Heavy Snow in Oregon, April 7, 2011

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE PENDLETON OR
1050 PM PDT WED APR 6 2011

UPDATED AVIATION DISCUSSION

.UPDATE...AN UPPER LEVEL TROUGH CONTINUES TO DIG SOUTH ALONG THE
PACIFIC NORTHWEST COAST THIS EVENING. THERE WAS SOME INSTABILITY
OVER THE AREA THIS AFTERNOON AND CONVECTIVE SHOWERS DEVELOPED OVER
THE COLUMBIA BASIN. A COUPLE PUT OUT A FEW LIGHTNING STRIKES AND
THERE WERE SEVERAL REPORTS OF SMALL PEA SIZED HAIL BUT THE SHOWERS
HAVE DISSIPATED AFTER SUNDOWN. UPSLOPE FLOW CONTINUES INTO THE
MOUNTAINS AND SEVERAL STATIONS ARE REPORTING SNOW. WILL KEEP THE
WINTER STORM WARNING FOR THE NORTHWEST BLUE MOUNTAINS OF OREGON
AND THE WINTER WEATHER ADVISORY FOR THE NORTHERN BLUE MOUNTAINS OF
OREGON GOING AND MONITOR FOR DECREASING ACTIVITY. OTHER WARNINGS
AND ADVISORIES WILL REMAIN IN EFFECT THOUGH THE 00Z RUN OF THE
NAM12 IS NOT AS BULLISH ON PRECIPITATION AS THE 18Z RUN. IT ALSO
MOVES THE SURFACE LOW SOUTH OF OUR AREA RATHER THAN THROUGH
CENTRAL OREGON AND THE OCHOCO-JOHN DAY HIGHLANDS. THIS REDUCES THE
CONFIDENCE SOMEWHAT IN THE WARNINGS AND ADVISORIES BUT THE EARLIER
FORECAST WAS TAKING A CONSERVATIVE APPROACH TO THE NAM12 DATA SO
IT MAY PROVE TO BE ACCURATE. HAVE DRIED OUT POPS SOMEWHAT FOR THE
REST OF THE EVENING IN THE COLUMBIA BASIN BUT OTHERWISE POPS
LOOKED GOOD. HAVE ALSO ADJUSTED TEMPERATURES UP A DEGREE OR TWO IN
PLACES TO MATCH TRENDS. MADE A FEW WIND ADJUSTMENTS IN THE
KITTITAS VALLEY AND COLUMBIA BASIN TO BETTER MATCH CURRENT
CONDITIONS. OVERALL CURRENT FORECAST WAS IN GOOD SHAPE AND JUST
MADE SOME MINOR ADJUSTMENTS. FORECAST UPDATE OUT SOON. PERRY

&&

.AVIATION...06Z TAFS...A WEATHER SYSTEM CONTINUES TO MOVE SOUTH
ALONG THE COAST AND WILL MOVE INLAND LATER TONIGHT AND TOMORROW. VFR
CONDITIONS WILL BE PREVALENT IN THE NORTHERN HALF OF THE AREA BUT IN
CENTRAL OREGON AND THE SOUTHERN BLUE MOUNTAINS AND THE OCHOCO-JOHN
DAY MOUNTAINS SNOW SHOWERS WILL BRING MVFR/IFR CEILINGS AND
VISIBILITIES AT TIMES AS THE HEAVY SHOWERS MOVE THROUGH THE AREA.
THIS WILL AFFECT KRDM AND KBDN. A FEW SNOW SHOWERS ARE POSSIBLE AT
KPDT AND KALW BUT SHOULD NOT DROP CONDITIONS BELOW MVFR LEVELS.
SHOWERS WILL TAPER OFF AFTER 18Z AND END BY 21-23Z WITH CEILINGS
LIFTING AND PARTIALLY CLEARING. WIND WILL GENERALLY REMAIN BELOW 15
KTS FOR THE NEXT 24 HOURS. PERRY

&&

.PREV DISCUSSION... /ISSUED 238 PM PDT WED APR 6 2011/

SHORT TERM...TONIGHT THROUGH SATURDAY...A POTENT UPPER LEVEL STORM
SYSTEM WILL CARVE OUT A 500 MB CLOSED LOW OVER THE AREA TONIGHT WITH
THE LOW SHIFTING SOUTH OF THE REGION ON THURSDAY. BASED ON THE
LATEST NAM GUIDANCE THIS WILL INDUCE CYCLOGENESIS OVER CENTRAL
OREGON LATE THIS EVENING AND RESULT IN AN AREA OF ENHANCED
LIFT/SNOWFALL OVERNIGHT INTO AT LEAST THURSDAY MORNING. THE LATEST
WINTER HIGHLIGHTS ARE BASED ON THIS SCENARIO PLAYING OUT. THE NAM
WOULD SUGGEST AN EVEN MORE BULLISH SNOW EVENT THAN THE OFFICIAL
FORECAST BUT THIS MODEL HAS A PROPENSITY TO OVERDEVELOP SMALL SCALE
LOW PRESSURE SYSTEMS. THAT LIMITS CONFIDENCE TO A CERTAIN DEGREE BUT
WITH THE STRONG DIGGING SYSTEM IT CERTAINLY SEEMS PLAUSIBLE THAT A
LOW WILL DEVELOP SOMEWHERE OVER CENTRAL OREGON AND ENHANCE THE
SNOWFALL. PRECIPITATION ON THURSDAY WILL BE AUGMENTED BY A LITTLE
DIURNAL HEATING AND STEEP LAPSE RATES...WITH AN ISOLATED
THUNDERSTORM NOT OUT OF THE QUESTION. WITH THE UPPER LOW MOVING
FARTHER AWAY BY THURSDAY NIGHT PRECIPITATION SHOULD BEGIN TO TAPER
OFF. A COUPLE OF RELATIVELY NICE DAYS ARE IN STORE FOR FRIDAY AND
SATURDAY WITH BELOW RATHER THAN MUCH BELOW TEMPERATURES. 78

LONG TERM...SATURDAY NIGHT THROUGH WEDNESDAY NIGHT...AN UPPER HIGH
PRESSURE RIDGE OVER THE INTERIOR PACIFIC NORTHWEST WILL MOVE EAST
WARD AND EXIT INTO IDAHO SATURDAY NIGHT AHEAD OF A LARGE...HIGH
AMPLITUDE...UPPER LEVEL TROUGH BETWEEN 135-140W. THE TROUGH WILL
USHER IN A WARM FRONT ON SUNDAY FOR INCREASING MOISTURE AND RAIN
LIKELY IN MOST OF THE FORECAST AREA. THE TROUGH WILL SWING INLAND
AND PUSH A COLD FRONT INTO THE FORECAST AREA SUNDAY EVENING WITH
THE FRONT EXITING INTO IDAHO OVERNIGHT. HENCE...RAIN SHOWERS AND
SNOW SHOWERS CAN BE EXPECTED SUNDAY NIGHT. A WEAK FLAT UPPER LEVEL
RIDGE OF HIGH PRESSURE THEN MOVES OVER THE REGION ON MONDAY FOR
DECREASING POPS...BUT THE NORTHERN BLUE MOUNTAINS WILL LIKELY SEE
OROGRAPHIC SNOW SHOWERS ON MONDAY. THE RIDGE PERSISTS OVER THE
FORECAST AREA MONDAY NIGHT. THE GFS AND ECMWF MODELS SHOW
SIGNIFICANT DIFFERENCES IN THE UPPER LEVEL PRESSURE PATTERN OVER
THE GULF OF ALASKA AND THE OFFSHORE WATERS NEAR THE COAST ON MONDAY
GOING FORWARD WITH THE ECMWF SHOWING ANOTHER HIGH AMPLITUDE UPPER
LEVEL TROUGH NEAR 137W BY MONDAY AFTERNOON WHEREAS THE GFS KEEPS A
WESTERLY FLOW ALOFT OVER THE SAME AREA ASSOCIATED WITH A FLAT HIGH
PRESSURE RIDGE. AS SUCH I HAVE LOW CONFIDENCE IN THE FORECAST MONDAY
NIGHT THROUGH WEDNESDAY NIGHT SO I AM GIVING THE FORECAST AREA
CLIMATOLOGICALLY HIGHER CHANCE POPS OVER THE MOUNTAINS AND A DRY
FORECAST FOR LOWER TERRAIN FOR THIS PERIOD.  POLAN

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  29  47  29  53 /  40  40  10   0
ALW  33  50  32  55 /  40  30  10   0
PSC  30  54  29  58 /  30  20  10   0
YKM  26  50  27  56 /  20  20  10   0
HRI  29  53  28  57 /  40  30  10   0
ELN  26  48  28  53 /  20  10  10   0
RDM  21  38  21  46 /  60  60  30   0
LGD  26  41  26  47 /  50  50  20  10
GCD  25  37  24  44 /  60  60  30  10
DLS  31  53  30  56 /  50  30  20   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...WINTER STORM WARNING UNTIL 5 PM PDT THURSDAY ORZ042-506.

     WINTER WEATHER ADVISORY UNTIL 5 PM PDT THURSDAY ORZ505.

     WINTER WEATHER ADVISORY UNTIL 5 AM PDT THURSDAY ORZ502.

     WINTER WEATHER ADVISORY UNTIL 5 PM PDT THURSDAY ORZ503.

     WINTER WEATHER ADVISORY UNTIL 5 PM PDT THURSDAY ORZ509.

WA...WINTER STORM WARNING UNTIL 5 AM PDT THURSDAY WAZ030.

&&

THREAT INDEX
THURSDAY : YELLOW
FRIDAY : GREEN
SATURDAY : 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

83/99/83

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE PENDLETON OR
226 PM PDT WED APR 6 2011

UPDATED HIGHLIGHTS FOR TONIGHT AND THURSDAY

ORZ041-042-044-049-050-502-503-505>509-WAZ024-026>030-520-521-
071415-
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-
226 PM PDT WED APR 6 2011

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

.DAY ONE...TONIGHT

SNOW
     NORTHWEST BLUE MOUNTAINS OF WASHINGTON, NORTH CENTRAL OREGON,
     EAST SLOPES OF THE OREGON CASCADES, 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 STRONG UPPER LEVEL STORM SYSTEM AND DEVELOPING LOW PRESSURE
WILL CAUSE SNOW...LOCALLY HEAVY TO FALL TONIGHT ACROSS A GOOD
PORTION OF OREGON AND SOUTHEAST WASHINGTON. NUMEROUS WINTER STORM
WARNINGS AND ADVISORIES ARE IN EFFECT. PLEASE REFER TO PDXWSWPDT
FOR MORE DETAILS.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

SNOW THURSDAY
     NORTHWEST BLUE MOUNTAINS OF WASHINGTON, NORTH CENTRAL OREGON,
     EAST SLOPES OF THE OREGON CASCADES, 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

MUCH OF THE SNOW ON THURSDAY SHOULD BE FOCUSED ACROSS OREGON AT
ELEVATIONS ABOVE 2000 FEET. LOCALLY HEAVY SNOW IS POSSIBLE IN SOME
AREAS AND WINTER ADVISORIES AND WARNINGS WILL CONTINUE THROUGH THE
DAY IN SOME AREAS. PLEASE REFER TO THE LATEST PDXWSWPDT FOR MORE
INFORMATION.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE REQUIRED.

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.