  33  45  36 /  10  60  70  20
ELN  39  33  43  32 /  20  70  60  10
RDM  46  32  47  31 /  30  60  60  20
LGD  46  35  49  31 /  20  40  80  20
GCD  44  32  46  35 /  20  40  80  20
DLS  45  37  48  39 /  20  70  70  30

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...NONE.
WA...AIR STAGNATION ADVISORY UNTIL 10 AM PST FRIDAY WAZ026>028.

&&

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

$$

90/99/98





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