Area Forecast Discussion
Issued by NWS Pendleton, OR

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000
FXUS66 KPDT 280102
AFDPDT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
602 PM PDT FRI MAR 27 2015

.SHORT TERM...TONIGHT AND SATURDAY...HAVE MADE SOME EARLY CHANGES TO
THE FORECAST FOR THIS EVENING AS CONVECTION IS SLOW TO DEVELOP. HAVE
REDUCED CHANCE OF PRECIPITATION THROUGH 3 Z TO SLIGHT CHANCE AND
THEN INCREASE POPS AFTER THAT THROUGH THE NIGHT MAINLY ACROSS THE
EASTERN PORTION OF THE FORECAST AREA. HAVE TAKEN THE MENTION OF
THUNDERSTORMS OUT OF CENTRAL OREGON THIS EVENING AND KEPT THE FOCUS
OVER THE EASTERN MOUNTAINS EAST OF A LINE FROM PRINEVILLE TO WALLA
WALLA. ALSO ADDED A SLIGHT CHANCE OF THUNDERSTORMS TO FAR NORTHEAST
OREGON FOR THE LATE OVERNIGHT PERIOD. THE COLD FRONT IS JUST NOW
COMING ONTO THE COAST AND SHOULD REACH THE CASCADES BETWEEN 3 AND
5Z. THE BEST FORCING IN THE ATMOSPHERE TO TRIGGER CONVECTION WILL BE
NOW THROUGH FRONTAL PASSAGE. REGIONAL RADARS ARE BEGINNING TO PICK
UP WEAK CONVECTIVE CELLS AND EXPECT THIS TO CONTINUE IN THE COMING
HOURS. FOLLOWING THE FRONTAL PASSAGE WINDY WESTERLY WINDS WILL
INCREASE AND PERSIST THROUGH EARLY SATURDAY AND THEN TAPER OFF IN
THE AFTERNOON.



&&

.PREV DISC... /ISSUED 230 PM PDT FRI MAR 27 2015/

SHORT TERM...TONIGHT THROUGH MONDAY. UPPER LEVEL TROUGH AND COLD
FRONT APPROACHING THE COAST. MODELS HAVE BEEN INDICATING INSTABILITY
OVER CENTRAL AND NORTHEAST OREGON THIS AFTERNOON INTO THE EVENING.
SATELLITE SHOW CUMULUS IS STARTING TO DEVELOP. WILL CONTINUE WITH A
SLIGHT CHANCE OF THUNDERSTORMS OVER THIS AREA. OTHERWISE THE PASSAGE
OF THE FRONTAL BOUNDARY WILL BRING CLOUDY SKIES LATE EVENING AND
OVERNIGHT WITH SHOWERS. WESTERLY FLOW ALOFT SATURDAY WITH CLEARING
SKIES. COMBINATION OF COLD ADVECTION AND PRESSURE RISES WILL RESULT
IN BREEZY TO WINDY CONDITIONS OVERNIGHT AND SATURDAY. EXPECTING SOME
LIGHT RAIN OVER THE COLUMBIA BASIN SO WILL HOLD OFF ON ANY BLOWING
DUST FOR NOW. TEMPS ABOUT 5-15 DEGREES COOLER TOMORROW. WESTERLY
FLOW ALOFT CONTINUES SUNDAY WITH A SYSTEM PASSING BY TO THE NORTH.
EXPECT SOME MID AND HIGH LEVEL CLOUDS. WINDS MUCH LIGHTER. AN
APPROACHING TROUGH WILL TURN THE FLOW MORE SOUTHWEST ON MONDAY.
SKIES WILL REMAIN PARTLY CLOUDY WITH HIGHS IN THE 60S TO LOWER 70S.
94

LONG TERM...MONDAY NIGHT THROUGH FRIDAY. A RETURN TO MORE
SPRING-LIKE TEMPERATURES AND SHOWERY CONDITIONS CAN BE EXPECTED NEXT
WEEK.  A STRONG COLD FRONT ON TUESDAY WILL LOWER SNOW LEVELS TO NEAR
4000-5000 FEET...AND COLD AIR BEHIND THE FRONT WILL BRING SNOW
LEVELS DOWN TO 3500 FEET TUESDAY NIGHT AND WEDNESDAY.  THERE IS NOT
A SIGNIFICANT AMOUNT OF MOISTURE WITH THE FRONT BUT THERE WILL
LIKELY BE SEVERAL INCHES OF SNOW ACCUMULATIONS IN THE MOUNTAINS.
DEEP COLD AIR ALOFT ON TUESDAY (500MB TEMPS DOWN TO -32F) WILL
STEEPEN LAPSE RATES...AND THERE COULD BE GRAUPEL MIXED WITH RAIN
SHOWERS IN THE LOWER ELEVATIONS.  SUSTAINED WINDS AT 20-30 MPH ARE
FORECAST FOR MOST OF THE FORECAST AREA TUESDAY.  ANOTHER SHORTWAVE
WILL QUICKLY FOLLOW ON WEDNESDAY.  THERE ARE DIFFERENCES IN THE
TIMING AND POSITION OF THIS NEXT SYSTEM...AS THE ECMWF IS FASTER AND
FARTHER SOUTH THAN THE GFS AND CANADIAN...BUT THE OVERALL SYNOPTIC
PATTERN WEDNESDAY AND WEDNESDAY NIGHT IS A NORTHWEST FLOW ALOFT THAT
WILL BRING A CHANCE OF SNOW SHOWERS IN THE MOUNTAINS AND A SLIGHT
CHANCE RAIN SHOWERS (SNOW ABOVE 3500 FEET) ELSEWHERE.  THERE SHOULD
BE A BREAK IN PRECIPITATION THURSDAY.  ON FRIDAY...THERE ARE
SIGNIFICANT DIFFERENCES IN THE GFS AND ECMWF AS BOTH MODELS BECOME
OUT OF PHASE WITH EACH OTHER.  IF THE GFS VERIFIES...THERE WILL BE
ANOTHER TROUGH BRINGING SHOWERS AND BREEZY WINDS TO THE REGION ON
FRIDAY WHILE THE ECMWF KEEPS THE UPPER LEVEL RIDGE OVER WA/OR. USED
THE ECENS FOR THE FORECAST WHICH IS A COMPROMISE OF BOTH SOLUTIONS
AND INTRODUCED 20-40 PERCENT CHANCE OF SHOWERS IN THE MOUNTAINS BUT
DRY CONDITIONS ELSEWHERE.  WISTER

AVIATION...00Z TAFS. LATEST VISIBLE SATELLITE SHOWS CUMULUS CLOUDS
DEVELOPING FROM SW DESCHUTES COUNTY NORTHEAST TO THE NORTHERN BLUE
MOUNTAINS.  THIS IS THE AREA THAT HAS THE BEST POTENTIAL FOR
ISOLATED LATE AFTERNOON AND EVENING THUNDERSTORMS.
THEREFORE...THERE WILL BE TOWERING CUMULUS OR CB CLOUDS IN THE
VICINITY OF KBDN, KRDM, AND KPDT AND POSSIBLY KALW FOR THE NEXT 6-8
HOURS. THE TIMING OF THE COLD FRONT WILL BE NEAR THE CASCADE RANGE
AROUND 10 PM THIS EVENING THEN OVER THE COLUMBIA BASIN AROUND
MIDNIGHT AND NEAR THE IDAHO BORDER BY 4AM SATURDAY.  WEST WINDS JUST
AHEAD AND BEHIND THE FRONT WILL INCREASE TO 15-25 KNOTS GUSTING TO
35 KNOTS. RAIN SHOWERS MAY ALSO LOWER CIGS/VSBYS TO MVFR
TONIGHT...MAINLY NEAR KPDT AND KALW.  WINDS AND CLOUDS WILL DECREASE
FROM 18Z-00Z SATURDAY. WISTER

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  49  64  40  65 /  60  10   0   0
ALW  52  66  43  65 /  70  10   0   0
PSC  51  67  42  68 /  40  10   0   0
YKM  45  66  37  65 /  20  10  10  10
HRI  50  67  41  68 /  50  10   0   0
ELN  45  62  37  64 /  20  10  10  10
RDM  38  61  31  65 /  30  10   0   0
LGD  44  60  34  61 /  50  20   0   0
GCD  43  60  33  63 /  40  20   0   0
DLS  50  66  39  67 /  20  20  10  10

&&

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

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

$$

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