Heavy Snow in Washington, April 5 to 6, 2011

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
845 PM PDT TUE APR 5 2011

.UPDATE...AN UPPER LEVEL TROUGH IS DEVELOPING OFFSHORE AND A WEAK
WAVE AT THE COASTLINE IS VISIBLE IN SATELLITE IMAGERY. A MOIST
WESTERLY FLOW IS MOVING INTO THE CASCADES AND RADAR SHOWS SHOWERS
DEVELOPING WEST OF THE CASCADES FROM PORTLAND NORTHWARD TO THE
CANADIAN BORDER. EXPECT THAT SHOWERS WILL MOVE ACROSS THE CASCADES
LATER TONIGHT AND GIVE MOST OF THE AREA A CHANCE OF SHOWERS AFTER
MIDNIGHT. SNOW LEVELS WILL DROP TO AROUND 3000 FEET LATE TONIGHT SO
SNOW WILL BE CONFINED MAINLY TO THE MOUNTAINS. PRECIPITATION AMOUNTS
WILL BE LIGHT BEFORE SUNRISE SO MOST LOCATIONS AWAY FROM THE CASCADE
CREST WILL SEE LESS THAN A HALF INCH OR SO OF SNOW OR A FEW HUNDREDS
OF AN INCH OF RAIN. COLDER AIR ALOFT WILL BE MOVING IN WITH THE
TROUGH SO TEMPERATURES WILL BE 5 TO 9 DEGREES COOLER THAN THE LAST
FEW NIGHTS BUT HEAVY CLOUD COVER WILL PREVENT A FREEZE IN THE
COLUMBIA BASIN. OTHERWISE LOWS WILL BE IN THE MID 20S TO LOWER 30S.
WINDS HAVE BEEN DROPPING OFF WITH THE ARRIVAL OF SUNDOWN AND AFTER A
BIT OF A LULL THIS EVENING WILL INCREASE BACK TO 10 TO 20 MPH AFTER
MIDNIGHT AS THE WAVE MOVES IN. WINDS WILL BE LIGHTER FROM THE BLUE
MOUNTAINS EASTWARD. CURRENT FORECAST IS GENERALLY IN GOOD SHAPE.
HAVE MADE A FEW MINOR WIND AND TEMPERATURE ADJUSTMENTS AND WILL
ISSUE A FORECAST UPDATE SHORTLY. PERRY

&&

.PREV DISCUSSION... /ISSUED 425 PM PDT TUE APR 5 2011/

SHORT TERM...TONIGHT THROUGH FRIDAY...ACTIVE WEATHER PATTERN TO
CONTEND WITH THE NEXT COUPLE OF DAYS AS AN UPPER LOW CARVES OUT OVER
THE AREA BEFORE MOVING TO THE SOUTH ON FRIDAY. THIS WILL RESULT IN
ANOTHER PRECIPITATION EVENT BUT THIS TIME THERE WILL BE PLENTY OF
COLD AIR FOR MOUNTAIN SNOWS. SNOW WILL BEGIN IN THE EASTERN
MOUNTAINS LATE TONIGHT AND CONTINUE UNTIL AT LEAST WEDNESDAY
EVENING. USING LATE SEASON SNOW CRITERIA THERE SHOULD BE ENOUGH SNOW
TO MEET ADVISORY CRITERIA FOR ALL THE MOUNTAIN ZONES. HAD LESS
CONFIDENCE IN WALLOWA COUNTY...JOHN DAY VALLEY...AND EAST SLOPES OF
OREGON CASCADES SO HELD OFF ON AN ADVISORY THESE AREAS FOR NOW.
SNOW LEVELS WILL BE RATHER LOW ESPECIALLY WEDNESDAY NIGHT SO ALL
AREAS COULD SEE A LITTLE SNOW. ON THURSDAY PRECIPITATION WILL BECOME
MORE SHOWERY IN NATURE WITH THE UPPER LOW OVERHEAD. COULD BE A STRAY
TSTM BUT NOT EXPECTING WIDESPREAD COVERAGE. BY FRIDAY SHOULD JUST
SEE WIDELY SCATTERED SNOW SHOWERS OVER THE EASTERN MOUNTAINS AS THE
LOW PULLS OFF TO THE SOUTHEAST. TEMPERATURES WILL BE QUITE COOL AND
AVERAGING ABOUT 10 DEGREES BELOW NORMAL FOR THIS TIME OF YEAR.

HAVE DECIDED TO CANCEL THE FLOOD WATCH. RIVERS AND STREAMS ARE STILL
RUNNING HIGH AND WILL CONTINUE TO DO SO FOR THE NEXT COUPLE OF DAYS.
HOWEVER WITH MUCH COLDER MOUNTAIN TEMPS...SNOWMELT/RUNOFF WILL BE
LESS OF A CONCERN AND THE OVERALL TREND IN RIVER/STREAM LEVELS
SHOULD BE GRADUALLY DOWNWARD. 78

LONG TERM...FRIDAY NIGHT THROUGH TUESDAY NIGHT...A MIGRATORY UPPER
LEVEL RIDGE OF HIGH PRESSURE WILL MOVE ACROSS THE PACIFIC NORTHWEST
FRIDAY NIGHT THROUGH SATURDAY NIGHT FOR SUBSIDENCE PRODUCING DRY
CONDITIONS AND TEMPERATURES WARMING ON SATURDAY. WHILE A STRONG
UPPER LEVEL TROUGH REACHES 135W.  A WARM FRONT AND INCREASING
MOISTURE TO THE WASHINGTON CASCADE CRESTS FOR A SLIGHT CHANCE OF
RAIN OVERNIGHT DURING THE PREDAWN HOURS ON SUNDAY.  HOWEVER...THE
LATEST 12Z GFS AND ECMWF RUNS BEGIN TO DISAGREE AT THIS POINT. THE
ECMWF MAINTAINS AN UPPER LEVEL HIGH PRESSURE RIDGE THROUGH SATURDAY
AFTERNOON WITH ONLY A FEW LINGERING SHOWERS OVER THE NORTHEAST
MOUNTAINS...WHILE THE MORE PROGRESSIVE GFS BRINGS THE NEXT WEATHER
SYSTEM INTO THE REGION ON SATURDAY. I HAVE SUBSTANTIALLY INCREASED
PRECIPITATION CHANCES ON SUNDAY SINCE BOTH GFS AND ECMWF MODELS
BRING A COLD FRONT INLAND BY SUNDAY AFTERNOON/EVENING.  WET WEATHER
WILL THEN PERSIST SUNDAY NIGHT THROUGH MONDAY AS THE MID/UPPER LEVEL
TROUGH WILL BE MOVING OVER THE INTERIOR PACIFIC NORTHWEST. IN
ADDITION...SUNDAY AFTERNOON THROUGH MONDAY AFTERNOON LOOK TO BE
BREEZY AS THE COLD FRONT USHERS IN TIGHT PRESSURE GRADIENTS. WEAK
TRANSITORY RIDGING WILL PRODUCE SUBSIDENCE FOR A DRY PERIOD FROM
MONDAY NIGHT THROUGH TUESDAY NIGHT.  POLAN

AVIATION...00Z TAFS...VFR WILL CONTINUE THROUGH THIS EVENING. AN
UPPER LEVEL SHORT WAVE WILL APPROACH THE COAST THIS EVENING AND THEN
MOVE INLAND AROUND MIDNIGHT. THIS SYSTEM WILL PRODUCE LOWERING CLOUD
BASES TONIGHT BY VIRTUE OF RAIN SPREADING TO TAF SITES FROM WEST TO
EAST AFTER 06/09Z. LOWER CEILINGS WILL BRING MVFR CONDITIONS TO TAF
SITES OVERNIGHT AND THROUGH WEDNESDAY MORNING. RAIN WILL END BY
AROUND AROUND 06/18Z TO 06/19Z. THE ONLY EXCEPTION WILL BE AT KYKM
WHERE DRY CONDITIONS ARE EXPECTED UNTIL AROUND 06/19Z WHEN SHOWERS
ARE EXPECTED THROUGH WEDNESDAY AFTERNOON.  POLAN

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  36  45  30  46 /  40  70  40  40
ALW  39  47  32  46 /  40  80  40  40
PSC  39  51  30  52 /  40  50  30  20
YKM  33  47  26  50 /  30  40  20  20
HRI  37  50  29  52 /  30  50  40  30
ELN  34  43  24  47 /  40  40  20  20
RDM  27  39  22  41 /  30  60  60  40
LGD  34  39  27  38 /  40  80  50  50
GCD  27  36  25  38 /  20  60  60  40
DLS  37  46  29  51 /  40  70  50  30

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...WINTER WEATHER ADVISORY FROM 5 AM WEDNESDAY TO 5 AM PDT THURSDAY
     ORZ506.

     WINTER WEATHER ADVISORY FROM 5 AM WEDNESDAY TO 5 AM PDT THURSDAY
     ORZ502.

     WINTER WEATHER ADVISORY FROM 5 AM WEDNESDAY TO 5 AM PDT THURSDAY
     ORZ503.

WA...WINTER WEATHER ADVISORY FROM 5 AM WEDNESDAY TO 5 AM PDT THURSDAY
     WAZ030.

&&

THREAT INDEX
WEDNESDAY : YELLOW
THURSDAY : GREEN
FRIDAY : 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

83/99/99

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE PENDLETON OR
127 PM PDT TUE APR 5 2011

UPDATED FOR SNOW ADVISORIES

ORZ041-042-044-049-050-502-503-505>509-WAZ024-026>030-520-521-
061415-
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-
127 PM PDT TUE APR 5 2011

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

.DAY ONE...TONIGHT

THE PROBABILITY FOR WIDESPREAD HAZARDOUS WEATHER IS LOW.

A MOIST PACIFIC STORM SYSTEM WILL BRING INCREASING CHANCES FOR RAIN
AND SNOW OVERNIGHT TONIGHT.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY

SNOW WEDNESDAY
     EAST SLOPES OF THE WASHINGTON CASCADES, NORTHWEST BLUE
     MOUNTAINS OF WASHINGTON, NORTH CENTRAL OREGON, EAST SLOPES OF
     THE OREGON CASCADES, GRANDE RONDE VALLEY, WALLOWA COUNTY,
     NORTHERN BLUE MOUNTAINS OF OREGON, SOUTHERN BLUE MOUNTAINS OF
     OREGON, FOOTHILLS OF THE SOUTHERN BLUE MOUNTAINS OF OREGON,
     JOHN DAY BASIN, OCHOCO-JOHN DAY HIGHLANDS

A MOIST AND COLD PACIFIC STORM SYSTEM AND COLD FRONT WILL BRING
LOWER ELEVATION RAIN AND MOUNTAIN SNOW TO THE AREA. SNOW COULD
EXTEND DOWN TO 1500 FEET ESPECIALLY WEDNESDAY NIGHT. THE EASTERN
MOUNTAINS COULD SEE SEVERAL INCHES OF SNOW AND SNOW ADVISORIES
ARE IN EFFECT FOR WEDNESDAY AND WEDNESDAY NIGHT. PLEASE SEE
PDXWSWPDT FOR MORE DETAILS.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE REQUIRED WEDNESDAY AND WEDNESDAY NIGHT.

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.