Heavy Snow in Oregon, May 5, 2010

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
227 AM PDT WED MAY 5 2010

.SHORT TERM...TODAY THROUGH THURSDAY NIGHT...COMPLEX WEATHER
SCENARIO IS UNFOLDING TODAY THROUGH TONIGHT AS UPPER LOW ALONG THE
WASHINGTON COAST MOVES SEWD ACROSS NE OREGON. PRECIPITATION MAINLY
IN THE FORM OF SNOW IS STARTING TO DEVELOP OVER NE OREGON IN ADVANCE
OF THE SYSTEM AND LATER TODAY UPSLOPE COMPONENT WILL ENHANCE
SNOWFALL OVER THE BLUE MOUNTAINS. MODEL QPF FIELDS HAVE BEEN A
LITTLE INCONSISTENT FROM RUN TO RUN...BUT IT DOES APPEAR THAT HEAVY
LATE SEASON SNOW WILL FALL OVER THE NORTHERN BLUE MOUNTAINS OF
OREGON AND SOUTHEAST WASHINGTON AS WELL AS PORTIONS OF WALLOWA
COUNTY TODAY THROUGH TONIGHT ABOVE 3500 FEET. LIGHTER BUT STILL
ADVISORY AMOUNTS CAN BE EXPECTED OVER MUCH OF THE REMAINDER OF
NORTHEAST AND E-CENTRAL OREGON ABOVE 3000 FEET. THERE WILL BE
MARGINAL INSTABILITY OVER THE AREA THIS AFTERNOON...BUT WITH
SURFACE-BASED CAPE LESS THAN 200 J/KG HAVE OPTED NOT TO INCLUDE
THUNDERSTORMS FOR WHAT SHOULD AMOUNT TO A COUPLE OF STRIKES OVER THE
WHOLE FORECAST AREA. TEMPERATURES WILL BE NEAR FREEZING TONIGHT FOR
PORTIONS OF THE BASIN AND FOOTHILLS BUT NOT EXPECTED TO GO MUCH
BELOW...SO HAVE OPTED NOT TO GO WITH A FREEZE WARNING AT THE PRESENT
TIME. ON THURSDAY CONDITIONS WILL IMPROVE AS WINDS FINALLY BECOME
LIGHT AND TEMPERATURES WARM INTO THE 60S AT THE LOWER ELEVATIONS...A
NICE SPRING DAY WHICH HAVE BEEN FEW AND FAR BETWEEN LATELY. 78

.LONG TERM...FRIDAY A WEAK UPPER LEVEL TROUGH AND LOW WILL MOVE
ACROSS THE PACIFIC NORTHWEST AND MAY TRIGGER A FEW SHOWERS IN THE
MOUNTAINS. SATURDAY THROUGH MONDAY MODELS AGREE ON OVERALL TROUGHING
IN THE PACIFIC NORTHWEST...BUT VARY ON THE DETAILS. DID NOT CHANGE
EXISTING FORECAST OF SLOWLY INCREASING POPS AS THE TROUGHING
DEVELOPS. BY MONDAY NIGHT THE GFS HAS THE LOW IN ARIZONA...TROUGHING
IN MONTANA...AND A RIDGE BUILDING OVER THE NORTHWEST. THE ECMWF
KEEPS THE LOW FARTHER NORTH AND NORTHEAST FLOW AROUND IT PROVIDING
WRAPAROUND MOISTURE AND PRECIPITATION OVER EASTERN WASHINGTON AND
OREGON. DID NOT CHANGE MUCH DUE TO MODEL UNCERTAINTY. LEFT THE LOWER
COLUMBIA BASIN DRY WITH LOW CHANCE POPS ELSEWHERE WHICH WOULD FIT
WITH SOME DRYING TO THE NORTH UNDER A BUILDING RIDGE...BUT DID NOT
DISCOUNT THE ECMWF LINGERING TROUGH.  COONFIELD

&&

.AVIATION...06Z TAFS...VFR CONDITIONS ARE GENERALLY EXPECTED THROUGH
THIS PERIOD. AN UPPER LOW IS EXPECTED TO MOVE OVER THE AREA
WEDNESDAY WITH VARYING AMOUNTS OF SHOWERS POSSIBLE. CIGS AND VIS MAY
GO BELOW VFR AT KPDT DUE TO HEAVIER MIXED SHOWERS OF RAIN AND/OR
SNOW AT SOME POINT BETWEEN 05/10 AND 05/16 UTC. FOR NOW WILL
INDICATE VIS OF 6 SM AND CIGS OF 3000 FT AGL. ELSEWHERE LOOK FOR
CIGS OF 3500 TO 8000 FT AGL WITH SHOWERS. INSTABILITY MAY BECOME
STRONG ENOUGH FOR A STRAY THUNDERSTORM WEDNESDAY AFTERNOON OVER
CENTRAL OREGON. FOR NOW WILL USE A CB REMARK TO INDICATE THE SLIGHT
POTENTIAL AT KRDM. SUSTAINED WINDS WILL INCREASE TO 10-25 KTS
WEDNESDAY AFTERNOON WITH THE STRONGEST WINDS EXPECTED AT KDLS. 90

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  48  31  59  32 /  70  30  10  10
ALW  49  34  61  35 /  50  30  10  10
PSC  57  32  66  35 /  20  20  10  10
YKM  54  30  62  34 /  20  10  10  10
HRI  55  33  64  33 /  30  20  10  10
ELN  53  32  62  33 /  20  10  20  20
RDM  45  21  57  23 /  30  20  10  10
LGD  41  29  55  27 /  70  70  10  10
GCD  39  23  54  25 /  70  50  10  10
DLS  56  34  64  38 /  30  20  10  10

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...WINTER WEATHER ADVISORY UNTIL 3 PM PDT THIS AFTERNOON ABOVE 3000
     FEET FOR THE ORZ505-506.

     WINTER STORM WARNING UNTIL 4 AM PDT THURSDAY ABOVE 3500 FEET FOR
     THE ORZ050-502.

     WINTER WEATHER ADVISORY UNTIL 10 PM PDT THIS EVENING ORZ503.

     WINTER WEATHER ADVISORY UNTIL 11 AM PDT THIS MORNING ABOVE 1500
     FEET FOR THE ORZ501.

     WINTER WEATHER ADVISORY UNTIL 10 PM PDT THIS EVENING ORZ049.

WA...WINTER STORM WARNING UNTIL 4 AM PDT THURSDAY ABOVE 3500 FEET FOR
     THE WAZ030.

&&

THREAT INDEX
TODAY : 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

78/76/76

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE PENDLETON OR
925 PM PDT TUE MAY 4 2010

UPDATED TO ADD SNOW ADVISORY TO THE FOOTHILLS OF THE OREGON BLUE
MOUNTAINS

ORZ041>044-049-050-501>506-WAZ024-026>030-501-502-051415-
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 OF WASHINGTON-
EAST SLOPES OF THE CENTRAL CASCADES OF WASHINGTON-
EAST SLOPES OF THE SOUTHERN CASCADES OF WASHINGTON-
925 PM PDT TUE MAY 4 2010

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

.DAY ONE...TONIGHT

SNOW TONIGHT
    NORTHERN BLUE MOUNTAINS OF OREGON, SOUTHERN BLUE MOUNTAINS
    OF OREGON, GRANDE RONDE VALLEY, FOOTHILLS OF THE OREGON BLUE
    MOUNTAINS ABOVE 1500 FEET.

SNOW WILL DEVELOP ACROSS THE BLUE MOUNTAINS AND BLUE MOUNTAIN
FOOTHILLS OVERNIGHT AS AN UPPER LEVEL LOW PRESSURE SYSTEM APPROACHES
THE AREA. A WINTER WEATHER ADVISORY FOR SNOW HAS BEEN ISSUED FOR THE
BLUE MOUNTAINS OF OREGON. PLEASE REFER TO PDXWSWPDT FOR MORE
DETAILS.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY

SNOW WEDNESDAY
    NORTHERN BLUE MOUNTAINS OF OREGON, SOUTHERN BLUE MOUNTAINS
    OF OREGON, GRANDE RONDE VALLEY, WALLOWA COUNTY, JOHN DAY
    BASIN, OCHOCO-JOHN DAY HIGHLANDS

ISOLATED THUNDERSTORMS WEDNESDAY
     FOOTHILLS OF THE BLUE MOUNTAINS OF WASHINGTON, NORTHWEST BLUE
     MOUNTAINS OF WASHINGTON, NORTH CENTRAL OREGON, CENTRAL 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

A LARGE LOW PRESSURE SYSTEM WILL GRADUALLY MOVE ACROSS WASHINGTON
AND OREGON ON WEDNESDAY.  THE SYSTEM WILL SPREAD COLD AIR AND DEEP
MOISTURE ACROSS EASTERN OREGON...RESULTING IN LOW SNOW LEVELS AND
SIGNIFICANT SNOW TO THE AREAS LISTED ABOVE.  WINTER WEATHER
ADVISORIES FOR SNOW HAVE BEEN ISSUED.  FOR DETAILS...REFER TO THE
NWS PRODUCT PDXWSWPDT.  THE AIR MASS IS UNSTABLE...AND A FEW
AFTERNOON THUNDERSTORMS ARE POSSIBLE ACROSS CENTRAL AND EASTERN
OREGON AND SOUTHEAST WASHINGTON.  THUNDERSTORMS ARE NOT EXPECTED TO
BE STRONG OR SEVERE...ALTHOUGH THERE IS A GOOD CHANCE OF SMALL HAIL.

AFTER THE LOW MOVES OUT OF THE REGION...CLOUDS WILL DECREASE AND
OVERNIGHT TEMPERATURES WILL FALL RAPIDLY WEDNESDAY NIGHT.  NEAR
RECORD LOWS ARE EXPECTED.  TEMPERATURES MAY REACH NEAR TO BELOW
FREEZING IN THE LOWER COLUMBIA BASIN AND THE BLUE MOUNTAIN FOOTHILLS
LATE WEDNESDAY NIGHT.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS LIKELY ACROSS THE NORTHEAST OREGON HIGHLANDS
ON 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.