Heavy Snow in Oregon, April 27 to 28, 2010

AREA FORECAST DISCUSSION...CORRECTION
NATIONAL WEATHER SERVICE PENDLETON OR
237 PM PDT TUE APR 27 2010

CORRECTED LONG TERM DISCUSSION AND EDITED SHORT TERM DISCUSSION

.SHORT TERM...TONIGHT THROUGH THURSDAY NIGHT...FOR THE REMAINDER OF
THIS AFTERNOON AND THIS EVENING...A MID/UPPER LEVEL SHORT WAVE WILL
MOVE NORTHEAST ACROSS CENTRAL AND NORTHEAST OREGON. THE SHORT WAVE
WILL PROVIDE STRONG DYNAMIC LIFT AND FORCING LEADING TO DIFFLUENT
FLOW IN THE UPPER ATMOSPHERE FOR CONVERGENCE AT LOW LEVELS AND
DIVERGENCE ALOFT. INFRARED AND VISIBLE SATELLITE IMAGERY LOOPS SHOW
A COLD FRONT STALLED OVER EASTERN WASHINGTON AND OREGON...WHICH WILL
MOVE SLOWLY INTO IDAHO THIS EVENING. ELEVATED INSTABILITY ALONG AND
AHEAD OF THE FRONT WILL PRESENT AN ENVIRONMENT FAVORABLE FOR
ISOLATED THUNDERSTORMS TO DEVELOP THIS AFTERNOON AND THIS EVENING...
MAINLY IN CENTRAL AND NORTHEAST OREGON AND IN SOUTHEAST WASHINGTON.
VERY STRONG VERTICAL WIND SHEAR WILL BE IN THIS SAME AREA THUS
INCREASING THE CHANCES FOR A FEW ORGANIZED AND LONG-LIVED
THUNDERSTORMS WITH UPDRAFTS CAPABLE OF PRODUCING HAIL AND ASSOCIATED
DOWNDRAFTS CAPABLE OF PRODUCING LOCALLY STRONG GUSTY WINDS. THIS
WILL CREATE AN ENVIRONMENT SUPPORTIVE OF AT LEAST STRONG TO
MARGINALLY SEVERE STORMS LATE THIS AFTERNOON IN CENTRAL AND
NORTHEAST OREGON. BREAKS IN CLOUD COVER ARE CONTRIBUTING TO SURFACE
HEATING AND STEEPENING LAPSE RATES ACROSS CENTRAL AND NORTHEAST
OREGON THIS AFTERNOON WITH A STRONG UPPER LEVEL LEFT QUADRANT JET
EXIT REGION AND MID-LEVEL COOLING. WILL MONITOR CONVECTIVE SITUATION
FOR STRONG THUNDERSTORMS FOR THE NEXT SEVERAL HOURS...AT LEAST UNTIL
9 PM PDT. SHOWERS ARE LIKELY OVERNIGHT INTO WEDNESDAY MORNING IN THE
EASTERN MOUNTAINS OF OREGON AND SOUTHEAST WASHINGTON.

WRAP AROUND MOISTURE ASSOCIATED WITH A MID/UPPER LEVEL LOW
DEVELOPING OVER EASTERN WASHINGTON/MONTANA WEDNESDAY ALONG WITH
MARGINAL INSTABILITY IN THE AFTERNOON AND EARLY EVENING WILL
INTRODUCE A SLIGHT CHANCE OF AFTERNOON/EVENING THUNDERSTORMS IN
CENTRAL AND NORTHEAST OREGON AND ALONG THE FOOTHILLS OF THE BLUE
MOUNTAINS AND IN THE BLUE MOUNTAINS IN SOUTHEAST WASHINGTON.

WRAP AROUND MOISTURE CONTINUES OVER EXTREME NORTHEAST OREGON ON
THURSDAY AND THURSDAY NIGHT FOR OROGRAPHIC RAIN/SNOW SHOWERS OVER
MOUNTAINS.  POLAN

.LONG TERM...FRIDAY THROUGH TUESDAY...THERE IS GENERAL AGREEMENT
WITHIN THE MID RANGE DATA FOR THE PERIOD FRIDAY THROUGH SATURDAY
NIGHT. THIS DATA INDICATES THAT AN UPPER RIDGE WILL BE OFF THE WEST
COAST WITH NORTHWEST FLOW OVER THE PACIFIC NORTHWEST. THIS FLOW
WOULD BE MOSTLY DRY THOUGH SOME SHOWERS MAY PERSIST NEAR THE
CASCADES AND OVER THE INTERIOR MOUNTAINS. UNCERTAINTY BEGINS TO
CREEP BACK INTO THE FORECAST BY SUNDAY THROUGH EARLY NEXT
WEEK...THOUGH THERE IS SOME INDICATION THAT THERE MAY SOME TREND
TOWARDS AGREEMENT AGAIN BY TUESDAY. FOR THE SUNDAY THROUGH MONDAY
PERIOD THOUGH...SOME DATA INDICATE A STRONG RIDGE OVER THE
PACNW...WHILE OTHER DATA SUGGESTS THAT ANOTHER TROUGH WILL PUSH IN
LATE SUNDAY AND MONDAY. FOR NOW WILL CONTINUE CURRENT FORECAST
SHOWING AN INCREASED CHANCE OF SHOWERS FROM SUNDAY ONWARD. 90

&&

.AVIATION...PREVIOUS DISCUSSION...18Z TAFS...A COLD FRONT CONTINUES
TO MOVE ACROSS THE REGION AND IS CURRENTLY IN THE VICINITY OF
KPSC...KPDT AND KALW. AS SUCH THESE THREE SITES HAVE SEE SOME
MODERATE RAIN AS WELL AS IFR AND MVFR CIGS/VIS. THE HEAVIEST PRECIP
IS AT THIS MOMENT MOVING NORTH AND NORTHEAST OUT OF KPSC AND KPDT.
THUS WILL INDICATE VFR CONDITIONS WITH LINGERING SHOWERS...MEANWHILE
WILL CONTINUE BELOW VFR CONDITIONS FOR THE FIRST 2 HOURS AT KALW.
AFTER 27/21 UTC EXPECT ALL SITES (KRDM...KDLS...KYKM...KPDT...KPSC
AND KALW) TO HAVE VFR CONDITIONS WITH SHOWERS IN THE VICINITY.
STRONGER BUILD UPS WITH THE POSSIBILITY OF THUNDER MAY OCCUR NEAR
KRDM...KPDT AND KALW LATE THIS AFTERNOON INTO THE EVENING. FOR NOW
WILL ONLY SUGGEST THIS OCCURRENCE WITH CB INDICATORS. WINDS WILL
INCREASE THIS AFTERNOON FROM THE WEST...THEN DECREASE OVERNIGHT. 90

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  37  56  38  54 /  60  40  30  30
ALW  42  57  43  55 /  60  40  30  30
PSC  42  62  43  60 /  20  30  10  20
YKM  38  58  40  55 /  20  20  10  20
HRI  41  60  42  58 /  30  40  10  20
ELN  38  57  41  54 /  20  20  10  20
RDM  29  49  27  46 /  30  40  20  30
LGD  39  48  36  46 /  70  50  20  40
GCD  35  47  34  45 /  60  50  30  40
DLS  43  57  43  54 /  30  20  20  20

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...NONE.
WA...NONE.
&&

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

99/90/90

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE PENDLETON OR
1026 AM PDT TUE APR 27 2010

UPDATED DAY ONE DISCUSSION TO REMOVE COMMENTS REGARDING WIND ADVISORY
FOR WALLOWA COUNTY WHICH EXPIRED AT 10 AM PDT THIS MORNING

ORZ041>044-049-050-501>506-WAZ024-026>030-501-502-281245-
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-
1026 AM PDT TUE APR 27 2010

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

.DAY ONE...TODAY AND TONIGHT

THUNDERSTORMS
     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 OF WASHINGTON, EASTERN
     COLUMBIA RIVER GORGE OF OREGON, NORTH CENTRAL OREGON, CENTRAL
     OREGON, LOWER COLUMBIA BASIN OF OREGON, GRANDE RONDE VALLEY,
     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, WALLOWA COUNTY

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

A PACIFIC COLD FRONT WILL PUSH ACROSS WASHINGTON AND OREGON TODAY
AND BRING WIDESPREAD RAIN TODAY AND TONIGHT. A LAYER OF ELEVATED
INSTABILITY ALOFT DUE TO COLD AIR IN THE MID/UPPER LEVELS WILL LEAD
TO A SLIGHT CHANCE OF THUNDERSTORMS THIS AFTERNOON AND EARLY THIS
EVENING. ANY THUNDERSTORMS THAT DO DEVELOP WILL HAVE A CHANCE OF
BECOMING STRONG WITH GUSTY WINDS AND HAIL BEING THE BIGGEST THREATS.
TONIGHT SNOW LEVELS WILL DROP TO AROUND 3500 FEET AND A COUPLE OF
INCHES OF SNOW IS POSSIBLE IN PORTIONS OF THE LISTED AREAS THOUGH
MOST POPULATED AREAS WILL SEE LESS THAN AN INCH OF SNOW.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY

THUNDERSTORMS WEDNESDAY
     NORTHWEST BLUE MOUNTAINS OF WASHINGTON, GRANDE RONDE VALLEY,
     WALLOWA COUNTY, NORTHERN BLUE MOUNTAINS OF OREGON, SOUTHERN
     BLUE MOUNTAINS OF OREGON, NORTHERN WHEELER AND SOUTHERN
     GILLIAM COUNTIES, JOHN DAY BASIN, OCHOCO-JOHN DAY HIGHLANDS

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

AN UPPER LEVEL TROUGH WILL REMAIN OVER THE REGION THROUGH THURSDAY
GIVING THE AREA GENERALLY UNSETTLED WEATHER. COLD AIR ALOFT WILL
LEAD TO ANOTHER CHANCE OF THUNDERSTORMS OVER THE EASTERN MOUNTAINS
ON WEDNESDAY AFTERNOON AND EARLY EVENING THOUGH THESE THUNDERSTORMS
ARE NOT EXPECTED TO BECOME STRONG. SNOW LEVELS WILL REMAIN AT AROUND
3500 TO 4000 FEET AND PORTIONS OF THE AREAS LISTED WILL HAVE UP TO 3
INCHES OF SNOW. A RIDGE WILL BUILD IN THE EASTERN PACIFIC NEXT
WEEKEND FOR WARMER AND LESS ACTIVE WEATHER THROUGH NEXT MONDAY.

.SPOTTER INFORMATION STATEMENT...

SKYWARN SPOTTER ACTIVATION MAY BE REQUIRED THIS AFTERNOON AND THIS
EVENING FOR ISOLATED THUNDERSTORMS...SOME POSSIBLY BECOMING STRONG
WITH HAIL AND GUSTY HIGH WINDS...WITH THE BEST POTENTIAL FOR STRONG
THUNDERSTORMS OCCURRING THIS AFTERNOON IN CENTRAL AND NORTHEAST
OREGON AND SOUTHEAST WASHINGTON.

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.

POLAN