Heavy Snow in Washington, December 12 to 13, 2009

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE PENDLETON OR
400 AM PST SAT DEC 12 2009

UPDATED AVIATION DISCUSSION

.SHORT TERM...TONIGHT AND TOMORROW...REGION CONTINUES TO BE UNDER A
VERY COMPLEX PATTERN ALOFT WITH THE POLAR JET AND THE SUBTROPICAL
JET APPROACHING EACH OTHER. THIS PLACES THE PACNW UNDER THE
INFLUENCE OF CONFLUENT FLOW ALOFT. A LOW ROTATING AROUND THE INSIDE
OF THE SUBTROPICAL JET SENDS A MID-LEVEL FRONT NORTHWARD ACROSS THE
AREA THIS MORNING.

ALONG WITH THE FRONT WILL BE A WARM NOSE EXTENDING ALONG THE
CASCADES DOWN TO THE GORGE AND NORTH CENTRAL OREGON THEN EXTENDING
EAST ACROSS THE OCHOCO MOUNTAINS. FEEL THAT PRECIPITATION WILL START
OUT AS SNOW ACROSS THIS AREA BUT QUICKLY RESULT IN A COMBINATION OF
SNOW AND SLEET. WAS NOT COMFORTABLE COMPLETELY RULING OUT FREEZING
RAIN AS VERTICAL TEMPERATURE PROFILES WARM ABOVE FREEZING FOR 2000
TO 4000 FEET BEFORE FALLING BELOW FREEZING AT THE SURFACE. THUS
INCLUDED SLIGHT CHANCE MENTION WITH ICE ACCUMULATIONS EXPECTED TO BE
VERY LIGHT SHOULD THEY OCCUR. AS SURFACE TEMPERATURES WARM THESE
AREAS WILL LIKELY SEE A PERIOD WHERE RAIN GETS MIXED INTO THE
SNOW...PARTICULARLY ACROSS CENTRAL OREGON.

ELSEWHERE...PRECIPITATION SHOULD REMAIN AS ALL SNOW...HOWEVER
AMOUNTS FROM THE 00Z AND 06Z MODEL RUNS HAVE DECREASED FROM PREVIOUS
RUNS OVER THE LAST 24 TO 36 HOURS. AS SUCH...HAVE REFINED
ACCUMULATIONS BUT MODELS STILL NOT DOING THE BEST JOB WITH THE
CURRENT TRENDS. CONFIDENCE IN QPF AMOUNTS AND THEREFORE SNOW AMOUNTS
IS STILL SHAKY AT BEST. THE ONE CONSISTENT FEATURE HAS BEEN THE
NAM12 STALLING THE PREVIOUSLY MENTIONED FRONT ACROSS PORTIONS OF FAR
SOUTHEAST OREGON AND NORTHEAST OREGON...INCLUDING THE LOWER BASIN,
BLUE MOUNTAINS AND BLUE MOUNTAIN FOOTHILLS. QPF AMOUNTS SEEM TO BE
SIGNIFICANTLY LIGHTER THAN PAST RUNS, BUT WILL STILL BE SIGNIFICANT
NONETHELESS.

WITH THE CURRENT ADJUSTMENTS, DO NOT PLAN ON CHANGING THE WINTER
HEADLINES AS SUBTLE SHIFTS IN THE STALLED FRONT OR POSITION OF THE
WARM NOSE COULD RESULT IN RAPIDLY CHANGING CONDITIONS.

FINALLY...THE WIND ADVISORY WILL CONTINUE AS PLANNED FOR THE
SOUTHERN GRANDE RONDE VALLEY AS WINDS HAVE CONTINUED TO REMAIN
STRONG AND QUITE GUSTY. STRONGEST WINDS SHOULD OCCUR FROM NOW
THROUGH LATE MORNING BEFORE GRADUALLY DECREASING DURING THE
AFTERNOON. DID INCLUDE MENTION OF PATCHY BLOWING SNOW AS WELL
THROUGH THE LADD AND PYLES CANYON AREAS AS SOME DRIFTING AND
VISIBILITY REDUCTIONS ARE EXPECTED WITH ANY SNOWFALL. /JBONK

SUNDAY AND SUNDAY NIGHT...THE OROGRAPHIC LIFT ASSOCIATED WITH A NW
FLOW ALOFT WILL AIDE IN CONTINUED SNOWFALL FROM THE BLUE MTN
FOOTHILLS EASTWARD WHERE A STATIONARY FRONT WILL REMAIN THROUGH
SUNDAY AFTERNOON. THE FRONT WILL EVENTUALLY MOVE INTO SE OREGON
SUNDAY NIGHT AS THE FLOW INCREASES FROM THE NORTH.  THE CURRENT
WINTER STORM WARNINGS FOR THE BLUE MTN FOOTHILLS AND THE NORTHERN
BLUE MTNS THROUGH SUNDAY AFTERNOON APPEAR ON TRACK BUT THE WARNING
MAY NEED TO BE EXTENDED INTO SUNDAY NIGHT IF THE FRONT IS SLOWER
THAN MODELS INDICATE.   JOHNSON

.LONG TERM...MONDAY THROUGH FRIDAY...THE ECMWF...GFS AND CANADIAN
MODELS ARE SHOWING WARM FRONT OVERRUNING PRECIPITATION RESULTING IN
LIGHT SNOW SPREADING EAST TO THE CENTRAL AND SOUTHERN WASHINGTON
CASCADES DURING THE DAY ON MONDAY. BEGINNING MONDAY NIGHT SEVERAL
INCHES OR MORE OF SNOW ACCUMULATION ARE POSSIBLE OVER A 24-36 HOUR
PERIOD FROM MONDAY NIGHT THROUGH TUESDAY NIGHT. SNOW ACCUMULATIONS
MAY REACH WINTER WEATHER ADVISORY OR WINTER STORM WARNING CRITERIA
ALONG THE EAST SLOPES OF THE CENTRAL AND SOUTHERN WASHINGTON
CASCADES...THE EASTERN COLUMBIA RIVER GORGE AND NORTH CENTRAL
OREGON. FARTHER EAST FROM THE CASCADES FROM MONDAY THROUGH TUESDAY
NIGHT WINDS AROUND 5000 FT MSL WILL BE FROM THE WEST...THUS
PRODUCING A MOUNTAIN SHADOWING EFFECT FOR LESSER SNOW ACCUMULATIONS
OVER THIS 36-48 HOUR PERIOD. PROGRESSIVE WEST-SOUTHWEST FLOW ALOFT
ON WEDNESDAY WILL KEEP A CHANCE OF PRECIPITATION MAINLY IN
CENTRAL...SOUTH CENTRAL AND SOUTHEAST WASHINGTON. ON THURSDAY AND
FRIDAY THE GFS AND ECMWF ARE AT ODDS ABOUT THE TIMING OF A BROAD
MOISTURE PLUME EMBEDDED IN SOUTHWEST FLOW AT MID/UPPER LEVELS OVER
THE NORTHEAST PACIFIC AND HOW FAR INLAND INTO THE PACIFIC NORTHWEST
THIS MOISTURE PLUME WILL EXTEND. THE GFS WANTS TO BRING A MOIST WARM
FRONT ACROSS THE FORECAST AREA THURSDAY/FRIDAY WHEREAS THE ECMWF IS
NOT AS PROGRESSIVE AND KEEPS THE REGION RELATIVELY DRY BY VIRTUE OF
A DEEPENING UPPER LEVEL TROUGH NEAR 140W... WHICH THE GFS MODEL DOES
NOT SHOW.  POLAN

&&

.AVIATION...12Z TAFS. CIGS AND VSBYS WILL LOWER AS THE DAY
PROGRESSES WITH A GOOD POTENTIAL FOR IFR/LIFR CONDITIONS AT ALL TAF
SITES DUE TO -SN. THE ONLY EXCEPTION MAY BE KYKM AS THE BAND OF SNOW
SHOWERS MAY NOT MAKE IT THAT FAR NORTH. KDLS, KALW, AND KPDT WILL
LIKELY SEE LIFR CONDITIONS THIS AFTERNOON AND OVERNIGHT. LIGHT
SURFACE WINDS ARE EXPECTED THROUGH THE PERIOD.  JOHNSON

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  26  22  29  26 /  90  90  80  40
ALW  26  27  31  28 /  90  90  80  50
PSC  25  20  33  25 /  80  70  40  20
YKM  25  18  31  20 /  40  20  20  20
HRI  25  20  32  25 /  80  80  60  20
ELN  25  13  32  18 /  20  20  20  20
RDM  35  26  35  24 /  80  70  40  20
LGD  30  25  31  27 /  70  70  70  60
GCD  32  28  33  26 /  80  80  60  30
DLS  28  27  35  26 /  80  60  30  30

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...WINTER WEATHER ADVISORY UNTIL 4 AM PST SUNDAY FOR ORZ041>043.

     WINTER STORM WARNING UNTIL 4 PM PST SUNDAY FOR ORZ044-501-502.

     WINTER WEATHER ADVISORY UNTIL 10 AM PST SUNDAY FOR ORZ503>506.

     WIND ADVISORY UNTIL 4 PM PST THIS AFTERNOON FOR ORZ049.

WA...WINTER WEATHER ADVISORY UNTIL 4 AM PST SUNDAY FOR WAZ024-502.

     WINTER STORM WARNING UNTIL 4 PM PST SUNDAY FOR WAZ029-030.

     WINTER WEATHER ADVISORY UNTIL 10 AM PST SUNDAY FOR WAZ028.

&&

THREAT INDEX
TODAY : RED
SUNDAY : YELLOW
MONDAY : 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

87/85/99/99

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE PENDLETON OR
742 PM PST FRI DEC 11 2009

UPDATED TO EXTEND WIND ADVISORY INTO SATURDAY

ORZ041>044-049-050-501>506-WAZ024-026>030-501-502-121500-
EASTERN COLUMBIA RIVER GORGE OF OREGON-NORTH CENTRAL OREGON-
CENTRAL OREGON-LOWER COLUMBIA BASIN OF OREGON-GRANDE RONDE VALLEY-
WALLOWA COUNTY-FOOTHILLS OF THE BLUE MOUNTAINS OF OREGON-
NORTHERN BLUE MOUNTAINS OF OREGON-
SOUTHERN BLUE MOUNTAINS OF OREGON-
NORTHERN WHEELER AND SOUTHERN GILLIAM COUNTIES-JOHN DAY BASIN-
OCHOCO-JOHN DAY HIGHLANDS-
EASTERN COLUMBIA RIVER GORGE OF WASHINGTON-KITTITAS VALLEY-
YAKIMA VALLEY-LOWER COLUMBIA BASIN OF WASHINGTON-
FOOTHILLS OF THE BLUE MOUNTAINS OF WASHINGTON-
NORTHWEST BLUE MOUNTAINS-
EAST SLOPES OF THE CENTRAL CASCADES OF WASHINGTON-
EAST SLOPES OF THE SOUTHERN CASCADES OF WASHINGTON-
742 PM PST FRI DEC 11 2009

THIS HAZARDOUS WEATHER OUTLOOK IS FOR CENTRAL AND NORTHEAST OREGON
AS WELL AS SOUTH CENTRAL AND SOUTHEAST WASHINGTON.

.DAY ONE...TONIGHT

PACIFIC MOISTURE WILL CROSS MANY AREAS OF THE PACIFIC NORTHWEST
PRODUCING WINTRY PRECIPITATION BEGINNING TONIGHT AND LASTING
THROUGH MOST OF THE WEEKEND. A GENERAL DESCRIPTION OF EXPECTED
CONDITIONS WILL FOLLOW. FOR SPECIFIC DETAILS, PLEASE REFER TO THE
WINTER WEATHER STATEMENT /PDXWSWPDT UUWS46 KPDT/.

WINTER MIX
     EAST SLOPES OF THE SOUTHERN CASCADES OF WASHINGTON, EASTERN
     COLUMBIA RIVER GORGE OF WASHINGTON, EASTERN COLUMBIA RIVER
     GORGE OF OREGON, NORTH CENTRAL OREGON, CENTRAL OREGON,
     NORTHERN WHEELER AND SOUTHERN GILLIAM COUNTIES, JOHN DAY BASIN,
     OCHOCO-JOHN DAY HIGHLANDS

SNOW
     SOUTHERN BLUE MOUNTAINS OF OREGON

A MIX OF MAINLY SNOW AND SLEET IS EXPECTED TO BEGIN THIS EVENING
ACROSS THE MOST OF THE AREAS MENTIONED ABOVE. PRIMARILY SNOW IS
EXPECTED TO BEGIN TONIGHT ACROSS THE SOUTHERN BLUE MOUNTAINS.

STRONG WIND
     GRANDE RONDE VALLEY

STRONG PRESSURE GRADIENTS WILL KEEP WINDY TO VERY WINDY CONDITIONS
IN THE LOWER GRANDE RONDE VALLEY CONTINUING. AREAS BETWEEN AND
INCLUDING LADD AND PYLES CANYONS WILL HAVE THE HIGHEST WIND SPEEDS.
FOR DETAILS SEE THE WIND ADVISORY /PDXNPWPDT WWUS76/.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY

WINTER MIX SATURDAY
     EAST SLOPES OF THE SOUTHERN CASCADES OF WASHINGTON, EASTERN
     COLUMBIA RIVER GORGE OF WASHINGTON, EASTERN COLUMBIA RIVER
     GORGE OF OREGON, NORTH CENTRAL OREGON, CENTRAL OREGON,
     NORTHERN WHEELER AND SOUTHERN GILLIAM COUNTIES, JOHN DAY
     BASIN, OCHOCO-JOHN DAY HIGHLANDS

SNOW SATURDAY
     LOWER COLUMBIA BASIN OF WASHINGTON, FOOTHILLS OF THE BLUE
     MOUNTAINS OF WASHINGTON, NORTHWEST BLUE MOUNTAINS, LOWER
     COLUMBIA BASIN OF OREGON, GRANDE RONDE VALLEY, WALLOWA COUNTY,
     FOOTHILLS OF THE BLUE MOUNTAINS OF OREGON, NORTHERN BLUE
     MOUNTAINS OF OREGON, SOUTHERN BLUE MOUNTAINS OF OREGON

SNOW SUNDAY
     LOWER COLUMBIA BASIN OF WASHINGTON, FOOTHILLS OF THE BLUE
     MOUNTAINS OF WASHINGTON, NORTHWEST BLUE MOUNTAINS, LOWER
     COLUMBIA BASIN OF OREGON, FOOTHILLS OF THE BLUE MOUNTAINS OF
     OREGON, NORTHERN BLUE MOUNTAINS OF OREGON, SOUTHERN BLUE
     MOUNTAINS OF OREGON, NORTHERN WHEELER AND SOUTHERN GILLIAM
     COUNTIES, JOHN DAY BASIN, OCHOCO-JOHN DAY HIGHLANDS

ACCUMULATING SNOW IS EXPECTED TO BEGIN FALLING ACROSS THE LOWER
COLUMBIA BASIN, THE BLUE MOUNTAIN FOOTHILLS, AND THE MOUNTAINS OF
NORTHEAST OREGON AND SOUTHEAST WASHINGTON ON SATURDAY WITH
ACCUMULATIONS CONTINUING THROUGH MOST OF SUNDAY. THE BULK OF THE
SNOWFALL IS EXPECTED SATURDAY NIGHT THROUGH SUNDAY MORNING.

SNOW AND SLEET WILL CONTINUE SATURDAY ACROSS THE SOUTHERN WASHINGTON
CASCADES, THE COLUMBIA GORGE, ALONG WITH CENTRAL, NORTH CENTRAL AND
EAST CENTRAL OREGON. PRECIPITATION WILL GRADUALLY SHIFT EASTWARD AND
TRANSITION TO ALL SNOW BEGINNING SATURDAY AFTERNOON WITH SOME AREAS
CONTINUING TO SEE SNOW THROUGH SUNDAY.

STRONG WIND SATURDAY
     GRANDE RONDE VALLEY

VERY WINDY CONDITIONS WILL CONTINUE THROUGH MOST OF SATURDAY MAINLY
BETWEEN AND INCLUDING LADD AND PYLES CANYONS. PERIODS OF SNOWFALL
MAY RESULT IN LOCAL VISIBILITY REDUCTIONS DOWN TO 1 MILE OR LESS
ACROSS SOUTHERN VALLEY LOCATIONS.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION WILL BE LIKELY.

WEATHER SPOTTERS ARE ENCOURAGED TO REPORT SIGNIFICANT WEATHER
CONDITIONS ACCORDING TO STANDARD OPERATING PROCEDURES.

GRAPHICAL FORECASTS OF WEATHER HAZARDS OUT TO SEVEN DAYS
ARE DISPLAYED ON THE WORLD WIDE WEB AT:

WWW.WRH.NOAA.GOV/PDT/CURRENTHAZARDS/HWO.HTML

ALL LETTERS IN THE ABOVE URL ARE LOWER CASE...EXCEPT THE H IN
CURRENTHAZARDS.