Heavy Snow in Washington, December 27 to 30, 2010

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
205 PM PST MON DEC 27 2010

.SHORT TERM...TONIGHT THROUGH THURSDAY.  TWO SURFACE LOWS AND
ASSOCIATED FRONTS WILL BRING AREAWIDE PRECIPITATION TONIGHT THROUGH
WEDNESDAY AFTERNOON.  THE FIRST LOW IS NOW MOVING TOWARDS ASTORIA
AND WILL TRACK EAST ACROSS WASHINGTON TONIGHT.  WARM ADVECTION
MOISTURE WILL SPREAD OVER THE REGION TONIGHT RESULTING IN INCREASING
SNOW LEVELS.  SNOW LEVELS WILL INITIALLY RANGE FROM 1500 FEET OVER
SOUTH CENTRAL WASHINGTON SLOPING UPWARDS TO 3500 FEET IN CENTRAL
OREGON THEN INCREASING TO AROUND 4500-5000 FEET OVER MOST OF THE
AREA ON TUESDAY.  IT IS A MOIST SYSTEM BRINGING 24-HR LIQUID AMOUNTS
UP TO 0.25 OF AN INCH IN THE BASIN AND AROUND 0.5-0.8 OF AN INCH IN
THE MOUNTAINS WITH THE HEAVIEST AMOUNTS ALONG THE WEST FACING SLOPES
OF THE BLUES AND JUST EAST OF THE CASCADE CREST.  THE WINTER STORM
WARNING FOR HEAVY SNOW ABOVE 4500 FEET IN THE NORTHERN BLUES LOOKS
VERY REASONABLE.  WILL ALSO ISSUE A WINTER WEATHER ADVISORY FOR SNOW
OVER THE SOUTHERN BLUE MOUNTAINS AND THE OCHOCO-JOHN DAY HIGHLANDS
ABOVE 4000 FEET FOR TONIGHT THROUGH WEDNESDAY MORNING.  FUTURE
SHIFTS WILL NEED TO CLOSELY MONITOR TEMPS/DEWPOINTS TO MAKE SURE
SNOW LEVELS ARE NOT LOWER THAN CURRENTLY IN THE FORECAST.  A GOOD
EXAMPLE WILL BE ALONG THE EAST SLOPES OF THE WA/OR CASCADES WHERE
PRECIPITATION WILL CHANGE OVER THE RAIN OVERNIGHT THROUGH TUESDAY
MORNING BUT MODERATE TO HEAVY SNOW MAY FALL BEFORE THE WARMER AIR
APPROACHES.

ANOTHER LOW WILL QUICKLY FOLLOW AND MOVE ACROSS OREGON ON TUESDAY.
MOST PRECIPITATION WILL FALL IN THE OREGON ZONES...AND A WESTERLY
FLOW WILL RESULT IN PRECIPITATION SHADOWING OFF THE CASCADES WITH
LIGHT AMOUNTS OVER THE COLUMBIA BASIN AND SURROUNDING VALLEYS.  THE
COLD FRONT MOVING ACROSS WA/OR ON TUESDAY NIGHT WILL LOWER SNOW
LEVELS DOWN TO THE BASIN FLOOR.  ON WEDNESDAY...AN UPPER LEVEL
TROUGH WILL BRING SCATTERED TO NUMEROUS SHOWERS WITH SNOW EXPECTED
AT ALL ELEVATIONS.  IT IS DIFFICULT TO PREDICT SNOW ACCUMULATIONS ON
WEDNESDAY...AS THE AIR MASS WILL BE UNSTABLE AND A FEW SHOWERS COULD
BRING BRIEF PERIODS OF MODERATE TO HEAVY SNOW.  THE UPPER TROUGH
WILL SHIFT INTO IDAHO WEDNESDAY NIGHT FOLLOWED BY A COLDER AND DRIER
NORTHERLY FLOW ALOFT.  PRECIPITATION WILL TAPER OFF FROM THE NORTH.
BY THURSDAY. ONLY SCATTERED SHOWERS ARE EXPECTED OVER THE CENTRAL
OREGON...THE JOHN DAY AREA...AND THE SOUTHERN BLUES WITH LITTLE OR
NO PRECIPITATION ELSEWHERE.

NO WIND HIGHLIGHTS ARE EXPECTED...ALTHOUGH IT WILL BE WINDY IN THE
GRANDE RONDE VALLEY WITH THE POSSIBILITY OF A COUPLE OF HOURS OF
ADVISORY CONDITIONS TUES MORNING. IT WILL ALSO BE VERY WINDY ALONG
SOME OF THE RIDGETOPS...AND SOME WINDS MAY MIX DOWN FOR LOCALLY
BREEZY/WINDY CONDITIONS...PARTICULARLY IN AREAS ACROSS SOUTH CENTRAL
WASHINGTON ON TUESDAY.  JOHNSON

.LONG TERM...THURSDAY NIGHT THROUGH MONDAY.  THURSDAY NIGHT AND
FRIDAY LOOK DRY AND COLD AS A WEAK UPPER RIDGE PASSES OVER THE AREA.
MODELS ARE HAVING LOTS OF PROBLEMS WITH TIMING AND POSITION OF
SECONDARY LOW THAT SHOULD AFFECT THE AREA SATURDAY.  ECMWF KEEPS ITS
CUTOFF LOW AND MOISTURE OVER NORTHERN CALIFORNIA WHILE THE GFS AND
TO SOME EXTEND THE CANADIAN HAVE A OPEN TROUGH MOVING INTO THE
PACIFIC NORTHWEST ON SATURDAY.  THE NORTH TO NORTHWEST FLOW
ASSOCIATED WITH EITHER SOLUTION WILL KEEPS TEMPERATURES BELOW NORMAL
THROUGH THE PERIOD WITH A SLOW MODERATION BY MONDAY. 93

&&

.AVIATION...00Z TAFS. MOIST SYSTEM WILL CONTINUE TO PUSH ONSHORE
OVERNIGHT. ALL TAF SITES SHOULD HAVE STEADY PRECIPITATION OVERNIGHT.
CONDITIONS WILL LOWER TO MVFR WITH LOCAL IFR THROUGH MIDDAY TUESDAY.
93

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  36  43  33  36 /  80  70  70  60
ALW  38  45  34  38 /  80  70  70  70
PSC  37  47  33  37 /  70  50  70  40
YKM  31  41  25  33 /  70  30  50  30
HRI  36  46  33  37 /  70  60  70  40
ELN  29  39  26  32 /  80  40  40  30
RDM  32  45  26  33 /  70  70  80  60
LGD  35  41  28  35 /  70  80  80  60
GCD  33  42  28  31 /  70  80  80  50
DLS  37  45  33  37 /  80  70  80  50

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...WINTER WEATHER ADVISORY FROM 10 PM THIS EVENING TO 10 AM PST
     WEDNESDAY ABOVE 4000 FEET FOR THE ORZ503-506.

     WINTER STORM WARNING FROM 10 PM THIS EVENING TO 10 AM PST
     WEDNESDAY ABOVE 4500 FEET FOR THE ORZ502.

WA...WINTER STORM WARNING FROM 10 PM THIS EVENING TO 10 AM PST
     WEDNESDAY ABOVE 4500 FEET FOR THE WAZ030.

&&

THREAT INDEX
TUESDAY : YELLOW
WEDNESDAY : GREEN
THURSDAY : 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

85/93/93

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE PENDLETON OR
240 PM PST MON DEC 27 2010

UPDATED FOR WINTER HIGHLIGHTS

ORZ041-042-044-049-050-502-503-505>509-WAZ024-026>030-520-521-
281415-
EASTERN COLUMBIA RIVER GORGE OF OREGON-NORTH CENTRAL OREGON-
LOWER COLUMBIA BASIN OF OREGON-GRANDE RONDE VALLEY-WALLOWA COUNTY-
NORTHERN BLUE MOUNTAINS OF OREGON-
SOUTHERN BLUE MOUNTAINS OF OREGON-JOHN DAY BASIN-OCHOCO-
JOHN DAY HIGHLANDS-
FOOTHILLS OF THE NORTHERN BLUE MOUNTAINS OF OREGON-
FOOTHILLS OF THE SOUTHERN BLUE MOUNTAINS OF OREGON-
EAST SLOPES OF THE OREGON CASCADES-
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 OF WASHINGTON-
EAST SLOPES OF THE WASHINGTON CASCADES-SIMCOE HIGHLANDS-
240 PM PST MON DEC 27 2010

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

.DAY ONE...TONIGHT

SNOW
     NORTHWEST BLUE MOUNTAINS OF WASHINGTON, NORTHERN BLUE
     MOUNTAINS OF OREGON, SOUTHERN BLUE MOUNTAINS OF OREGON,
     OCHOCO-JOHN DAY HIGHLANDS

A PACIFIC SYSTEM WILL BRING MODERATE TO HEAVY SNOW TO THE  BLUE
MOUNTAINS AND THE OCHOCO-JOHN DAY HIGHLANDS TONIGHT. SNOW LEVELS
WILL INCREASE...BUT ACCUMULATIONS OF 9-12 INCHES ARE EXPECTED OVER
THE NORTHERN BLUE MOUNTAINS ABOVE 4500 FEET TONIGHT INTO EARLY
TUESDAY MORNING. A WINTER STORM WARNING FOR HEAVY SNOW IS IN EFFECT
FOR THIS AREA. THE SOUTHERN BLUE MOUNTAINS AND THE OCHOCO-JOHN DAY
HIGHLANDS WILL NOT SEE AS MUCH SNOW AS THE NORTHERN BLUE MOUNTAINS
BUT ENOUGH TO WARRANT A WINTER WEATHER ADVISORY FOR SNOW.  FOR
DETAILS PLEASE SEE NWS PRODUCT...PDXWSWPDT.

ELSEWHERE...ISOLATED TO SCATTERED RAIN OR SNOW SHOWERS WILL PERSIST
TODAY. THE ABOVE MENTIONED SYSTEM WILL ALSO BRING RAIN AND SNOW TO
MANY LOCATIONS TONIGHT. SNOW LEVELS WILL GENERALLY RUN BETWEEN 3000
AND 4000 FEET TONIGHT...THOUGH THEY COULD BE LOCALLY LOWER OVER
YAKIMA AND KITTITAS COUNTIES EARLY TUESDAY MORNING. SNOW AMOUNTS
OUTSIDE OF THE BLUE MOUNTAINS AND THE OCHOCO-JOHN DAY HIGHLANDS WILL
VARY FROM LESS THAN AN INCH UP TO 3 INCHES.

.DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY

SNOW TUESDAY
     NORTHWEST BLUE MOUNTAINS OF WASHINGTON, NORTHERN BLUE
     MOUNTAINS OF OREGON, SOUTHERN BLUE MOUNTAINS OF OREGON,
     OCHOCO-JOHN DAY HIGHLANDS

SNOW WEDNESDAY...AREAWIDE

SNOW WILL CONTINUE TO ACCUMULATE IN THE BLUE MOUNTAINS AND THE
HIGHER ELEVATIONS OF THE OCHOCO-JOHN DAY HIGHLANDS TUESDAY THROUGH
WEDNESDAY MORNING.

ELSEWHERE...THE RAIN AND SNOW FROM TONIGHT/S SYSTEM WILL CONTINUE
INTO TUESDAY MORNING. THERE MAY BE A SLIGHT BREAK IN...OR AT LEAST A
LET UP IN...THE PRECIPITATION TUESDAY AFTERNOON. A SECOND...COLDER
SYSTEM WILL MOVE THROUGH THE AREA TUESDAY NIGHT AND WEDNESDAY. THIS
SYSTEM WILL CAUSE SNOW LEVELS TO FALL EARLY WEDNESDAY MORNING...
ALLOWING SNOW TO AFFECT ALL AREAS MID AND LATE WEDNESDAY MORNING.
COLDER AND GENERALLY DRIER CONDITIONS WILL SETTLE OVER THE REGION
THURSDAY THROUGH SUNDAY. ANY PRECIPITATION THAT DOES FALL LATE IN
THE WEEK AND OVER THE WEEKEND WILL BE IN THE FORM OF SNOW.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE REQUIRED FOR SNOW ACCUMULATIONS TONIGHT
THROUGH WEDNESDAY.

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.