Area Forecast Discussion
Issued by NWS Pendleton, OR

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000
FXUS66 KPDT 210525
AFDPDT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
1020 PM PDT MON APR 20 2015

.SHORT TERM...STRONG UPPER RIDGE REMAINS OVER THE REGION TONIGHT
INTO TUESDAY MORNING WITH MAINLY CLEAR SKIES. AN UPPER TROUGH WILL
BE APPROACHING THE COAST DURING THE DAY. SOUTHWEST FLOW WILL BE
DEVELOPING DURING THE AFTERNOON WITH SOME WEAK INSTABILITY. EXPECT
TO HAVE SOME CUMULUS OVER THE MOUNTAINS BY MID AFTERNOON. MODELS
STILL IMPLY SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS MAY DEVELOP
OVER CENTRAL AND NORTHEAST OREGON IN THE EVENING AND CONTINUE
OVERNIGHT. TEMPS WILL BE ON THE WARM SIDE TUESDAY WITH HIGHS IN THE
70S TO LOWER 80S. WESTERLY WINDS WILL INCREASE DURING THE DAY IN
RESPONSE TO THE APPROACHING TROUGH. MUCH COOLER WEDNESDAY AS THE
TROUGH MOVES THROUGH THE FORECAST AREA. 94

.AVIATION...06Z TAFS. MAINLY CLEAR SKIES TONIGHT. INCREASING CIRRUS
TUESDAY. SCT CUMULUS OVER THE MOUNTAINS IN THE AFTERNOON AND
EVENING. SLIGHT CHANCE OF SHOWERS OR THUNDERSTORMS RDM BDN AFTER
00Z. LIGHT WINDS TONIGHT THEN WESTERLY WINDS INCREASING TUESDAY TO
10-25KT.

&&

.PREV DISC... /ISSUED 438 PM PDT MON APR 20 2015/

SHORT TERM...TONIGHT THROUGH THURSDAY...AN UPPER LEVEL HIGH
PRESSURE RIDGE WILL CONTINUE OVER THE PACIFIC NORTHWEST THROUGH
TONIGHT. THIS RIDGE WILL SHIFT EAST TUESDAY DUE TO THE APPROACH OF
AN UPPER TROUGH. CONDITIONS TONIGHT THROUGH TUESDAY MORNING WILL BE
FAIR AND DRY WITH MAINLY LIGHT WINDS. OVERNIGHT LOWS WILL BE A BIT
WARMER THAN THIS MORNING DUE TO A WARMER DAY TODAY. INCREASING
SOUTHERLY FLOW ALOFT AHEAD OF THE APPROACHING PACIFIC TROUGH WILL
PUSH MOISTURE AND INSTABILITY NORTH FROM CALIFORNIA TUESDAY
AFTERNOON AND EVENING. AS SUCH ISOLATED TO SCATTERED SHOWERS WILL
DEVELOP OVER SOUTH CENTRAL OREGON TUESDAY AFTERNOON AND THEN WORK
THEIR WAY NORTH INTO CENTRAL AND EAST CENTRAL OREGON LATER TUESDAY
AFTERNOON AND TUESDAY EVENING. THERE WILL BE ENOUGH INSTABILITY FOR
A FEW THUNDERSTORMS OVER CENTRAL AND EAST CENTRAL OREGON LATE
AFTERNOON INTO THE EVENING AS WELL. A FEW SHOWERS MAY BE POSSIBLE
OVER THE WASHINGTON CASCADE EAST SLOPES THOUGH INCREASING WEST WINDS
SHOULD BE A LIMITING FACTOR. THE AREA OF SHOWERS IN CENTRAL AND EAST
CENTRAL OREGON WILL MOVE NORTH-NORTHEAST OVERNIGHT INTO WEDNESDAY.
THUS THESE SHOWERS ARE EXPECTED TO AFFECT THE BLUE MOUNTAINS AND
THEIR ADJACENT FOOTHILLS, THE GRANDE RONDE VALLEY AND WALLOWA COUNTY
AT VARIOUS TIMES WEDNESDAY. WINDS WILL INCREASE ACROSS THE COLUMBIA
BASIN, THE COLUMBIA GORGE AND THE KITTITAS VALLEY TUESDAY NIGHT.
THESE WINDS WILL PERSIST INTO WEDNESDAY. WINDS IN THE KITTITAS
VALLEY ARE EXPECTED TO REACH 30 TO 35 MPH SUSTAINED WITH HIGHER
GUSTS, AND WILL ISSUE A WIND ADVISORY FOR THIS AREA. MOST OF THE
SHOWERS WILL END WEDNESDAY NIGHT. MAY SEE A FEW SHOWERS NEAR THE
CASCADE CREST THURSDAY, AND POSSIBLY A FEW OVER EASTERN WALLOWA
COUNTY. OTHERWISE THURSDAY SHOULD BE DRY WITH SEASONAL TEMPS. 90

LONG TERM...THURSDAY NIGHT THROUGH MONDAY NIGHT...THE LONG TERM
PERIOD WILL BE QUITE ACTIVE WITH SEVERAL SYSTEMS MOVING THROUGH THE
AREA. THE FIRST AND WEAKER TROUGH WILL BE OVER THE FORECAST AREA
THURSDAY NIGHT INTO FRIDAY. THIS SYSTEM LOOKS FAIRLY MOISTURE
STARVED AND THEREFORE JUST ADDED A SLIGHT CHANCE TO CHANCE FOR
SHOWERS INTO THE FORECAST DURING THIS TIME. WESTERLY WINDS COULD
TURN A BIT BREEZY LATE THURSDAY NIGHT INTO FRIDAY NIGHT OVER PARTS
OF THE AREA. THIS WEATHER SYSTEM THEN EXITS THE AREA WITH A BRIEF
BREAK FOR FRIDAY NIGHT INTO SATURDAY MORNING. BY LATER SATURDAY AND
INTO SUNDAY A VERY DIFFLUENT UPPER LEVEL FLOW PATTERN DEVELOPS OVER
THE PACIFIC NORTHWEST WITH A LARGE PLUME OF MOISTURE BEING PUSHED
INTO THE AREA IN RESPONSE TO THE CYCLONIC FLOW AROUND A LARGE UPPER
LEVEL LOW LOCATED IN THE SOUTHERN GULF OF ALASKA. THIS PATTERN WILL
BRING A GOOD CHANCE FOR RAIN AND HIGH ELEVATION SNOW SATURDAY NIGHT
THROUGH SUNDAY NIGHT...SNOW LEVELS WILL BE QUITE HIGH...GENERALLY
ABOVE 6000 FEET. THERE WILL LIKELY BE A SHORT BREAK IN BETWEEN
SYSTEMS EARLY MONDAY...WITH THE NEXT WAVE APPROACHING THE REGION
MONDAY NIGHT AND CONTINUING BEYOND THE EXTENDED PERIOD. WITH THE
SERIES OF SYSTEMS OVER THE CWA LOOK FOR BREEZY OR EVEN WINDY
CONDITIONS FOR MANY LOCATIONS SUNDAY AND MONDAY...AT THIS TIME
SOUTHWEST WINDS OF 15-25 MPH WITH HIGHER GUSTS ARE LOOKING POSSIBLE
BOTH SUNDAY AND MONDAY AFTERNOON. THIS WILL BE SOMETHING TO CONTINUE
TO WATCH AS WE DRAW CLOSER AND GUIDANCE IS ABLE TO BETTER HONE IN ON
THE DETAILS. OVERALL EXPECT BOTH HIGH AND LOW TEMPERATURES TO REMAIN
VERY CLOSE TO THE SEASONAL AVERAGE THROUGHOUT THE EXTENDED PERIOD
FOR MOST LOCATIONS. 77

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  44  78  47  63 /   0  10  10  30
ALW  49  78  49  64 /   0  10  10  30
PSC  40  81  48  68 /   0   0  10  10
YKM  43  79  47  65 /   0  10  10  10
HRI  39  81  47  67 /   0   0  10  10
ELN  44  77  46  61 /   0  10  10  10
RDM  32  73  35  61 /   0  20  20  10
LGD  35  76  45  60 /   0  10  20  30
GCD  36  76  40  62 /   0  10  30  40
DLS  46  75  49  62 /   0  10  10  10

&&

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

&&

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

$$

94





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