Heavy Snow in Idaho, December 18 to 20, 2010

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE POCATELLO ID
215 PM MST FRI DEC 17 2010

.SHORT TERM...TONIGHT THROUGH SUNDAY NIGHT. STRONG FETCH OF
MOISTURE PUSHING INTO CALIFORNIA AND STRETCHING ACROSS NEVADA THIS
AFTERNOON PER WV IMAGERY. MODELS PROG SLIGHT HEIGHT RISES ACROSS
EASTERN IDAHO...EFFECTIVELY TURNING FLOW SOUTHWEST. THIS SHOULD
ALLOW AREAS OF LIGHT SNOW OVER NORTHERN NEVADA TO TURN NORTH
OVERNIGHT. HAVE LEFT WEAK POPS OVERNIGHT ALONG SOUTHERN BORDER.
MAIN PUSH OF MOISTURE INTO EASTERN IDAHO ARRIVES WITH SHORTWAVE
EARLY DURING THE DAY SATURDAY. TEMPS APPEAR TO REMAIN COLD ENOUGH
FOR ALL SNOW THOUGH ELEVATIONS BELOW 4000 FT MAY SEE A TEMPORARY
MIX DURING THE AFTERNOON. SOUTHERLY FLOW AT LOWER AND MID LEVELS
SHOULD FOCUS PRECIP GENERATION IN THE UPSLOPE AREAS OF THE EASTERN
MAGIC VALLEY AND THE CENTRAL MOUNTAINS EARLY IN THE DAY. GIVEN THE
SLIGHT WARMING AND SLIGHTLY TWEAKED QPF...SNOW AMOUNTS NOW A BIT
LOWER FOR SNAKE PLAIN REGIONS FOR SATURDAY INTO SATURDAY NIGHT. AS
A RESULT HAVE DROPPED WINTER STORM WARNING FOR SHOSHONE TO CRATERS
OF THE MOON/ARCO AND LEFT A WINTER WEATHER ADVISORY FOR ALL OF
EASTERN MAGIC VALLEY IN ITS PLACE. THE REMAINING WATCH AREAS HAVE
BEEN UPGRADED TO A WINTER STORM WARNING GIVEN CONFIDENCE OF HEAVY
24 HOUR SNOW AMOUNTS GENERALLY ABOVE 7000 FT. BRIEF BREAK OCCURS
LATE SATURDAY NIGHT INTO EARLY SUNDAY BUT NEXT SHORTWAVE BRINGS
ADDITIONAL PRECIP TO THE REGION. SUNDAY DOES APPEAR TO BE THE
WARMEST BUT KEPT TEMPS SLIGHTLY BELOW GUIDANCE AS BUFFER PROFILES
SUPPORT ONLY A VERY THIN WARM LAYER /50MB DEEP/ NEAR THE SURFACE
SUNDAY. CONTINUED PRECIP THROUGH THE DAY MAY PREVENT THE AIRMASS
FROM WARMING TOO DRAMATICALLY THOUGH A MIX IS LIKELY AT LEAST
BELOW 4500 FEET. OTHERWISE...SUNDAY NIGHT APPEARS TO BE THE NEXT
BEST SHORT BREAK IN SHORT TERM AS SECOND MAJOR SHORTWAVE SHIFTS
INTO MONTANA AND WEAK TRANSITORY SHORTWAVE RIDGE PUSHES INTO
REGION. DMH

.LONG TERM...MONDAY THROUGH NEXT FRIDAY.
GFS AND EUROPEAN NOW SHOWING SIGNIFICANT DIFFERENCES IN LONG TERM
PERIOD.  EUROPEAN STILL PORING IN WARM AIR IN THE WEDNESDAY TO
THURSDAY TIME FRAME WHILE THE GFS CLOSES OFF 500 MILLIBAR LOW AND
TRACKS IT SOUTH THROUGH SOUTHERN NEVADA AND UTAH KEEPING COLD AIR
OVER SOUTHEAST IDAHO THROUGH THE PERIOD.  WITH THESE DIFFERENCES
THE GFS IS DRY WEDNESDAY INTO FRIDAY WHILE THE EUROPEAN IS MUCH
WETTER.  WITH THE VAST DIFFERENCES IN THE MODELS DID NOT ALTER GRIDS
ALL THAT MUCH GOING WITH AT LEAST A CHANCE OF PRECIPITATION THROUGH
THE PERIOD WITH SLIGHTLY WARMER THAN NORMAL TEMPERATURES.
GK

&&

.AVIATION...WIDESPREAD VFR CONDITIONS TODAY AHEAD OF SYSTEM
APPROACHING SATURDAY.  SHOULD REMAIN VFR TONIGHT BUT EVENTUALLY SNOW
SHOULD MOVE INTO ALL TAF SITES SATURDAY MORNING AND DROPPED ALL
SITES TO IFR IN SNOW BETWEEN 12Z AND 18Z SATURDAY.
GK

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WARNING FROM 5 AM SATURDAY TO 11 AM MST SUNDAY
ABOVE 7000 FEET FOR THE IDZ023-025.

WINTER STORM WARNING FROM 5 AM SATURDAY TO 5 AM MST SUNDAY
IDZ031.

WINTER WEATHER ADVISORY FROM 5 AM SATURDAY TO 5 AM MST SUNDAY
IDZ017.

WINTER STORM WARNING FROM 5 AM SATURDAY TO 5 AM MST SUNDAY ABOVE
7500 FEET FOR THE IDZ018.

&&

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE POCATELLO ID
620 AM MST FRI DEC 17 2010

IDZ017>025-031-032-181330-
EASTERN MAGIC VALLEY-SAWTOOTH MOUNTAINS-UPPER SNAKE HIGHLANDS-
UPPER SNAKE RIVER PLAIN-LOWER SNAKE RIVER PLAIN-
SOUTH CENTRAL HIGHLANDS-CARIBOU HIGHLANDS-
CACHE VALLEY/IDAHO PORTION-WASATCH MOUNTAINS/IDAHO PORTION-
BIG AND LITTLE WOOD RIVER REGION-LOST RIVER/PAHSIMEROI-
620 AM MST FRI DEC 17 2010

THIS HAZARDOUS WEATHER OUTLOOK IS FOR EASTERN IDAHO.

.DAY ONE...TODAY AND TONIGHT

A CHILLY DAY IS EXPECTED ACROSS EASTERN IDAHO. SOME DENSE FREEZING
FOG WILL BE AROUND THROUGH MID MORNING. THE AREAS OF CONCERN ARE
IN AND AROUND I-84 FROM THE I-84/86 INTERCHANGE TO THE UTAH
BORDER...THE IDAHO PART OF THE CACHE VALLEY AND AROUND BEAR LAKE. BY
TONIGHT...CLOUDS WILL BE INCREASING FROM THE SOUTHWEST. A SLIGHT
CHANCE OF SNOW IS FORECAST FOR THE SOUTHERN HIGHLANDS AND WESTERN
PORTIONS OF THE CENTRAL MOUNTAINS.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY

SNOW WILL INCREASE ACROSS THE AREA SATURDAY AND CONTINUE INTO
SATURDAY NIGHT. SNOW WILL BE MODERATE TO HEAVY AT TIMES. DESPITE
TEMPERATURES WARMING TO NEAR FREEZING DURING THE DAY IN SOME LOWER
VALLEYS...ALL AREAS SHOULD SEE SNOWFALL. BREEZY CONDITIONS ARE
EXPECTED AT MID AND UPPER ELEVATIONS AS WELL AS AREAS WITH DOWNVALLEY
WINDS DRAINING INTO THE SNAKE PLAIN...INCLUDING MOST OF THE MAGIC
VALLEY. THE FOLLOWING ARE SNOW TOTALS THROUGH SUNDAY MORNING...

*WESTERN PORTIONS OF THE CENTRAL MOUNTAINS...8 TO 13 INCHES.

*NORTHERN PORTIONS OF THE CENTRAL MOUNTAINS...1 TO 5 INCHES AND
 LOCALLY HIGHER.

*UPPER SNAKE HIGHLANDS...4 TO 10 INCHES.

*SOUTHEASTERN MOUNTAINS...5 TO 12 INCHES.

*SOUTHERN HIGHLANDS...1 TO 3 INCHES IN THE VALLEYS AND UP TO 7
 INCHES IN THE MOUNTAINS.

*SNAKE PLAIN...2 TO 5 INCHES WITH 6 TO 9 INCHES ACROSS THE
 NORTHERN HALF OF THE MAGIC VALLEY AND CRATERS OF THE MOON.

ADDITIONAL SNOWFALL WILL OCCUR SUNDAY AND SUNDAY NIGHT...WITH THE
HIGHEST AMOUNTS ACROSS THE WESTERN PORTIONS OF THE CENTRAL
MOUNTAINS AND THE HIGHER ELEVATIONS OF THE EASTERN MOUNTAIN
RANGES. DURING THE DAY SUNDAY...PORTIONS OF THE MAGIC VALLEY AND
LOWER VALLEYS NEAR THE UTAH BORDER WILL SEE TEMPERATURES PUSHING
INTO THE MID AND UPPER 3OS WHICH WILL PRODUCE A MIX OF RAIN AND
SNOW. THIS WILL LIMIT SNOWFALL IN SOME AREAS UNTIL SUNDAY NIGHT.

PERIODS OF RAIN AND SNOW WILL CONTINUE INTO THE MIDDLE OF NEXT
WEEK. THE BOTTOM LINE IS THAT IT APPEARS TO BE A RATHER LONG
PERIOD OF WET WEATHER ESPECIALLY IN THE HIGHER ELEVATIONS. THOSE
WHO ARE GOING TO BE TRAVELLING OR IN THE BACKCOUNTRY ARE STRONGLY
URGED TO STAY ABREAST OF THE LATEST FORECASTS AND STATEMENTS
REGARDING NOT ONLY THE WEATHER THIS WEEKEND...BUT ALSO FOR THE
NEXT SEVERAL DAYS.

.SPOTTER INFORMATION STATEMENT...

WE ASK TRAINED SPOTTERS AND CITIZENS TO REPORT SIGNIFICANT
WEATHER CONDITIONS WHEN IT IS SAFE TO DO SO. THESE CONDITIONS MAY
INCLUDE HAIL...TORNADOES...STRONG WIND...DUST STORMS...SNOWFALL...
EXTREME COLD TEMPERATURES...FREEZING RAIN OR HEAVY RAIN...DENSE
FOG...AND FLOODING OR ICE JAMS. INFORMATION ABOUT THESE HAZARDOUS
CONDITIONS SHOULD BE CALLED INTO YOUR NATIONAL WEATHER SERVICE
OFFICE IN POCATELLO USING THE 1-800 SEVERE WEATHER HOTLINE...OR
208-233-0834.