Area Forecast Discussion
Issued by NWS Pendleton, OR

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000
FXUS66 KPDT 211155 AAA
AFDPDT

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE PENDLETON OR
454 AM PDT TUE APR 21 2015

UPDATED AVIATION DISCUSSION

.SHORT TERM...TODAY THROUGH THURSDAY...THE FORECAST AREA CAN EXPECT
ONE MORE DAY OF WARM TEMPERATURES AND DRY CONDITIONS AS AN UPPER
RIDGE CONTINUES TO INFLUENCE THE CWA. EXPECT HIGH TEMPERATURES TO BE
SIMILAR TO MONDAY WITH READINGS IN THE 70S TO LOWER 80S IN THE LOWER
ELEVATIONS AND MAINLY 60S IN THE MOUNTAINS. A COLD FRONT AND UPPER
TROUGH WILL MOVE INTO THE REGION TONIGHT AND WEDNESDAY. THIS WILL
BRING SIGNIFICANTLY COOLER TEMPERATURES...RAIN SHOWERS AND POSSIBLE
THUNDERSTORMS AS WELL AS INCREASING WINDS DUE TO A TIGHTENING
PRESSURE GRADIENT. MAIN THREAT FOR THUNDERSTORMS WILL BE OVER
CENTRAL OREGON LATE THIS AFTERNOON AND THIS EVENING. THE WINDS WILL
INCREASE ENOUGH IN THE KITTITAS VALLEY TO WARRANT A WIND ADVISORY
THERE BEGINNING AT MIDNIGHT TONIGHT AND CONTINUING THROUGH 8 PM
WEDNESDAY. ELSEWHERE IT WILL BECOME BREEZY TO WINDY AS WELL BUT
WINDS NOT AS STRONG AS IN THE KITTITAS VALLEY. TEMPERATURES WILL
COOL DOWN TO THE 60S IN THE LOWER ELEVATIONS AND MID 40S TO MID 50S
MOUNTAINS FOR WEDNESDAY AND THURSDAY. A PROGRESSIVE PATTERN WILL
PERSIST INTO THURSDAY WITH ANOTHER TROUGH AND COLD FRONT MOVING INTO
THE CWA...KEEPING TEMPERATURES COOL AND POSSIBLE MAINLY MOUNTAIN
SHOWERS. WINDS WILL BE LIGHTER ON THURSDAY BUT IT IS STILL EXPECTED
TO BECOME BREEZY IN THE AFTERNOON IN THE KITTITAS VALLEY AND THE
EASTERN COLUMBIA RIVER GORGE. 88

.LONG TERM...THURSDAY NIGHT THROUGH MONDAY...THE EXTENDED PERIOD
CONTINUES THE PROGRESSIVE UPPER LEVEL FLOW PATTERN, THUS ALLOWING
PACIFIC SYSTEMS TO MOVE INTO THE REGION. THURSDAY NIGHT THE 00Z GFS
AND ECMWF RUNS INDICATE THE UPPER LEVEL TROUGH MOVING SOUTHEAST OVER
SOUTHERN BRITISH COLUMBIA AND THE PACIFIC NORTHWEST. THE MAIN
DYNAMIC LIFT WILL REMAIN WEST OF THE CASCADES THROUGH OVERNIGHT AND
THEN ON FRIDAY THE UPPER TROUGH PERSISTS OVER VANCOUVER ISLAND THUS
KEEPING FORECAST AREA IN A SOUTHWEST FLOW ALOFT, WHICH KEEPS
MOISTURE STREAMING ACROSS THE EASTERN PORTIONS OF WASHINGTON AND
OREGON FOR A CHANCE OF SHOWERS IN THE BLUE MOUNTAINS. DOWNSLOPE
WESTERLY WINDS ALOFT WILL KEEP CENTRAL AND NORTH CENTRAL OREGON AS
WELL AS SOUTH CENTRAL WASHINGTON DRY DURING FRIDAY. SNOW LEVELS ON
FRIDAY WILL BE 4000-5000 FEET. FRIDAY NIGHT A WESTERLY FLOW ALOFT
WILL KEEP DOWNSLOPE SINKING AIR WHICH WILL BRING DRY CONDITIONS TO
THE REGION. OVER THE WEEKEND A VERY LARGE LONGWAVE TROUGH SLOWLY
MOVES TOWARD THE COAST AND PUSHES A WARM FRONT AS WELL TOWARD THE
COAST, BUT THE FRONT STAYS OFFSHORE THROUGH SUNDAY FOR DRY
CONDITIONS. SATURDAY NIGHT AND SUNDAY THE FRONT PUSHES INLAND FOR
INCREASING POPS AND RAIN LIKELY OVER THE EASTERN MOUNTAINS AND ALONG
THE EAST SLOPES OF THE CASCADES. CONFIDENCE IS LOW FOR FORECAST FOR
MONDAY BY VIRTUE OF SIGNIFICANT DIFFERENCES BETWEEN 00Z GFS AND
ECMWF RUNS IN TERMS OF PLACEMENT AND AMPLITUDE ON AN UPSTREAM LONG
WAVE IN THE NORTHEAST PACIFIC. THE ECMWF SHOWS AN UPPER LEVEL RIDGE
OF HIGH PRESSURE BUILDING OVER PACIFIC NORTHWEST FOR DRY CONDITIONS,
WHEREAS THE GFS MODEL SHOWS THE AFOREMENTIONED LONGWAVE TROUGH
DIGGING SOUTHEAST AND ONSHORE DURING THE DAY ON MONDAY THUS PUSHING
A COLD FRONT INLAND AND INTO FORECAST ON MONDAY. I LEANED TOWARD THE
00Z GFS FOR MONDAY, THUS HAVE INCLUDED A CHANCE FOR RAIN ON MONDAY
RATHER THAN DRY CONDITIONS, WHICH THE ECMWF INDICATED.  POLAN

&&

.AVIATION...12Z TAFS...MAINLY CLEAR SKIES CONTINUING THROUGH THIS
MORNING, BUT WITH SCATTERED CIRRUS MOVING NORTH ALONG THE CASCADES
IN THE MORNING. INCREASING CIRRUS THIS AFTERNOON. SCT CUMULUS OVER
THE MOUNTAINS IN THE AFTERNOON AND EVENING. SLIGHT CHANCE OF SHOWERS
OR THUNDERSTORMS OVER HIGHER TERRAIN AND MOUNTAINS IN CENTRAL OREGON
FROM 00Z TO 06Z/22ND. HAVE A TEMPO GROUP IN THE TAF FOR KBDN FOR
-SHRA THIS EVENING. LIGHT WINDS TONIGHT THEN WESTERLY WINDS
INCREASING THIS AFTERNOON TO 15-25 KTS.  POLAN

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  76  47  60  34 /  10  10  10   0
ALW  76  49  61  38 /  10  10  10   0
PSC  81  48  67  38 /   0  10  10   0
YKM  79  47  64  37 /  10  10  10   0
HRI  81  47  66  36 /   0  10  10   0
ELN  77  46  60  38 /  10  10  10   0
RDM  73  35  60  25 /  20  20  10   0
LGD  76  45  59  32 /  10  20  30  10
GCD  76  40  61  32 /  10  30  40  10
DLS  75  49  61  39 /  10  10  10   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...NONE.
WA...WIND ADVISORY FROM MIDNIGHT TONIGHT TO 8 PM PDT WEDNESDAY
WAZ026.

&&

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

$$

88/99/99





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