Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 241355 AAB
AFDPDT

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE PENDLETON OR
655 AM PDT THU APR 24 2014

UPDATED SHORT TERM DISCUSSION

.SHORT TERM...TODAY THROUGH SATURDAY AFTERNOON...UPPER LEVEL TROUGH
DIGGING SOUTH OFFSHORE WILL BACK FLOW ALOFT TO SOUTH TODAY JUST
AHEAD OF A COLD FRONT. AIR MASS WILL BECOME UNSTABLE BY LATE THIS
MORNING. NEW 06Z NAM12 MOS GUIDANCE SHOWS 30-60 PERCENT CHANCE OF
THUNDERSTORMS AT HERMISTON, PENDLETON, WALLA WALLA, MEACHAM AND AT
LA GRANDE FROM 11AM THIS MORNING THROUGH THIS AFTERNOON. AS SUCH I
AMENDED THE WEATHER GRID FOR THIS AFTERNOON TO INDICATE THAT THERE
IS A CHANCE OF THUNDERSTORMS ALONG THE FOOTHILLS OF THE BLUE
MOUNTAINS EASTWARD THROUGH WALLOWA COUNTY AS WELL AS IN CROOK,
WHEELER, AND GRANT COUNTIES. MODELS ALSO SHOW A VORTICITY MAX MOVING
ACROSS FORECAST ARE TODAY, WHICH WILL PROVIDE GOOD DYNAMIC LIFT. IN
ADDITION, A COLD FRONT WILL MOVE THROUGH THE FORECAST AREA THIS
AFTERNOON AND ACT AS A TRIGGER FOR THUNDERSTORM DEVELOPMENT IN
EASTERN OREGON AND SOUTHEAST WASHINGTON. SCATTERED SHOWERS EXPECTED
TONIGHT AND FRIDAY WITH A SLIGHT CHANCE OF THUNDERSTORMS FRIDAY
AFTERNOON OVER THE BLUE MOUNTAINS. FRIDAY LOOKS TO BE DRY DUE TO
HIGH PRESSURE.  POLAN

.LONG TERM...SATURDAY NIGHT THROUGH THURSDAY...SATURDAY NIGHT WILL
SEE AN UPPER LEVEL TROUGH MOVING OFF TO THE EAST WHILE ANOTHER
SYSTEM IN A MOIST AND PROGRESSIVE WESTERLY FLOW WILL BE MOVING INTO
THE AREA. THIS WILL GIVE US A CHANCE OF RAIN WITH THE MOUNTAINS
HAVING A RAIN/SNOW MIX SATURDAY NIGHT THROUGH SUNDAY. THE MOISTURE
WILL BEGIN TO TAPER OFF SUNDAY NIGHT WITH JUST A SLIGHT CHANCE OF
RAIN IN THE LOWER ELEVATIONS AND A CHANCE OF RAIN AND SNOW SHOWERS
IN THE MOUNTAINS ABOVE 4500 FEET. MONDAY WILL SEE RIDGING BUILDING
OVER THE AREA AND THE LOWER ELEVATIONS WILL BE DRY WHILE A SLIGHT
CHANCE OF RAIN AND SNOW SHOWERS WILL CONTINUE IN THE MOUNTAINS.
MODELS ARE IN AGREEMENT IN HAVING THE RIDGE REMAIN OVER THE AREA
THROUGH AT LEAST WEDNESDAY NIGHT WHICH WILL GIVE US A PERIOD OF DRY
WEATHER AND A WARMING TREND. THE GFS WANTS TO BRING AN UPPER LOW TO
THE CANADIAN BORDER AREA, POSSIBLY ON THURSDAY, THOUGH THE TIMING
CHANGES ON EACH OF THE LAST COUPLE OF RUNS WHILE THE ECMWF DOES NOT
HAVE THIS FEATURE. IF THIS SYSTEM PROVES TO BE REAL, THE GFS IS
USUALLY TOO FAST BRING THEM IN THIS FAR OUT IN THE LONG TERM PERIOD
SO HAVE KEPT THE FORECAST DRY THOUGH POPS WERE RAISED TO AROUND 10
PERCENT IN THE WASHINGTON CASCADES. HIGHS WILL BE IN THE MID 50S TO
MID 60S WITH MID 40S TO MID 50S IN THE MOUNTAINS SUNDAY AND MONDAY
THEN RISE TO THE 70S WITH 60S IN THE MOUNTAINS TUESDAY THROUGH
THURSDAY. PERRY

&&

.AVIATION...12Z TAFS...AN UPPER LEVEL TROUGH WILL SEND MOIST AIR
INTO THE AREA ON A SOUTHWEST FLOW TODAY. THIS WILL CREATE ENOUGH
INSTABILITY FOR SHOWERS THROUGH THE DAY THOUGH THERE MAY BE A LULL
FROM 15Z TO 18Z. ADDITIONALLY THE INSTABILITY MAY GENERATE ISOLATED
THUNDERSTORMS OVER MUCH OF THE AREA FROM 18Z TO 00Z AND LINGER ON
THROUGH 03Z FROM THE BLUE MOUNTAINS EASTWARD. HAVE ADDED VCTS AND A
CB LAYER FOR KPDT, KALW AND KPSC WHERE THUNDER IS LIKELIEST. SHOWERS
WILL END BY 03Z THOUGH ANOTHER DISTURBANCE WILL BEGIN ENTERING THE
AREA FROM THE SOUTH AFTER 06Z AND KRDM AND KBDN MAY SEE A MIX OF
RAIN AND SNOW SHOWERS THROUGH 12Z. SURFACE WINDS ARE ALREADY
INCREASING EARLY THIS MORNING AND ALL TAF SITES WILL HAVE WINDS OF
15 TO 25 KTS WITH GUSTS TO 35 KTS FROM 18Z TO 02Z. WINDS WILL
DECREASE TO 15 KTS OR LESS AFTER 05Z. PERRY

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  58  39  57  38 /  80  60  60  20
ALW  58  42  58  42 /  90  60  70  30
PSC  64  43  63  41 /  60  20  20  10
YKM  59  35  60  36 /  50  10  20  10
HRI  62  42  61  39 /  60  40  40  20
ELN  57  36  59  35 /  60  10  20  10
RDM  55  30  49  27 /  50  60  60  20
LGD  53  36  52  35 /  80  70  80  50
GCD  54  34  46  30 /  80  70  90  40
DLS  60  40  60  40 /  60  40  40  30

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...NONE.
WA...NONE.
&&

THREAT INDEX
TODAY : GREEN
FRIDAY : GREEN
SATURDAY : GREEN

GREEN: NONE OR LIMITED NEED FOR WATCHES, WARNINGS, OR ADVISORIES.
YELLOW: A FEW WATCHES, WARNINGS, OR ADVISORIES POSSIBLE OR IN EFFECT.
RED: NUMEROUS WATCHES, WARNINGS, OR ADVISORIES POSSIBLE OR IN EFFECT.

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

$$

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