Winter Storm Warning 7, NWS Pendleton, OR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
250 AM PDT FRI MAR 28 2008

.SHORT TERM...TODAY THROUGH SATURDAY.  A CHALLENGING FORECAST IS IN
STORE FOR TODAY AND TONIGHT WITH SEVERAL WEATHER CONCERNS...
SPECIFICALLY SNOW ACCUMULATION AND WINDS.  A VERTICALLY STACKED LOW
CURRENTLY CENTERED 50N/135W WILL MOVE ONSHORE THIS MORNING THEN
ACROSS WA/OR THIS AFTERNOON AND EVENING.  THERE IS A STRONG UPPER
LEVEL JET ALONG THE BOTTOM OF THE TROUGH AND VERY COLD AIR ALOFT.
SNOW LEVELS WILL LOWER TO THE BASIN FLOOR WITH A POTENTIAL FOR
ACCUMULATIONS IN ALL ZONES.  THE QUESTION IS WHO WILL RECEIVE
AMOUNTS IN THE ADVISORY OR WARNING CATEGORY.  CURRENT ADVISORIES FOR
THE WA CASCADE EAST SLOPES...THE SOUTHERN BLUE MTNS...AND WALLOWA
COUNTY APPEAR ON TRACK BUT WILL SHORTEN THE ADVISORY TIME FOR THE
EAST SLOPES THROUGH THIS EVENING RATHER THAN EARLY SAT MORNING.
WILL ALSO INCLUDE A SNOW ADVISORY FOR THE KITTITAS VALLEY.  WILL
UPGRADE THE SNOW ADVISORY TO A WINTER STORM WARNING FOR THE NORTHERN
BLUES EFFECTIVE UNTIL SAT AFTERNOON.  THERE WILL REMAIN STRONG
OROGRAPHIC LIFT AND UPPER LEVEL SUPPORT THROUGH SATURDAY...AND
BLOWING SNOW WILL BE A CONCERN.  WILL ISSUE A SNOW AND BLOWING SNOW
ADVISORY FOR THE JOHN DAY BASIN AND OCHOCO HIGHLANDS.

AGAIN...THERE IS A POTENTIAL FOR SNOW ACCUMULATIONS IN ALL ZONES
THIS AFTERNOON AND TONIGHT. THE AMOUNTS IN THE OREGON PORTION OF THE
BLUE MTN FOOTHILLS AND THE CONDON/FOSSIL AREA COULD BE CLOSE TO SNOW
ADVISORY.  THE BEST POTENTIAL FOR PRECIPITATION IN THESE AREAS WILL
BE LATE THIS AFTERNOON WHEN THE SURFACE LOW AND COLD FRONT MOVES
ACROSS EASTERN OREGON...YET THE GROUND MAY BE TOO WARM AND
PRECIPITATION DURATION NOT LONG ENOUGH FOR SIGNIFICANT
ACCUMULATION.

IT WILL BECOME WINDY TONIGHT AND SATURDAY DUE TO STRONG SURFACE
GRADIENTS AND WINDS ALOFT.  HOWEVER...THE SURFACE LOW IS TRACKING
FARTHER SOUTH THAN PREVIOUSLY INDICATED BY THE MODELS.  THE NAM HAS
BACKED OFF ON WINDS ALOFT.  WILL NOT ISSUE ANY ADVISORIES ALTHOUGH
LOCAL WINDS MAY GUST TO 45 MPH.

ON SATURDAY...THE PACIFIC NW WILL BE UNDER THE INFLUENCE OF THE COLD
UPPER TROUGH FOR CONTINUED SHOWERS AND BREEZY/WINDY CONDITIONS.
GRAUPEL IS ALSO LIKELY WITH SOME SHOWERS...AS HAS BEEN THE CASE THE
PAST SEVERAL DAYS.  JOHNSON

.LONG TERM...SATURDAY NIGHT THROUGH MONDAY NIGHT...REGION REMAINS
UNDER THE INFLUENCE OF AN UPPER LEVEL LOW WITH THE CENTER TRANSITING
NEARLY OVERHEAD THE CWA ON SUNDAY. AS SUCH...HAVE FOLLOWED MORE OF A
PATTERN RECOGNITION APPROACH RATHER THAN ANY SPECIFIC MODEL QPF.
COLD CORE ALOFT WILL LEAD TO UNSTABLE CONDITIONS WITH SHOWERS
POSSIBLE EVERYWHERE GIVEN THE COLD CORE ALOFT. EXPECT ACCUMULATING
SNOW LEVELS TO MAX OUT AT 2500-3000 FEET WITH A QUICK INCH OR TWO
FROM ANY PASSING SHOWER MAINLY AT ELEVATIONS ABOVE 4000 FEET. LOWER
ELEVATIONS, INCLUDING THE BASIN, COULD SEE A RAIN/SNOW MIX AND ALL
SNOW UNDER THE HEAVIER SHOWERS BUT WITH NO ACCUMULATIONS AS GROUND
TEMPERATURES SHOULD BE PLENTY WARM UNDER PARTLY CLOUDY SKIES.
TEMPERATURES ON SUNDAY WILL CONTINUE TO REMAIN BELOW NORMAL. SOME
SHOWERS WILL CONTINUE INTO THE EARLY EVENING AND DISAPPEAR ENTIRELY
TOWARDS SUNSET AS THE LOW MOVES EAST OF THE AREA. A BRIEF RIDGE
BEGINS TO BUILD OFFSHORE GIVING MOST AREAS A TEMPORARY BREAK FROM
THIS ACTIVE PATTERN. JBONK

TUESDAY THROUGH THURSDAY...NO CHANGES MADE...PREVIOUS DISCUSSION
FOLLOWS...SPLIT FLOW IS OVER THE AREA ON TUESDAY AS A TROUGH OF LOW
PRESSURE SWINGS THROUGH NORTHERN WASHINGTON AND A LOW PRESSURE
SYSTEM IS LOCATED OFF THE NORTHERN CALIFORNIA COAST. THIS WILL GIVE
THE MOUNTAINS...MAINLY NORTHWEST BLUES A CHANCE OF PRECIPITATION.
MODELS ARE COMING INTO MORE AGREEMENT WITH THE TROUGH CONSOLIDATING
AS THE MAIN LOW MOVES THROUGH CALIFORNIA ON WEDNESDAY.  THERE IS
SOME WEAK RIDGING WEDNESDAY NIGHT BEFORE SOUTHWEST FLOW BRINGS IN
MORE MOISTURE THURSDAY AHEAD OF NEXT LOW PRESSURE SYSTEM.
TEMPERATURES WILL BE SEASONAL. 93

&&

.PREVIOUS AVIATION DISCUSSION...VFR CONDITIONS AND LIGHT WINDS WILL
PREVAIL OVERNIGHT. AS THE NEXT FRONTAL SYSTEM MOVES INTO THE AREA
LATER TONIGHT/FRIDAY MORNING...CLOUDS WILL BEGIN TO INCREASE OVER
EASTERN WASHINGTON AND OREGON AFTER 08-10Z. RAIN AND SNOW ARE
EXPECTED TO IMPACT KDLS...KYKM AND KRDM BY 15Z...AND KPSC...KPDT AND
KALW BY 20Z. MVFR CONDITIONS WILL BE POSSIBLE NEAR SHRA AT ALL
LOCATIONS AND IFR WILL BE POSSIBLE IN SNSH AT KRDM AND KYKM. WINDS
WILL IN INCREASE TO 10-20 KTS BY AFTERNOON. 82

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  45  31  47  30 /  60  60  30  20
ALW  46  33  49  30 /  60  60  30  20
PSC  47  32  54  30 /  60  40  20  10
YKM  43  26  51  28 /  60  30  20  10
HRI  46  31  53  30 /  60  40  20  10
ELN  41  25  48  25 /  70  40  20  20
RDM  39  17  40  17 /  70  50  20  10
LGD  40  27  39  24 /  70  60  30  20
GCD  42  22  39  22 /  70  60  30  20
DLS  44  34  52  31 /  80  40  20  10

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...SNOW AND BLOWING SNOW ADVISORY FROM 11 AM THIS MORNING TO 10 PM
     PDT THIS EVENING FOR ORZ505-506.

     WINTER STORM WARNING FROM 11 AM THIS MORNING TO 3 PM PDT
     SATURDAY FOR ORZ502.

     SNOW AND BLOWING SNOW ADVISORY FROM 11 AM THIS MORNING TO 5 AM
     PDT SATURDAY FOR ORZ049-050-503.

WA...WINTER STORM WARNING FROM 11 AM THIS MORNING TO 3 PM PDT
     SATURDAY FOR WAZ030.

     SNOW ADVISORY FROM 11 AM THIS MORNING TO 10 PM PDT THIS EVENING
     FOR WAZ026-501-502.

&&

TI:YGG
FOR ADDITIONAL WEATHER INFORMATION, CHECK OUR WEB SITE AT...
WWW.WEATHER.GOV/PENDLETON
85/87/93

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