Area Forecast Discussion
Issued by NWS Pendleton, OR

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000
FXUS66 KPDT 211126 AAA
AFDPDT

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE PENDLETON OR
426 AM PDT MON APR 21 2014

UPDATED AVIATION DISCUSSION

.SHORT TERM...TODAY THROUGH WEDNESDAY...A WEAK RIDGE OF HIGH
PRESSURE WILL KEEP THE FORECAST AREA DRY THIS MORNING IN MOST AREAS
WITH THE EXCEPTION BEING THE CASCADE EAST SLOPES. PRECIPITATION IS
EXPECTED TO BEGIN SPILLING OVER THE CASCADES TODAY AS THE NEXT
WEATHER SYSTEM APPROACHES THE CWA. MOISTURE WILL SPREAD EASTWARD
THIS AFTERNOON AND THIS EVENING AS THIS NEXT SYSTEM MOVES INTO THE
PACIFIC NORTHWEST. A SOUTHWEST FLOW WILL DEVELOP AND PUMP MOISTURE
NORTHWARD INTO THE CWA. PRECIPITATION AMOUNTS TODAY THOUGH WILL BE
VERY LIGHT AS THE MAIN BRUNT OF THIS SYSTEM IS NOT EXPECTED TO
ARRIVE UNTIL TONIGHT AND TUESDAY. A SURFACE LOW WILL DEVELOP OVER
SOUTH CENTRAL OREGON THIS EVENING AND THEN RIDE NORTHEAST OVERNIGHT.
AS IT DOES MOISTURE AND PRECIPITATION WILL INCREASE ACROSS THE CWA
FROM SOUTHWEST TO NORTHEAST...ESPECIALLY OVER THE MOUNTAINS. BY
TUESDAY MORNING PRECIPITATION WILL COVER THE ENTIRE CWA WITH LIKELY
TO CATEGORICAL POPS. THIS LOOKS TO BE A FAIRLY MOIST WEATHER SYSTEM
WITH ALL AREAS RECEIVING A CONSIDERABLE AMOUNT OF PRECIPITATION.
SNOW LEVELS WILL BE MODERATELY HIGH SO THERE IS NO THREAT OF WINTER
WEATHER EXCEPT FOR THE HIGHEST ELEVATIONS. THE PRECIPITATION WILL BE
MAINLY STRATIFORM THROUGH TUESDAY MORNING. THEN THE UPPER TROUGH
WITH COLDER AIR ALOFT WILL CROSS OVER THE CWA WHICH WILL DESTABILIZE
THE ATMOSPHERE AND CAUSE THE PRECIPITATION TO BECOME MORE SHOWERY BY
TUESDAY AFTERNOON. THE FLOW ALOFT WILL THEN BECOME MORE WESTERLY
AGAIN WHICH WILL CAUSE DOWNSLOPE DRYING TO TAKE PLACE IN THE VALLEYS
TO THE LEE OF THE CASCADES AND THE LOWER COLUMBIA BASIN. WILL
THEREFORE BEGIN TO LOWER POPS IN THESE AREAS BEGINNING LATE TUESDAY.
TUESDAY NIGHT OROGRAPHIC UP SLOPE SHOWERS WILL CONTINUE OVER THE
MOUNTAINS WITH A CONTINUED DECREASE OVER THE LOWER COLUMBIA BASIN
AND ADJACENT VALLEYS...INCLUDING CENTRAL OREGON TO THE LEE OF THE
CASCADES. A COOLER NORTHWEST FLOW WILL DEVELOP ON WEDNESDAY WHICH
WILL KEEP UP SLOPE RAIN AND HIGHER ELEVATION SNOW SHOWERS GOING OVER
THE MOUNTAINS AND JUST A SLIGHT CHANCE OF SHOWERS ELSEWHERE.
TEMPERATURES WILL COOL DOWN ON BOTH TUESDAY AND WEDNESDAY AS THE
UPPER TROUGH MOVES ACROSS THE CWA AND BRINGS IN A COOLER AIR MASS.
UNSETTLED WEATHER WILL CONTINUE INTO THE EXTENDED FORECAST PERIOD
WITH MORE WEATHER SYSTEMS EXPECTED. 88

.LONG TERM...WEDNESDAY NIGHT THROUGH MONDAY...A WET PATTERN WILL
CONTINUE THROUGH MUCH OF THE LONG TERM PERIOD. A TROUGH WILL HAVE
MOVED OFF TO THE ROCKIES BY WEDNESDAY NIGHT. A WEAK RIDGE WITH A
MOIST WESTERLY FLOW WILL RAPIDLY MOVE ACROSS THE AREA WEDNESDAY
NIGHT AS ANOTHER SYSTEM APPROACHES THE COAST. THE WARM FRONT FROM
THIS SYSTEM WILL MOVE ACROSS THE CASCADES AFTER MIDNIGHT FOLLOWED BY
THE TRAILING COLD FRONT THURSDAY AFTERNOON AND EVENING. THERE WILL
BE A CHANCE OF RAIN FOR THE ENTIRE AREA WEDNESDAY NIGHT THROUGH
THURSDAY NIGHT. THIS SYSTEM WILL SET UP AN UPPER LEVEL TROUGH ALONG
THE COAST THAT WILL MOVE ACROSS THE PACIFIC NORTHWEST FRIDAY AND
FRIDAY NIGHT. THE UNSTABLE CONDITIONS WITH THE TROUGH WILL KEEP A
CHANCE OF RAIN SHOWERS FRIDAY AND FRIDAY NIGHT THOUGH IT WILL BE
TAPERING OFF OVERNIGHT. SATURDAY AND SATURDAY NIGHT LOOK AS IF THERE
WILL BE A BREAK BETWEEN SYSTEMS THOUGH I HAVE KEPT A SLIGHT CHANCE
OF RAIN SHOWERS IN THE LOWER ELEVATIONS AND A CHANCE OF SHOWERS IN
THE MOUNTAINS UNTIL CONFIDENCE IN THE MODELS IMPROVE. MODELS DIFFER
WITH THEIR HANDLING OF A FRONT ARRIVING SUNDAY THROUGH MONDAY. THE
ECMWF HAS IT ARRIVING LATE SATURDAY NIGHT WITH SHOWERS THROUGH
SUNDAY EVENING THEN ANOTHER DISTURBANCE ARRIVING MONDAY. THE 00Z GFS
BRINGS A WEAK FRONT TO THE CASCADES SATURDAY NIGHT THAT FIZZLES OUT
WITH LITTLE IF ANY RAIN ON OUR SIDE OF THE CASCADES THEN A STRONGER
SYSTEM WITH A GOOD MOISTURE FEED SUNDAY NIGHT THROUGH MONDAY THAT
RIDES NORTHWARD THROUGH THAT TIME FRAME WITH RAIN CONFINED MAINLY TO
THE CASCADES AND NORTHERN BLUE MOUNTAINS. GIVEN THE GENERAL RUN TO
RUN AND MODEL TO MODEL DISAGREEMENT, HAVE KEPT A SLIGHT CHANCE OF
RAIN IN THE LOWER ELEVATIONS AND A CHANCE OF RAIN IN THE MOUNTAINS
SUNDAY THROUGH MONDAY. TEMPERATURES WILL BE IN THE 60S WITH 50S IN
THE MOUNTAINS. PERRY

&&

.AVIATION...12Z TAFS...A FRONT WITH BROKEN TO OVERCAST CLOUDS WILL
MOVE INTO THE AREA THIS MORNING WITH CEILINGS AT 8000-10000 FEET AGL
THIS MORNING THEN STEADILY LOWERING TO 2000-5000 FEET AFTER 00Z.
RAIN, MODERATE AT TIMES, WILL START AROUND 22Z AT WESTERN TAF SITES
AND AROUND 06Z AT EASTERN TAF SITES AND WILL CONTINUE THROUGH 12Z.
WINDS WILL GENERALLY REMAIN BELOW 15 KTS THOUGH A FEW HIGHER GUSTS
WILL BE POSSIBLE THIS AFTERNOON, ESPECIALLY AT KBDN AND KRDM. PERRY

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  65  44  55  39 /  10  70  80  30
ALW  68  47  56  42 /  10  50  80  40
PSC  70  49  60  44 /  10  60  70  20
YKM  67  41  57  37 /  20  70  60  20
HRI  69  46  58  41 /  10  70  80  20
ELN  65  41  54  36 /  30  70  70  20
RDM  65  36  47  31 /  30  70  80  30
LGD  67  40  50  36 /  20  70  80  40
GCD  66  37  45  30 /  20  70  80  40
DLS  68  47  55  43 /  30  70  80  30

&&

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

THREAT INDEX
TODAY : GREEN
TUESDAY : GREEN
WEDNESDAY : 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

$$

88/83/83





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