Area Forecast Discussion
Issued by NWS Pendleton, OR

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000
FXUS66 KPDT 202243
AFDPDT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
243 PM PST SAT DEC 20 2014

.SHORT TERM...TONIGHT THROUGH SUNDAY NIGHT...THE STRONG AND WET
PACIFIC STORM CONTINUES TO MOVE INTO AND ACROSS THE INTERIOR
NORTHWEST THIS AFTERNOON. PRECIP CHANCES WILL REMAIN HIGH AREAWIDE
THIS EVENING AS THE SYSTEM`S WARM FRONT MOVES GRADUALLY ACROSS THE
REGION. SNOW LEVELS HAVE BEEN SLOW TO RISE TODAY, REMAINING BETWEEN
4300 TO 5000 FEET MSL OVER MOST OF THE AREA. THE EXCEPTIONS HAVE
BEEN OVER WALLOWA COUNTY WHERE THE SNOW LEVELS ARE NOW NEAR 4000
FEET, AND OVER KITTITAS COUNTY WHERE THEY REMAIN BETWEEN 2100 AND
2500 FEET. WITH THE SNOW LEVELS LINGERING BELOW 3000 FEET OVER
WESTERN KITTITAS COUNTY INTO THE EVENING, HAVE EXTENDED THE WINTER
WEATHER ADVISORY UNTIL 10 PM. SNOW LEVELS AREAWIDE SHOULD RISE THIS
EVENING AS THE WARM FRONT MOVES THROUGH THE REGION. WINDS HAVE NOT
INCREASED AS QUICKLY AS EXPECTED DUE TO THE PRECIP AND THE SLOW
ARRIVAL OF THE WARM FRONT. WILL CONTINUE ALL CURRENT WIND HIGHLIGHTS
THOUGH, AS STILL EXPECT WINDS TO INCREASE BEHIND THE WARM FRONT. THE
FLOW BEHIND THE WARM FRONT WILL SHIFT TO BEING MORE WESTERLY. THIS
FLOW WILL REMAIN QUITE MOIST AND PRECIP WILL CONTINUE ACROSS THE
REGION THROUGH SUNDAY. AREAS NEAR THE CASCADE CREST, AND THOSE PRONE
TO UPSLOPE AFFECTS, WILL CONTINUE TO SEE HIGH CHANCES OF PRECIP LATE
TONIGHT THROUGH SUNDAY. MEANWHILE PRECIP CHANCES IN AREAS, SUCH AS
THE LOWER COLUMBIA BASIN, WILL SEE LOWER PRECIP CHANCES DUE TO
DOWNSLOPE AFFECTS. SNOW LEVELS WILL RUN AROUND 5000 FEET OR HIGHER
SUNDAY, THUS SNOW WILL BE LIMITED TO THE HIGHEST ELEVATIONS. THE
STRONG WINDS WILL CONTINUE INTO SUNDAY MORNING, THEN SLOWLY DECREASE
SUNDAY AFTERNOON AND EVENING. THE AMOUNT OF AVAILABLE MOISTURE WILL
DECREASE, WHILE THE FLOW BECOMES NORTHWESTERLY SUNDAY NIGHT. THIS
WILL RESULT IN A GRADUAL WIND DOWN OF THE PRECIP. 90

.LONG TERM...MONDAY THROUGH WEDNESDAY NIGHT...NORTHWEST FLOW WILL
PREVAIL ON MONDAY WITH DECREASING CHANCES OF PRECIPITATION. A RIDGE
IS EXPECTED TO MOVE ACROSS THE AREA ON TUESDAY AND TUESDAY NIGHT
WITH DRY CONDITIONS AND HAVE INCLUDED PATCHY FOG IN THE COLUMBIA
BASIN. ON WEDNESDAY A TROUGH OF LOW PRESSURE WILL BE DROPPING SOUTH
ACROSS WASHINGTON INTO OREGON WITH A CHANCE OF PRECIPITATION. THERE
IS SOME DIFFERENCE IN THE MODELS ON THE POSITION OF THE LOW AND THE
AMOUNT OF COLD AIR PUSHING SOUTH. HAVE INCREASED SNOW LEVELS
SLIGHTLY WITH RAIN IN THE LOWER ELEVATIONS AND MOUNTAIN SNOW THROUGH
WEDNESDAY NIGHT. 93

CHRISTMAS DAY THROUGH SATURDAY NIGHT...NORTHWEST FLOW WILL SET IN AS
THE CHRISTMAS EVE SYSTEM THAT BROUGHT RAIN TO THE LOWLAND AND
MOUNTAIN SNOW EXITS THE AREA. SLIGHT CHANCE SNOW SHOWERS WILL
CONTINUE ALONG THE EAST SLOPES OF THE WASHINGTON CASCADES...AND INTO
THE YAKIMA AND KITTITAS VALLEYS...WITH A CHANCE OF SNOW SHOWERS
ALONG THE NORTHEAST MOUNTAINS. EXPECT CONDITIONS TO GRADUALLY DRY
OUT ACROSS ALL AREAS THROUGH FRIDAY EVENING.

THE NEXT POTENTIAL WAVE OF PRECIPITATION WILL BE FRIDAY EVENING
THROUGH THE WEEKEND...BUT THERE IS GREAT DISAGREEMENT IN THE MODELS
AS TO HOW MUCH PRECIPITATION WILL OCCUR AND HOW COLD IT WILL GET.
THE LATEST GFS MODEL IS EXTREMELY AGGRESSIVE WITH A COLD ARCTIC
INTRUSION...HOWEVER THE COLDEST AIR WOULD NOT ARRIVE UNTIL EARLY
NEXT WEEK. THE ECMWF HAS MORE PRECIPITATION THAN THE GFS MOVING IN
SATURDAY NIGHT BUT THE COLD AIR BEGINS TO EXIT INTO EARLY NEXT WEEK.
HAVE HEDGED THE FORECAST TOWARD THE ECMWF BUT DECIDED TO UNDERCUT
POP ACROSS THE BASIN...KEEPING THE LOWER ELEVATIONS MOSTLY DRY WITH
A SLIGHT CHANCE TO CHANCE OF SNOW ELSEWHERE. WEBER

&&

.AVIATION...00Z TAFS...RAIN WILL CONTINUE ACROSS MUCH OF THE REGION
OVERNIGHT WITH MOSTLY MFR CIGS/VSBYS DUE TO THE PRECIPITATION AND
BR. WINDS WILL INCREASE ESPECIALLY AFTER 06Z. WINDS COULD REACH
20-30KT WITH GUSTS TO 45KT FROM THE WSW AT KPDT, KALW, KRDM, AND
KBDN AND CONTINUE THROUGH 18Z SUNDAY. AFTER 18Z SUNDAY...MOST
LOCATIONS WILL BE RAIN SHADOWED WITH IMPROVING CONDITIONS. 93

&&

.HYDROLOGY...HEAVY RAIN IS EXPECTED OVER THE OREGON CASCADES THROUGH
SUNDAY WITH SNOW LEVELS RISING ABOVE 8000 FEET. THIS WILL PUSH
STREAMS AND RIVERS ALONG THE EAST SLOPES OF OREGON CASCADES TO
BANKFULL WITH FLOODING EXPECTED ALONG THE LOWER DESCHUTES. THE BLUE
MOUNTAINS WILL ALSO GET HEAVY RAIN WITH 1 TO 2 INCHES EXPECTED LATE
SATURDAY THROUGH SUNDAY, THE LARGE RIVERS ARE NOT EXPECTED TO FLOOD,
BUT SMALLER STREAMS MAY SEE MINOR FLOODING. ALONG THE EAST SLOPES OF
THE WASHINGTON CASCADES, COOLER AIR AND LESS PRECIPITATION HAS BEEN
SEEN OVERNIGHT AND IT APPEARS MAIN PUSH OF MOISTURE WILL BE FURTHER
SOUTH WITH NEWER FORECASTS COMING IN JUST BELOW FLOOD STAGE FOR THE
NACHES RIVER. FLOOD WATCHES WILL CONTINUE THROUGH SUNDAY NIGHT AS
HEAVIEST PRECIPITATION AREAS COME IN FOCUS. 93

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  48  58  38  48 /  90  80  40  10
ALW  49  58  40  49 /  90  90  50  10
PSC  48  58  37  49 /  80  40  10  10
YKM  40  54  35  45 /  80  30  20  10
HRI  48  59  37  52 /  80  50  20  10
ELN  39  49  34  43 / 100  40  20  10
RDM  46  57  35  47 /  80  70  20  10
LGD  44  53  37  46 / 100 100  80  20
GCD  43  46  36  47 / 100  80  60  20
DLS  45  56  39  51 / 100  80  30  10

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...     FLOOD WATCH THROUGH MONDAY AFTERNOON ORZ041-509>511.

     FLOOD WATCH THROUGH MONDAY AFTERNOON ORZ049-050-502-503-505>508.

     WIND ADVISORY UNTIL NOON PST SUNDAY ORZ044.

     HIGH WIND WARNING UNTIL 7 AM PST SUNDAY ORZ509.

     HIGH WIND WARNING UNTIL NOON PST SUNDAY ORZ510-511.

     WIND ADVISORY UNTIL NOON PST SUNDAY ORZ507.

     HIGH WIND WARNING UNTIL NOON PST SUNDAY ORZ508.

WA...FLOOD WATCH THROUGH MONDAY AFTERNOON WAZ024-026-027-520-521.

     FLOOD WATCH THROUGH MONDAY AFTERNOON WAZ029-030.

     WIND ADVISORY UNTIL NOON PST SUNDAY WAZ028.

     HIGH WIND WARNING UNTIL NOON PST SUNDAY WAZ521.

     WIND ADVISORY UNTIL NOON PST SUNDAY WAZ029.

     WIND ADVISORY UNTIL NOON PST SUNDAY WAZ027.

     WINTER WEATHER ADVISORY UNTIL 10 PM PST THIS EVENING FOR WESTERN
     KITTITAS COUNTY IN THE WAZ520.

&&

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

$$

90/93/89/93







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