Heavy Snow in Oregon, December 19 to 20, 2007

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
225 PM PST WED DEC 19 2007

.SHORT TERM...TONIGHT THROUGH FRIDAY NIGHT...SATELLITE IMAGERY SHOWS
A WEATHER SYSTEM MOVING INTO THE PACIFIC NORTHWEST. THE COLD FRONT
ASSOCIATED WITH THIS SYSTEM IS CURRENTLY JUST OFF SHORE AND IS
EXPECTED TO MOVE INLAND AND OVER THE AREA TONIGHT. PRECIPITATION IS
GRADUALLY INCREASING OVER THE AREA AHEAD OF THE FRONT. WITH THE WARM
TEMPERATURES...LOWER LOCATIONS ARE RECEIVING RAIN WHILE HIGHER
ELEVATIONS ARE RECEIVING SNOW. EXPECT THE SNOW LEVELS TO LOWER
OVERNIGHT AS COLDER AIR BEHIND THE COLD FRONT MOVES INTO THE REGION.
PRECIPITATION AMOUNTS IN CENTRAL OREGON WILL BE ENOUGH FOR 3 TO 5
INCHES OF ADDITIONAL SNOW AND THUS A SNOW ADVISORY WILL BE ISSUED
FOR TONIGHT INTO TOMORROW MORNING. TEMPERATURES WILL COOL AFTER
SUNDOWN IN THIS AREA AND ALLOW FOR SNOW TO ACCUMULATE. WINDS AROUND
THE REGION WILL BE BREEZY TO WINDY THIS EVENING BEFORE DECREASING
OVERNIGHT.

A TROUGH OF LOW PRESSURE WILL KEEP A CHANCE OF PRECIPITATION OVER
THE AREA TOMORROW AND WINDS WILL BECOME WEST TO NORTHWEST. THIS WILL
ALLOW FOR UPSLOPE SHOWERS ACROSS THE MOUNTAINS OF NORTHWEST OREGON
AND SOUTHWEST WASHINGTON. TEMPERATURES WILL BE 5 TO 10 DEGREES
COOLER THAN TODAY. WINDS WILL ALSO INCREASE DURING THE DAY WITH
BREEZY CONDITIONS EXPECTED. THE TROUGH WILL MOVE TO THE EAST
THURSDAY NIGHT AND A RIDGE WILL BUILD INTO THE AREA ON FRIDAY.
PRECIPITATION CHANCES WILL DECREASE ACROSS THE REGION WITH DRY
CONDITIONS EXPECTED IN THE LOWER ELEVATIONS. MOIST CONDITIONS COULD
LEAD TO THE DEVELOPMENT OF MORNING FOG ACROSS THE BASIN AND AREA
VALLEYS FRIDAY MORNING. DK

.LONG TERM...SATURDAY THROUGH WEDNESDAY...AN OCCLUDED FRONT WILL
MOVE THROUGH THE PACIFIC NORTHWEST SATURDAY. THE EFFECT OF THE
CASCADES WILL DISRUPT FRONTAL CHARACTERISTICS AND LIMIT
PRECIPITATION TO THE EAST. THIS WILL RESTRICT HIGH POPS TO SLOPOVER
PRECIPITATION NEAR THE CREST ON SATURDAY. THE UPPER LEVEL TROUGH
WILL KEEP A CHANCE OF PRECIPITATION OVER EASTERN WASHINGTON AND
OREGON SATURDAY NIGHT AND SUNDAY MORNING. THERE WILL BE A BRIEF
BREAK BEFORE THE NEXT SYSTEM MOVES THROUGH SUNDAY NIGHT AND MONDAY
MORNING. KEPT LOW POPS SUNDAY OVER THE PRECIPITATION SHADOWED LOWER
COLUMBIA BASIN DUE TO SOME UNCERTAINTY IN TIMING...EVEN THOUGH I AM
CERTAIN THERE WILL BE A BREAK. THE JETSTREAM WITH THE SUNDAY NIGHT
AND MONDAY SYSTEM WILL BE FARTHER SOUTH ALLOWING BETTER DYNAMIC
SUPPORT...SO PREDICTING LIKELY TO HIGH CHANCE POPS SUNDAY NIGHT OVER
THE ENTIRE CWA. THERE WILL BE A PERSISTENT SOUTHERLY WIND SUNDAY
AFTERNOON THROUGH EARLY MONDAY MORNING AHEAD OF THE FRONT...SO SNOW
LEVELS WILL REMAIN 1500-4000 FEET OVER EASTERN WASHINGTON AND
OREGON...WITH THE LOWEST LEVELS IN THE YAKIMA AND KITTITAS VALLEYS
WHERE UPSLOPE CONDITIONS WILL KEEP COLDER AIR OVER THE VALLEYS. THIS
SETUP USUALLY PRODUCES WINDY CONDITIONS OVER THE SOUTHERN GRANDE
RONDE VALLEY AND POSSIBLY THE HIGHER ELEVATIONS IN WALLOWA COUNTY.
AFTER THE FRONT PASSES MONDAY COOLER AND DRIER AIR WILL BE OVER THE
AREA AS A TRANSIENT RIDGE MOVES OVER THE PACIFIC NORTHWEST TUESDAY.
ANOTHER SYSTEM WILL MOVE THROUGH TUESDAY NIGHT AND WEDNESDAY...WITH
MORE UNCERTAINTY IN TIMING AND STRENGTH AS GFS HAS A SLOWER AND MORE
AMPLIFIED SYSTEM THAN THE ECMWF.   COONFIELD

&&

.AVIATION...EXPECT MAINLY LOW END VFR WITH PERIODS OF MVFR CIGS NEAR
SHOWERS WHEN VISIBILITY MAY DECREASE IN -SHSN. SOME CLEARING BEHIND
WAVE 14-18Z TOMORROW WITH MID CLOUDS LINGERING INTO AFTERNOON AT PDT
AND ALW. 76

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  37  40  28  33 /  50  20  10  10
ALW  39  43  30  33 /  50  20  10  10
PSC  35  44  27  33 /  50  20  10  10
YKM  30  39  22  30 /  50  20  10  10
HRI  35  42  26  34 /  50  20  10  10
ELN  27  35  20  29 /  60  20  10  10
RDM  30  36  17  31 /  70  60  20  10
LGD  34  38  23  29 /  60  40  20  10
GCD  32  36  23  26 /  60  50  20  10
DLS  35  43  30  39 /  60  30  20  10

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...SNOW ADVISORY UNTIL 11 AM PST THURSDAY FOR ORZ043.

WA...NONE.
&&

TI:YGG
FOR ADDITIONAL WEATHER INFORMATION, CHECK OUR WEB SITE AT...
WWW.WEATHER.GOV/PENDLETON
84/76/76

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE PENDLETON OR
155 PM PST WED DEC 19 2007

ORZ041>044-049-050-501>506-WAZ024-026>030-501-502-201415-
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-
155 PM PST WED DEC 19 2007

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

.DAY ONE...TONIGHT

SNOW
     CENTRAL OREGON

LOW PRESSURE SYSTEM WILL MOVE ACROSS THE PACIFIC NORTHWEST BRINGING
RAIN/SNOW AND WINDY CONDITIONS. THE MOUNTAINS WILL RECEIVE SEVERAL
INCHES OF SNOW ACCUMULATION ALONG WITH GUSTY SOUTHWEST WINDS. A SNOW
ADVISORY HAS BEEN ISSUED FOR CENTRAL OREGON THROUGH THURSDAY
MORNING. PLEASE REFER TO PRODUCT ID PDXWSWPDT FOR MORE DETAILS.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

THE PROBABILITY FOR WIDESPREAD HAZARDOUS WEATHER IS LOW.

ACTIVE WEATHER PATTERN WILL CONTINUE WITH FRONTS MOVING ACROSS THE
REGION EVERY FEW DAYS BRINGING RAIN AND SNOW.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE REQUIRED TONIGHT INTO THURSDAY FOR CENTRAL
OREGON.

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.