Heavy Snow in Oregon, December 28 to 29, 2003

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOISE IDAHO
945 PM MST SAT DEC 27 2003

.DISCUSSION...FOR SOUTHEAST OREGON AND SOUTHWEST IDAHO. SATELLITE
IMAGERY HAS A SHORTWAVE TROUGH DROPPING SOUTHEAST FROM WASHINGTON
TONIGHT.  THIS WILL BRING A FEW INCHES OF SNOW TO OUR NORTHERN ZONES
TONIGHT AND SUNDAY.  THE HEAVY SNOW WARNING FOR THIS HAS BEEN
DOWNGRADED TO A SNOW ADVISORY. HAVE ALREADY UPDATED THE ZONES AND
STATEMENT FOR THIS.  MEANWHILE...A DEVELOPING STORM SYSTEM OFF THE
OREGON COAST CONTINUES TO MOVE EASTWARD AND IS ON TRACK FOR SUNDAY
NIGHT AND MONDAY.  SEVERAL INCHES OF SNOW ARE POSSIBLE WITH THIS
SYSTEM FOR THE VALLEYS AND MUCH MORE FOR THE MOUNTAINS.  THE WINTER
STORM WATCH CONTINUES FOR OUR ENTIRE AREA SUNDAY NIGHT AND MONDAY.

&&

.PREV DISCUSSION...FINALLY A SYSTEM THAT WILL HAVE AN IMPACT ON THE
POPULATION CENTERS OF THE SNAKE RIVER VALLEY.  BUT FIRST THINGS
FIRST. A VERY COMPLEX PATTERN ON SATELLITE TODAY WITH THE FIRST
IMPORTANT PLAYER (A VIGOROUS SHORT WAVE) DROPPING SOUTHEAST FROM
B.C. THE MAIN THING WITH THIS FEATURE IS THAT IT WILL CONTINUE TO
KEEP COLD AIR SUPPLIED OVER THE REGION AS IT PUSHES POLAR AIR
SOUTH.  LIMITED MOISTURE FROM THIS SYSTEM BUT DYNAMICS RATHER
IMPRESSIVE. IN COORDINATION WITH PARTNER OFFICES, HAVE DECIDED ON
HEAVY SNOW WITH THIS FEATURE WITH FAVORABLE WESTERLY FLOW ON
NORTH-SOUTH MOUNTAIN RANGES.  WOULD LIKE TO SEE MORE QPF BUT WENT
WITH WARNING TONIGHT/SUNDAY ANYWAY.  MAIN FOCUS THEN SHIFTS SOUTH
SUNDAY NIGHT INTO MONDAY AS A HUGE PLUME OF MID PACIFIC MOISTURE
SPREADS EASTWARD ALONG 40N.  AS MENTIONED ABOVE, COLD AIR BEING
RESUPPLIED BY POTENT B.C. SHORT WAVE WILL EVENTUALLY INTERACT WITH
THIS MOISTURE PLUME SPILLING OVER THE SIERRA RANGE AND ACROSS
NORTHERN NEVADA/SOUTHWEST IDAHO. MEANWHILE, A STRONG JET WILL DIVE
SOUTHEAST ACROSS OREGON PLACING THE FORECAST AREA ON THE CYCLONIC
SIDE AND LEFT EXIT REGION. THIS SCENARIO COMBINED WITH GOOD
OVERRUNNING FROM THE SOUTH AND WEST SHOULD MAKE FOR AN ALMOST IDEAL
SETUP FOR SNOW. NUMERICAL GUIDANCE SEEMS TO AGREE WITH BEST CATEGORY
SNOW IN MOS OUTPUT REACHING ALL THE WAY UP TO 8 INCHES FROM BURNS
EASTWARD TO TWIN FALLS.  BOISE GETS LESS BUT POSSIBLY UP TO 4 INCHES
OR MORE HERE TOO. CRITICAL TO THIS SCENARIO PANNING OUT WILL BE THE
PLACEMENT OF THE DEVELOPING SURFACE LOW AND LOCATION OF THE
ACCOMPANYING WARM FRONT.  IDEALLY, HEAVIEST SNOW SHOULD DEVELOP
100-200 MILES NORTH OF THE SURFACE LOW.  MODEL SCENARIOS ALL A
LITTLE DIFFERENT IN LOCATION OF THESE FEATURES BUT GENERAL IDEA OF
OPEN WAVE STRUCTURE WITH A DEEPENING LOW NEARBY IS THE SAME. LATEST
WATER VAPOR LOOPS SHOW PACIFIC MOISTURE PLUME PRETTY FAR NORTH AND
IT HASNT TURNED EAST YET. THIS IS A GOOD SIGN IN THAT WHEN MOISTURE
FINALLY TURNS EAST IT WILL HAVE A GOOD TRAJECTORY TOWARD OUR CWFA.
AS SYSTEM PULLS OUT MONDAY AFTERNOON A STRONG SURFACE GRADIENT PULLS
IN BEHIND PRODUCING WINDY CONDITIONS WITH BLOWING AND DRIFTING TO
THE REAR OF THE SURFACE LOW.  TUESDAY FEATURES A COLD NORTHERLY FLOW
ON FRESH SNOWPACK AND DEPENDING ON AREAL EXTENT AND DEPTH OF SNOW,
MAY KEEP HIGH TEMPS IN THE TEENS AND 20S.

.LONG TERM...WEDNESDAY THROUGH SATURDAY...THE EXTENDED PERIOD BEGINS
QUITE COLD AND DRY WITH THE WESTERN FRINGE OF A CANADIAN SURFACE
HIGH OVER THE REGION.  DEPENDING ON SNOW COVER FROM THE SUNDAY
NIGHT/MONDAY STORM SYSTEM...MORNING LOW TEMPERATURES COULD BE EVEN
COLDER THAN THE CURRENT FORECAST ALREADY 6-8 DEGREES BELOW NORMAL.
A WEAK SHORTWAVE PASSES TO THE NORTH ON WEDNESDAY AND BRINGS A
RETURN OF MOISTURE TO THE REGION...HOWEVER POPS REMAIN LOW AS
DYNAMICS ARE LACKING.  THE NEXT MAJOR TROUGH DROPS INTO THE GULF OF
ALASKA LATE WEDNESDAY AND TEMPERATURES BEGIN TO REBOUND TO NEAR
NORMAL WITH A WARM FRONT PASSING TO THE NORTH ON THURSDAY.  A COLD
FRONTAL PASSAGE IS FORECAST FOR FRIDAY WITH A BLANKET OF CHANCE POPS
ACROSS THE CWA.  SOME UNCERTAINTY WITH HOW MUCH COLD AIR MAKES ITS
WAY INTO THE REGION SATURDAY AS MANY MODELS SUGGEST THE HEART OF THE
COLD MAY HAVE TO WAIT FOR A SECONDARY COLD PUSH TO COME LATER IN THE
WEEKEND.  OVERALL...MUCH BETTER MODEL AGREEMENT TODAY AND THE TREND
IS WARMER...PARTICULARLY FOR THE WEDNESDAY THROUGH EARLY FRIDAY
TIME-FRAME AHEAD OF THE NEXT MAJOR SYSTEM.

&&

.BOI WATCHES/WARNINGS/ADVISORIES...
.ID...SNOW ADVISORY TONIGHT AND SUNDAY IDAHO ZONES 11/13.
      WINTER STORM WATCH ZONES 11>16 AND 29-30 SUNDAY
       NIGHT AND MONDAY.
.OR...SNOW ADVISORY TONIGHT AND SUNDAY ZONE 62.
      WINTER STORM WATCH ZONES 61>64 SUNDAY NIGHT/MONDAY.

&&

DISC........TE
PREV DISC...GS
LONG TERM...RH

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE BOISE ID
6 AM MST SAT DEC 27 2003

IDZ012-014>016-028>030-ORZ061>064-281300-
CAMAS PRAIRIE-HARNEY COUNTY-LOWER TREASURE VALLEY-
MALHEUR COUNTY-OWYHEE MOUNTAINS-SOUTHERN TWIN FALLS COUNTY-
SOUTHWEST HIGHLANDS-UPPER TREASURE VALLEY-WESTERN MAGIC VALLEY-
6 AM MST (5 AM PST) SAT DEC 27 2003

THIS HAZARDOUS WEATHER OUTLOOK IS FOR SOUTHWEST IDAHO AND SOUTHEAST
OREGON.

.DAY ONE...TODAY

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

IDZ011-013-ORZ062-281300-
BAKER COUNTY-BOISE MOUNTAINS-WEST CENTRAL MOUNTAINS-
6 AM MST SAT DEC 27 2003

THIS HAZARDOUS WEATHER OUTLOOK IS FOR THE BOISE MOUNTAINS-
THE WEST CENTRAL MOUNTAINS AND BAKER COUNTY OREGON-

.DAY ONE...TODAY

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY

...WINTER STORM WATCH IN EFFECT FOR SUNDAY...

SNOW WILL SPREAD OVER THE AREA TONIGHT AND INCREASE ON SUNDAY WITH
ACCUMULATIONS OF UP TO 2 INCHES TONIGHT AND UP TO ANOTHER 5 INCHES
ON SUNDAY.

.SPOTTER INFORMATION STATEMENT...WEATHER SPOTTERS ARE ENCOURAGED TO
REPORT SIGNIFICANT WEATHER CONDITIONS ACCORDING TO STANDARD OPERATING
PROCEDURES.