Area Forecast Discussion
Issued by NWS Pendleton, OR

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000
FXUS66 KPDT 242230
AFDPDT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
230 PM PST MON NOV 24 2014

.SHORT TERM...TONIGHT THROUGH THURSDAY...WET AND WINDY OVER THE NEXT
24 HOURS. HIGH PRESSURE IN THE EASTERN PACIFIC IS DIRECTING A PLUME
OF MOISTURE UP AND OVER THE RIDGE DIRECTING IT INTO WASHINGTON AND
NORTHERN OREGON IN THE FORM OF A WARM FRONT. RADARS IN WESTERN
WASHINGTON ARE ALREADY FILLING IN AS RAIN ARRIVES INTO WESTERN
WASHINGTON THIS AFTERNOON. THE WESTERLY FLOW WILL DIRECT THIS INTO
THE CASCADES AND THEN INTO EASTERN WASHINGTON AND NORTHEAST OREGON
OVERNIGHT. COPIOUS AMOUNTS OF PRECIPITATION ARE EXPECTED OVER THE
NEXT 24 HOURS UNDER THIS PATTERN FOR THE CASCADES AND THE MOUNTAINS
OF NORTHEAST OREGON AND SOUTHEAST WASHINGTON ON THE ORDER OF 1 TO 3
INCHES WHICH COULD CREATE SOME SMALL STREAM ISSUES GOING FORWARD.
THERE WILL BE SOME RAIN SHADOWING TAKING PLACE ALONG THE EAST SLOPES
OF THE CASCADES SO PRECIPITATION AMOUNTS FROM REDMOND TO YAKIMA AND
THE TRI-CITIES WILL BE LIGHT AND LIMITED. MOST OF THE PRECIPITATION
WILL FALL AS RAIN DUE TO SNOW LEVELS RISING TO AROUND 8000 FEET BY
TUESDAY. SOME STRONG WINDS ALOFT WILL BE ACCOMPANYING THIS WARM
FRONT SO EXPECT INCREASING WESTERLY WINDS OVERNIGHT AND CONTINUING
INTO TUESDAY. THE MOISTURE WILL BEGIN TO LIFT NORTHWARD LATE TUESDAY
AND TUESDAY NIGHT AS THE RIDGE MOVES INLAND. THIS WILL LIFT THE MAIN
RAIN BAND NORTH OF THE FORECAST AREA WITH JUST THE WASHINGTON
CASCADES MAINTAINING A CHANCE OF PRECIPITATION INTO WEDNESDAY. THEN
ON THURSDAY A WEAK COLD FRONT WILL APPROACH FROM THE WEST INCREASING
THE CHANCE OF PRECIPITATION TO THE ENTIRE CASCADE REGION BUT LOOKS
TO REMAIN DRY ACROSS THE REST OF THE FORECAST AREA FOR THANKSGIVING
DAY. TEMPERATURES WILL BE ON THE RISE AS THE WARM FRONT COMBINED
WITH THE UPPER LEVEL RIDGE WILL BRING 50S AND EVEN SOME LOW 60
DEGREE MAX TEMPERATURES TO THE FORECAST AREA THROUGH MIDWEEK.
OVERNIGHT LOW TEMPERATURES WILL REMAIN MILD.

.LONG TERM...THURSDAY NIGHT THROUGH MONDAY NIGHT...THE RIDGE OF HIGH
PRESSURE THAT WAS IN PLACE WILL BEGIN TO BREAK DOWN THURSDAY NIGHT
INTO FRIDAY AS A COLD FRONT MOVING IN FROM CANADA WILL GRADUALLY
SHIFT THE FLOW OUT OF THE WEST.  AT THE SAME TIME AN UPPER LEVEL LOW
OFF THE PACIFIC WILL MOVE IN TOWARDS THE COAST ALLOWING FOR A MOIST
SOUTHERLY FLOW TO MEET UP WITH THE COLD FRONT TO THE NORTH.  RIGHT
NOW THE OVERALL MODEL CONSENSUS HAS THE PRECIPITATION UP TO THE
OR/WA BOARDER...WITH SOME DISCREPANCIES AS TO HOW MUCH PRECIPITATION
WILL MOVE NORTH OF THE WASHINGTON STATE LINE BY SUNDAY MORNING.  THE
OTHER ISSUE IS THE COLD AIR INTRUSION TO THE SOUTH.  BY SATURDAY
NIGHT...THE COLD AIR SHOULD COVER MOST OF WASHINGTON...BUT THERE IS
THE POSSIBILITY OF IT REACHING DOWN INTO CENTRAL OREGON AS WELL.
THIS MAKES THE RAIN/SNOW PREDICTION DIFFICULT.  AREAS OF UNCERTAINTY
IN THE EXTENDED...HAVE BEEN NOTED WITH A CHANCE OF RAIN OR SNOW.
NOW BY SUNDAY MORNING ALL AREAS NORTH OF DESCHUTES...CROOK...AND
GRANT COUNTY OREGON SHOULD BE COLD ENOUGH FOR SNOW.  THIS IS OF
COURSE IS THE AREA OF DISCREPANCY AS TO HOW MUCH PRECIPITATION WILL
FALL NORTH OF THE OR/WA BOARDER.  RIGHT NOW THE HEAVIEST QPF AMOUNTS
LOOK TO BE OVER CENTRAL AND NORTH CENTRAL OREGON...ALONG WITH THE
SOUTHERN BLUE MOUNTAINS...AND THE FOOTHILLS OF THE SOUTHERN BLUES.

SUNDAY NIGHT INTO MONDAY THE MODELS DIVERGE WITH CONTINUED COLD AIR
OVER THE AREA. GFS HAS A DRY NORTHWEST FLOW PUSH THE LOW OFF TO THE
SOUTHEAST...AND ECMWF CONTINUES TO HAVE THE LOW SIT OFF THE NORTHERN
CALIFORNIA COAST...SPINNING UP MOISTURE FROM THE SOUTH...BUT
SIGNIFICANT COLD AIR STILL REMAINS IN PLACE.  THIS ALLOWS FOR THE
MAIN FORM OF PRECIPITATION TO BE SNOW ACROSS ALL AREAS.

THE ONLY OTHER NOTE WOULD BE THAT THE POTENTIAL FOR FREEZING RAIN
ALWAYS EXISTS WHEN WARM AIR OVERRUNS THE COLD AIR.  SO FAR MODELS
SEEM TO KEEP THE PRECIPITATION AS A MIXTURE OF RAIN OR SNOW...AND
WARM AIR OVERRUNNING COLD AIR IS LESS PREDOMINATE.  HOWEVER THE
PREVIOUS SYSTEM FROM NOV 12-14 HAD SOME SIMILARITIES TO THIS
SYSTEM...AND SIGNIFICANT ICE ACCUMULATIONS OCCURRED IN PARTS OF
CENTRAL OREGON. AGAIN...CURRENT MODELS DO NOT INDICATE A DEFINITIVE
FREEZING RAIN SOUNDING IN THE EXTENDED...BUT CERTAIN AREAS COULD BE
VERY SUSCEPTIBLE TO FREEZING RAIN.    WEBER


&&

.AVIATION...18Z TAFS...VFR CONDITIONS ARE EXPECTED OVER THE NEXT 12
HOURS...WITH MVFR/IFR CONDITIONS TO FOLLOW FROM 06Z-18Z TUESDAY.
RAIN WILL BEGIN TO ENTER TAF SITES AFTER 3Z AND MAY PERSIST ON AND
OFF AT SOME TAF SITES THROUGH 18Z TOMORROW.  EXPECT POTENTIAL
MVFR/IFR CONDITIONS AS CIGS AND VISIBILITIES LOWER THIS EVENING AND
TUESDAY MORNING. WINDS WILL GENERALLY BE 5-15KTS. WEBER    WEBER


&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  44  57  46  59 /  90  70  10   0
ALW  45  57  50  59 /  90  80  20  10
PSC  43  56  47  58 /  70  20  10   0
YKM  37  52  39  53 /  50  10  10  10
HRI  44  58  47  59 /  70  20  10   0
ELN  36  50  40  53 /  60  20  20  10
RDM  39  58  36  59 /  20  10   0   0
LGD  40  50  41  51 / 100 100  30   0
GCD  38  51  39  52 /  60  40  10   0
DLS  44  58  46  59 /  60  30  20  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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