Heavy Snow in Idaho, December 27 to 28, 2014

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE POCATELLO ID
316 AM MST SAT DEC 27 2014

.SHORT TERM...TODAY THROUGH SUNDAY NIGHT. OUR NEXT STORM TO IMPACT
EASTERN IDAHO IS ON OUR DOOR STEP THIS MORNING. FIRST THINGS
FIRST...AND THAT IS THE LOW CLOUDS/FOG/FLURRIES ACROSS MUCH OF THE
SNAKE PLAIN AND SOME ADJACENT VALLEY LOCATIONS. IT LOOKS LIKE THIS
WILL SLOWLY DISSIPATE AS THE DAY WEARS ON. SOME OF THE FOG IS VERY
DENSE AND WITH VERY COLD TEMPERATURES...WE WILL LIKELY SEE SOME
SLICK SPOTS. THE FIRST REAL INKLING OF SNOW ARRIVES IN THE CENTRAL
MOUNTAINS THIS AFTERNOON. SNOW SPREAD SOUTH AND EAST OVERNIGHT. WE
WILL SEE DOWNSLOPE SHADOWING OUT ACROSS THE ARCO DESERT AND ALSO
POTENTIALLY SOME VALLEYS NEAR THE UTAH BORDER. THE FOCUS FOR
HEAVIER SNOW THEN SHIFTS TO THE SOUTHERN AND EASTERN HIGHLANDS
TOMORROW AS WELL AS SOME OF THE BENCHES ALONG THE INTERSTATE
CORRIDOR. WE WILL SEE LINGERING SNOWS ACROSS THE CENTRAL
MOUNTAINS. IT ALSO APPEARS LATE IN THE DAY...WE WILL SEE A
CONVERGENCE BAND DEVELOPING ACROSS THE SNAKE PLAIN. RIGHT NOW THE
CONSENSUS HAS THAT BAND STRETCHING FROM NEAR ARCO TO POCATELLO AT
5PM. HOW FAR SOUTHWEST THAT BAND MOVES AND ALSO ANY SECONDARY
BANDS WILL BE DEPENDENT ON HOW QUICKLY THE REALLY COLD AIR PUSHES
ACROSS THE DIVIDE AND INTO EASTERN IDAHO SUNDAY NIGHT. THE MODELS
ARE NOT AGREEING ON THAT AT THE MOMENT. THE GFS ONLY HAS THE
COLDEST AIR PUSHING INTO THE UPPER PLAIN BY MONDAY MORNING...WHILE
THE NAM PUSHES IT TO THE MAGIC VALLEY. WE SPLIT THE DIFFERENCE FOR
NOW. WINDS WILL BE BREEZY AND THAT WILL CREATE SOME BLOWING AND
DRIFTING ISSUES WHETHER IT'S SNOW FROM CHRISTMAS...THIS STORM OR
BOTH. 6-12 INCHES OF NEW SNOW IS FORECAST FOR THE WESTERN CENTRAL
MOUNTAINS AS WELL AS MOST OF THE EASTERN HIGHLANDS. THE LOST
RIVER/PAHSIMEROI REGION AS WELL AS HAILEY AND KETCHUM PROPER WILL
ONLY SEE 1-4 INCHES. THE SOUTH CENTRAL HIGHLANDS SHOULD SEE 2-6
INCHES AS WELL AS THE CACHE VALLEY. THE SNAKE PLAIN IS FORECAST TO
SEE AS LITTLE AS AN INCH IN THE ARCO DESERT AND 2-5 INCHES WITH
LOCALLY HIGHER AMOUNTS ON THE BENCHES. BASED ON THE CURRENT
FORECAST AND WHAT HAPPENED ON CHRISTMAS WE HAVE UPGRADED THE
WESTERN CENTRAL MOUNTAINS...ALL OF THE EASTERN HIGHLANDS AND MOST
OF THE SNAKE PLAIN TO WINTER STORM WARNINGS. THE LOST
RIVER/PAHSIMEROI REGION...THE SOUTH CENTRAL HIGHLANDS AND EASTERN
MAGIC VALLEY WILL REMAIN AS ADVISORIES FOR NOW. KEYES

.LONG TERM...MONDAY THROUGH NEXT FRIDAY. COLD TROUGH DROPS SOUTHWARD
THROUGH IDAHO AND OREGON MONDAY. EXPECTING GENERALLY LIGHT
ACCUMULATIONS OF SNOW THAT LINGERS THROUGH MONDAY NIGHT. THE 00Z
MODELS RUNS HAVE TAKEN A PRETTY SIGNIFICANT SHIFT WITH THE TRACK OF
THIS DISTURBANCE TO THE WEST. THAT ALSO BRINGS THE RISK OF MORE COLD
AIR PUSHING THROUGH THE MOUNTAIN PASSES BETWEEN MONTANA AND IDAHO.
MODEL OUTPUT GUIDANCE DROPPED TEMPERATURES SEVERAL DEGREES OVER THE
12Z RUN. MINUS 12 SUGGESTED FOR IDAHO FALLS WEDNESDAY MORNING...AND
4 BELOW AT POCATELLO. ISLAND PARK WILL BE A VERY DIFFICULT
FORECAST...GFS GUIDANCE LOWERS TEMPERATURES TO 32 BELOW AT
YELLOWSTONE WEDNESDAY MORNING. CLOUD COVER WILL BE CRITICAL TO THE
FORECAST. FOR NOW HAVE DROPPED FORECAST LOWS TO THE 10-15 BELOW RANGE
AND WILL CONSIDER COLDER TEMPERATURES IF MODELS ARE CONSISTENT AND
OBSERVATIONS IN MONTANA AND CANADA SUPPORT IT. MORE CLOUDS AND
POTENTIAL FOR SNOW WILL STREAM OVER THE HIGH PRESSURE RIDGE NEAR
130W LATE IN THE WEEK...THURSDAY/FRIDAY SPREADING INTO IDAHO IN
NORTHWESTERLY FLOW ALOFT. RS

&&

.AVIATION...SATELLITE IMAGERY SHOWS LOW STRATUS IFR/MVFR CLOUD DECK
MOVING FROM NEAR KJER AND KBYI EASTWARD TOWARDS KPIH AND KIDA.
TIMING WILL BE DIFFICULT BUT WINDS WILL INCREASE BY LATE MORNING
COMBINED WITH SOME SURFACE HEATING SHOULD HELP SCATTER OR LIFT CLOUDS
AT KPIH...WHILE KIDA WILL BE MORE PERSISTENT UNTIL EARLY AFTERNOON.
CLOD FRONT EXPECTED TO REACH KSUN BY 28/06Z AND KBYI/KPIH/KIDA BY
28/12Z. STAYING WITH THE NAM12 IDEA TRYING TO MOVE PRECIPITATION
THROUGH IN 3 TO 5 HOURS. RS

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WARNING FROM 5 PM THIS AFTERNOON TO 5 PM MST SUNDAY
IDZ020-021.

WINTER STORM WARNING FROM 5 PM THIS AFTERNOON TO 11 PM MST
SUNDAY IDZ023-025.

WINTER WEATHER ADVISORY FROM 11 PM THIS EVENING TO 11 PM MST
SUNDAY IDZ022-024.

WINTER STORM WARNING FROM 11 AM THIS MORNING TO 5 PM MST SUNDAY
IDZ018-031.

WINTER STORM WARNING FROM 5 PM THIS AFTERNOON TO 5 PM MST SUNDAY
IDZ019.

WINTER WEATHER ADVISORY FROM 11 PM THIS EVENING TO 5 PM MST
SUNDAY IDZ017.

WINTER WEATHER ADVISORY FROM 11 AM THIS MORNING TO 5 PM MST
SUNDAY IDZ032.

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