Blizzard and Heavy Snow in Oregon, December 20 to 22, 2008

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE PENDLETON OR
420 AM PST SAT DEC 20 2008

UPDATED AVIATION DISCUSSION

.SHORT TERM...TODAY THROUGH SUNDAY NIGHT...A WEAK DISTURBANCE
COMBINED WITH UPSLOPE FLOW WILL ALLOW LIGHT SNOW SHOWERS TO CONTINUE
IN THE EASTERN MOUNTAINS AND BLUE MOUNTAIN FOOTHILLS THIS MORNING.
THESE SHOWERS SHOULD TAPER OFF BY AFTERNOON AS DRIER AIR MOVES IN
FROM THE NORTH. TO THE WEST...SNOW ALONG THE CASCADE CREST IS
EXPECTED TO SPILL OVER INTO CENTRAL AND NORTH CENTRAL OREGON TODAY
AS ANOTHER PACIFIC STORM SYSTEM PUSHES INLAND. WARM ADVECTION
PRECIPITATION IS EXPECTED TO SPREAD ACROSS MUCH OF OREGON AND INTO
CENTRAL WASHINGTON BY THIS EVENING. THIS SYSTEM IS INCREDIBLY MOIST
AND HAS THE POTENTIAL TO PRODUCE HEAVY SNOW. WINTER STORM WARNINGS
WILL BE ISSUED FOR CENTRAL AND NORTH CENTRAL OREGON...AS WELL AS FOR
THE EASTERN COLUMBIA RIVER GORGE...THE EAST SLOPES OF THE WASHINGTON
CASCADES AND THE YAKIMA AND KITTITAS VALLEYS. THE REMAINDER OF THE
LOCAL FORECAST AREA WILL REMAIN UNDER A WINTER STORM WATCH FOR THE
TIME BEING.

THE UPPER LOW THAT IS DRIVING THIS WINTER STORM WILL LEAVE THE GULF
OF ALASKA AND PROGRESS SOUTHWARD ALONG THE CANADIAN COAST ON
SATURDAY NIGHT...MOVING OVER THE PACIFIC NORTHWEST BY SUNDAY NIGHT.
THIS STORM TRACK WILL ACT TO PULL ADDITIONAL MOISTURE INTO THE AREA
FROM THE EASTERN PACIFIC...ALLOWING PERIODS OF HEAVY SNOW TO PERSIST
THROUGH AT LEAST MONDAY MORNING.  CALDER

.LONG TERM...MONDAY THROUGH FRIDAY...THE AFOREMENTIONED UPPER LOW
WILL MOVE ACROSS THE FORECAST AREA ON MONDAY AND KEEP SNOW LIKELY
OVER CENTRAL AND NORTHEAST OREGON WITH A CHANCE OF SNOW OVER THE
LOWER COLUMBIA BASIN ON MONDAY. THE SYSTEM WILL EXIT THE REGION
MONDAY NIGHT WITH A CHANCE OF SNOW LINGERING OVER THE EASTERN OREGON
MOUNTAINS INTO TUESDAY. THE REGION WILL REMAIN UNDER THE INFLUENCE
OF A PROGRESSIVE UPPER LEVEL FLOW PATTERN THUS KEEPING US IN A
CHANCE OF SNOW EACH DAY THROUGH THE REMAINDER OF THE PERIOD.  POLAN

&&

.AVIATION...12Z TAFS...UPSLOPE WINDS WILL PRODUCE SNOW SHOWERS AT
KPDT...KALW AND KDLS RESULTING IN MVFR CONDITIONS THIS MORNING.
CONDITIONS AT KPDT AND KALW WILL IMPROVE THIS AFTERNOON AND BECOME
VFR WITH BKN-OVC CEILINGS ABOVE 3000 FT AGL. KPSC WILL REMAIN DRY
UNTIL AROUND 03Z SUNDAY. THIS EVENING A WARM FRONT WILL BEGIN MOVING
INTO THE AREA WITH A RETURN TO MVFR/VFR CEILINGS/VISIBILITIES BY
VIRTUE OF LIGHT SNOW SPREADING FROM SOUTHWEST TO NORTHEAST DURING
THE LATE AFTERNOON AND EVENING. SNOW WILL BEGIN AT KRDM BY LATE THIS
MORNING AND AT KYKM BY LATE THIS AFTERNOON WHILE PERIODS OF LIGHT
SNOW WILL CONTINUE THROUGHOUT TODAY AT KDLS. THE SNOW WILL SPREAD TO
KPDT ...KPSC AND KALW THIS EVENING WITH SNOW PRODUCING MVFR/IFR
CEILINGS/VISIBILITIES THIS EVENING CHANGING TO IFR/LIFR CONDITIONS
AS CEILINGS AND VISIBILITIES DETERIORATE AFTER 03Z ON SUNDAY. WINDS
WILL BE UNDER 15 KTS FOR THE NEXT 24 HOURS.  POLAN

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  14  10  22  15 /  20  80  90  70
ALW  12  11  24  17 /  20  70  90  70
PSC  13  12  24  18 /  10  70  90  60
YKM  15  10  22  12 /  10  80  90  70
HRI  13  10  22  14 /  20  70  90  60
ELN  12   8  20  11 /  10  80 100  70
RDM  27  13  33  14 /  40 100 100  90
LGD  18  15  29  24 /  10  70  90  80
GCD  25  22  31  23 /  30  80  90  90
DLS  22  15  22  20 /  30  90 100  70

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...WINTER STORM WARNING FROM 7 PM THIS EVENING TO 10 AM PST MONDAY
     FOR ORZ041.

     WINTER STORM WATCH FROM THIS EVENING THROUGH LATE SUNDAY NIGHT
     FOR ORZ044-049-050-501>506.

     WINTER STORM WARNING FROM NOON TODAY TO 10 AM PST MONDAY FOR
     ORZ042-043.

WA...WINTER STORM WARNING FROM 7 PM THIS EVENING TO 10 AM PST MONDAY
     FOR WAZ024-026-027-501-502.

     WINTER STORM WATCH FROM THIS EVENING THROUGH LATE SUNDAY NIGHT
     FOR WAZ028>030.

&&

TI:RRY
FOR ADDITIONAL WEATHER INFORMATION, CHECK OUR WEB SITE AT...
WWW.WEATHER.GOV/PENDLETON
82/99/99

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE PENDLETON OR
505 AM PST FRI DEC 19 2008

ORZ041>044-049-050-501>506-WAZ024-026>030-501-502-201300-
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-
505 AM PST FRI DEC 19 2008

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

.DAY ONE...TODAY AND TONIGHT

THE PROBABILITY FOR WIDESPREAD HAZARDOUS WEATHER IS LOW.

SNOW SHOWERS IMPACTING EASTERN PORTIONS OF THE LOWER COLUMBIA
BASIN...THE BLUE MOUNTAIN FOOTHILLS AND THE MOUNTAINS OF EASTERN
OREGON WILL TAPER THROUGHOUT THE DAY. ALTHOUGH UPSLOPE FLOW COULD
ALLOW SOME MOUNTAIN SHOWERS TO CONTINUE OVERNIGHT...SIGNIFICANT
SNOWFALL ACCUMULATIONS ARE NOT EXPECTED.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY

SNOW SATURDAY THROUGH THURSDAY
     EAST SLOPES OF THE CENTRAL CASCADES OF WASHINGTON, EAST SLOPES
     OF THE SOUTHERN CASCADES OF WASHINGTON, 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, 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

ANOTHER STORM WILL MOVE INTO THE REGION ON SATURDAY WITH EFFECTS
LASTING INTO MONDAY. EXPECT THIS WILL BE ANOTHER WIDESPREAD SNOW
EVENT WITH ACCUMULATIONS EXPECTED AT ALL LOCATIONS. ALTHOUGH
UNCERTAINTY REMAINS AS TO SPECIFIC AMOUNTS...SIGNIFICANT SNOWFALL IS
LIKELY. A WINTER STORM WATCH HAS BEEN ISSUED FOR THE ENTIRE LOCAL
FORECAST AREA. REFER TO NWS PRODUCT PDXWSWPDT FOR DETAILS.

YET ANOTHER STORM SYSTEM APPEARS IT WILL AFFECT THE REGION BEGINNING
TUESDAY AFTERNOON AND EVENING. SPECIFIC IMPACTS REMAIN RELATIVELY
UNCERTAIN AT THIS TIME. HOWEVER...ACTIVE WINTER WEATHER IS LIKELY TO
LAST THROUGH THE END OF NEXT WEEK.

.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.